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Dental Radiology [1 ed.]
 9783132004214, 3132004219

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Dental Radiology

An d reas Fu h r m an n , DDS Foren sic Odon tologist Depar t m en t of Legal Medicin e Cen ter for Diagn ost ics Un iversit y Medical Cen ter Ham bu rg-Eppen dorf Ham bu rg, Germ any

304 illu st rat ion s

Th iem e St u t tgar t • New York • Delh i • Rio de Jan eiro

Librar y of Congress Cataloging-in -Pu blicat ion Dat a Fuh rm an n , An dreas, auth or. [Zah närztlich e Radiologie. English ] Den t al radiology / An dreas Fuh rm ann . p. ; cm . In cludes bibliograph ical referen ces an d in dex. ISBN 978-3-13-200421-4 (alk. paper) – ISBN 978-3-13-200431-3 (e-book) I. Title. [DNLM: 1. Diagn ost ic Im aging. 2. Radiography, Den tal—m ethods. W N 230] RK309 617.6’07572—dc23 2014047560 Th is book is an auth orized t ran slat ion of th e 1st Germ an edit ion p ub lish ed an d copyrigh ted 2013 by Georg Th iem e Verlag, St u t tgar t . Tit le of th e Germ an edit ion : Zah n ärztlich e Radiologie Tran slator: Su zyon O’Neal Wan drey, Berlin , Germ any Illust rators: Angelika Brann er, Hoh enpeissen berg, Germ any; Joach im Horm an n , St ut tgart , Germ any Eugen Roth poem t ran slated an d reprodu ced w ith kin d p erm ission of Carl Han ser Verlag, Mun ich , Germ any © 2015 by Georg Th iem e Verlag KG

Im p or t an t n ote: Medicin e is an ever-ch anging scien ce u n d ergoing con t in u al develop m en t . Research an d clin ical experien ce are con t in ually expan d ing ou r kn ow ledge, in p art icu lar ou r kn ow ledge of prop er t reatm ent an d drug th erapy. In sofar as th is book m en t ions any dosage or app lication , read ers m ay rest assu red th at th e au th ors, editors, an d p u blish ers h ave m ade ever y e or t to en su re t h at su ch referen ces are in accordan ce w it h t h e st ate of k n ow ledge at t h e t im e of p rod u ct ion of t h e b ook. Never th eless, th is d oes n ot involve, im p ly, or exp ress any gu aran tee or responsibilit y on th e part of th e publish ers in respect to any dosage in st ruction s an d form s of applicat ion s stated in th e book. Ever y u ser is requ ested to exam in e carefu lly th e m an u fact u rers’ lea et s accom panying each drug an d to ch eck, if n ecessar y in con su lt at ion w ith a p hysician or sp ecialist, w h eth er th e d osage sch edu les m en tion ed th erein or the con t raindicat ion s st ated by th e m an ufact urers di er from th e statem en ts m ade in the presen t book. Such exam in at ion is part icu larly im p ort an t w ith d rugs th at are eith er rarely u sed or h ave been n ew ly released on th e m arket . Ever y dosage sch edu le or ever y form of app licat ion u sed is en t irely at th e u ser’s ow n risk an d respon sibilit y. Th e au th ors an d p u blish ers requ est ever y u ser to rep or t to th e p u blish ers any discrepan cies or in accuracies not iced. If errors in th is w ork are fou n d after p u blicat ion , errat a w ill be p osted at w w w.th iem e.com on th e produ ct descript ion page. Som e of th e produ ct n am es, p aten ts, an d registered d esign s referred to in th is book are in fact registered t rad em arks or prop rietar y n am es even th ough sp eci c referen ce to th is fact is n ot alw ays m ade in th e text. Th erefore, th e ap p earan ce of a n am e w ith ou t design ation as p rop riet ar y is n ot to be con st ru ed as a rep resen t at ion by t h e p u blish er th at it is in th e p u blic dom ain .

Th iem e Publish ers St ut tgar t Rü digerst rasse 14, 70469 St u t tgart , Germ any +49 [0]711 8931 421, cu stom erser vice@th iem e.de Th iem e Publish ers New York 333 Seven th Aven ue, New York, NY 10001 USA +1 800 782 3488, custom erser vice@th iem e.com Th iem e Publish ers Delh i A-12, Second Floor, Sector-2, Noida-201301 Ut tar Pradesh , In dia +91 120 45 566 00, cu stom erser vice@t h iem e.in Th iem e Publish ers Rio, Th iem e Pu blicações Ltda. Argen t in a Bu ilding 16th oor, Ala A, 228 Praia d o Bot afogo Rio de Jan eiro 22250-040 Brazil +55 21 3736-3631 Cover design : Th iem e Publish ing Grou p Typeset t ing by L42 Media Solu tion s, Berlin , Germ any Prin ted in Germ any by Aprin ta, Wem ding ISBN 978-3-13200-421-4 Also available as an e-book: eISBN 978-3-13200-431-3

54321

Th is book, in clu d ing all par ts th ereof, is legally p rotected by copyrigh t. Any u se, exp loit at ion , or com m ercializat ion ou t sid e th e n arrow lim its set by copyrigh t legislation w ith ou t th e pu blish er’s con sen t is illegal an d liable to p rosecu t ion . Th is ap p lies in p art icu lar to p h otostat rep rodu ct ion , copying, m im eograph ing or du p lication of any kin d, tran slat ing, p rep arat ion of m icro lm s, an d elect ron ic dat a p rocessing an d storage.

To Chrissi and Kat i

A m aster advised h is devotees To on ly believe in w h at on e sees. An d yet – th is w e sh ou ld recon ceive, Som e only see w h at th ey believe. Eugen Roth

Contents Preface

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Acknow ledgments

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

x xi

1

History and Development of Dental Radiography .

2

Radiation Physics .

2.1

Types of Radiation . . . . . . . . . . . . . . . .

8

2.5.2

Ion izat ion . . . . . . . . . . . . . . . . . . . . . . 10

2.2

Direct and Indirect Ionization . . . . . . . .

8

2.6

Interactions betw een X-rays and Matter . . . . . . . . . . . . . . . . . . . . 10

2.3

Corpuscular and Photon Radiation . . . . .

2.3.1 2.3.2

Corpu scu lar Radiat ion . . . . . . . . . . . . . . Ph oton Rad iat ion . . . . . . . . . . . . . . . . .

8 8 8

2.6.1 2.6.2

Absorpt ion —Ph otoelect ric E ect . . . . . . . . 10 Scat tered Radiat ion —Com pton E ect . . . . . 11

2.7

Radioactivity . . . . . . . . . . . . . . . . . . . 11

2.8

Production of X-rays . . . . . . . . . . . . . . 12

2.8.1 2.8.2

Den t al X-ray Equ ipm en t . . . . . . . . . . . . . 12 Addit ion al Equ ip m en t Needed for Dose Lim it at ion an d Im provem en t of X-ray Im age Qu alit y . . . . . . . . . . . . . . . . . . . 17

2.4

. . . . . . . . . . . . . . . . . . . . . . . . .

2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

Interactions betw een Radiation and Matter . . . . . . . . . . . . . . . . . . . .

9

2.5

Fundamental Physical Processes Involved in the Transfer of Photon Energy to Matter . . . . . . . . . . . 10

2.5.1

Excit at ion . . . . . . . . . . . . . . . . . . . . . . 10

3

Dose Terms and Dose Units Used for Ionizing Radiation .

4

The Biology of Radiation E ects

4.1

Fundamentals . . . . . . . . . . . . . . . . . . 26

4.4

Repair Mechanisms for the Restoration of DNA . . . . . . . . . . . . . . . 27

4.2

Direct and Indirect E ects of Radiation . . . . . . . . . . . . . . . 27

4.5

Biological E ects of Radiation Damage . . . . . . . . . . . . . . . 27

. . . . . . . . . . . . . . . . . . . . 22

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.3

E ects of Ionizing Radiation on DNA . . . . . . . . . . . . . . . . 27

5

Radiation Pathology

5.1

Natural Radiation Exposure . . . . . . . . . 30

5.1.1 5.1.2

Cosm ic Radiat ion . . . . . . . . . . . . . . . . . 30 Terrest rial Radion uclides . . . . . . . . . . . . 30

5.2

Arti cial Radiation Exposure . . . . . . . . . 30

6

Image Formation and Image Processing

6.1

Fundamentals . . . . . . . . . . . . . . . . . . 34

6.1.1 6.1.2

Su m m at ion E ect . . . . . . . . . . . . . . . . . 34 Tangen t ial E ect . . . . . . . . . . . . . . . . . . 35

6.2

Image Receptor-Independent Factors In uencing Image Formation . . . . . . . . 35

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.3

Stochastic and Deterministic E ects of Ionizing Radiation . . . . . . . . . . . . . . . . 31

5.3.1 5.3.2

Stoch ast ic E ect s . . . . . . . . . . . . . . . . . 31 Determ in ist ic E ects . . . . . . . . . . . . . . . 31

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5

Object Con t rast . . . . . . . . . . . . . Curren t In ten sit y an d Exposure Tim e Inverse Squ are Law . . . . . . . . . . . High Volt age . . . . . . . . . . . . . . . Scat tered Rad iat ion . . . . . . . . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

36 36 36 36 37

vii

Content s 6.3

6.3.1

Screen less Film s . . . . . . . . . . . . . . . . . . 37

7

Digital Dental Radiography

7.1

Sensors . . . . . . . . . . . . . . . . . . . . . . . 47

7.1.1

Sp at ial Resolut ion . . . . . . . . . . . . . . . . . 48

6.3.2

Radiographic Film w ith In ten sifying Screens

6.4

Processing of Radiographic Films . . . . . . 42

41

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

7.2

Storage Phosphor Imaging Plates . . . . . 48

7.3

Advantages of Digital Radiography . . . . 50

8

Radiation Protection and Quality Assurance in Dental Radiology

8.1

History of Radiation Protection . . . . . . . 54

8.1.1

St ru ct u re of th e In tern at ion al Com m ission on Radiological Protect ion . . . . . . . . . . . 54 Tasks an d Con ten t of th e Variou s Act ivit ies of th e In tern at ion al Com m ission on Radiological Protect ion . . . . . . . . . . . 54

8.1.2

. . . . . . . . . . . . . 54

8.4.2

Preven t ion of Acciden t s an d Protect ion again st Exist ing or Un regulated Radiat ion Risks . . . . . . . . . . . . . . . . . . 55

8.5

Implementation of Recommendations by the International Commission on Radiological Protection . . . . . . . . . . . . 55

8.2

Responsibility for Radiation Protection . . 55

8.2.1 8.2.2

Su per visor y Du t y of the Govern m en t . . . . . 55 Adm in ist rat ion an d Man agem en t of Safet y . 55

8.6

Quality Assurance in Dental Radiology . . 56

8.6.1

St an dards . . . . . . . . . . . . . . . . . . . . . . 56

8.3

Need and Justi cation . . . . . . . . . . . . . 55

8.7

8.4

Optimization of Radiation Protection . . . 55

Procedures to Ensure Compliance w ith Basic Principles of Radiation Protection . . . . . . . . . . . . . . 56

8.4.1

Lim it at ion an d Mon itoring of In dividu al Dose Lim its . . . . . . . . . . . . . . 55

9

Practical Dental Radiography

9.1

Intraoral Radiography . . . . . . . . . . . . . 58

9.1.1 9.1.2 9.1.3 9.1.4 9.1.5 9.1.6 9.1.7 9.1.8

Qu alit y Criteria for In t raoral Radiography Prin cip les of Project ion Geom et r y . . . . . Paralleling Tech n ique . . . . . . . . . . . . . Bisect ing-angle Tech n ique . . . . . . . . . . Righ t-angle Tech n ique . . . . . . . . . . . . Bitew ing Radiography . . . . . . . . . . . . Radiograp h ic Measurem en t Tech niques . Occlu sal Radiography . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

. . . . . . . .

. . . . . . . .

58 59 61 67 72 73 74 74

9.3.1 9.3.2 9.3.3

Pan oram ic Radiography w ith a Slit Collim ator 79 Pan oram ic Radiograp hy w ith an In t raoral Source . . . . . . . . . . . . . . . . . . 80 Rot at ion al Pan oram ic Radiography . . . . . . 80

9.4

Cone Beam Computed Tomography . . . . 109

9.4.1

Tech n ique an d Im age Form at ion in Con e Beam Com pu ted Tom ography . . . . Lim itat ion s of Com puted Tom ography an d Con e Beam Com pu ted Tom ography . . . . Volum e Size . . . . . . . . . . . . . . . . . . Clin ical In dicat ion s for Con e Beam Com pu ted Tom ography . . . . . . . . . . .

9.4.2

9.2

Conventional Tomography . . . . . . . . . . 77

9.3

Panoramic Tomography . . . . . . . . . . . . 79

10

Anatomy and Topography of the Facial Skeleton

10.1

The Teeth and Tooth-supporting Structures . . . . . . . . . . . . . . . . . . . . . 121

10.2

viii

Radiographic Film and Intensifying Screen-Dependent Factors that In uence Image Formation . . . . . . . . . . 37

The Mandible . . . . . . . . . . . . . . . . . . . 123

9.4.3 9.4.4

. . 109 . . 112 . . 114 . . 114

. . . . . . . . . . . . . . . . . . . . . . . . . . 120

10.3

The Maxilla . . . . . . . . . . . . . . . . . . . . 124

10.4

Panoramic Radiographic Anatomy . . . . . 125

10.4.1 Th e Man dible . . . . . . . . . . . . . . . . . . . 125 10.4.2 Th e Maxilla an d Midface . . . . . . . . . . . . 128

Content s

11

Radiographic Findings and Diagnosis

11.1

Systematic Image Analysis and Interpretation . . . . . . . . . . . . . . . . . . 134

11.1.1 Film an d Mon itor View ing Con dit ion s . . . . 134 11.1.2 Steps from Fin dings to Diagn osis . . . . . . . . 134

11.2

Assessment and Diagnosis of the Most Common Pathological Changes . . . . . . . 136

11.2.1 Cariou s Lesion s . . . . . . . . . . . . . . . . . . 136

References

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 11.2.2 Horizon t al Bon e Loss w ith Ver t ical Bon e Defects . . . . 11.2.3 Ap ical Periodon t it is . . . . . 11.2.4 Cyst ic Lesion s . . . . . . . . 11.2.5 Malign an t Lesion s . . . . . . 11.2.6 Bon e Diseases of th e Jaw . . 11.2.7 Sialolith iasis . . . . . . . . . 11.2.8 Tooth Fract ures . . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

139 141 143 145 155 157 158

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

ix

Preface Great p rogress h as been m ade in den tal radiology in th e last 30 years. Th is is part icularly t ru e for tech n ical developm en ts, bu t also for edu cat ion an d t rain ing in den t al radiology at u n iversit ies. Th e in t rodu ct ion of digit al im age receptors can be view ed as a m ileston e in th e tech n ological d evelop m en t of den tal radiology. Th e in t rodu ct ion of con e beam com pu ted tom ography gave den t ist s th e rst fu lly edged tech n ology for th ree-dim en sion al im aging of th e orom axillofacial region . In p arallel, rad iat ion protect ion legislat ion h as been th orough ly revised . Radiat ion p rotect ion an d im age qualit y are t w o closely in tert w in ed p illars of th e X-ray ordin an ce. Over th e years, th e In tern at ion al Com m ission on Radiological Protect ion h as in t roduced in creasingly con crete an d d etailed p rovision s. Th e “as low as reason ably ach ievable” (ALARA) prin ciple, w h ich st ates th at th e pat ien t sh ou ld on ly be exp osed to as m u ch radiat ion as reason ably n ecessar y, m u st also be applied in full to den t al radiology. Th e key to h igh -qualit y radiograph ic diagn osis is com preh en sive t rain ing du ring den t al sch ool; th is ser ves to en su re th at , in later pract ice, in dividuals w ill on ly be exposed to X-rays if really n ecessar y. Den t ist s also learn in den tal sch ool h ow to p erform p ract ical radiat ion p rotect ion p rocedu res an d h ow to obt ain radiograph s of good diagn ost ic im age qu alit y. Moreover, con t in u ing ed u cat ion an d t rain ing during th e course of profession al pract ice is essen t ial. On ly th ose profession als w h o h ave u p -to-date radiological kn ow ledge an d skills can perform X-ray procedu res resp on sibly. Th is book d escribes th e essen t ials of den t al radiography w ith ou t w h ich it w ou ld be im possible to un derst an d th e con cepts of im age qualit y an d radiat ion protect ion .

x

Likew ise, it explain s th e fun dam en tals of X-ray physics an d provides pract ical in form at ion an d in st ruct ion s for th e di eren t tech n iqu es used in den t al radiography. Th e book is design ed as a step -by-step guide to h elp st u den t s learn d en t al radiograp hy. At th e sam e t im e, it w as con ceived as a referen ce to h elp den t ists in private pract ice an d h osp itals ach ieve opt im al resu lt s in den t al X-ray diagn ost ics in -o ce or in th e un iversit y teach ing set t ing. A good kn ow ledge of th e tech n iques of in t raoral radiography an d den t al p an oram ic radiograp hy is cru cial to obt ain ing good radiograph ic im age qualit y. Th e tech n iqu e of con e beam com p u ted tom ograp hy is becom ing m ore an d m ore est ablish ed. An exact kn ow ledge of X-ray im age form at ion an d of th e diverse possibilit ies for using th e en orm ous am oun t s of dat a collected is n ecessar y for opt im al use of th is w ide-ranging tech n ique. At th e en d of th e X-ray exam in at ion , th e t ask at h an d is in terpretat ion of th e n dings, w h ich plays an in creasingly im p ort an t role in den t al radiology. Even pan oram ic radiograph s can provide a large n um ber of n dings. Im ages from con e beam com pu ted tom ography yield far m ore diagn ost ic in form at ion . Th erefore, m any pract ical aids are given for th e opt im al in terpret at ion of result s. In order to keep radiat ion exposure as low as possible, a just ifying in dicat ion m ust be est ablish ed before begin n ing any t ype of X-ray exam in at ion . A precise kn ow ledge of th e m any diagn ost ic p ossibilit ies is also absolu tely n ecessar y, in order to respect th e ALARA prin ciple in den t al radiology. Correct pract ical perform an ce of th e exam in at ion resu lt s in h igh d iagn ost ic im age qu alit y. If all step s are perform ed an d executed according to th e latest st an dards of scien ce an d tech n ology, th en opt im al diagn osis is assured. Andreas Fuhrm ann, DDS

Acknow ledgments First an d forem ost , I w ould like to th an k Professor Dr. Fried rich An ton Pasler, w h o asked an d en couraged m e to w rite a textbook of den tom axillofacial radiology. I give h im great credit for th is because, by doing so, h e virt ually design ated h is su ccessor. I con sider it a great h on or th at h e ch ose m e. Th is book is th e p roduct of m any years of pract ical an d th eoret ical exp erien ce gain ed w h ile teach ing at th e Depart m en t of Radiology of th e Cen ter for Den t al an d Oral Medicin e, Un iversit y Med ical Cen ter Ham bu rg-Ep pen dorf, Germ any. How ever, it is n ot possible to w rite such a book w ith ou t su pport . First , I w ou ld like to th an k m y w ife An n e for h er p at ien ce an d u n derstan ding. Likew ise, I am ver y m u ch in debted to m y st a for a w ide range of su pp or t . I w ould also like to express m y grat it ude to Dr. Christ ian Urbanow icz and Dr. Daria Wojciukiew icz from Thiem e

Verlag, w ho super vised the original Germ an edit ion w ith large am ou n ts of u n derstan ding an d pract ical assistan ce, an d to Angelika-Marie Findgot t from Th iem e Publishers St ut tgart, w ith out w hom there w ould h ave been no English edition. The English version has again show n that dental radiology is a ver y special and challenging eld of radiology that dem ands a high level of expertise an d a deep understanding of th e com plex issues involved. Suzyon O’Neal Wandrey, w ho provided the translation of the Germ an edit ion, and Dr. Mart ina Habeck, w ho m anaged the editorial stages of th e project, did an outstanding job in creating th is English version an d m aking m any valu able suggest ions for im provem ent . Finally, I w ould like to exten d a n ote of th an ks to Ruth Gu tberlet , w h o tran slated the poem by Eugen Roth w ith w it and skill.

xi

Chapter 1 History and Development of Dental Radiography

History and Developm ent of Dent al Radiography

1 History and Development of Dental Radiography

1

W hile conduct ing experim en ts in his laborator y at the Physics In stit ute of the Universit y of Wü rzburg, Germ any, on Novem ber 8, 1895, physicist Wilh elm Conrad Röntgen obser ved th at “a paper screen w ash ed w ith barium –platin ocyan ide ligh ts u p brilliantly and fluoresces equally w ell, w hether the treated side or th e other be t urned tow ard th e disch arge t ube. The fluorescence w as obser vable t w o m eters aw ay from th e apparat us.” ( Fig. 1.1). Th ese are th e w ords th at Rön tgen used to describe the discover y h e m ade w h ile experim en t ing w ith cath ode ray t u bes. After repeat ing th e experim ents several tim es, he felt certain th at h e h ad in deed discovered “a new kind of rays.” Th e rst p relim in ar y ph otograph ic eviden ce of th is discover y p robably sh ow ed h is ow n h an d, but th e rst “roen tgen ogram ” on reliable record w as th at of h is w ife’s h an d, t aken on Decem ber 22, 1895. Rön tgen p u blish ed th e details of h is discover y an d n dings in th ree com m un icat ion s: ● Prelim in ar y com m u n icat ion dated Decem ber 28, 1895: On a New Kind of Rays ( Fig. 1.2) ● Secon d com m u n icat ion dated March 9, 1896: On a New Kind of Rays ● Th ird com m u n icat ion dated March 10, 1897: Further Observat ions on the Propert ies of X-rays.













Rön tgen h im self referred to th is n ew t yp e of radiat ion as “X-rays.” At th e m eet ing of Germ an Physico-Medical Societ y on Jan u ar y 23, 1896, w h ere h e presen ted h is discover y, it w as decid ed to call th em “Roen tgen rays” in stead . Th e n am e “X-rays” is st ill u sed in English -speaking count ries today. Im p or tan t dates in th e h istor y an d develop m en t of den tal radiography are described below. ● 1896: Th e r st X-rays of t h e teet h w ere p robably t aken in late Jan u ar y an d early Febru ar y 1896. Th e rst d en t al radiograp h s on record are th ose of Fried rich Ot to Walkh o , a Germ an den t ist w h o lay m ot ion less on th e oor for 25 m in utes to ach ieve blur-free im ages d uring th e long exposu re t im e n eeded. Oth er d en t al X-rays from th is early p eriod w ere taken by Germ an

Fig. 1.1 Fluorescence of intensifying screens of three di erent thicknesses.

2





physicist Walter Kön ig. In th e follow ing years, th e in t rodu ct ion of X-ray t u bes w ith a p lat in u m p late an ode cut th e exposure t im e in h alf. 1896: C. Edm u n d Kells described th e rst lm -h old er for den t al radiography, w h ich w as m ade of h igh ly perm eable alum in um . Kells is th u s credited as being th e fath er of th e paralleling tech n ique. How ever, th e glass plates u sed as im age receptors at th at t im e w ere gen erally h eld in th e pat ien t’s m outh by th e den t ist . 1897: Th e rst dou ble-coated cellu loid lm s w ere m ade in 1897 but w ere n ot used in rout in e pract ice un t il 1923. 1897: Edison an d Geh ler developed in ten sifying screen s th at w ere coated w ith calciu m t ungstate. 1904–1907: The bisecting-angle technique of intraoral radiography was described by t wo independent researchers, Price (1904) and Cieszynski (1907) ( Fig. 1.3). 1904–1925: Th e r st d en t al X-ray m ach in e w as developed in 1904. How ever, th e angular t u be required for th is m ach in e w as n ot develop ed u n t il 1919 by Garretson , an d w as rst in st alled in den t al X-ray equipm en t in 1925. Th ese tech n ical advan ces m ade it possible to capt u re di eren t angles of in ciden ce of th e beam w ith m u ch bet ter precision . 1921: Fren ch inven tor An dré Bocage, th e fou n der of conven t ion al tom ograp hy, ap plied for a p aten t for a fu n ct ion al tom ograph ic un it . 1921: Ow ing to th e lack of su itable lm -h olders for th e paralleling tech n ique, Collin s Le Master proposed th e use of “a roll of absorben t cot ton cem en ted or oth erw ise secu red to th e lm h old er,” to align th e plan e of th e lm perp en dicu lar to th e axis of th e teeth . 1925: How ard R. Raper develop ed th e bitew ing exam in at ion tech n ique for opt im al detect ion an d diagn osis of approxim al caries.

Fig. 1.2 Detail of the title page of the Proceedings of the Meeting of the Würzburg Physico-Medical Societ y, Germany, in 1895.

History and Developm ent of Dent al Radiography

1

a

b

Fig. 1.3a, b Im age distortion in the root region associated with use of the bisecting-angle technique. (From : Pasler FA, Visser H. Zahn m edizinische Radiologie. 2nd ed. Stut tgart: Thieme; 2000. Farbatlanten der Zahnmedizin; Band 5.) a Bisecting-angle technique: Positioning of the lm packet. b Zygom atic bone projecting to the root region.

Fig. 1.4 X-ray sphere introduced by Siem ens.











1928: Th e rst den t al X-ray u n its w ith h igh -volt age protect ion w ere p laced on th e m arket . 1931: Hofrath an d Broadben t in t rodu ced cep h alom etric radiograp hy in to orth odon t ics. 1933: Th e rst X-ray system s h ou sing th e X-ray t u be an d gen erator in a single u n it w ere developed. Th e Siem en s X-ray sph ere is th e m ost fam ou s represen t at ive of th is grou p of d en t al X-ray m ach in es ( Fig. 1.4). Th e so-called single-t an k con st ru ct ion m eth od w as th u s in t roduced in to den tal radiography ( Fig. 1.5). 1933: Nu m at a developed a p an oram ic radiograp hy m eth od capable of im aging th e en t ire upper or low er d en t al arch u sing a slit-beam tech n iqu e ( Fig. 1.6). 1946–1952: Paatero in dep en den tly developed a sim ilar system in 1946. Un like Nu m ata, Paatero con t in u ed to develop h is inven t ion . Bet w een 1949 an d 1952, h e in t rodu ced an X-ray m ach in e for p an oram ic tom ography or pan tom ography ( Fig. 1.7).

Fig. 1.5 Modern technology has greatly reduced the size of the dental X-ray head. A large older m odel is shown on the left, and a signi cantly scaled-down m odern dental X-ray head (Heliodent 70) is shown on the right. The space required for the transform er is highlighted in blue.











1956: Th is year m arked th e in t rodu ct ion of th e Panorex X-ray m ach in e, th e rst dou ble eccen t ric p anoram ic un it . 1959–1961: In th is p eriod, th ere w as con t in u ed developm en t proceeding from th e pan tom ograph to th e or th opan tom ogram . 1961: Magn i cat ion w as in t roduced to pan oram ic radiography by Ot t an d Blackm an ( Fig. 1.8 and Fig. 1.9). 1974: Fu rth er develop m en t of den t al pan oram ic tom ography started in 1974. 1982: Th e Zon arc p an oram ic X-ray m ach in e ( Fig. 1.10), w h ich h ad m any n ew scan n ing program s for th e h ead an d n eck region , w as in t roduced ( Fig. 1.11).

3

History and Developm ent of Dent al Radiography

Fig. 1.6 Schem atic diagram of a panoram ic radiograph (based on Num ata’s m ethod of slit-beam intraoral panoram ic radiography).

1

Dental X-ray tubehead with slit aperture A long, flexible film packet is pressed firm ly to the lingual surfaces of the teeth

The X-ray tube revolves around the patient’s jaw, and the patient rem ains still during im aging

Fig. 1.7 Panoram ic radiograph of a patient by Paatero.

Fig. 1.8 Status-X panoramic X-ray apparatus by Siem ens.

4

Fig. 1.9 This m agni ed panoram ic radiograph taken with the Status-X shows a residual root in the right m axillary sinus of the upper jaw.

History and Developm ent of Dent al Radiography

1

Fig. 1.10 Zonarc panoramic radiography device for supine patients.

Fig. 1.11 Zonarc panoramic radiography device for midfacial imaging.

Fig. 1.13 Galileos cone beam computed tom ography system.





Fig. 1.12 NewTom cone beam computed tomography system for supine patients.











1998: Digital con e beam com pu ted tom ography (CBCT) w as in t roduced as a tom ograph ic m eth od design ed speci cally for im aging of bony st ruct ures in th e h ead region ( Fig. 1.12). 2007: The Galileos digital CBCT system for standing and seated patients ( Fig. 1.13) was launched on the m arket. 2010: A com bin ed pan oram ic radiograp hy an d CBCT system w as in t rodu ced.

1985: Th e Scan ora, a com bin ed system for pan oram ic radiograp hy an d conven t ion al spiral tom ography, w as in t rodu ced in 1985. 1987: Th is year m arked th e begin n ing of d igit al rad iograp h y in d en t al, oral, an d m axillofacial surger y. 1995: Digit al tech n ology for p an oram ic radiograp hy w as in t rodu ced. 1995: “Tran sverse p an oram ic tom ograp hy” w as th e bu zzw ord in 1995.

5

Chapter 2 Radiation Physics

2.1 Types of Radiation

8

2.2 Direct and Indirect Ionization

8

2.3 Corpuscular and Photon Radiation

8

2.4 Interactions bet ween Radiation and Mat ter

9

2.5 Fundam ent al Physical Processes Involved in the Transfer of Photon Energy to Mat ter 10 2.6 Interactions bet ween X-rays and Mat ter

10

2.7 Radioactivit y

11

2.8 Product ion of X-rays

12

Radiation Physics

2 Radiation Physics 2.1 Types of Radiation All life on our plan et is exposed to differen t t ypes of n at urally occu rring radiat ion . Th is radiat ion gen erally occurs in th e form of elect rom agn et ic w aves th at differ on ly by w avelength . Som e radiat ion can be seen or felt if it occu rs at a few sp ecific w avelength s but , in m ost cases, radiat ion can n ot be detected by our sen se organ s. Th is applies in part icular to rays w ith ver y sh or t w avelength s beyon d th e u lt raviolet en d of th e ligh t spect rum . Radiat ion is de n ed as th e em ission an d prop agat ion of en ergy. W h en radiat ion st rikes an object , th e en ergy gen erated in th e radiat ion eld t riggers in teract ion s in th e object . Th e body can w ith stan d a good deal of rad iat ion bu t biological dam age st ar ts w h en it is exposed to sh or t-w avelength rad iat ion . Radiat ion in th e in frared range is perceived as heat radiat ion th at is n ot u n com fort able. Ult raviolet radiat ion , h ow ever, st ar ts to in du ce dam age associated w ith ch em ical react ion s in th e skin th at can p rod u ce su n bu rn . Radiat ion at even sh orter w avelength s is able to kn ock elect ron s ou t of an atom . Th is process is called ion izat ion an d su ch radiat ion is referred to as ion izing radiat ion .

2

Note There are t wo basic t ypes of radiation: ionizing radiation and nonionizing radiation.

2.2 Direct and Indirect Ionization Radiat ion is fu r th er ch aracterized by th e m an n er in w h ich it s ion izing effect s occur. In th e case of directly ion izing radiat ion , th e en ergy from elect rically ch arged par t icles is t ran sferred directly to th e irradiated st ruct ures. Alph a par t icles, beta part icles, an d p roton s are t ypes of directly ion izing radiat ion . In in d irectly ion izing radiat ion , in teract ion s w ith th e irradiated m at ter result in th e gen erat ion of elect rically ch arged p ar t icles w h ich , in t urn , t ran sfer th eir en ergy to surrou n ding st ru ct ures. X-rays an d gam m a rays are form s of in directly ion izing radiat ion .

2.3 Corpuscular and Photon Radiation Ion izing radiat ion can be divided in to t w o t ypes, according to it s physical con sisten cy: corpuscular radiat ion an d ph oton radiat ion . Th e fact th at n uclei m ay be st able or u n stable is on e reason w hy th ese t w o t ypes of radiat ion occur. St able n u clei are an im por tan t par t of ou r ever yday lives an d are gen erally h arm less. Un stable n uclei, on th e oth er h an d, em it ion izing radiat ion an d it is im port an t to protect th e body from th is t ype of radiat ion as w ell as p ossible.

2.3.1 Corpuscular Radiation Alph a an d bet a radiat ion are com m on t ypes of corpuscu lar radiat ion . Corpuscular radiat ion is directly ion izing radiat ion gen erated by th e spon t an eous decay of un stable atom ic n uclei. Th is process is kn ow n as radioact ivit y. Alph a par t icles con sist of h elium n uclei, w h ile bet a part icles are h igh -energy free elect ron s. Alp h a an d bet a rays con sist of part icles w ith rest m ass; th erefore, th ey h ave a relat ively sh ort range. Typically, alph a radiat ion h as a range of on ly a few cen t im eters in air. It s range in t issue is less th an 1 m m because th e at ten uat ion of radiat ion passing th rough t issue is ver y large. Th e range of bet a radiat ion depen ds on th e en ergy of th e radiat ion an d varies from a few m eters in air to on ly a few m illim eters in t issue.

2.3.2 Photon Radiation X-rays an d gam m a rays are form s of elect rom agn et ic radiat ion .

B E

Fig. 2.1 Electromagnetic waves. B: magnetic ux densit y; E: electric eld strength. (Adapted from : Zabel H. Kurzlehrbuch Physik. Stut tgart: Thieme; 2011.)

8

2.4 Interactions bet ween Radiation and Mat ter

Fig. 2.2 The electrom agnetic spectrum . (From : Zabel H. Kurzlehrbuch Physik. Stut tgart: Thiem e; 2011.)

10 –6 nm 10 –5 nm 10 –4 nm

Gam m a rays

2

10 –3 nm 10 –2 nm 10 –1 nm

X-rays

400 nm

1 nm 10 nm 100 nm

Violet Blue

Ultraviolet radiation

Green

1,000 nm = 1 m 10 m

Visible light

100 m

Infrared radiation

1,000 m = 1 mm 10 m m = 1 cm

Yellow Orange Red 700 nm

Microwaves

10 cm 100 cm = 1 m 10 m 100 m 1,000 m = 1 km

Radio waves

10 km 100 km

Elect rom agn et ic w aves are m ade from elect ric an d m agn et ic elds. Elect ric elds an d m agn et ic elds are closely related . Elect rom agn et ic w aves are t ran sverse w aves becau se th e elect ric eld w aves are perpen dicular to th e m agn et ic u x den sit y ( Fig. 2.1). Un like corp u scu lar radiat ion , p h oton radiat ion h as n o rest m ass. Th erefore, it t ravels at th e sp eed of ligh t in air as w ell as in a vacu um . Th e en t ire elect rom agn et ic spect ru m con sist s of ph oton an d elect rom agn et ic radiat ion w avelength s, ranging from ver y long-w avelength radio w aves to ver y sh or tw avelength gam m a rays ( Fig. 2.2).

2.4 Interactions betw een Radiation and Matter Th e m ain p hysical p rocesses involved in en ergy t ran sfer are th e excit at ion an d ion izat ion of atom s exposed to radiat ion . Kn ow ledge of th e st ruct ure of atom s is th erefore n eeded to u n derstan d th e processes associated w ith ion izat ion .

From th e w ork of Ern est Ruth erford (1911) an d Niels Boh r (1913), it is kn ow n th at an atom con sist s of a posit ively ch arged n ucleu s surroun ded by a sh ell of n egat ively ch arged elect ron s th at t ravel in circular orbits aroun d th e n ucleu s. Th e n um ber of elect ron s correspon ds to th e atom ic n um ber or n uclear ch arge of th e atom . Th e atom ic n um ber is equivalen t to th e n um ber of protons in th e n ucleus. Th e ch aracterist ic posit ion of an elem en t on th e periodic table is determ in ed by it s atom ic n um ber. Atom s n orm ally h ave an equal n um ber of elect ron s an d proton s, so th ey are elect rically n eut ral. Th e fact th at th e elect ron s revolve arou n d th e n ucleu s in di eren t path s is im p ort an t for variou s react ion s involving ph oton s. Th e orbit s or sh ells are represen ted, from th e n ucleu s out w ards, by th e let ters K, L, M, N, O, P, an d Q. Each sh ell can accom m odate a xed n um ber of elect ron s. Th e sh ell capacit y ranges from t w o elect ron s in th e K sh ell to 18 elect ron s in th e M sh ell. Th e n u m ber of elect ron s th at can be accom m odated in a sh ell in creases w ith th e atom ic n um ber of an elem en t . Th e h igh er th e atom ic n um ber of an elem en t , th e larger th e n um ber of elect ron s th at it can accom m odate. Th is, in t urn , h as an e ect on th e absorpt ion beh avior of th e elem en t .

9

Radiation Physics

Note The m ore electrons an element has, the more photons it can absorb. This fact plays an important role in the recognition of di erent tissues and in diagnostics.

2

2.5 Fundamental Physical Processes Involved in the Transfer of Photon Energy to Matter W h en in com ing p h oton s st rike m at ter, t w o p hysical processes m ay occu r: excitat ion or ion izat ion .

2.5.1 Excitation Th e addit ion of en ergy to an atom from an extern al sou rce can cau se elect ron s to be displaced from an in n er sh ell of th e atom to an outer sh ell. Th is ver y brief st ate is called excit at ion . In th e p rocess of excitat ion , n o elect ron is ejected from th e atom an d n o ion izat ion occurs. Sin ce th e sh ells of an atom m u st alw ays be fu ll, th e vacan cies created in n ow in com p lete in n er sh ells m u st , in t u rn , be filled by elect ron s from ou ter sh ells. In th e p rocess, th e elect ron s th at fall from th e ou ter sh ells to fill th e vacan cies in th e in n er sh ells em it en ergy in th e form of elect rom agn et ic ph oton rad iat ion . Th e vacan cies left in th e ou ter sh ell resu lt ing from th is elect ron m ovem en t m u st , in t u rn , be filled by oth er free elect ron s. If th ese elect ron sh ell-to-sh ell t ran sit ion s occu r in th e region of th e in n erm ost sh ell, th en en ough en ergy is gen erated for th e p roduct ion of X-rays. Sin ce th e w avelength of th ese X-rays is depen den t on th e speci c t ype of an ode m aterial, th is kin d of radiat ion is referred to as ch aracterist ic X-rays. Conversely, elect ron sh ell-to-sh ell t ran sit ion s in th e region of th e m iddle sh ells result in th e product ion of u lt raviolet ligh t , an d th ose in th e region of th e outerm ost sh ell resu lt in th e produ ct ion of low -level en ergy perceived as visible ligh t .

Note Electron shell-to-shell transitions in the region of the innermost shell of an atom result in the release of energy in the form of electrom agnetic radiation at wavelengths in the range of X-rays.

10

2.5.2 Ionization Ion izat ion occurs w h en th e en ergy of an in ciden t ph oton is com pletely absorbed an d t ran sferred to an elect ron . Th e am oun t of en ergy t ransferred in th e process is so great th at it overcom es th e bin ding en ergy of th e elect ron , kn ocking th e elect ron out of it s sh ell an d eject ing it from th e atom . Such an atom is said to be ion ized. Th e ejected elect ron can , in t u rn , ion ize oth er atom s.

2.6 Interactions betw een X-rays and Matter W h en in ciden t X-rays collide w ith m at ter, th ey pass th rough th e m at ter but are at ten uated in th e process. In physical term s, th e en ergy of th e ph oton s is eith er ab sorbed or propagates fur th er as scat tered radiat ion . Th e am oun t of at ten uat ion is determ in ed by th e th ickn ess, den sit y, an d atom ic n u m ber of th e irradiated m aterial.

Note As X-rays pass through the body, the X-ray beam is attenuated, or weakened as a result of the absorption of photons and the production of scat tered radiation.

2.6.1 Absorption—Photoelectric E ect Th e absorpt ion of radiat ion t akes place m ain ly w ith in th e in n er sh ells of an atom . Sin ce X-ray beam s con sist s of ph oton s, X-ray absorpt ion is also referred to as th e ph otoelect ric effect ( Fig. 2.3). A fract ion of th e en ergy of th e in com ing X-ray ph oton is used to eject an elect ron from its in n er sh ell, an d th e em it ted ph oton receives th e rem aining en ergy as kin et ic en ergy. Subsequen tly, th e ejected elect ron in duces m ore ph otoelect ric effect s in oth er atom s. As in excitat ion , th e vacan cy left in th e in n er sh ell of an atom du e to th e eject ion of elect ron s is th en lled by elect ron s dropping dow n from ou ter sh ells. Th e en ergy released in th e process is em it ted from th e atom in th e form of ch aracterist ic X-radiat ion . Th e ph otoelect ric e ect plays a crucial role in diagn ost ic radiography, w h ere volt ages of up to 100 kilovolt s (kV) are applied. Th e low er th e kilovoltage level, th e greater th e ph otoelect ric absorpt ion , an d th e h igh er th e atom ic n um ber of th e irradiated m aterial, th e greater th e ph otoelect ric e ect . Th is is w hy bony st ruct u res are best visu alized at low er kilovolt age levels of aroun d 50 kV. From levels of aroun d 60 kV, th e ph otoelect ric e ect decreases sh arply w ith in creasing kilovolt age, w ith a proport ion al in crease in scat tered radiat ion . Th e size of th e t w o fract ion s is ap proxim ately equ al at 60 kV.

2.7 Radioactivit y

e e

_

2

_

Photon

Photon

Nucleus

Nucleus

K shell

K shell

L shell

L shell

Fig. 2.3 Photoelectric e ect. (From : Schwenzer N, Ehrenfeldt M, eds. Chirurgische Grundlagen. 4th ed. Stut tgart: Thiem e; 2008.)

2.6.2 Scattered Radiation— Compton E ect Besides th e ph otoelect ric effect , th e secon d p hysical process th at p lays an im port an t role in diagn ost ic radiology is th e Com pton effect , or Com pton scat tering. Th e Com p ton effect also involves th e eject ion of an elect ron from it s atom ic sh ell. How ever, un like th e ph otoelect ric effect , outer-sh ell elect ron s are affected rath er th an in n er-sh ell elect ron s. Becau se ou ter-sh ell elect ron s h ave relat ively low bin ding en ergy, they can be m ore easily ejected from an atom . Th erefore, on ly a fract ion of th e in com ing ph oton en ergy is requ ired to eject th ese elect ron s. Th e rem ain ing en ergy is d eflected from th e atom , at an angle of 0 to 180 degrees, as a scat tered ph oton . Th erefore, th e angle of scat tering can be qu ite large ( Fig. 2.4). In spite of th e en ergy loss, th e ejected elect ron an d scat tered radiat ion can st ill u n dergo fu rth er ion izat ion in teract ion s. Sin ce scat tered X-rays can t ravel in all direct ion s, th ey st rike th e im age receptor (e. g., X-ray lm ) from arbit rar y angles. Th erefore, scat tering results in a sign i can t reduct ion of con t rast . Th e Com pton e ect is a m ajor factor determ in ing th e en ergy level u sed in den t al X-ray im aging. At 60 kV, p h otoelect ric an d Com pton -e ect in teract ion s are ap p roxim ately equ al. Classical scat tering w ith out en ergy loss an d pair produ ct ion does n ot play a role in diagn ost ic radiology. Th e reason for th is is th at classical scat tering on ly occu rs w ith ver y “soft” X-rays an d pair product ion on ly occurs in th e m ega elect ron volt (MeV) range.

Fig. 2.4 Compton scat tering. (From : Schwenzer N, Ehrenfeldt M, eds. Chirurgische Grundlagen. 4th ed. Stut tgart: Thiem e; 2008.)

Note The photoelectric e ect has its greatest e ect at low voltages of up to ~ 50 kV. X-ray im ages produced in this low-voltage range are characterized by high contrast. This high contrast is possible because the scat tered radiation component is very sm all, resulting in very sharp visualization of bony structures. On the other hand, these so-called soft-rays are associated with a very large degree of absorption and thus disproportionately high radiation exposure. This is why all dental X-ray machines that used to operate at 50 kV were prohibited. Today, radiation protection guidelines stipulate that the kilovoltage of dental X-ray machines must not be less than 60 kV. This operating kilovoltage achieves a good compromise bet ween the qualit y of the dental X-ray image and radiation exposure.

2.7 Radioactivity Atom s w ith st able n u clei h ave an equ al n u m ber of proton s an d n eut ron s. If, h ow ever, th e n um ber of n eut ron s differs from th e n um ber of proton s (th at is, if th e n eut ron to proton rat io is too low or too h igh ), th en th e atom h as an un st able n ucleus. Un stable n uclei u n dergo radioact ive decay at variable rates an d are ult im ately conver ted back in to st able n uclei. Nuclei un dergoing radioact ive decay are term ed rad ioact ive n u clides (radioact ive isotop es), or radion uclides (radioisotopes) for sh ort . Radioact ivit y refers to th e process of radioact ive decay. Radioact ive radiat ion con sist s m ain ly of alph a part icles (h eliu m n u clei), beta p ar t icles (elect ron s), an d gam m a rays (ver y h igh -en ergy elect rom agn et ic radiat ion ).

11

Radiation Physics It is categorized by sou rce as terrest rial, cosm ic, or art i cial radiat ion . Th e di eren t t yp es of rad iat ion h ave differen t m ech an ism s of act ion .

2.8 Production of X-rays

2

2.8.1 Dental X-ray Equipment In den tal X-ray equ ipm en t , th e X-ray gen erator an d X-ray t ube are con tain ed togeth er in th e sam e radiat ion -p roof h ou sing. Th is m od ern single-tan k design allow s th e m an ufact u re of sm all an d easy-to-h an d le X-ray m ach in es, w h ich are ver y w ell suited for use in den t al radiography ( Fig. 2.5 an d Fig. 2.6). Th e X-rays are gen erated in a glass X-ray t ube ( Fig. 2.7). Th e glass X-ray t u be con tain s all th e essen t ial techn ical com p on en t s requ ired for th e gen erat ion of X-rays. Th e X-ray t u be an d th e gen erator produ cing th e h igh an d low voltage n eeded for th e product ion of X-rays are located togeth er in th e radiat ion -proof h ousing. Th e radiat ion -proof X-ray t u be h ou sing is com p letely lled w ith oil, w h ich act s as an in sulator. Th e radiat ion -proof h ou sing of all X-ray m ach in es m u st be in spected regu larly to preven t leakage radiat ion . Oil leakage is a sure sign of defect s in th e radiat ion -p roof h ou sing. If oil leakage is detected, operat ion of th e equip m en t m ust be stopp ed im m ediately.

Fig. 2.5 Dental X-ray tube with a short spacer cone (m ay no longer be used today).

12

X-ray Tube Design X-rays are p rodu ced w h en h igh -speed elect ron s com ing from th e cath ode are sudden ly decelerated or stopped by th e an ode ( Fig. 2.8). To produce X-rays, several tech n ical requirem en t s m ust be m et . First , the X-ray t u be m ust be sealed in an evacuated glass envelop e. Secon d, it m u st h ave a cath ode th at ser ves as th e source of elect ron s. Th ird, a braking m ech an ism m ust be presen t th at is capable of w ith st an ding th e h igh tem perat ures produ ced by th e decelerat ion of h igh en ergy elect ron s, w h en tem perat ures as h igh as 2,500 °C m ay occu r. Th e m aterial requ irem en ts for th e cath ode an d an ode are th us ext rem ely h igh . Last but n ot least , th e X-ray t ube m u st h ave a good cooling system th at m u st be able to con du ct h eat aw ay e cien tly.

Cathode To en sure an adequate supply of elect ron s for accelerat ion , a filam en t h eat ing circu it delivers low volt age (8– 12 V) an d curren t (3–6 A) to th e cath ode filam en t . Th e filam en t , w h ich gen erally con sist s of a coiled t ungsten w ire, is th u s h eated to in can descen ce (2,000 °C). Ow ing to th e in ten se h eat , elect ron s det ach from th e m et al surface an d

2.8 Production of X-rays

Fig. 2.8 High-speed electrons striking the anode. (From : Albes G. Facharztprüfung Radiologie. 2nd ed. Stut tgart: Thiem e; 2010.)

Tube voltage

2

Evacuated envelope Anode

Filam ent

Cathode Electrons

X-rays

Cathode

Anode

are released as a cloud of elect ron s in a process kn ow n as th erm ion ic em ission . Sin ce th e focal sp ot on th e an od e is sm aller th an th e elect ron clou d em it ted from th e t u ngsten w ire, th e elect ron s m u st be gu ided tow ard th e an ode. Th e Weh n elt cylin der, a n egat ively ch arged elect rode th at su rrou n d s th e cath ode, ser ves to focus an d guide th e em it ted elect ron beam so th at it converges an d st rikes th e an ode at a precisely d e n ed poin t , to produ ce th e sm allest focal spot possible ( Fig. 2.9).

High voltage is n ecessar y for th e gen eration of X-rays. In accordance w ith radiat ion protect ion guidelines, dental X-ray m ach in es m ust n ot be operated at voltages of less than 60 kV. The curren t intensit y is generally less than 1 A. Sin ce den t al X-ray m ach in es w ork on low t ube curren t , stat ion ar y an odes can be used ( Fig. 2.10). St at ion ar y an odes con sist of a sm all t u ngsten –rh en ium plate (an ode target) em bedded in a block of cop per designed to dissipate h eat . Rot at ing an odes are u sed in X-ray m ach in es w ith h igh er perform an ce, th at is, m ach in es that produce m ore elect ron s th at bom bard th e an ode ( Fig. 2.11). William Coolidge in t roduced th e rot at ing an ode in 1916. Rotating an odes h ave a circu lar rotat ing p late th at rotates at speeds of 3,000 to 90,000 rpm . Rot at ing an odes dist ribute th e h eat produced in th e process of X-ray gen erat ion over a larger area, w h ich redu ces th e overh eat ing an d w earing of an ode m aterial. Tungsten –rh en ium alloy is used as th e an ode m aterial. To reduce geom et ric un sh arpn ess, th e size of th e focal spot sh ould be as sm all as possible. How ever, for m aterial reason s (ow ing to h igh -tem p erat u re h eat produ ct ion ), th e so-called focal spot can n ever be an act ual poin t source. Th erefore, th ere w ill alw ays be som e degree of geom et ric un sh arpn ess, w h ich w ill in evit ably im pair im age qualit y to som e exten t .

Anode A secon d circu it is n eeded to p rodu ce th e h igh voltage required to accelerate th e elect ron s tow ard th e an od e. Unlike th e filam en t h eat ing circu it , th e accelerat ing circuit run s on ver y h igh volt age an d low cu rren t .

Fig. 2.10 Stationary anode.

13

Radiation Physics

Evacuated X-ray tube

Fig. 2.11 Rotating anode. (From : Zabel H. Kurzlehrbuch Physik. Stut tgart: Thieme; 2011.)

Rotating anode (= tungsten target) Stator

Rotor

2 ~ 10 V

Grounding

+ 60,000 V

Filam ent Electron beam

X-rays

Fig. 2.12 Angulation of the anode for the production of a sm all apparent focal spot (schem atic diagram). Electrons Actual focal spot

Anode angle

Central beam

Apparent focal spot

To m ake th e focal spot size as sm all as possible, it is ar ti cially redu ced by using an angled t arget an d th e lin e focu s p rin cip le. Con sequen tly, th e size of th e e ect ive focal spot is sm aller th an th at of th e act ual focal spot . Th is is accom plish ed by angu lat ion of th e an ode relat ive to th e beam ( Fig. 2.12). Ow ing to th e ver t ical con gu rat ion of th e lam en t an d Weh n elt cylin der, a n arrow rect angular focal spot is produ ced on th e sm all (~2 m m ) t u ngsten –rh en iu m p late of th e an ode. By ch anging th e an ode angle to ~15 d egrees, th e sh ape of th e apparen t focal spot also ch anges. In stead of appearing as a lin e, th e projected elect ron s from th e lam en t are n ow focused as a rect an gle, correspon ding to th e app aren t (e ect ive) focal spot . Den t al X-ray m ach in es h ave an e ect ive focal spot size of ~0.6 × 0.6 m m .

14

Multi-pulse Generators Mult i-pulse gen erators h ave been used for m any years to im prove th e perform an ce of den t al X-ray m ach in es. In gen erators of th is t ype, th e prim ar y m ain s voltage of altern at ing (AC) cu rren t is rect ified an d sm ooth ed an d th en processed an d t ran sform ed in to h igh er-frequ en cy AC volt age. Th is t ran sform ed volt age is su bjected to fu rth er h igh -frequen cy t ran sform at ion , rect ificat ion , an d sm ooth ing ( Fig. 2.13). Mult i-pulse gen erators in crease th e e cien cy of den tal X-ray m ach in es sign i can tly an d protect th em from volt age uct uat ion s in th e pow er grid.

2.8 Production of X-rays

Mains synchronization

DC link filter

Inverter

Highvoltage transform er

Highvoltage rectifier

Highvoltage capacitor

Tube

2

U

t

Fig. 2.13 Operating principle of a multi-pulse generator.

Note An X-ray tube has t wo electrical circuits: a lament heating circuit that supplies low voltage and current to the cathode for the generation and em ission of electrons, and a high-voltage circuit that supplies accelerating voltage to the anode for the acceleration of electrons produced at the lam ent. An increase in lam ent heating voltage results in increased em ission of electrons. If the lament heating voltage cannot be adjusted, then the num ber of electrons produced m ust be controlled by adjusting the exposure tim e. The am ount of electrons a ects the degree of blackening (densit y) of X-ray lm. An increase in voltage (kV) results in generation of X-rays with higher energy, shorter wavelengths, and greater penetrating power. The decision to use high voltage depends on the thickness and densit y of the imaged object. An increase in voltage a ects contrast but not densit y (the degree of darkening of X-ray lm ).

Interactions of Electrons w ith the Anode Material W h en elect ron s are su dden ly decelerated or stopp ed by th e an od e, 99 %of th e en ergy of th e elect ron s is converted in to h eat , an d on ly 1 % is conver ted in to X-rays. Tw o p hysical processes lead to th e gen erat ion of t w o di eren t t yp es of X-rays: (1) ch aracterist ic X-rays, w h ich are p rodu ced w h en elect ron s from th e cath ode st rike elect ron s on th e in n erm ost sh ells of an atom , an d (2)

brem sst rah lung, or “braking radiat ion ,” w h ich is produced from th e kin et ic en ergy lost by elect ron s th at are decelerated by th e n u cleu s of an atom .

Characteristic X-rays Ch aracterist ic X-rays are produced by in teract ions of th e elect ron s com ing from th e cath ode w ith sh ell elect ron s in th e atom s of th e an ode m aterial. According to th e Boh r m odel of th e atom , elect ron s can m ove from sh ell to sh ell arou n d th e n u cleu s of an atom , but can n ot exist out side of th e sh ells. Th e n um ber of elect ron s in a given sh ell is exactly de n ed an d can n ot be ch anged w ith out con sequ en ces for th e atom . W h en a h igh -speed elect ron com ing from th e cath ode en ters th e atom , disp laces an elect ron from an in n er sh ell, an d eject s it from th e atom , leaving a vacan cy in th e sh ell, th en th is vacan cy m u st be lled by an oth er elect ron . Con sequen t ly, an elect ron from a h igh er-en ergy ou ter sh ell m u st fall dow n to th e low er-en ergy in n er sh ell to ll th e vacan cy left by th e ejected elect ron . Th e vacan cy in th e outer sh ell m ust , in t urn , be lled by an oth er elect ron . En ergy is th ereby released in th e form of ch aracterist ic X-rays, or ch aracterist ic radiat ion ( Fig. 2.14).

Bremsstrahlung W h en elect ron s from th e cath ode com e close to th e n ucleus, th ey are deflected in th e elect ric field of th e n ucleus. Th e kin et ic en ergy lost by th e elect ron s in th e process does n ot “van ish ” but is converted in to ph oton s, or en ergy quan t a.

15

Radiation Physics

Fig. 2.14 Characteristic X-rays (schem atic diagram ). (From : Albes G. Facharztprüfung Radiologie. 2nd ed. Stut tgart: Thiem e; 2010.)

Characteristic X-rays

2

Nucleus Characteristic X-rays

K shell

L shell

M shell

Brem sstrahlung photon 3 Electron 3 Brem sstrahlung photon 2

Electron 2 Electron 1

Fig. 2.15 Brem sstrahlung (schem atic diagram ). (From : Albes G. Facharztprüfung Radiologie. 2nd ed. Stut tgart: Thiem e; 2010.)

Brem sstrahlung photon 1

Atom ic nucleus

Ver y t iny fract ion s (a few th ou san d th s) of th e elect ron s lose all of th eir kin et ic en ergy im m ediately. In oth er w ord s, th e tot al en ergy level of th ese elect ron s is used for th e p rod u ct ion of p h oton s. Th erefore, th e vast m ajorit y of th e elect ron s em it on ly a variable port ion of th eir kin et ic en ergy in th e form of h eat u n t il th ey are converted, so m ost of th e ph oton s em it ted by th ese elect ron s h ave a low er en ergy level th an th e form er t ype. Th erefore, all en ergy levels are rep resen ted an d th is produ ces a con t in u ous sp ect ru m of brem sst rah lung ( Fig. 2.15).

Note Brem sstrahlung is the product of the interaction of incident electrons with the electric elds of the nuclei of the anode m aterial. Because the individual electrons are decelerated di erently, this results in the production of an X-ray spectrum with a range of di erent wavelengths.

16

Properties and Characteristics of X-rays Ow ing to th eir ion izing effect , X-rays h ave ver y special propert ies an d ch aracterist ics th at can be ut ilized in variou s w ays. ● At ten u at ion : W h en X-rays p en et rate m at ter, th ey are at ten uated (w eaken ed) by absorpt ion an d scat tering. ● Lu m in escen ce: X-rays st im u late cert ain su bst an ces to em it ligh t . Th e prin ciple of lum in escen ce is used for X-ray im age in ten si cat ion an d dose reduct ion ( Fig. 2.16). ● Ion izat ion : X-rays ion ize air an d gases an d can th u s be m easured. ● Ph otoelect r ic e ect : X-rays h ave a ph otoelect ric e ect an d darken X-ray lm ( Fig. 2.17). ● Sem icon d u ctor e ect : X-rays ch ange th e ch arge an d con duct ivit y of sem icon ductors (th is h as applicat ion s in digit al radiography).

2.8 Production of X-rays How ever, th e w eakest X-rays in th e beam are already ltered by m aterials presen t w ith in th e radiat ion -proof t ube h ousing before th ey reach th e exit w in dow of th e t ube h ou sing. Th e m aterials respon sible for th is in h eren t lt rat ion are th e glass envelope of th e X-ray t ube an d th e su rroun ding oil th at in su lates th e radiat ion -proof X-ray t ube h ousing. In h eren t lt rat ion h as th e e ect of an alu m in um lter w ith a th ickn ess of 1 to 2.5 m m . Total t ube lt rat ion is th erefore de n ed as in h eren t lt rat ion an d addit ion al lt rat ion by alum in u m lters.

2

Note Fig. 2.16 X-ray beam generates light on an intensifying screen.

Total tube ltration is required by law. According to international standards, the total tube ltration m ust be equivalent to at least 1.5 m m of aluminum in dental X-ray equipm ent operating up to 70 kV, and equivalent to at least 2.5 m m of alum inum in equipm ent operating at m ore than 70 kV.

Collimator

Fig. 2.17 Dental X-ray lm.

2.8.2 Additional Equipment Needed for Dose Limitation and Improvement of X-ray Image Quality Som e ad dit ion al equ ipm en t is n eeded to en sure th e opt im al im p lem en tat ion of X-ray m ach in es, especially in den tal radiograp hy. Fu ll com p lian ce w ith th e cu rren t gu idelin es for radiat ion p rotect ion an d im age qu alit y is requ ired for ever y X-ray taken . Th is also applies to th e addit ion al equipm en t u sed in radiograp hy.

Filtration of X-rays Filt rat ion of X-rays is m an dator y, ow ing to th e in h om ogen eit y of brem sst rah lung. Most X-rays con sist of low -en ergy radiat ion th at is com p letely absorbed in body t issues an d th u s does n ot con t ribu te to im age form at ion . Alth ough th is low -en ergy radiat ion does n ot h ave any u sefu l e ect s, it m ay, h ow ever, h ave injurious e ect s. Con sequ en tly, alu m in u m lt er s m u st be u sed to p reven t in dividu als from being exposed to th ese rays.

Collim ators are used to n arrow th e beam to th e desired size an d sh ape. W h en ext raoral radiography is perform ed using large im age receptors, th e beam m ust be lim ited, in order to leave a visible u n exposed m argin . Th is ser ves to en sure th at th e beam is n ot larger th an n ecessar y. In t raoral radiograp hy is p erform ed u sing sm all im age receptors, h ow ever, so it is n ot advisable or n ecessar y to leave an u n exp osed m argin . In t raoral X-rays are su bject to di eren t p rin cip les, w h ich requ ire th at a collim ator or spacer con e is used to lim it th e beam an d th us reduce th e area of th e radiat ion eld at th e en d of th e spacer con e to a diam eter of n o m ore th an 6 cm . To en su re th at im age receptors of all t yp es an d sizes are covered, th e guidelin es fu rth er st ipulate th at th e diagon al of th e u seful radiat ion eld at th e en d of th e spacer con e m ust be n o m ore th an 1 cm larger th an th e diagon al of th e act ive surface area of th e largest im age receptor used. In pract ice, th is m ean s th at a sm aller secon dar y collim ator m ust be used w h en th e im age receptor is sm aller th an 3 × 4 cm .

Spacer Cone Th e spacer con e ( Fig. 2.18 an d Fig. 2.19) is of sp ecial im por tan ce in den tal radiography. It h as th ree im port an t fu n ct ion s: ● Beam -in d icat in g d evice (BID): In in t raoral radiography, it is im perat ive th at th e X-ray beam an d th e target teeth of in terest be properly align ed w ith each oth er. ○ W hen using the bisecting-angle technique w ithout fo cusing adjustm ent, it is best to at tach a pointed spacer con e to the X-ray tube housing, to ensure proper alignm ent of the X-ray beam and im age receptor.

17

Radiation Physics

2

Fig. 2.18 Round cone with a round collim ator and a radiation eld of 6 cm .

Fig. 2.19 Secondary collimator with an adapted rectangular aperture designed to lim it the dose to a sm all area of skin ( eld).

Fig. 2.20 Long spacer cone with a sm all secondary collim ator.

W h en th e paralleling tech n ique is used, it is best to u se a long st raigh t spacer con e w ith a sm all secon dar y collim ator, to en sure proper align m en t w ith th e localizer ring ( Fig. 2.20). Sp acer: ○ In dep en den t of sh ap e an d length , th e sp acer con e m u st be posit ion ed as close as possible to th e skin on th e pat ien t’s ch eek. ○ If th e dist an ce w ere larger, th e irradiated area of skin (radiat ion eld) w ould be large. Th is w ould result in p at ien t exposu re exceeding th e m axim u m dose lim it s, an d th e X-ray im age con t rast w ould decrease becau se of an in crease in th e am oun t of scat tered radiat ion reach ing th e im age receptor. Collim ator h old er: Th e collim ator is m ou n ted on th e spacer con e becau se th e length of th e spacer con e cor relates w ith th e size of th e collim ator eld. Becau se th e radiat ion eld size m ust rem ain con st an t , th e collim ator eld size m u st in crease or decrease in accordan ce w ith ch anges in th e length of th e sp acer con e. ○





18





For exam p le, if th e sp acer con e is relat ively sh or t (10 cm ), th en a relat ively large collim ator eld size is n eeded to m ain tain th e radiat ion eld at a con stan t size of 6 cm ( Fig. 2.21). Ow ing to beam divergen ce, th e size of th e collim ator eld decreases as th e length of th e spacer con e in creases, to p reven t th e radiat ion eld from exceeding th e p rescribed diam eter size of 6 cm ( Fig. 2.22).

Collimator Geometry and Radiographic Technique W hen using the paralleling technique of in traoral radiography, th e im age receptor (e. g., film packet) is placed in side a film -holder. Targeting accuracy in creases significan tly w h en im age receptors are u sed. Sm all, rectangu lar secondar y collim ators that are specifically designed for the im age receptor m ay be used for this purpose. Secondar y collim ators can redu ce th e field size on th e skin su rface by up to 50 %, w hich is a m ajor advantage ( Fig. 2.23).

2.8 Production of X-rays

Fig. 2.21 Short spacer cone with a large collim ator.

2 6-cm radiation field

Fig. 2.22 Long spacer cone with a sm all collim ator.

6-cm radiation field

Round spacer cone Rectangular spacer cone Film

Fig. 2.23 Comparison of round versus rectangular collimation.

19

Chapter 3 Dose Terms and Dose Units Used for Ionizing Radiation

Dose Term s and Dose Unit s Used for Ionizing Radiation

3 Dose Terms and Dose Units Used for Ionizing Radiation To qu an t itat ively describe th e exten t an d th e effect s of ion izing radiat ion on th e body, un it s for th e m easurem en t of ion izing radiat ion m ust be defin ed. Because th e exten t an d effect s of rad iat ion depen d on m any factors, several differen t dose un it s are n eeded to describe th e variou s in teract ion s. Th e m ost im p ort an t of th ese d ose u n its are defin ed below.

3

Ion d ose: Th e ion dose is a m easu re of th e ch arges produced by th e X-ray t u be in a given volu m e of air. Th is dose un it is u sed in m et rology. It s physical un it is th e coulom b per kilogram (SI u n it: C/kg). Th erefore, th e ion dose can also be described as th e qu ot ien t of ch arge an d m ass. Rad iat ion absorbed d ose: Th e radiat ion absorbed dose is a m easu re of th e am ou n t of radiat ion absorbed by th e body, referring to th e e ect of rad iat ion on th e d i eren t t ypes of body t issu es. Becau se th e e ect s of th e radiat ion var y by t issue t ype, th e absorpt ion of radiat ion is also depen den t on th e t yp e of t issu e involved. Th e rad iat ion absorbed d ose is th u s a m easu re of absorbed en ergy. It is de n ed as th e qu ot ien t of th e absorbed en ergy im par ted by ion izing radiat ion on a given volum e elem en t of a speci c m aterial an d th e m ass of th is volum e elem en t . Th e radiat ion absorbed dose can n ot be m easu red directly bu t can on ly be calcu lated from th e ion dose an d th e absorp t ion coe cien t . It s p hysical u n it is th e gray (SI u n it: Gy), w h ere on e gray equ als on e jou le per kilogram (1 Gy = 1 J/ kg).

Equ ivalen t d ose: The equivalent dose takes into account the di erent biological e ect of radiat ion of different ionization densit y in t issue. The equivalen t dose is thu s th e un it used in radiat ion protect ion . Its physical un it is the sievert (SI unit: Sv), w hich is used to dist inguish the equivalen t dose from th e radiat ion absorbed dose. ● Radiat ion w eigh t in g factor (W R): Di erent radiat ions h ave di erent ion izat ion densities. Therefore, som e form s of radiation h ave h igh biological e ect iven ess, w h ile oth ers h ave low biological e ect iven ess. X-rays, beta rays, gam m a rays, and electron beam s are assign ed a radiation w eigh ting factor (W R) of 1. The W R of n eutron beam s is 10 to 20, an d th at of alph a part icles is 20. ● Lin ear en er gy t ran sfer (LET): Th e in ten sit y an d spat ial dist ribut ion of ion izat ion produced by radiat ion is greatly dep en d en t on th e t yp e of radiat ion . Th e LET is a m easure of th e so-called radiat ion qualit y. Th is un it in dicates th e order of m agn it u de of in teract ion bet w een a cer tain t ype of radiat ion an d irradiated m at ter. Th e n um ber of ion izat ion s th at radiat ion produces per un it dist an ce as it t ravels th rough t issu e is a m easu reable param eter of lin ear en ergy t ran sfer. Alph a par t icles are ver y den sely ion izing radiat ion . Neu t ron s an d proton s are on ly h alf as den sely ion izing, an d X-radiat ion is sparsely ion izing radiat ion w ith a low ion izat ion den sit y ( Fig. 3.1). Th erefore, th e equ ivalen t dose correspon ds to th e radiat ion absorbed dose m ult iplied by th e radiat ion w eigh t -

Cells (schematic diagram ) x

Photon Beta particle x

Alpha particle

x Ionization Other interactions

22

x

x

x x

x

x

50 µm

x

x x

Fig. 3.1 Linear energy transfer (LET). (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thieme; 2000. Farbatlanten der Zahnm edizin; Band 5.)

Dose Term s and Dose Unit s Used for Ionizing Radiation ing factor, W R. Sin ce X-rays h ave a W R of 1, th e equivalen t dose is n u m erically equ ivalen t to th e radiat ion absorbed dose in den tal rad iography. E ect ive d ose: Th e e ect ive dose equ ivalen t , or e ect ive dose, w as in t roduced as a param eter for est im at ing th e risk of can cer associated w ith radiat ion exp osu re, in a di eren t iated m an n er. Th e rat ion ale beh in d th is is th at som e organ s of th e body are m ore sen sit ive to radiat ion th an oth ers. Th e radiosen sit ivit y est im ates for th e variou s t issue t yp es are accu rate, becau se th ey are based on dat a from a large n u m ber of cases, in cluding sur vivors of th e atom ic bom bings in Hirosh im a an d Nagasaki. By taking th e n um ber of death s as th e basis of calcu lat ion , it is possible to calcu late an organ or t issu e w eigh t ing factor for each p ar t of th e body, based on it s radiosen sit ivit y. Th e In tern at ion al Com m ission on Radiological Protect ion (ICRP) recalculated its t issue w eigh t ing factors in 2007. Becau se of th is, th e valu es for m any organ s h ave ch anged sin ce th e last ICRP recom m en dat ion s w ere pu blish ed in 1979 ( Table 3.1). Th e e ect ive dose is th e su m of th e equ ivalen t doses for each organ or t issue irradiated, m ult iplied by th eir respect ive t issu e w eigh t ing factors. It th u s rep resen t s th e e ect ive dose for th e w h ole body. Th e SI un it of e ect ive d ose is th e siever t (Sv). In addit ion to th ese basic dose term s an d u n it s u sed in d osim et r y, oth er im port an t dose term s play an im por tan t role in th e ever yday u se of X-rays.

Focus distance (in cm )

Dose (in µGy)

30

Table 3.1 Tissue weighting factors (WT) Tissue or organ

W T 1991

W T 2007

Gonads

0.20

0.05

Red bone marrow

0.12

0.12

Colon

0.12

0.12

Lung

0.12

0.12

Stom ach

0.12

0.12

Breast

0.05

0.12

Liver

0.05

0.05

Esophagus

0.05

0.05

Thyroid

0.05

0.05

Skin

0.01

0.01

Bone surface

0.01

0.01

Brain

0.01

Kidney

0.01

Salivary glands

0.01

Remainder

Dose–area product (in µGy• cm ²)

40

25

1,000

60

10

100

1,000

120

2.5

400

1,000

=

0.10

Dose–area p rod u ct : Th e dose–area product is th e in ciden t radiat ion dose m u lt iplied by th e irradiated su rface area. All n ew X-ray m ach in es, in cluding th ose used in den t ist r y, m ust calculate an d display valu es of dose–area product . A record of th e DAP m eter reading is m ade after each exam in at ion ( Fig. 3.2).

Surface area (in cm ²)

X

0.05

3

Fig. 3.2 Dose–area product. (From: Pasler FA, Visser H. Zahnmedizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.)

23

Chapter 4 The Biology of Radiation E ects

4.1 Fundam ent als

26

4.2 Direct and Indirect E ect s of Radiation

27

4.3 E ect s of Ionizing Radiation on DNA

27

4.4 Repair Mechanism s for the Restoration of DNA

27

4.5 Biological E ect s of Radiation Dam age

27

The Biology of Radiation E ect s

4 The Biology of Radiation E ects 4.1 Fundamentals Th e p rocesses th at ult im ately lead to th e biological effects of radiat ion in t issues st ar t w ith th e physical process of absorpt ion . Th e en ergy input from radiat ion in duces con siderable st ru ct ural ch anges in th e t issu es. Com pared w ith oth er agen t s w ith toxic effect s on cells, ion izing radiat ion h as th e h igh est biological efficien cy an d th e h igh est dam age p oten t ial. Th e biological effect of radiat ion develops in a series of p rocesses, st ar t ing w ith p hysical ch anges (p hysical p h ase) th at lead to ch em ical ch anges (ch em ical p h ase) an d, ult im ately, biological ch anges in th e DNA (biological ph ase). W h en radiat ion passes th rough m at ter, it is at ten u ated by absorpt ion an d scat tering processes. Th e resultan t t ran sfer of en ergy to th e irradiated m aterial leads to th e

4

release of elect ron s. Th ese ch arged part icles, in t urn , con t in uou sly in duce furth er ion izat ion processes w ith con st an tly decreasing en ergy. Th e elect ron s released in ph otoelect ric an d Com pton in teract ion s h ave su cien t en ergy to in duce furth er ion izat ion or st im u late th e em ission of fur th er radiat ion on th eir ow n . Th is results in th e product ion of ph oton s w ith less en ergy. How ever, even th ese low er-en ergy ph oton s from th ese various processes st ill h ave en ough en ergy for fur th er st im ulat ion of atom s an d m olecules. Overall, con siderable h eat is gen erated by th e prim ar y an d secon dar y processes involved in th e in teract ion of radiat ion w ith m at ter. Th ese physical processes lead to ch em ical ch anges in th e irradiated area, w h ich can ult im ately lead to biological ch anges.

Radiation field of high-energy photons

Interactions with atom s

Release of electrons (photoelectric, Compton, and Auger effect s)

Scat tered photons (coherent scat tering, Compton scat tering)

Bremsstrahlung photons, characteristic X-radiation

Ionization, excitation, heat

Chem ical effect s Changes in biom olecular structures

Biological effect s Repair processes, degeneration, malignant transform ation, m utation

Fig. 4.1 Schem atic diagram of the e ects of radiation in tissue. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnmedizin; Band 5.)

26

4.5 Biological E ect s of Radiation Dam age

Note Only the fraction of ionizing radiation that undergoes interaction with the tissue can cause biological e ects. All the biological e ects of ionizing radiation are the result of the transfer of energy to the tissue ( Fig. 4.1).

Protein–DNA crosslink

P P G C T A P P C G P P A+T

Base dam age and base release

4.2 Direct and Indirect E ects of Radiation Ion izing radiat ion can h ave d irect or in direct effects. St ru ct u ral ch anges w ith in th e cells, an d m acrom olecular ch anges, are direct effect s, an d ch anges du e to th e p rodu ct ion of free radicals in th e w ater of th e cell are in direct effect s. Free radicals are h igh ly react ive fragm en ts of m olecu les. Th ey t rigger a variet y of bioch em ical react ion s, su ch as hydroxylat ion , decarboxylat ion , redu ct ion , an d oxidat ion . Th ese p rocesses can in d u ce bioch em ical alterat ion s in n orm al biom olecular st ruct ures an d bon ds. Living cells are ~90 % w ater. Th e radiolysis of w ater resu lt s in th e p rodu ct ion of OH• radicals as an oxidan t species, an d in th e product ion of hydrogen radicals, free elect ron s, OH– ion s an d H+ ion s as reducing species. Th e form at ion of peroxide can also occur du e to in teract ion w ith oxygen . Exp osu re to X-rays an d oth er t ypes of low lin ear en ergy t ran sfer ion izing radiat ion pred om in an tly cau ses in d irect e ect s, w h ich are respon sible for up to 70 % of th e overall e ect .

4.3 E ects of Ionizing Radiation on DNA DNA is by far th e m ost crit ical t arget for radiat ion dam age in a cell. It is, h ow ever, th e m ain poin t of at t ack of ion izing radiat ion . DNA is th e carrier of gen et ic in form at ion . It ser ves to preser ve an d repair th e body th rough it s abilit y to p rodu ce id en t ical replicas in cell division an d th e capacit y to p ass on gen et ic in form at ion through th e gen erat ion s. Dam age to DNA seriou sly in terferes w ith th e biological balan ce of th e living organ ism . Ion izing radiat ion can result in several t ypes of dam age to DNA. Th e m ost com m on t ypes are ch anges in bases such as thym in e, cytosin e, aden in e, an d gu an in e. DNA single-st ran d breaks an d ch anges in sugars are th e secon d m ost com m on t ype. DNA d ou ble-st ran d breaks are n ot so com m on ( Fig. 4.2).

Double-strand break Single-strand break A+T P

P

4

Single-strand break with base dam age (exam ple of a clustered lesion)

Fig. 4.2 DNA dam age. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnmedizin; Band 5.)

4.4 Repair Mechanisms for the Restoration of DNA Cells h ave effect ive m ech an ism s for th e flaw less repair of th e m ajor port ion (u p to 97 %) of radiat ion -in duced dam age to th eir DNA w ithin a few h ours. Th ese repair m ech an ism s ser ve to restore th e DNA, suppress can cer develop m en t , an d preven t m ut at ion s. Th e repair processes occur qu ickly—som e repairs are com pleted in on ly a few m in u tes. Most of th e dam age is repaired w ith in several h ours. Th e rem ain ing residual dam age accou n t s for less th an 5 % of th e tot al dam age. In DNA single-st ran d breaks, the com plem entar y st ran d of th e DNA double helix that is st ill present is used as a tem plate for the restoration , via the respect ive en zym es. Even DNA double-st rand breaks can be repaired; th is occurs in a process referred to as nonhom ologous end-join ing.

4.5 Biological E ects of Radiation Damage Radiat ion -in duced dam age to th e DNA m ay cause differen t t ypes of effects, depen ding on th e severit y an d locat ion of dam age. ● Im p air m en t of cell fu n ct ion gen erally lead s to p rogram m ed cell death , depen ding on th e severit y of im pairm en t . ● Program m ed cell d eath (apoptosis) is a n orm al physiological process that occurs in all living organism s. It ser ves to en su re th at cells th at are n ot fu n ct ion ing properly are identi ed as such and dest royed before the

27

The Biology of Radiation E ect s start of cell division. Apoptosis m ay, how ever, result in determ in istic radiat ion dam age if the radiat ion causes th e cell death rate to rise above a certain level. Determ in ist ic radiation e ects occur above a threshold dose.

4

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Mu t at ion s resu lt in ch anges in th e gen et ic ch aracterist ics of su bsequ en t gen erat ion s of cells. Mu t at ion s m ay cau se or con t ribu te to th e m align an t t ran sform at ion of som at ic cells.

Chapter 5 Radiation Pathology

5.1 Natural Radiation Exposure

30

5.2 Arti cial Radiation Exposure

30

5.3 Stochastic and Determ inistic E ect s of Ionizing Radiation

31

Radiation Pathology

5 Radiation Pathology 5.1.2 Terrestrial Radionuclides

5.1 Natural Radiation Exposure Exp osu re to n at u ral backgroun d radiat ion is in evit able becau se it is a n at u ral part of th e environ m en t . Major sources of n at u ral radiat ion in clu d e cosm ic radiat ion an d th e decay of radion u clides th at occur n at urally in th e h um an environ m en t an d in th e h u m an body.

5.1.1 Cosmic Radiation It is kn ow n th at cosm ic rays con sist of rad ion u clides from galact ic an d solar sources, but th eir origin is st ill n ot com pletely u n d erstood. Prim ar y cosm ic radiat ion con sists m ain ly of p roton s, p h oton s, an d elect ron s th at in teract w ith atom s in th e at m osph ere, resu lt ing in th e p rodu ct ion of secon dar y cosm ic rays. Th e am ou n t of n at u ral exposu re to cosm ic radiat ion depen ds on th e alt it ude of th e locat ion of m easu rem en t . In cen t ral Eu rope, th e an n u al effect ive dose of cosm ic rad iat ion is ~0.3 m Sv at sea level, an d ~1 m Sv at an alt it ude of 2,500 m . Exposu re to cosm ic radiat ion is of special sign i can ce to igh t p erson n el. Th erefore, gu idelin es recom m en ding th at th e exposu re of air crew to cosm ic radiat ion sh ould be t aken in to accou n t in occu p at ion al exp osu re est im ates are already in p lace. W h ile th e in ten sit y of cosm ic radiat ion rem ain s relat ively con st an t , th e in ten sit y of solar radiat ion varies dep en ding on th e solar cycle an d solar act ivit y ( ares).

5

Terrest rial radiat ion is n at ural radiat ion origin at ing from th e decay of th e radion u clides in th e Ear th’s surface. Radion uclides are t aken up in th e h um an body w ith food, air, an d drin king w ater. Th e th ree m ain radion uclides in th e Ear th’s crust are uran ium , th oriu m , an d pot assium . Oth er radion uclides are m em bers of th e n at ural decay series of uran ium an d th orium . Radon exposure (1.4 m Sv) m akes up th e largest fract ion of th e tot al radiat ion dose due to terrest rial radion u clides. Radon is in h aled as a gas in en closed spaces. Radon gas is a product of th e radioact ive decay of u ran ium an d th oriu m . It escapes by diffusion from th e soil in to th e air an d th en seeps in to h ouses an d bu ildings ( Fig. 5.1).

5.2 Arti cial Radiation Exposure Th e ion izing radiat ion an d radioact ive m aterials used in m edicin e are th e largest sou rce of ar t ificial radiat ion exposure associated w ith civilizat ion . Diagn ost ic radiat ion m akes u p th e largest fract ion of th ese exp osu res. Radio th erapy an d nu clear m edicin e con t ribu te on ly 10 % to th e tot al an n u al d ose of 1.5 m Sv from m edical radiat ion . All oth er sources such as th e Ch ern obyl n uclear pow er plan t acciden t , atom ic bom b fallout , n uclear pow er plan t s, an d radiat ion u sed in research an d n u clear tech n ology produce less th an 0.02 m Sv per year ( Fig. 5.2).

1 Cracks in basem ent walls 2 Cracks in pipes and ducts 3 Cracks in the foundation 4 Seams bet ween basement walls and the foundation plate

5 2

1

4 3

Fig. 5.1 Radon pathways into a house.

30

5 Cable duct s

5.3 Stochastic and Determ inistic E ect s of Ionizing Radiation

Artificial radiation sources

Natural radiation sources

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Cosm ic radiation 0.3 m Sv/year

Chernobyl < 0.02 m Sv/year Atom ic bom b fallout < 0.01 m Sv/year

Food 0.3 m Sv/year

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Inhalation of radon and its decay product s 1.4 mSv/year

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Medical use of ionizing radiation and radioactive substances 1.5 m Sv/year

Research, nuclear technology, household < 0.01 mSv/year Nuclear facilities < 0.01 m Sv/year

A

Terrestrial radiation 0.4 mSv/year 0 Average annual dose

Occupational exposure 0.24 m Sv/year

5

Occupationally exposed workers

Fig. 5.2 Radiation exposure (dose per person per year). (Adapted from : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnmedizin; Band 5.)

5.3 Stochastic and Deterministic E ects of Ionizing Radiation 5.3.1 Stochastic E ects Th e stoch ast ic effect s of ion izing radiat ion occu r by ch an ce, th at is, are determ in ed by a ran dom dist ribut ion of p robabilit ies ( Fig. 5.3). Th erefore, on e can on ly p redict th e st at ist ical probabilit y of biological effect s occurring in a given popu lat ion of in dividuals w ith iden t ical radiat ion exp osu re. Stoch ast ic effect s m ay n ot occur un t il after a laten t period of several years. It is im p ossible to predict w h eth er stoch ast ic effect s w ill occu r in a given in dividu al. Th ere is n o th resh old dose for th e occurren ce of stoch ast ic e ect s. Un icellular processes are involved in th e occurren ce of stoch ast ic radiat ion e ects. Malign an t t ran sform at ion of a som at ic cell, or a m ut agen ic e ect on germ cells, is a ran dom occu rren ce determ in ed by ch an ce dam age to th e respect ive DNA. Th eoret ically, a single h igh -en ergy ph oton can release secon dar y elect ron s th at , on th eir orbit in th e cell n u cleu s, m ay in duce DNA dam age result ing in stoch ast ic e ects. Th e p robabilit y of occu rren ce of sto ch ast ic e ect s in creases w ith dose. How ever, th e severit y of th e resu lt ing e ect is n ot dose depen den t . Th e stoch ast ic e ect s of radiat ion in clu de: ● Gen et ic defect s ● Can cer.

5.3.2 Deterministic E ects A biological effect of radiat ion is ch aracterized as determ in ist ic if th e effect occurs as a direct resu lt of exposure to a specific dose of radiat ion . Un like stoch ast ic effect s, determ in ist ic effect s occur on ly after exposure to radiat ion exceeding a cert ain th resh old dose. Th e th resh old dose is th e dose w h ere th e n um ber of cells killed by radiat ion in creases to such a degree th at it rises above th e n orm al level. Th e severit y of dam age to th e affected t issue in creases w ith in creasing dose. Th e laten t p eriod bet w een exposure an d th e on set of th e determ in ist ic effect varies, depen ding on th e t ype of t issue involved an d th e radiat ion dose level. Th e acu te effect s of radiat ion appear after a laten t period of a few h ours to days, w h ile th e ch ron ic late effects m ay take years to m an ifest th em selves. Th e determ in ist ic e ect s of radiat ion ( Fig. 5.4) alw ays arise from m ult icellular m ech an ism s. Th e in duct ion of dam age exceeding th e cellular repair capacit y leads to an in crease in cell death or degen erat ive processes. Th e effects on ly becom e clin ically m an ifest after a large n u m ber of cells h ave been dam aged . It is im perat ive th at th e radiat ion doses used in diagn ost ic im aging do n ot cause determ in ist ic dam age. Th e m ost com m on form s of early radiat ion -in du ced dam age du e to determ in ist ic e ects in clu d e: ● Er yth em a ● Ulcers ● Acute radiat ion sickn ess. Late effect s in clude a variet y of: ● Tissu e ch anges ● Vascu lar ch anges.

31

Radiation Pathology

Fig. 5.3 Stochastic e ects of radiation (e ects that occur by chance).

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Chapter 6

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There is no threshold dose Severit y is not dose dependent The probabilit y of occurrence increases with dose Even the smallest doses have the potential to induce dam age Effects become statistically significant only after a ce rtain frequency of occurrence Cancer, leukem ia, and m utations m ay be induced by radiation

Dose

ge

Fig. 5.4 Determ inistic e ect s of radiation.

Severity

There is a threshold dose The severit y of damage increases with dose

of

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Image Formation and Image Processing

6.1 Fundam ent als

34

6.2 Im age Receptor-Independent Factors In uencing Im age Form ation

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6.3 Radiographic Film and Intensifying Screen-Dependent Factors that In uence Im age Form ation 37 6.4 Processing of Radiographic Film s 42

Im age Form ation and Im age Processing

6 Image Formation and Image Processing

6

34

6.1 Fundamentals

6.1.1 Summation E ect

Im age form at ion w ith X-rays is sign ifican tly differen t from th e form at ion of im ages by visible ligh t th at w e are fam iliar w ith . Un like visible ligh t , X-rays p ass th rough th e body an d form im ages of th e di erent st ru ct ures th ey en coun ter, according to th e law s of cen t ral project ion . Cen t ral project ion m ean s th at X-rays d iverge as th ey t ravel in a st raigh t lin e from a poin t source focu s to th e an ode. As X-rays pass th rough t issu es, di eren t st ruct u res of di eren t den sit ies absorb an d scat ter di eren t fract ion s of th e radiat ion , resu lt ing in at ten u at ion of th e beam . Th e degree of X-ray at ten u at ion varies dep en ding on th e com posit ion (den sit y) of th e irradiated objects. Th e variable pat tern of blacken ing resu lt ing from th is reects th ese di eren ces in opt ical den sit y of th e object s. Th e degree of absorpt ion of X-rays is determ in ed by th e n u m ber of elect ron s per atom of a given elem en t . St ru ct u res m ade of elem en t s w ith a large n um ber of elect ron s, as re ected by a h igh atom ic n u m ber, absorb m ore X-rays th an th ose m ade of elem en t s w ith a low atom ic n u m ber. Osseou s st ru ct u res con t ain calcium , w h ich h as a relat ively h igh atom ic n u m ber. Th erefore, bon e ap p ears w h ite an d part icu larly p rom in en t on radiograph s. Th e reason for th is is th at X-rays th at st rike bon e are alm ost en t irely absorbed an d do n ot reach th e im age receiver. Tissues th at are n ot as den se as bon e absorb m uch less X-rad iat ion an d th erefore appear as variably dark to black sh adow s. Bet w een th ese t w o ext rem es—w h ite or black—are m any sh ades of gray. Th e correspon ding im age gen erated by th e im age receptor is m ade visible by developing th e lm , or by digit al im age processing. Th e n um ber of gray levels or con t rast displayed varies from system to system . Un like p h otography, X-radiat ion does n ot produce a “p ict u re.” An X-ray im age is m erely th e resu lt of th e variable at ten u at ion of X-rays by th e irradiated object s. Th e resu lt ing ligh t an d dark areas m ust be in terpreted an d correlated to th eir resp ect ive an atom ical st ru ct u res. A precise u n derstan ding of th e p rin cip les of X-ray im age form at ion , an d a detailed kn ow ledge of th e an atom y of th e region of th e body being exam in ed, are th u s n ecessar y for th e in terpretat ion of radiographic im ages. However, observer experience is just as im portant: com parison w ith know n radiographic im ages is the only way to im prove the reliabilit y and accuracy of interpretation of the radiographic appearances of anatom ical structures of variable densit y. The fact that we com pare things we observe w ith sim ilar and fam iliar things stored in our m em ory is a natural m ental process. The larger the num ber of sim ilar and fam iliar things stored in the m em ory (for exam ple, radiographic im ages), the greater the experience of the observer. Greater experience allow s the observer to identify structures on radiographs m ore quickly and accurately.

Th e fact th at an X-ray im age is th e su m m at ion of differen t con secut ive st ru ct ures in th ree-dim en sion al space in to a t w o-dim en sion al im aging plan e m akes radiograph ic in terpret at ion even m ore ch allenging. In dividual det ails on an X-ray im age m ay be in dist inguish able, ow ing to th is su m m at ion effect ( Fig. 6.1). It m ay be n ecessar y to t ake an X-ray from a differen t project ion angle, to visualize su ch “h idden ” st ruct ures. Th e m ain problem of X-ray im aging is th at it depict s th ree-dim en sion al object s in a t w o-dim en sion al plan e. It is di cult for th e in experien ced radiograph er to m en t ally t ran slate a th ree-dim en sion al object in to a t w o-dim en sion al radiograp h . Likew ise, it is h ard to gain an im pression of th ree-dim en sion alit y from a t w o-dim en sion al im age. Con sidering th is kn ow ledge of th e physical prin ciples of X-ray im age form at ion , th e rst step is to learn to perceive th e di eren t gray levels as di erent degrees of atten uat ion caused by t issues of di eren t den sit ies. Th e n ext step is to learn to t ran slate th e gray-scale in form at ion in to vivid th ree-dim en sion al im pression s of th e irradiated organ s. Th e last step is to learn to dist inguish n orm al from abn orm al. In oth er w ords, th e obser ver m u st learn to dist inguish th e radiograph ic appearan ces of n orm al an atom ical st ruct ures an d varian t s from abn orm al an atom ical st ru ct u res an d p ath ological ch anges. Th us, radiograph ic in terpretat ion is com plicated by th e t w o-dim en sion alit y of X-ray im ages an d by th e su m m at ion (superim posit ion ) of sh adow s from con secut ive st ruct ures. An oth er X-ray opt ical ph en om en on th at in u en ces th e iden t i cat ion an d in terpretat ion of radiograph ic appearan ces m u st also be con sidered: th e tangen t ial e ect .

Fig. 6.1 Sum m ation of shadows in an X-ray im age (schem atic representation). (From : Pasler FA. Zahnärztliche Radiologie. 5th ed. Stut tgart: Thiem e; 2008.)

6.2 Im age Receptor-Independent Factors In uencing Im age Form ation

6.1.2 Tangential E ect Objects th at are ver y den se or th ick are readily seen on radiograph ic im ages. Conversely, st ru ct ures th at are ver y sm all absorb ver y lit tle radiat ion ; th erefore, th ey m ay be ver y h ard to visu alize if th e X-ray im age w as t aken from th e w rong p roject ion angle. Th e on ly w ay to clearly display sm all, cu r ved, an d th in st ruct ures is to align th e beam p arallel to th ese objects. Th is applies, in part icu lar, to st ru ct u res in th e alveolar region an d to th e th in bon e w alls in th e m axillar y sin us area. Th e im age form ed is th en th e su m m at ion of bon e w all st ru ct u res align ed parallel to th e cen t ral ray. Hard-t issue st ruct ures align ed perpen dicu lar or oblique to th e cen t ral ray at th e m om en t of exposure are eith er n ot visible or on ly sligh tly visible on radiograp h s, even if th ey are ver y den se an d th ick. Take, for exam ple, th e h ard palate, w h ich can be visualized in on ly a few beam p roject ion s. If th e th in h ard p alate is align ed perp en dicular to th e cen t ral ray, th e area of th e h ard palate w ill n ot be visible, ow ing to its lack of th ickn ess. On ly th e m argin al areas are visible as sh adow lin es, ow ing to th eir cu r vat ure ( Fig. 6.2). Desp ite th ese di cult ies, th e goal of radiography m ust be to depict an atom ical st ruct ures as accu rately an d realist ically as possible. To facilit ate radiograph ic in terpret at ion an d p reven t errors, it is essen t ial to en sure th at th e gray-level in form at ion u sed to produ ce th e X-ray im ages is processed exactly in accordan ce w ith prescribed rules. Th is is don e by u sing st an d ard rad iograp h ic p roject ion s.

Radiologist Guido Holzkn ech t (1931) said, “From th e tot al n um ber of possible radiograph ic project ion s, th e on es best su ited to disp lay th e largest n u m ber of ch anges kn ow n to occur by experien ce w ith th e sm allest n um ber of project ion s m ust be selected.”

Note The use of standard radiographic procedures is an im portant elem ent of dental radiography. Standardized imaging procedures contribute to qualit y assurance and reduce radiation exposure.

By acqu iring st andard radiograph ic project ion s according to recogn ized rules, t arget st ru ct ures can be im aged w ith th e greatest accu racy possible. Th e visualizat ion of organ s using w ell-kn ow n st an dard project ion s h as dist in ct ben e t s for radiograph ic diagn ost ics. It is th e on ly w ay to obt ain a t rue-to-scale repro duct ion of speci c st ru ct ures in a kn ow n form . Moreover, radiograph s sh ould alw ays provide an exact in dicat ion of the den sit y of an atom ical st ruct ures, so th at ch anges can be clearly iden t i ed. In den t al radiography, w e kn ow th at cer t ain law s of project ion m ust be kn ow n an d applied, especially w h en taking in t raoral radiograp h s. For bet ter u n derst an ding, th e factors th at in u en ce X-ray im age form at ion can be divided in to t w o m ain categories: ● Factors th at are in depen den t of th e im age receptor ● Factors th at are determ in ed by th e im age receptor system .

6

6.2 Image ReceptorIndependent Factors In uencing Image Formation

Fig. 6.2 Tangential e ect in the m axillary region.

Th e degree of pen et rat ion of X-rays is depen den t on th e X-ray w avelength , w h ich , in t urn , is depen den t on th e h igh voltage ap p lied to th e X-ray t u be. As th e th ickn ess or den sit y of an irradiated object in creases, th e degree of pen et rat ion of X-rays m u st also be in creased by in creasing th e volt age. Th e variable absorpt ion of X-rays by th e di eren t t issu es of th e body produ ces variable sh adow pat tern s of th e irradiated st ruct u res an d organ s, w h ich are seen as project ion im ages on th e radiograph . Den se st ruct ures su ch as bon es st rongly absorb X-rays an d produce variable d egrees of sh ad ow ing. Loose st ru ct u res su ch as softt issues, cavit ies, an d air absorb lit tle or n o X-rays an d th us ap p ear radiolu cen t (w h ite), ow ing to th eir low den sit y. Th e superim posit ion of st ru ct ures from di eren t levels of an object is referred to as ad d it ion . Th e opposite e ect , cau sed by spaces con tain ing air, is called su b t ract ion . Th ese addit ion an d subt ract ion e ect s m ay com plicate

35

Im age Form ation and Im age Processing radiograph ic diagn ost ics, esp ecially w h en th ey occu r in th e cran iofacial region , w h ere a ver y large n u m ber of an gular bony st ru ct u res of d i eren t th ickn esses are closely posit ion ed togeth er in close proxim it y to soft-t issues an d air- lled cavit ies. Th e age of th e p at ien t is an oth er im por tan t factor, par t icu larly in den t al radiography, becau se of age-related ch anges in th e calcium con ten t of bon e. Last but n ot least , p at h ological ch an ges resu lt in altered absorpt ion deviating from th e ch aracterist ic X-ray absorpt ion of h ealthy t issu es.

x Dose = 1 2x

Dose = ¼

6.2.1 Object Contrast Ver y low an d ver y h igh degrees of absorpt ion produ ce ver y dark, den se, an d brigh t low -den sit y areas on th e radiograph . Th e large differen ces bet w een th ese ext rem e den sit ies resu lt in h igh con t rast . Th e degrees of absorp t ion bet w een th ese ext rem es form th e gray-scale range of rad iograp hy. Th e differen ce bet w een th e m axim um an d m in im u m opt ical den sit y w ith w h ich a st ruct ure is disp layed is referred to as object con t rast . Th e on ly factors th at in flu en ce object con t rast are th e object t ype an d beam qu alit y. Oth er factors su ch as cu rren t in ten sit y, source-to-film dist an ce, exp osu re t im e, an d film ch aracterist ics h ave n o effect on object con t rast . Digit al im age processing is th e on ly w ay to ch ange th e prim ar y object con t rast of a radiograph ic im age.

6

6.2.2 Current Intensity and Exposure Time Th e am ou n t of X-rays gen erated in a given exposure t im e, in secon ds (s), dep en d s on th e am ou n t of cu rren t , in m illiam p eres (m A), ap plied to th e filam en t of th e cath ode. Accordingly, th e produ ct of cu rren t an d exp osu re t im e determ in es th e im age den sit y w ith out affect ing th e con t rast . If tech n ically p ossible, th e sam e effect can be ach ieved by ch anging th e exposu re t im e, or, if th is is n ot possible, by var ying th e cu rren t . Th e m illiam p ere–secon d product (th e p roduct of m illiam perage an d exposu re t im e in secon ds) rem ain s th e sam e in eith er case.

6.2.3 Inverse Square Law Th e d ist an ce from th e radiat ion source to th e irradiated object is an oth er factor to con sider. As th e dist an ce from th e sou rce in creases, th e in ten sit y of X-radiat ion d ecreases, ow ing to at ten u at ion , an d th e den sit y p er u n it area decreases, ow ing to th e divergen ce an d con e-sh aped sp at ial dist ribu t ion of th e beam . Th erefore, dist an ce h as a m ajor in flu en ce on th e degree of film darken ing, or radiograp h ic d en sit y. X-rays, as w ell as ligh t rays, follow th e inverse square law ( Fig. 6.3), w h ich st ates th at th e in ten sit y of radia-

36

Fig. 6.3 Inverse square law (schematic representation). (From : Pasler FA. Zahnärztliche Radiologie. 5th ed. Stut tgart: Thiem e; 2008.)

t ion decreases in inverse propor t ion to th e square of th e distan ce from th e radiat ion source. Th is h as im port an t im plicat ion s for radiat ion protect ion . Distan ce is th e best protect ion again st radiat ion . Th eoret ically, if th e dist an ce from th e X-ray source to th e object in creases by a factor of t w o, th e radiat ion inten sit y m ust be in creased by a factor of four to obt ain th e sam e degree of blacken ing. How ever, w h en th e sourceto-target dist an ce is in creased, a sm aller collim ator size is used to keep th e eld size con st an t (6 cm ) w ith out h igh er radiat ion exposure.

6.2.4 High Voltage Any ch ange in voltage resu lt s in a ch ange in th e pen et rating pow er of X-rays. Th e h igh er th e pen et rat ing p ow er, th e sm aller th e fract ion of X-rays absorbed an d th e larger th e n um ber of X-rays reach ing the im age receptor. Th e en d resu lt is a redu ct ion of con t rast , w h ich occurs because th e absorpt ion differen ces in t issue becom e sm aller an d few er con t rast levels are d isp layed. At th e sam e t im e, th e propor t ion of scat tered radiat ion in creases w ith in creasing volt age. From a voltage of ~60 kV an d h igh er, th e percen t age of scat tered radiat ion exceeds th e percen tage of absorbed radiat ion . High er volt age does h ave an in u en ce on lm darken ing, but th e price for th is is a loss of con t rast . Th e re duct ion of con t rast due to scat tered radiat ion can be decreased to a cert ain exten t . In den t al radiograp hy, th is can be accom plish ed by reducing th e size of th e radiat ion eld, an d th rough appropriate ltering. In general radiology, anti-scat ter grids are used to reduce scat tering. Anti-scat ter grids consist of parallel strips

6.3 Radiographic Film and Intensifying Screen-Dependent Factors that In uence Im age Form ation of lead, w h ich ser ve to absorb scat tered radiation that strikes th e grid at an angle. Ant i-scat ter grids are position ed bet w een th e patient and the lm . They do n ot attenuate the prim ar y beam , w hich is im portant for im age form at ion .

6.3 Radiographic Film and Intensifying Screen-Dependent Factors that In uence Image Formation

6.2.5 Scattered Radiation

6.3.1 Screenless Films

W h en X-rays p ass th rough an object , th ey are eith er absorbed or scat tered in all direct ion s. Becau se th is socalled secon dar y radiat ion scat tered from th e object h as differen t angles of in ciden ce, it leads to a reduct ion of con t rast . A p ract ical w ay to reduce th e scat tered radiat ion com pon en t is to u se th e sm allest collim ator possible. W h en taking sku ll rad iograph s w ith larger form at s, an t i-scat ter grids are placed bet w een th e pat ien t an d th e im age receptor, to in tercept scat tered radiat ion ( Fig. 6.4).

Den t al radiology is un iqu e, in th at th e film s used to acquire den t al radiograph s com e both w ith an d w ith out in ten sifying screen s. In t raoral radiograp hy is th e on ly bran ch of rad iograp hy w h ere screen less lm s are used. In t raoral radiograph s are expected to provide h igh con t rast an d ver y h igh resolu t ion (sh arpn ess) on th e on e h an d, an d h igh lm speed an d sen sit ivit y on th e oth er ( Fig. 6.5).

Large radiation source

6

The main characteristics used to describe the qualit y of radiographic lms are: ● Contrast ● Sharpness (resolution) ● Film speed (sensitivit y). Con t rast : As a gen eral rule, den t al radiograph ic lm m ust h ave h igh con t rast to be able to accurately di eren t iate bet w een n e st ruct u res located close togeth er in th e den tal region . Factors related to scat tered radiat ion an d lm developm en t in uen ce lm con t rast . Film con t rast in creases w ith h igh er lm -developm en t tem perat ure. Reuse of developer result s in a decrease in lm con t rast .

Scat tered radiation

Film

Note

Lead line grid

Fig. 6.4 Scat tered radiation and anti-scat ter grid. (From : Zabel H. Kurzlehrbuch Physik. Stut tgart: Thieme; 2011.)

Fig. 6.5 Dental X-ray lm .

Fig. 6.6 Lead line grid.

37

Im age Form ation and Im age Processing Sh ar p n ess (resolu t ion ): Becau se in t raoral rad iography is in ten ded for th e visu alizat ion an d di eren t iat ion of ver y n e st ru ct ures, it requires th e use of lm s w ith a h igh degree of sh arpn ess. Gen erally speaking, lm sh arp n ess is m easu red in term s of resolut ion , or resolving pow er. In p ract ice, resolut ion is m easured u sing h igh -con t rast lead lin e grids in un it s of lin e pairs (lp) per m illim eter ( Fig. 6.6). Film sp eed (sen sit ivit y): Film speed is a ected both by th e n u m ber an d by th e sh ap e an d size of th e silver brom ide (AgBr) cr ystals p resen t in th e lm em u lsion . The m ore cr yst als th ere are, th e faster th e lm w ill be. How ever, th ere are lim its to th e n u m ber of silver brom id e cr ystals th at is tech n ically feasible. Th e sh ap e an d st ruct ure of th e silver brom ide cr ystals h as been im proved through th e developm en t of n ew cr yst allin e form s. Conven t ion al silver brom id e cr ystals w ere ver y sm all and ch aracterized by h igh resolu t ion . How ever, because their sen sit ivit y w as low, th ey requ ired sign i can tly longer exposure t im es th an m odern cr ystals. Fu r th er research led to th e developm en t of t abular cr yst als (Tgrain s), w h ich lie along th e surface of th e em ulsion layer such th at th e at side of th e cr ystal is st ru ck by th e in ciden t X-ray beam ( Fig. 6.7 an d Fig. 6.8). Ow ing to th is con gu rat ion , t abu lar cr yst als h ave sign i can tly h igh er absorpt ion ch aracterist ics th an th e older sp h erical cr yst als. In accordan ce w ith ISO 3665 st an dards for th e classi cat ion of in t raoral radiograp h ic lm , th ree d i eren t classes of lm speed are dist inguish ed an d are ch aracterized by th e let ters D, E, an d F. Th e use of E-speed lm resu lts in ~50 % dose redu ct ion com pared w ith D-sp eed lm , bu t th e di eren ce bet w een E-speed an d F-speed lm is n ot as h igh .

6

Th e on ly reason w hy F-speed lm is faster is becau se of its h igh er develop ing tem perat u re. According to th e ISO 3665 st an dards, in t raoral lm developed in autom at ic processors using a roller t ran spor t system an d at h igh er tem perat ure (28 °C) is classi ed as F-speed lm . How ever, if it is developed m an u ally or on an oth er t ype of autom atic processor at 20 °C, th en it is classi ed as E-speed lm .

Note Only the faster E-speed and F-speed lm s should be used in intraoral radiography because they provide the sam e diagnostic im aging qualit y as D-speed lm but can reduce the radiation dose by up to 50 %.

Fig. 6.8 T-grain crystals under an electron microscope.

Fig. 6.7a, b Comparison of di erent lm crystals. a Conventional crystals. b T-grain crystals.

38

6.3 Radiographic Film and Intensifying Screen-Dependent Factors that In uence Im age Form ation

Fig. 6.9 Cross-sectional structure of radiographic lm.

Film base

Adhesive layer Emulsion layer Protective layer

Fig. 6.10 Dental X-ray lm packaging and components (from left to right): plastic cover, front and back, lm, black cardboard, and lead foil.

6

Construction of Radiographic Film

Fig. 6.11 If X-ray lm is exposed on the wrong side, the pattern em bossed on the lead foil can be seen.

To obtain the m axim um yield of X-rays and light from the intensifying screen, the em ulsion layer of radiographic film m ust contain as m any silver brom ide crystals as is technically feasible. Since each em ulsion layer can contain only a lim ited num ber of silver brom ide crystals, m ost radiographic film s have t wo layers of em ulsion, one on the front and one on the back ( Fig. 6.9). The central film base separating the t wo layers is a thin polyester sheet ~0.2 m m thick. Polyester is a transparent and flam e-retardant m aterial. A thin layer of adh esive is applied to each side of the lm base. The adhesive layers serve to rm ly attach the em ulsion containing the silver brom ide crystals to the lm base. Each em ulsion layer is em bedded in gelatin. The gelatin not only serves as a binder for the em ulsion layer, but also a ects the speed (sensitivit y) and contrast of the lm . Finally, the lm is enclosed in a protective layer designed to prevent m echanical dam age, safeguard the em ulsion, and im prove gliding of th e lm th rough the lm processors. On ly a few incident X-rays strike intraoral lm s w ith out an intensifying screen. Therefore, in addition to the t w osided coatings described above, the lm s have another layer that contains as m uch silver as is technically feasible. Modern n on -screen dental lm s con tain ~200 g of silver per square m eter, w h ereas radiographic lm s w ith an in tensifying screen only h ave ~40 g of silver per square m eter. The m ain reason for this di erence is probably the price of silver, in addition to the use of an intensifying screen. Th e lm packaging m ust be ligh t an d w aterproof an d m ust provide su cien t st abilit y. Th e covers are m ade of plast ic. To provide st abilit y, th e lm is also en cased in cardboard ( Fig. 6.10).

39

Im age Form ation and Im age Processing

a

b

c

Fig. 6.12a–c Over-exposure, norm al exposure, and under-exposure. a Too light. b “Norm al.” c Too dark.

4.0 Shoulder

3.5

Dm ax

3.0

Optical

density

6

2.5 2.0 Linear region

1.5 1.0

0.5 Base plus fog 0

Toe

0.3

a

0.6

0.9

1.2

density l a

0.6

Opti

c

a

l

density

2.2

c Opti

1.8

Log relative exposure

2.2

Exposure latitude Log relative exposure

b

1.5

Displayed contrast

0.6

Exposure latitude Log relative exposure Displayed contrast

Fig. 6.13a, b Characteristic curves. (From : Ewen K, ed. Moderne Bildgebung. Stut tgart: Thieme; 1998.) a Characteristic curve of radiographic lm showing log relative exposure and the resulting optical densit y. Dmax: m axim um optical densit y. b Characteristic curves of lm s with di erent contrast characteristics. The lm on the right, which has a steeper linear region or slope, has higher contrast but low exposure latitude. The lm on the left, which has lower contrast, has wider exposure latitude and is especially well suited for radiographs of areas that require high-contrast im aging, such as the facial skeleton.

40

6.3 Radiographic Film and Intensifying Screen-Dependent Factors that In uence Im age Form ation On th e back side of th e lm casset te, th ere is a th in sh eet of lead foil th at absorbs both th e radiat ion th at passes th rough th e lm as w ell as th e scat tered radiat ion th at reach es th e lm from th e t issu es. Th e lead foil ser ves to provide rad iat ion p rotect ion an d to im prove im age qu alit y. A pat tern em bossed on th e lead foil in dicates w hen radiograph ic lm is m istaken ly exposed from th e back. If th e lm is exposed on th e w rong side, th e X-ray appears too ligh t an d th e p at tern can be seen ( Fig. 6.11).

Graphical Representation of Film Characteristics: Characteristic Curve Th e ch aracterist ic cu r ve d escribes th e relat ion sh ip bet w een film exp osu re—in clu d ing developm en t—an d th e resu lt ing opt ical den sit y. W h en exp osing an d develop ing radiograp h ic lm , th e goal is to en su re th at th e opt ical den sit y of th e lm is alw ays in a range th at is suitable for diagn ost ic in terpretat ion ( Fig. 6.12). Th e ch aracterist ic cur ve, or den sit y cu r ve, is a grap h u sed to sh ow h ow th e ch aracterist ics of th e rad iograp h ic lm a ect th e X-ray im age ( Fig. 6.13). Th e ch aracterist ic cu r ve is com posed of di eren t region s. Th e m iddle lin ear region of th e cur ve (slope) reveals th e m ost im p or t an t in form at ion abou t th e con t rast of th e lm . Th e steeper th e lin ear region or slope, th e h igh er th e con t rast of th e lm . Th e t w o cu r ved p or t ion s at th e begin n ing an d en d of th e cu r ve are referred to as th e toe an d sh oulder of th e cu r ve. Th ey m ark th e region s th at are n ot su it able for diagn ost ic radiology. Th e ch aracterist ic cu r ve d oes n ot st art at zero. In stead, it start s at a level called b ackgrou n d fog. Backgrou n d fog is th e in h eren t level of backgrou n d blacken ing th at m ay occu r on radiograp h ic lm , bu t th e fog den sit y m u st n ot exceed a level of 0.25. Backgroun d fog is caused by th e base an d th e em u lsion of radiograp h ic lm . Film storage con dit ion s, as w ell as environ m en tal con dit ion s in th e darkroom , are factors th at can resu lt in an in crease in backgrou n d fog levels.

Fluorescen ce h as a long h istor y, an d it w as th e glow from such a layer of uorescen t m aterial th at led to th e discover y of X-rays. In ten sifying screen s h ave been used sin ce th e begin n ing of radiography. Calcium t ungstate ph osph ors w ere u sed for decades. Sin ce 1978, calcium t ungstate screen s h ave been replaced w ith rare-ear th screen s using green -glow ing gadolin iu m ph osph ors. Calcium t u ngst ate an d gadolin ium cr yst als h ave in dividual ligh t-em ission ch aracterist ics, w h ich m u st be precisely m atch ed, to correspon d to th e ch aracterist ics of th e lm ( Fig. 6.14 an d Fig. 6.15). Th e sen sit ivit y of a screen / lm system is determ in ed by th e dose th at in du ces a speci ed degree of blacken ing of th e lm . Th e sen sit ivit y class is m ain ly determ in ed by screen th ickn ess. Th e speed of in ten sifying screen s is divided in to dim en sion less speed classes. On ly class 200 to 250 an d 400 fast screen s w ith h igh in ten sifying pow er are used in den tal radiography.

6

Fig. 6.14 Calcium tungstate crystals.

6.3.2 Radiographic Film w ith Intensifying Screens Intensifying screens are used in com bination w ith radiographic film s for all extraoral im ages. Intensifying screens are t ypically m ounted on the inside of film cassettes, on both the front and back of the cassette. Like radiographic film s, intensifying screens consist of a plastic base layer to w hich an em ulsion layer is attached. The em ulsion con tains fluorescent crystals. The m ain purpose of intensifying screens is to reduce the am ount of radiation needed for the production of radiographic im ages, by reinforcing the action of X-rays. This occurs as a result of lum inescence of the incident X-rays that strike the intensifying screen; the lum inescence is in the range of the visible light spectrum .

Fig. 6.15 Gadolinium crystals (rare earths).

41

Im age Form ation and Im age Processing

Note High-speed (400) intensifying screens m ust be used for the acquisition of cephalom etric radiographs in children. All other extraoral radiographs can be taken using intensifying screens with a speed of 200 to 250 ( Fig. 6.16).

Disadvantages of Intensifying Screens In ten sifying screen s ach ieve dose redu ct ion for th e pat ien t , at th e exp en se of im age qualit y. On e of th e m ain factors respon sible for th e blu rring associated w ith in ten sifying screen s is th e size of th e cr ystals: screen cr yst als are n ot as sm all as silver brom ide cr yst als. Th e th ickn ess of th e screen is an oth er im portan t factor. Th e th icker th e screen , th e longer th e d ist an ce th e ligh t m u st t ravel an d th u s th e greater th e degree of scat tering. Th is e ect in creases if ligh t does n ot st rike any silver brom ide cr yst als in th e rst em ulsion (st riking on ly th ose in th e secon d em u lsion ), or if th e em u lsion

6

is exposed from th e rear by ligh t re ected from th e back w all of th e casset te. Th is e ect is referred to as crossover. Crossover can also h ave an adverse e ect on im age qu alit y ( Fig. 6.17).

6.4 Processing of Radiographic Films Radiograph ic film can be developed by m an ual, sem i-au tom at ic, or fu lly au tom at ic p rocessing m eth ods. Th e in t roduct ion of m odern qualit y assu ran ce st an dards h ave m ade m an ual an d sem i-autom at ic processing pract ically obsolete. On e of th e m any advan tages of autom at ic processing at h igh er tem perat ures is th at h igh er tem perat ure result s in an in crease in lm speed an d con t rast . Th u s, t w o pract ical ben e t s of fully autom at ic developm en t are reduct ion of th e pat ien t dose an d addit ion al im p rovem en t of im age qu alit y. Th e roller t ran sport system of autom at ic processors m eets th e qualit y assu ran ce requirem en t s for radiograph ic lm developm en t in accordan ce w ith in tern at ion al st an dards ( Fig. 6.18). If n o darkroom is available, th e autom at ic processor can be t ted w ith a dayligh t loader th at allow s safe lm develop m en t ( Fig. 6.19).

Fig. 6.16 Casset te and lm .

1

2

3

4

Fig. 6.17 Screen unsharpness (schem atic diagram ). (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thieme; 2000. Farbatlanten der Zahnm edizin; Band 5.)

5

Cassette Front screen Emulsion Film base Emulsion Back screen Cassette

42

6.4 Processing of Radiographic Film s

Chapter 6

1

6

2

3

4

5 Fig. 6.19 Automatic processor with daylight loading apparatus.

Fig. 6.18 Autom atic processor with rollers: 1 Film feed, 2 Developer, 3 Fixer, 4 Wash water, 5 Dryer, 6 Outlet. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.)

6

43

Chapter 7 Digital Dental Radiography

7.1 Sensors

47

7.2 Storage Phosphor Im aging Plates

48

7.3 Advant ages of Digit al Radiography

50

Digit al Dent al Radiography

7 Digital Dental Radiography Th e u se of d igit al im age receptors in den t al radiograp hy began w ith th e lau n ch of th e first com m ercial system in 1986. Th is tech n ology, called th e RadioVisioGraphy system , u sed a ch arge-cou p led device (CCD) for d igit al in t raoral X-ray im aging. Digital im aging plate scan n er system s w ere in t rodu ced as th e secon d digit al X-ray im aging tech n ology in th e m id-1990s.

Fig. 7.1 Digital radiography sensor and cable.

Meanw h ile, th e tech n ology used in in t raoral an d ext raoral digit al im aging system s h as becom e so good th at th e diagn ost ic im age qualit y of digit al X-rays is n ow equal, if n ot su perior, to th at of conven t ion al X-rays.

Fig. 7.2 Digital im aging plate with protective cover.

7 Input phosphor screen

Photodiodes

Output phosphor screen

Fig. 7.3 Flat panel detector (schematic diagram ).

Signal processing

Incident X-rays

Photons

Input phosphor screen

Incident X-rays

46

Electrons

Electrodes of electron optics

Evacuated tube

Output phos- CCD phor screen chip

Optical iris

Fig. 7.4 Image intensi er (schem atic diagram). CCD: charge-coupled device.

7.1 Sensors Th e term digit al radiography, or digit al X-ray im aging, refers to th e tech n iqu e of acqu isit ion an d display of radiograp h ic im ages by m ean s of elect ron ic data-processing tech n ology. Conven t ion al X-ray im ages are acqu ired using a radiograph ic lm or lm –screen com bin at ion. Digital X-rays, on th e oth er h an d, are acquired an d processed u sing digital sen sor system s an d im aging plates. A com p uter w ith approp riate soft w are is n eeded to process and display th e digital im age data on a h igh -perform an ce m on itor. All digital im aging system s n eed a system for th e conversion of an alog sign als in to digital im age sign als, an d a detector th at convert s X-ray ph oton s in to elect ric ch arges. Several di eren t devices are used for th is purpose in den tal d igit al X-ray im aging: ● Sen sors ( Fig. 7.1) an d im aging plates ( Fig. 7.2) are u sed in digit al in t raoral an d pan oram ic radiography system s. ● Flat p an el detectors ( Fig. 7.3) an d, in som e cases, im age in ten si ers ( Fig. 7.4) are u sed in con e beam com p u ted tom ography (digit al volum e tom ography).

Th e im age sen sors u sed in den t al digital radiography di er, in som e cases sign i can tly, in th eir st ruct ure an d m ode of operat ion . Th ere are th ree t ypes available: ● CCD sen sors ● CMOS sen sors (com plem en t ar y m et al oxid e sem icon du ctors) ● CdTe sen sors (cadm ium telluride sen sors).

7.1 Sensors

CMOS sen sor s: CMOS sen sors use a di eren t readout tech n ique, in w h ich each pixel can be read out in dividually. Fu rth erm ore, each pixel h as its ow n am pli er for an alog sign al processing an d it s ow n an alog-to-digit al con verter. Sin ce CMOS sen sors can perform th ese an d m any oth er fu n ct ion s, th ey are called act ive pixel sen sors (APS). This tech n ology w ill replace th e old CCD-based tech n ology becau se it en ables CMOS sen sors to ach ieve faster readout t im es an d less n oise th an CCD sen sors.

Sen sors are im age-capt u ring devices th at con sist of quadrat ic ligh t-sen sit ive ph otodiodes. Each ph otodiode act s as a pict u re elem en t , w h ich is abbreviated as pixel. Th e en ergy of th e in cid en t p h oton s is t ran sferred to th e elect ron s of a sem icon du ctor th at acts as a capacitor (e. g., a CCD ch ip ). Th e ch arges gen erated in th e process ow in to a “poten t ial p ot ,” w h ere th ey are collected an d th en read ou t ( Fig. 7.5).

X-rays

CCD sen sor s: CCD sen sors read ou t ch arges as follow s: the elect ron s are t ran sported across th e ch ip row by row, in th e ver t ical an d th e h orizon t al direct ion , from on e pixel to th e n ext , as in a bucket brigade. Th e elect rical an alog sign als are th en am p li ed an d converted in to digital sign als by an an alog-to-digital conver ter. Th e m ain disadvan t age of CCD sen sors is th at if th ere are ver y large am oun t s of ch arge (th at is, over-exposure), th e sm all poten t ial pot s over ow. Th is is re ected as in k-blot-t ype zon es of radio lucen cy on th e im ages. Th is problem , kn ow n as bloom ing, is on e of th e reason s w hy CCD sen sors are being in creasingly replaced by CMOS sen sors. Oth er disadvan tages of CCD sen sors are th eir n arrow exposure lat it ude (ow ing to bloom ing) an d relat ively long readou t t im e.

Visible light

7

Im age displayed on the monitor

A/ D

Scintillator

CCD

Signal processing

Standard PC

Fig. 7.5 Signal processing with a digital sensor (schem atic diagram ). CCD: charge-coupled device. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thieme; 2000. Farbatlanten der Zahnmedizin; Band 5.)

47

Digit al Dent al Radiography Cd Te sen sor s: CdTe sen sors h ave a th in layer of cadm iu m tellu ride rath er than a ligh t-em it t ing layer. Alm ost all sen sors today w ork w ith a lu m in escen t layer th at is rm ly vap or-dep osited on th e sen sor, sim ilar to an in ten sifying screen . W h ereas th e rst gen erat ion of sen sors h ad layers dop ed w ith rare-ear th ion s, cesium iodide (CsI) is u sed today. Cesiu m iod ide cr yst als are ch aracterized by th eir sm all size an d narrow, t apered n eedle st ruct ure. Th is tech n ology redu ces ligh t scat ter n early com p letely. The ligh t p rotects th e sen sor from X-rays, w h ich h ave ext rem ely sh or t w avelength s. CdTe sen sors w ere develop ed in an at tem pt to digit ize X-rays w ith ou t ligh t an d to obt ain radiograp h ic im ages w ith even bet ter resolu t ion .

7.1.1 Spatial Resolution Th e spat ial resolu t ion of a sen sor is depen den t on th e physical p ixel size. Modern sen sors h ave a pixel size of 15 × 15 µm . Sp at ial resolu t ion is gen erally expressed in u n it s of lin e p air s p er m illim eter (lp/m m ). Sen sors w ith a pixel size of 15 × 15 µm h ave a th eoret ical sp at ial resolu t ion of 33 lp /m m . How ever, th is th eoret ical m ath em at ical p hysical valu e is n ever ach ieved in pract ice, ow ing to several in terfering factors, such as im age n oise an d geom et rical u n sh arp n ess. Im age n oise is prod u ced by th e ran d om m an n er in w h ich ph oton s are dist ributed in a de n ed area of th e im age receptor. Th e n oise com p on en t is solely dep en den t on th e n u m ber of p h oton s in cid en t on th e detector. Th erefore, th e dow n sid e of in creasing th e dose (to im prove im age qu alit y) is a larger n oise com pon en t . Geom et r ic u n sh ar p n ess is th e loss of detail caused by in creasing th e size of th e focal sp ot (n on -p oin t sou rce), w h ich , togeth er w ith oth er un favorable im aging param eters, can decrease im age qu alit y to a variable degree. Pixel b in n in g is an oth er procedure u sed in digit al im age p rocessing. In bin n ing, th e ch arge from four adjacen t pixels is gen erally com bin ed to sh orten p rocessing t im es

7

an d to reduce storage requirem en ts. An oth er im port an t ben e t of pixel bin n ing is th at it can reduce th e dose to th e p at ien t . In any case, it m u st be n oted th at p ixel bin n ing o ers several advan t ages but redu ces spat ial resolu t ion .

7.2 Storage Phosphor Imaging Plates In con t rast to th e in ten sifying screen s, storage ph osph or im aging plates do n ot conver t X-rays in to visible ligh t im m ediately; in stead, excited elect ron s are “t rapped” in th e cr yst al lat t ice of th e storage ph osph or layer of th e plate. Storage ph osph or im aging plates are sem icon ductor plates w ith a storage ph osph or layer, w h ich gen erally con sist s of a europium -doped bariu m fluoroh alide ph osph or. Th e storage ph osph or layer con t ain s so-called elect ron t raps, or ch em ical t raps ( Fig. 7.6). A laser is used to scan th e storage ph osp h or im aging p late an d conver t th e laten t im age in to a digital im age, by th e process of ph otost im ulated lum in escen ce (PSL) ( Fig. 7.7).

Protective layer

Storage phosphor layer

Conductive layer Support layer Light-shielding layer Backing layer

Fig. 7.6 Structure of an im aging plate. The imaging plate consist s of a layer of X-ray sensitive crystals (storage phosphor layer), usually europium -doped barium uorohalide phosphor (BaFBr:Eu 2+) on a polyester base (support layer).

Fig. 7.7 Imaging plate readout. HeNe: helium –neon. (From : Pasler FA, Visser H. Zahnmedizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnmedizin; Band 5.)

Rotating m irror Laser beam (HeNe laser: 632.8 nm)

Light guidance

Photom ultiplier

Signal processing

A Storage phosphor layer

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D

Computer system (PC, storage, m onitor)

7.2 Storage Phosphor Im aging Plates

Fig. 7.8 Imaging plates of di erent form ats.

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Fig. 7.10 Im aging plate scanner for sm all form ats.

Fig. 7.9 Im aging plate scanner.

Den t al digit al in t raoral an d pan oram ic im aging system s com e equ ipp ed w ith variou s digit al in t raoral or pan oram ic storage ph osph or im aging plates ( Fig. 7.8) and th e ap p rop riate scan n ers to read th em ( Fig. 7.9 an d Fig. 7.10). As in lu m in escen ce, X-ray exposure causes th e europ ium elect ron s to rise to a h igh er en ergy level, referred to

as th e excited st ate. Th ey do n ot fall back to th eir grou n d st ate im m ediately, bu t are rst stored in elect ron t raps in th e storage ph osph or layer, w h ere th ey rem ain as th e u n processed laten t im age for up to 7 h ours ( Fig. 7.11). Subsequen tly, th e storage ph osph or screen is scan n ed an d st im ulated by laser ligh t , in ducing th e release of elect ron s. As a result , th e elect ron s fall back to th eir origin al en ergy level (groun d st ate), em it t ing en ergy as ph oton s of visible ligh t in th e process. Th ese ph oton s of em it ted ligh t (lu m in escen ce) are coun ted by a ph otom ult iplier. Th e data are th en for w arded to th e an alog-to-digital converter an d digit ized by th e com puter ( Fig. 7.12). On e of th e m ain advan tages of storage ph osph or im aging plates is th eir w ide dyn am ic range, w h ich is n ow paralleled by th at of som e CMOS sen sors. How ever, un like digit al sen sor tech n ology, storage ph osph or im aging plates require h igh er doses of radiat ion for n oise-free im aging. In pract ice, th e h an dling of storage ph osph or im aging plates is ver y sim ilar to th at of den t al X-ray lm . Storage

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Digit al Dent al Radiography

Electrons in the storage phosphor fall back to the ground state

The stored energy is released as visible light and converted into a digital signal

Electrons in the storage phosphor in an unstable excited state

X-rays strike the storage phosphor screen

Laser light strikes and stim ulates the storage phosphor

Electrons in the storage phosphor in a stable excited state

Fig. 7.11 Process of photostim ulated lum inescence.

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Fig. 7.12 Process of reading a phosphor storage im aging plate. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.)

X-rays Exposure

Light Erasure

Scanning

Laser beam stim ulates im aging plate, creating lum inescence

Excited state Ground state

Readout

Plate illum inated with strong light for erasure of residual excitation

ph osp h or im aging plate system s m ay at rst seem easier to u se th an digital sen sor system s, bu t th is assessm en t is relat ive because th e pract ical execu t ion of digital in t raoral im aging d ep en ds on several oth er factors besides th e im age receptor. Even if storage p h osph or im aging plates are ver y sim ilar to conven t ion al lm , it is im port an t to rem em ber th at th ey are ver y delicate an d can be easily dam aged by im prop er h an d ling. W h en m ech an ically in du ced dam age occu rs, ever y scratch produces a visible bright lin e on th e im age ( Fig. 7.13 an d Fig. 7.14). Th ese dam age-related m arks in crease th e risk of m isdiagn osis.

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7.3 Advantages of Digital Radiography Wid e dyn am ic ran ge: Th e im age qualit y of digit al X-ray im ages is determ in ed by th e n um ber of ph oton s conver ted in to elect ric sign als an d u sed to p rodu ce th e im age. Detect ive qu an t u m e cien cy (DQE) is a m easu re used to describe h ow m any (percen t age fract ion ) in ciden t quan t a are converted in to im aging sign als. Th erefore, th e DQE value describes th e sen sit ivit y of a detector. Th e dose range th at th e digit al im age receptor can con vert in to act ion able dat a is referred to as th e dyn am ic range. Digit al radiography system s ach ieve a m u ch h igh er yield th an conven t ion al X-ray system s. Th e ch aracterist ic cur ve describes th e con t rast ch aracterist ics of th e

7.3 Advant ages of Digit al Radiography for conven t ion al lm is lin ear, th e u seful range is ver y sm all ( Fig. 7.15). Com parison of ch aracterist ic cur ves sh ow s th at lm h as a dyn am ic range of aroun d 1:30, w h ereas im aging plates h ave dyn am ic ranges ap proaching 1:10,000. Elim in at ion of d evelop in g an d xin g solu t ion s: Th e use of processing ch em icals for lm developm en t is ver y problem at ic. It is ver y t im e consu m ing becau se processing m ach in es m u st be clean ed regu larly. In m ost cases, th e processing ch em icals m ust be replaced on ce a m on th . Disposal of th e used ch em icals t akes t im e an d m on ey, an d ult im ately places an ext ra burden on th e environ m en t .

Fig. 7.13 Scratches on an imaging plate.

Digit al im ages can be ed ited an d en h an ced : Th e lm developm en t process is un alterable. Th e w ork steps an d procedures involved in radiograph ic lm processing are covered in detail by st an dard operat ing procedu res, w h ich m ust be follow ed to th e let ter. Th is also m ean s th at correct exposure an d lm processing procedu res are key determ in an ts of th e qualit y of an X-ray im age. Th e radiograph leaving th e processing m ach in e is th e n al im age. If n ot develop ed p roperly, it m ay app ear too ligh t or dark, or m ay n ot h ave en ough con t rast ( Fig. 6.12). In any case, post-processing of developed radiograph ic lm gen erally is n ot possible an d, if it is, th en it is ver y costly an d reduces im age qualit y. Digit al im ages can be edited in m any w ays to com pen sate for exposu re errors. How ever, it m ust n ot be forgot ten th at su cien t darken ing by an adequate n um ber of ph oton s is n eeded to produce radiograph s of diagn ost ic qualit y. It is w rong to th in k th at edit ing un derexposed digit al im ages can m ake up for in su cien t opt ical den sit y an d im age qualit y. Ever y im age receptor requires th e radiat ion dose speci ed in it s system requirem en t s to ach ieve th e n ecessar y im age qualit y.

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More rap id availabilit y: Digit al radiograph s are m ore rapidly available th an lm radiograph s. Film develop m en t in autom at ic processors t akes alm ost eigh t m in utes. Digit al sen sors display im ages on th e m on itor im m ediately after exposure. Im aging plates take a bit longer, ow ing to th eir longer readout t im es. Th e im aging plate w ork ow resem bles th at of lm developm en t , except th at a scan ner is u sed in stead of a processing m ach in e. Fig. 7.14 Heavily scratched im aging plate.

lm . Conven t ion al lm h as an S-sh aped ch aracterist ic cu r ve, an d on ly a sm all port ion of th e cu r ve, th e lin ear part , is relevan t for im aging. In con t rast , th e ch aracterist ic cu r ve for digit al radiography is con t in uously lin ear. Becau se on ly th e m iddle par t of th e ch aracterist ic cu r ve

Dat a storage an d t ran sfer: Digit al im ages can be easily stored an d qu ickly ret rieved from m em or y. Th erefore, th ey can n ot be lost (conven t ion al den tal radiograph s w ere often lost or m isplaced). Elect ron ic dat a storage saves space an d can be carried out sim ult an eously at m ult iple sites.

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Digit al Dent al Radiography

10,000

Fig. 7.15 Characteristic curves of conventional lm , digital sensors, and storage phosphor im aging plates. (From: Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnmedizin; Band 5.)

4

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c a i t

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i

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Chapter 8 Radiation Protection and Quality Assurance in Dental Radiology

8.1 History of Radiation Protection

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8.2 Responsibilit y for Radiation Protection

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8.3 Need and Justi cation

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8.4 Optim izat ion of Radiation Protection

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8.5 Im plem ent ation of Recom m endations by the International Com m ission on Radiological Protection

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8.6 Qualit y Assurance in Dent al Radiology

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8.7 Procedures to Ensure Com pliance with Basic Principles of Radiation Protection 56

Radiation Protection and Qualit y Assurance in Dent al Radiology

8 Radiation Protection and Quality Assurance in Dental Radiology Th e t w o p illars of den t al rad iology are radiat ion p rotect ion an d im age qu alit y. In X-ray im aging, th e goal of any exp osure is to obt ain th e requ ired im age qu alit y at th e low est p ossible dose.

8.1 History of Radiation Protection Th e fact th at X-rays can also cau se dam age w as recogn ized even at th e begin n ing of th e h istor y of th e u se of Roen tgen rays for diagn ost ic an d th erapeu t ic p u rposes. Th e rst report s of radiat ion derm at it is, a side e ect of radiat ion ch aracterized by sun burn -like skin react ion s, w ere p u blish ed in 1896. Th e developm en t of skin can cer secon dar y to radiat ion derm at it is w as rst described in 1902, in th e Germ an jou rn al en t itled Advances in the Field of X-rays and Nuclear Medicine. In 1911, 94 cases of skin can cer d evelop ing on h ealthy skin after prolonged radiat ion exposu re w ere classi ed as radiat ion can cer. Radiat ion dam age an d ch anges to germ cells w ere detected soon th ereafter. Scien t i c proof of th e m u tagen ic e ect s of radiat ion , h ow ever, w as n ot est ablish ed un t il 1927, w h en H. J. Mu ller publish ed th e results of h is fruit y (Drosophila) exp erim en t s. In resp on se to th ese n dings, th e In tern at ion al Com m ission on Radiological Protect ion (ICRP) w as fou n ded at th e Secon d In tern at ion al Congress of Rad iology in Stockh olm in 1928. Th e goal of th e ICRP is to n d w ays an d m ean s to con t in u ou sly redu ce radiat ion exposure, in order to provide w orkers, th e p opu lat ion in gen eral, an d p at ien ts in part icu lar bet ter p rotect ion from ion izing radiat ion .

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8.1.1 Structure of the International Commission on Radiological Protection Th e ICRP con sist s of th e m ain com m ission an d five st an ding com m it tees devoted to th e follow ing subject areas: ● Radiat ion e ect s ● Doses from radiat ion exposu re ● Radiat ion p rotect ion in m edicin e ● Ap p licat ion of th e com m ission’s recom m en dat ion s ● Protect ion of th e environ m en t . A scien t ific secret ariat in Sw ed en oversees th e ICRP an d it s com m it tees. In addit ion to th e perm an en t com m ittees, th e ICRP also h as tem p orar y task grou ps th at deal w ith sp ecific t asks an d problem s of radiat ion p rotect ion .

54

Th e ICRP is an in depen den t organ izat ion th at collaborates closely w ith m any oth er in tern at ion al organ izat ion s. It h as m ore th an 200 volun teer m em bers from over 30 coun t ries aroun d the w orld. Leading scien t ist s an d policy-m akers in th e eld of radiat ion protect ion are in clu ded in it s ran ks. Som e of th e m ost im por tan t organizat ion s th at collab orate closely w ith th e ICRP are: ● Eu rop ean ALARA Net w ork (EAN) ● European Com m ission (EC) ● European Nuclear In stallat ion s Safet y St an dards In it iat ive (ENISS) ● European Platform on Preparedn ess for Nuclear an d Radiological Em ergency Response and Recover y (NERIS) ● Heads of th e Eu ropean Rad iological Protect ion Com p eten t Auth orit ies (HERCA) ● Ibero-Am erican Forum of Radiological an d Nuclear Regulator y Agen cies (FORO) ● In tern at ion al Atom ic En ergy Agen cy (IAEA) ● In tern at ion al Com m ission on Radiological Un it s an d Measu rem en ts (ICRU) ● In tern at ion al Radiat ion Protect ion Associat ion (IRPA) ● Un ited Nat ion s Scien t i c Com m it tee on th e E ect s of Atom ic Radiat ion (UNSCEAR) ● World Health Organ izat ion (W HO).

8.1.2 Tasks and Content of the Various Activities of the International Commission on Radiological Protection In it ially (in 1928), lim itat ion of th e h ours of w ork involving m edical radiat ion sources w as th e on ly recom m en dat ion for radiat ion protect ion in m edicin e, an d th e first th resh old w as defin ed in 1934. Scien t i cally based eviden ce of in creased can cer in ciden ce am ong Am erican radiologist s, an d th e kn ow n cases of leukem ia after th e atom ic bom bings in Japan, ch anged opin ion s regarding th e th resh old above w h ich dam age from ion izing radiat ion m igh t occur. Con sequen tly, m on th ly an d an n ual lim its for w orkers an d for th e populat ion w ere recom m en ded in 1956. Th e realizat ion th at it is n ot possible to set a th resh old led to th e recom m en dat ion to lim it th e radiat ion dose to th e low est level possible. Th is w ording w as later im proved an d re n ed to in clu d e ph rases su ch as: ● “To th e low est level” (1955) ● “As low as p ract icable” (1959) ● “As low as reason ably ach ievable” (ALARA) (1966) ● “As low as reason ably achievable, econ om ic an d social factors t aken in to accoun t” (1973).

8.5 Im plem ent ation of Recom m endat ions by the International Com m ission on Radiological Protection Th e m ain object ive is to redu ce th e dose to accept able levels. W h en doing so, determ in ist ic effect s m u st be avoided an d stoch ast ic effect s reduced to an accept able level. Th e term “accept able level” is defin ed relat ive to oth er risks of daily life. Togeth er w ith th e IAEA, th e ICRP com piled several Fundam ental Safet y Principles, w h ich w ere publish ed in 2006.

8.4.1 Limitation and Monitoring of Individual Dose Limits Lim its m ust be in t roduced an d it m ust be en su red th at radiat ion doses to in dividu als do n ot exceed th e lim it s specified for th e respect ive con dit ion s.

8.2 Responsibility for Radiation Protection

8.4.2 Prevention of Accidents and Protection against Existing or Unregulated Radiation Risks

Th e sole person bearing th e resp on sibilit y for protect ion again st ion izing radiat ion is th e doctor or den t ist respon sible for th e radiology equ ip m en t w ith w h ich th e radiograp h s are t aken .

Avoidable dam age from ion izing radiat ion m ust be preven ted by all reason able m ean s. Th e protect ion an d reduct ion of exist ing or un regu lated (n at ural) radiat ion risks m ust be respon sible an d opt im ized.

8.2.1 Supervisory Duty of the Government

8.5 Implementation of Recommendations by the International Commission on Radiological Protection

It m u st be en su red th at each st ate h as an effect ive legal an d regu lator y fram ew ork for radiat ion p rotect ion . In depen den t an d com p eten t regu lator y auth orit ies m u st en su re th at n at ion al law s an d regulat ion s are follow ed.

8.2.2 Administration and Management of Safety Effect ive adm in ist rat ion an d qu alit y-assured m an agem en t of protect ion from th e risks of ion izing radiat ion m u st be pract iced by organ izat ion s th at are affected by radiat ion risks, or th at operate facilit ies an d engage in act ivit ies th at give rise to radiat ion risks.

8.3 Need and Justi cation No rad iat ion risk can be ju st ified u n less it h as a n et p osit ive ben efit . Ever y radiograp h requ ires ju st ificat ion , an d any m edical radiat ion exposure in den t ist r y m ust h ave a sufficien t n et posit ive ben efit .

8.4 Optimization of Radiation Protection Th e ALARA p rin cip le m ust be applied to all X-ray exam in at ion s. In oth er w ords, radiat ion exposure m ust alw ays be kept as low as reason ably ach ievable.

Th e recom m en dat ion s form u lated by th e ICRP are adopted by th e respon sible com m it tees an d publish ed in th e form of gu idelin es th at ser ve as th e prescribed legal basis for pract ical im plem en tat ion of th e com m ission’s recom m en dat ion s in th e differen t coun t ries. Th e m ost im port an t radiat ion protect ion organ izat ion in Europe is th e European Atom ic En ergy Com m un it y (EURATOM), w h ich w as foun ded in 1959. Th is in tern at ion al organ izat ion , est ablish ed by th e Treat ies of Rom e, regulates th e use of radioact ive m aterials an d ser ves as th e in tern at ion al basis for all n at ion al regulat ion s. Th e EC is w orking on speci c radiat ion protect ion guidelin es. After h earings by th e European Parliam en t an d adopt ion by th e Coun cil of Min isters, th ese guidelin es w ill be bin ding for all Mem ber States an d m ust be im plem en ted in n at ion al law. EURATOM th us declared th e Fundam ental Safet y Principles of th e ICRP bin ding for all EU Mem ber States, in Direct ive 2009/71/EURATOM. Th e in dividu al Mem ber St ates are en couraged to im plem en t th e en acted guidelin es in n at ion al law. Th e United St ates h as a w ell-developed system of organ izat ion s respon sible for radiat ion protect ion . Th ese in clu de th e follow ing organ izat ion s, am ong oth ers: ● Biological E ect s of Ion izing Radiat ion Com m it tee (BEIR) ● Environ m en tal Protect ion Agen cy (EPA) ● Nat ion al Cen ter on Devices an d Radiological Health (NCDHR) ● Nat ion al Cou n cil on Radiat ion Protect ion an d Measurem en t s (NCRP) ● Nuclear Regu lator y Com m ission (NRC)

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Radiation Protection and Qualit y Assurance in Dent al Radiology ● ● ●

Occu p at ion al Safet y an d Health Adm in ist rat ion (OSHA) U. S. Depart m en t of Health an d Hu m an Ser vices U. S. Food an d Drug Adm in ist rat ion (FDA).

In add it ion , th e u se of X-ray equipm en t is regulated by th e in d ivid u al states, in cooperat ion w ith th e FDA. Th ey m an age th e regist rat ion an d con t rol of X-ray equipm en t u sed in th e m edical, den tal, an d veterin ar y applicat ion s. Th e NCRP pu blish es recom m en dat ion s for radiat ion protect ion in d en t ist r y. It also issu es report s on top ics su ch as “Radiat ion Protect ion in Den t ist r y” an d “Im plem en t at ion of th e Prin ciple of As Low As Reason ably Ach ievable (ALARA) for Medical an d Den tal Person n el.” In su m m ar y, it can be st ated th at in creasing n um bers of coun t ries aroun d th e w orld h ave est ablish ed n at ional gu idelin es on radiat ion protect ion in den tal X-ray facilit ies. In m any cases, th ese are t ype test s. For exam ple, th e devices are tested for con form it y to n at ion al requ irem en t s w h en rst in st alled. Th ese test s in clude dose m easurem en t s, determ in at ion of h alf-valu e layer, lt rat ion tests, an d volt age ch ecks. Th e tech n ician w h o evalu ates th ese valu es sen d s th e resu lt s to th e com peten t au th orit y. Th is p roced u re ser ves to en sure th e successful m on itoring of d en t al radiograph ic equipm en t in th e respect ive coun t r y.

8

8.6 Quality Assurance in Dental Radiology Qualit y assu ran ce is a broad term th at in cludes all plan n ed an d system at ic act ion s by th e den t ist to provide con fiden ce th at: ● Th e X-ray exam in at ion is n ecessar y an d app ropriate for diagn osis of th e clin ical problem at h an d ● Th e radiograp h p rovides ad equ ate diagn ost ic in form at ion to add ress th e clin ical quest ion s being asked ● Th e con ten ts of th e radiograp h can be in terpreted correctly an d m ade available in a t im ely m an n er ● Th e X-ray exam in at ion can be perform ed w ith m in im u m radiat ion exp osu re an d w ith m in im u m discom fort to th e p at ien t .

8.6.1 Standards Regarding tech n ical con cern s in radiology, th ere are st an dard s govern ing qu alit y assuran ce in part icular, as w ell as stan dards th at play a m ajor role in regulat ing th e tech n ology u sed in X-ray equ ip m en t . In t er n at ion al Basic Safet y St an d ard s (BSS) w ere in t rodu ced for in tern at ion al stan dard izat ion p u rposes. Th ese globally valid stan dards ap ply to all m an u fact urers of den tal X-ray equipm en t .

56

Un iform in tern at ion al accep t an ce test s for X-ray equ ip m en t st ill do n ot exist , despite variou s at tem pt s to in t roduce such st an dards. In m ost cases, on ly t ype test s an d regular qu alit y in spect ion s are perform ed. How ever, it is im por tan t to h ave in tern at ion al st an dards th at are recogn ized an d obser ved across all borders. Th e In tern at ion al Organ izat ion for St an dardizat ion’s (ISO’s) Tech n ical Com m it tee 106 Den t ist r y is respon sible for th e developm en t an d im plem en t at ion of all ISO st an dards related to den t ist r y. In Europe, th e European Com m it tee for Stan dardizat ion is respon sible for th e developm en t of gen erally ap plicable st an dards. EN 60601 is th e stan dard th at covers safet y requirem en ts for m edical elect rical equipm en t an d system s. Th ere is a special series of st an dards for den t al radiology, for exam ple, EN 60601-2-63 for den t al ext raoral X-ray equ ip m en t , an d EN 60601-2-65 for den t al in t raoral X-ray equipm en t . In th e USA, th e Am erican Den tal Associat ion (ADA) St an dards Com m it tee on Den t al Produ ct s is th e respon sible body for st an dards for den tal X-ray equ ip m en t . Th e ADA represen t s th e in terest s of Am erican den t ist s aroun d th e w orld, by collaborat ing w ith organ izat ion s such as th e ISO.

8.7 Procedures to Ensure Compliance w ith Basic Principles of Radiation Protection Gen erally speaking, it can be said th at th e follow ing procedures, as described in th e curren t guidelin es of th e EC, en sure th at th e goals of radiat ion protect ion an d qualit y assuran ce can be m et: ● Risk/b en e t assessm en t for ju st i cat ion of th e u se of ion izing radiat ion ● Valid clin ical in d icat ion for any radiological exam in at ion after th e gen eral m edical/den t al exam in at ion ● Opt im izat ion p roced u res: ○ Ad equ acy an d qu alit y of prem ises an d equ ip m en t ○ Qualit y assuran ce ○ Qualit y con t rol program ○ Pat ien t dose m easu rem en t an d assessm en t ● Design at ion of resp on sibilit ies, in clu ding lin es of au th orit y an d radiat ion safet y respon sibilit ies ● Ad equ ate t rain in g in th e rad iological p rocedu res to be perform ed an d th e corresp on ding radiat ion p rotect ion requ irem en ts ● Con t in u in g ed u cat ion an d t rain in g, w h ich is n ecessar y as a result of th e rapid developm en ts in m edical scien ce an d tech n ology.

Chapter 9 Practical Dental Radiography

9.1 Intraoral Radiography

58

9.2 Conventional Tom ography

77

9.3 Panoram ic Tom ography

79

9.4 Cone Beam Com puted Tom ography

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Practical Dent al Radiography

9 Practical Dental Radiography 9.1 Intraoral Radiography In t raoral radiography w as th e m ost im p or t an t den t al im aging tech n iqu e for decades but lost som e of it s im p ortan ce after th e in t rod u ct ion of p an oram ic rad iography an d digit al con e beam com pu ted tom ography (CBCT). In m any cases, in t raoral radiography is st ill of great diagn ost ic valu e in den tal radiography, w h en used as a sup plem en t ar y exam in at ion for opt im al visu alizat ion of th e teeth an d adjacen t st ruct ures. Becau se in t raoral single-tooth radiograph s var y greatly depen ding on th e n dings an d are prim arily used to sh ow n e det ail, th ey m ust m eet ver y h igh diagn ost ic im age qu alit y st an dards. Th e diagn ost ic im age qualit y of in t raoral radiograph s depen ds m ain ly on th e t yp e an d qu alit y of p erform an ce of th e in t raoral radiograp hy tech n iqu e. Also, as th e develop m en t of in t raoral radiograph ic tech n iques h as sh ow n , th e u se of tech n ical aids su ch as an app rop riate lm h olding device h as proved to be an oth er im port an t factor. In t raoral radiography is perform ed according to cert ain basic p rin cip les th at ser ve to en sure th at all diagn ost ically im port an t im age feat u res, det ails, an d clin ically relevan t st ru ct u res are visu alized according to th e cu rren t stan dards of den t ist r y an d tech n ology. According to th ese st an dards, all in t raoral radiograph s m u st p rovide com p lete, superim posit ion -free, an d distor t ion -free orth ogon al im ages of th e teeth . Th e im age qualit y of th e radiograph m u st be good en ough to ensu re u n equ ivocal diagn osis of th e crow n , pu lp, root can al, period on t al ligam en t , ap ical region , can cellou s bon e, an d n eigh boring st ru ct u res. Th e radiograph er m ust em ploy a radiograph ic tech n iqu e th at m eet s th ese requ irem en t s. W h en th e gen eral rules of cen t ral ray project ion are con sid ered in th is con text , it qu ickly becom es eviden t th at th ere are qualitat ive di eren ces in th e available tech n iqu es for in t raoral radiology an d th at n ot ever y tech n iqu e produ ces resu lts of th e desired qu alit y.

9



Su p er im p osit ion -free or t h ogon al im agin g: ○ In t raoral radiography plays a m ajor role in diagn osis of caries. Th erefore, p eriapical an d (in part icu lar) bitew ing radiograph s m u st be acqu ired in su ch a w ay th at th e in terproxim al su rfaces are sh ow n w ith out su p erim posit ion ( Fig. 9.2). ○ Regardless of w h ich radiograph ic tech n ique is u sed, th e su ccessfu l product ion of superim posit ion -free im ages is solely depen den t on th e qualit y of execu t ion . ○ Ever y in t raoral radiograph m ust provide a superim posit ion -free view of th e in terproxim al areas. Th e on ly p erson respon sible for en su ring th at th is is accom plish ed is th e person w h o t akes th e radiograph s. Regardless of w h ich adju st m en t system is u sed, beam angu lat ion m u st be in dividu ally adju sted for each pat ien t , to ach ieve orth ogon al project ion geom et r y. W h en posit ion ed orth ogon ally, th e cen t ral ray is directed perpen dicu lar to th e in terproxim al su rfaces of th e teeth . Or th ogon al project ion geom et r y

Fig. 9.1 Correct maxillary periapical radiograph of the entire tooth.

9.1.1 Quality Criteria for Intraoral Radiography To en able com preh en sive an d opt im al diagn ost ics, in t raoral radiograp h s m u st m eet th e follow ing im age qu alit y criteria: ● Com p leten ess of visu alizat ion : ○ Th e en t ire crow n , root , an d p eriap ical region m u st be sh ow n on th e in t raoral rad iograp h . ○ Radiograp h s lacking crow n s or root t ips n o longer m eet m od ern den tal radiography st an dard s ( Fig. 9.1). Fig. 9.2 Orthogonal im aging of teeth 17 to 15.

58

9.1 Intraoral Radiography

Fig. 9.3a, b Orthogonal projection geom etry. a Schem atic: in orthogonal im aging, the central ray projects toward the projection radius from a given position. b Radiograph acquired with orthogonal projection geom etry.





is best ach ieved by aim ing th e cen t ral ray perpen dicu lar to th e im agin ar y lin e of th e bu ccal su rfaces of th e teeth , an d by placing th e lm parallel to th is lin e. Based on th e lm posit ion , it is easy to ch eck w h eth er th e beam is correctly aim ed perpen dicular to th e tooth ( Fig. 9.3). Rep rod u cib ilit y: ○ In t raoral radiograp h s m u st be rep rodu cible. W h en in terp ret ing radiograp h s, den t ists basically com pare th em to th e im ages stored in th eir m em or y. Th is is th e key to opt im al in terpret at ion of n ew X-rays. Moreover, it is som et im es n ecessar y to com pare p reviou s X-rays of a given case to follow -up X-rays over t im e. ○ Th e u se of stan dardized rad iograp h ic procedu res is cru cial for diagn ost ic reliabilit y. W h en taking in t raoral radiograph s, th e tooth axis m ust alw ays be perpendicular to th e low er edge of th e lm or bite block. If th is ru le is follow ed w h en posit ion ing th e X-ray lm , a h igh degree of reproducibilit y can be ach ieved. ○ Th e rep rod u cibilit y of radiograph ic im ages is a ver y im p or tan t elem en t of diagn ost ics. To be com parable, in t raoral radiograph s m u st be t aken in th e sam e m an n er an d m u st sh ow th e t arget an atom ical st ru ct u res in th e sam e m an n er. Reprodu cibilit y facilitates th e iden t i cat ion of di eren ces, regardless of w h eth er th ese are n orm al varian ts or path ologic ch anges ( Fig. 9.4). Distor t ion -free im agin g: th e su ccessfu l p rodu ct ion of d istort ion -free im ages of th e teeth is h igh ly tech n ique sen sit ive. Distort ion pract ically n ever occu rs: ○ if a long con e (30 cm ) is used ○ if th e cen t ral ray of th e X-ray beam is perpen dicular to th e im age receptor an d (ideally) to th e long axis of th e tooth ( Fig. 9.5 an d Fig. 9.6).

9.1.2 Principles of Projection Geometry Th e basic prin ciples of project ion geom et r y can be sum m arized as follow s: ● Th e X-ray beam m u st be directed p erp en d icu lar to th e im age receptor an d th e object ( Fig. 9.7). ● Beam divergen ce m u st n ot occu r. A long con e is requ ired for th e produ ct ion of parallel rays in in t raoral radiography. Moreover, a suit able film -h olding device is cru cial to en sure th at th e X-rays are directed perpen dicular to th e film or oth er t ype of im age receptor. How ever, t rue parallelism bet w een th e tooth an d th e im age receptor can n ot alw ays be ach ieved, ow ing to th e anatom ical con st rain ts w ith in th e oral cavit y.

9

Implementation and Application of the Rules of Projection Geometry The requirem ents for ideal im aging vary, depending on the individual radiographic technique. At the sam e tim e, the extent to w hich the rules of projection geom etry can be applied vary and m ust be know n. The greater the extent of conform it y w ith the rules of projection geom etry, the higher the qualit y of the im age from the radiographic technique w ill be. Regardless of w h ich radiograph ic tech n ique is used, th ere is alw ays a com prom ise bet w een th e ach ievable an d th e ideal p roject ion geom et r y for in t raoral rad iography ( Fig. 9.8). Th is applies regardless of w h eth er radiograp h ic lm , sen sors, or ph osph or storage plates are used. Alth ough it is n ot possible to m eet all th e requirem en t s for ideal project ion geom et r y, it is crucial to use an in t raoral radiology tech n ique th at com es as close to th e ideal as p ossible.

59

Practical Dent al Radiography

Fig. 9.4a, b Reproducible and correct tooth positioning. a Reproducibilit y: the long axis of the tooth (arrow) m ust be perpendicular to the bite block. b Radiograph acquired with correct tooth positioning.

9 Fig. 9.5 Maxillary radiograph with distortion characteristic of the bisecting-angle technique.

Fig. 9.7 Schematic of the X-ray source and beam path relative to the object of interest and the im age receptor ( lm, sensor, or phosphor storage plate).

Fig. 9.6 The comparison radiograph obtained with the paralleling technique has no distortion.

Fig. 9.8 Ideal positioning for intraoral radiography (schem atic). (With the kind perm ission of Dentsply Rinn.)

60

9.1 Intraoral Radiography

Periapical Radiography

9.1.3 Paralleling Technique

Th e conven t ion al p eriapical radiograph is u sed to obt ain a view of th e en t ire tooth an d it s su rrou n ding st ru ct u res. Tw o film sizes are em ployed for periapical radiography: 3 × 4 cm an d 2 × 3 cm . Periapical radiograph s of th e prem olars an d m olars are u su ally t aken w ith th e lm packet (n orm ally 3 × 4 cm ) in serted h orizon t ally. Horizon t ally p osit ion ed lm can record u p to th ree teeth . If sm aller lm sizes are u sed, th e lm packet m u st be posit ion ed uprigh t , to capt u re th e en t ire length of th e tooth . Both 3 × 4 cm an d 2 × 3 cm lm sizes m ay be used for periap ical an terior radiograph s. Th e lm packet sh ou ld alw ays be in serted u p righ t for can in e an d an terior periap icals ( Fig. 9.9 an d Fig. 9.10).

Principles of the Paralleling Technique

Fig. 9.9 Typical anterior radiograph.

Fig. 9.10 Typical posterior radiograph.

Two radiographic techniques are used in periapical radiography: the paralleling technique and the bisecting-an gle technique. The goal of the paralleling technique is to achieve the ideal positioning requirem ents for intraoral radiography. One of the m ain requirem ents, recognized by even the early pioneers of dental radiology, is that the film should be positioned parallel to the long axis of the tooth under investigation. Other requirem ents are that the film m ust be flat and that the central ray of the X-ray beam m ust be oriented perpendicular to the tooth and the film . C. E. Kells is considered to be the founder of the paralleling technique. The use of a suitable lm -holding device is necessary because the patients them selves cannot hold the lm in the correct position. The rst lm -holder for the paralleling technique was introduced by Kells in 1896, but proved unsatisfactory in practice. Several di erent lm holding devices for the paralleling technique were developed in subsequent years, but decades passed before one was introduced that proved e ective in everyday practice. Con sequen tly, th e bisect ing-angle tech n ique rem ain ed th e stan dard tech n iqu e of periapical radiograp hy for decades. Later research w ork by F. G. Fit zgerald (1947) an d D. T. Waggen er (1947), t ran slated in to p ract ice by W. J. Updegrave (1951), ult im ately m ade it possible to gain th e scien t i c basis n eeded to est ablish th e paralleling tech n iqu e as a bet ter altern at ive to th e bisect ing-angle tech n iqu e. A t ypical lm -h older design ed for th e p aralleling tech n ique is sh ow n in Fig. 9.11. ● A long con e (30 cm ) sh ould be u sed for th e paralleling tech n iqu e. ○ In stead of a sh or t con e (see Fig. 2.5), a long con e (see Fig. 2.6), or posit ion -in dicat ing device, is em ployed for th e paralleling tech n ique, to en sure th at on ly parallel rays con t ribu te to im age form at ion . Th is ser ves to m in im ize im age m agn i cat ion . ○ From orth odon t ic radiography, it is kn ow n th at a ver y long focus-to-object distan ce (FOD) produces radiographs w ith ver y low distortion . Because orth odon t ic radiography capt ures im ages of alm ost th e en tire skull, a distance of at least 1.5 m is required to ensure

9

Fig. 9.11 Film -holder for the paralleling technique. (With the kind perm ission of Dentsply Rinn.)

61

Practical Dent al Radiography



th at th e skull is on ly st ruck by parallel rays. Because the eld size u sed in periapical radiography is m uch sm aller (6 cm ), a distance of only 30 cm is su cient to en sure th at th e part of the beam used for X-ray im age form ation on ly consists of parallel rays. ○ Previously, a longer exposure tim e was said to be the m ain disadvantage of a large FOD, because this is associated w ith a higher risk of unsharpness. However, m odern high-perform ance dental X-ray system s that use ultrasensitive im age receptors ( lm as well as phosphor storage plates and sensors) have extrem ely short exposure tim es. Consequently, the use of a longcone technique should not result in im pairm ent of im age qualit y due to m otion blur. The m inim um length requirem ent for long cones is 20 cm . Parallel rays m u st be d irected p er p en d icu lar to t h e im age recep tor. Th e lm , sen sor or ph osph or storage plate m u st alw ays be posit ion ed in th e bite block of th e h older, su ch th at th e parallel rays are directed perpen dicu lar to th e im age receptor an d th e long axis of th e tooth (see Fig. 9.8).



Th e im age receptor m ay be p laced in t h e m id d le of t h e oral cavit y. ○ Th e m iddle of th e oral cavit y is th e site w h ere th e greatest d egree of p arallelism can be ach ieved bet w een th e im age receptor an d th e tooth to be radiograph ed. On ly th e h eigh t of th e h ard palate can rest rict or preven t th eir parallel posit ion ing. ○ How ever, it sh ould be rem em bered th at because posterior teeth often h ave bifurcated root s th at are n ot parallel to each oth er, absolute parallelism can n ever be ach ieved, even if th e h eigh t of th e palate is su cien t ( Fig. 9.12).

E ect s of Increasing the Object-to -Film Dist ance Becau se th e large FOD of 20 to 30 cm resu lts in p arallel rays, in creasing th e object-to-film dist an ce by up to 2 cm w ill n ot h ave a n egat ive effect on im age qualit y or sh arp n ess. Th e th eoret ical in crease in geom et ric un sh arpn ess is n egligible.

Function and Im port ance of the Bite Block

9 Fig. 9.12 The lm packet is positioned in the m iddle of the oral cavit y such that the central ray (arrow) is perpendicular to the lm .

Long cone Indicator rod Aim ing ring Bite block

Fig. 9.13 Correct positioning of the lm -holder in contact with the tooth crown and hard palate. The central ray of the X-ray beam consists of m ostly parallel rays. It is perpendicular to the im age receptor and (ideally) to the long axis of the tooth. (With the kind perm ission of Dent sply Rinn.)

62

A bite block is an essen t ial com pon en t of film -h olders used for th e paralleling tech n ique. It ser ves to en sure good an d stable fixat ion of th e film -h older ( Fig. 9.13). Th e lm is alw ays in con t act w ith th e h ard palate on th e m axillar y side, an d w ith th e oor of th e m outh or th e dorsum of th e tongue on th e m an dibular side. Th ese con tact poin t s provide ver y st able an d secure posit ion ing of th e lm p acket in th e oral cavit y. Likew ise, th is con stellat ion en sures th at th e en t ire tooth is sh ow n on th e radiograph if th e X-ray beam is correctly align ed. Moreover, if th e pat ien t h as a sh allow palate, foresh orten ing of th e teeth w ill be m in im al an d th e long object-to- lm d ist an ce p ar t ially com pen sates for th is. The bite block elim inates the need for adjustm ent of the vertical angle, as is necessary w ith the bisecting-angle technique. Consequently, the use of a bite block enhances the reproducibilit y of periapical radiographs by elim inating arbitrary adjustm ent of the vertical angle. With the paralleling technique, the vertical angle is solely determ ined by the anatom ical space conditions and is the sam e for each radiograph. Because the crow n is in contact w ith the platform of the bite block, and the im age receptor is in contact w ith the hard palate, the respective position of the im age receptor is xed and de ned. In m ost cases, there is a high degree of parallelism bet ween the tooth and the im age receptor. There is never a signi cantly large angle bet ween the tooth and the im age receptor, except in a few patients w ith an extrem ely shallow palate. These cases underline the advantages of the paralleling technique, in w hich parallel rays are always oriented perpendicular to the im age receptor, independent of the anatom ical situation.

9.1 Intraoral Radiography

Im port ance of Film -holders for Orthogonal Projection Geom etry

Im port ance of Film -holders for Repro ducibilit y

Orth ogon al project ion geom et r y can be ach ieved m ore reliably w ith film -h olding devices th an w ith out film h olders or bite blocks ( Fig. 9.14 an d Fig. 9.15; see also Fig. 9.3).

If a film -h olding device is used, th e pat ien t can n ot in fluen ce th e posit ion of th e film . Th erefore, th e use of a film -h old er m akes it p ossible to obt ain a stan dard film posit ion in w h ich th e long axis of th e teeth is alw ays orien ted perpen dicular to th e bite block. Th is en h an ces th e reproducibilit y of th e radiograph s (cf. Fig. 9.4, w h ich sh ow s reproducible project ion geom et r y w ith correct root align m en t).

Note The paralleling technique is easier to use than the bisecting-angle technique: if the lm -holder is positioned correctly, orthogonal beam angulation is the only adjustm ent needed.

An in t raoral radiograph is used for th e visualizat ion of individual teeth . A conven t ion al full-m ou th series con sist s of 14 in t raoral radiograph s ( Fig. 9.16). In m odern den tal radiography, a full-m outh series gen erally is n ot just ified because a pan oram ic radiograph can visu alize th e m ajorit y of th e teeth w ith th e sam e diagn ost ic qualit y. In special cases, th e pan oram ic radiograph m ay be su pplem en ted by in d ividu al in t raoral radiograph s as n eeded. Bitew ing radiography h as a special st at us in den t al radiography: it is th e best rad iograp h ic tech n iqu e for th e detect ion of in terproxim al caries.

Fig. 9.14 Orthogonal projection geometry for the prem olars. (With the kind perm ission of Dent sply Rinn.)

9

Paralleling Technique : Methodology In th e paralleling tech n ique, th e crow n s of th e teeth m ust be firm ly posit ion ed on th e bite block an d th e film packet m ust be posit ion ed in th e m outh as follow s:

Fig. 9.15 Orthogonal projection geometry for the molars. (With the kind perm ission of Dent sply Rinn.)

7,6

5,4

3

2,1, 1,2

3

4,5

6,7

7,6

5,4

3

2,1, 1,2

3

4,5

6,7

7,6

5,4,3d

3m

2,1, 1,2

7,6

5,4,3d

3m

2,1, 1,2

3m

3m

3d,4,5

6,7

3d,4,5

6,7

Fig. 9.16 Full-m outh series of 14 radiographs. The upper panel shows the usual full-m outh series for adult s, and the low er panel shows that used for evaluation of the periodontal status. The num bers re ect the tooth num bers. M: m esial; d: distal. (From: Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnmedizin; Band 5.)

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Practical Dent al Radiography

a

b

c

Fig. 9.17a–c Diagonal position of the lm -holder during insertion. a Diagonal position outside the mouth. b Diagonal position inside the mouth. c Incorrect position inside the m outh.





Ma xilla: in con t act w ith th e h ard palate an d oor of th e n ose (see Fig. 9.8) Man d ible: in con t act w ith th e oor of th e m ou th or d orsu m of th e tongu e (see Fig. 9.25).

Th is posit ion ing geom et r y provides a h igh degree of stabilit y an d decisively con t ribu tes to obt ain ing a correctly adju sted exposu re w ith good im age qu alit y. It also en su res th at th e en t ire tooth w ill be sh ow n on th e radiograph . Th is requires proper align m en t of th e spacer con e, aim ing ring, an d in dicator rod. If th is is en su red , parallelism of th e tooth an d im age receptor is on ly dep en d en t on th e h eigh t of th e h ard palate. Th e u se of a long con e can overcom e an atom ical lim itat ion s associated w ith a sh allow palate because th e parallel rays an d in creased object-to- lm dist an ce associated w ith a long con e p reven t radiograph ic d istort ion an d m in im ize foresh orten ing.

9

Inserting the Film -holder in the Mouth Th e film -h older m u st be in ser ted an d p osit ion ed in th e oral cavit y, w h ile en su ring th at th e crow n s are in con tact w ith th e bite block. Th e film -h older is in ser ted in to th e m ou th in a gen tle, t w ist ing m ot ion w ith ou t jerky m ovem en t s. Th e tech n iqu es for in ser t ion in d ifferen t part s of th e m axillar y an d m an d ibular arch are described below.

Maxillary Prem olars and Molars Th e film -h old er is h eld diagon ally an d in serted in to th e m ou th in an u pw ard m ot ion ( Fig. 9.17); th e bite block an d th e fron t p ar t of th e in dicator rod sh ou ld lie com pletely w ith in th e oral cavit y ( Fig. 9.18). Th e lm packet is posit ion ed in th e m iddle of th e oral cavit y, to en su re th at th e lm is parallel to th e tooth , w h ile accom m odat ing it s h eigh t as th e space in th e oral cavit y allow s. Sin ce prem olars an d m olars usu ally h ave bifurcated root s, it is im possible to posit ion th e lm in th e oral cavit y so th at it is absolutely parallel to th e root s.

64

Fig. 9.18 Correct position inside the mouth.

Th e bite block is in serted in su ch a w ay th at it rst com es in con tact w ith th e crow n before th e lm touch es th e p alate, oor of th e m ou th , or dorsu m of th e tongu e. Next , th e h older m u st be align ed orth ogon ally. It is pivoted m ore dist ally for m olars an d m ore m esially for prem olars. Th e posit ion of th e im age receptor is crucial: th e plan e of th e lm packet m ust be t angen t ial to th e tooth un der invest igat ion (see, e. g., Fig. 9.15). In addit ion to en suring or th ogon al project ion geom et r y, it is also im port an t to en sure th at th e h older is n ot t ilted for w ard or backw ard an d th at th ere is n o space or angle bet w een th e crow n s an d th e bite block. On ce the h older is correctly posit ion ed, th e pat ien t is in st ructed to close th e teeth slow ly on th e bite block an d h old it rm ly bet w een th e teeth w ith out excessive pressu re ( Fig. 9.19). Next , th e operator m ust slide th e aim ing ring dow n th e in dicator rod to th e pat ien t’s ch eek; th is ser ves to en sure th at th e m axim um lim it s of eld size are n ot exceeded. Th e op erator th en ch ecks to m ake su re th at th e h old er is st ably in p lace. Fin ally, th e spacer con e is align ed so th at it s longit udin al axis is parallel to th e in dicator rod an d th e collim ator is parallel to th e in dicator ring.

9.1 Intraoral Radiography

Fig. 9.19 Errors caused by bending of lm: correct position (top); bend in lm (arrow, bottom left); bent edge (arrow, bottom right). (With the kind perm ission of Dentsply Rinn.)

9 Fig. 9.20 Anterior holder for the paralleling technique. (With the kind perm ission of Dentsply Rinn.)

Fig. 9.21 Anterior holder placem ent inside the m outh. (With the kind perm ission of Dentsply Rinn.)

Fig. 9.22 Anterior holder placement for anterior and canine periapicals. (With the kind permission of Dentsply Rinn.)

Maxillary Incisors and Canines An an terior h older is posit ion ed u prigh t in th e an terior region ( Fig. 9.20). Th e h older is in serted in to th e oral cavit y at th e best angle p erm it ted by th e bite block ( Fig. 9.21). Th e pat ien t is in st ru cted to close th e teeth slow ly on th e bite block an d h old it firm ly bet w een th e teeth w ith out excessive p ressure.

For can in e periapicals, th e h older is rotated sligh tly to th e righ t or left ( Fig. 9.22). Th e axis of th e can in es m ust be align ed in th e cen ter of th e im age receptor. Especially w h en taking can in e periapicals, it is crucial to en sure th at th e tooth axis is perpen dicu lar to th e bite block an d n ot t ilted tow ard th e roots ( Fig. 9.23).

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Practical Dent al Radiography

Fig. 9.23a–c Canine periapical radiographs. a Periapical radiograph showing bone loss in tooth 43. b Periapical radiograph of bridge abutm ent tooth 13. c Periapical radiograph of endodontically treated tooth 23.

9

Fig. 9.24 Film insertion angle for m andibular radiographs.

Fig. 9.25 Film placed along the m idline of the tongue.

Mandibular Prem olars and Molars Alth ough th e m an dible m ay seem to offer ideal an atom ical con dit ion s for p arallel tooth an d film align m en t , experien ce h as sh ow n th at m any p at ien t s fin d th e film packet pressing again st th e floor of th e m outh too pain ful. Con sequ en tly, th ey ten d to pu sh film p acket s an d p h osph or storage plates w ith sh arp edges ou t of p osit ion , w h ich m ay resu lt in th e root t ips being cu t off th e radiograph . An altern at ive m eth od is to p osit ion th e film packet on th e dorsu m of th e tongue. Because th e tongue is less sensit ive th an th e floor of th e m ou th , th e film p acket is usu ally bet ter tolerated on th e tongue. Di cu lt an atom ical con dit ion s th at p reven t th e use of a lm -h older are en coun tered in th e m an dibu lar arch m ore often th an in th e m axillar y arch . In th ese cases, th e operator m u st decide w h eth er in t raoral rad iograp hy is possible an d, if so, w ith w h ich tech n iqu e a radiograph cou ld be obtain ed.

66

Fig. 9.26 Film placed on the dorsum of the tongue.

9.1 Intraoral Radiography

Long axis of the toot h Bisector

Isosceles triangle

Fig. 9.27 Schem atic of the bisecting-angle technique. (From: Schwenzer N, Ehrenfeldt M, eds. Chirurgische Grundlagen. 4th ed. Stut tgart: Thiem e; 2008.)

90°

Tooth

Film

Bisector

Long axis of the film

Occlusal plane

9.1.4 Bisecting -angle Technique

Fig. 9.28 Bisecting-angle technique (bot tom) versus paralleling technique (top).

Th e lm -h older is h eld diagon ally an d in serted d ow n w ard in to th e m ou th . Th e bite block an d th e fron t part of th e in dicator rod lie com p letely w ith in th e oral cavit y ( Fig. 9.24). If th e pat ien t n ds th e lm n ext to th e tooth too un com for table on th e oor of the m ou th , th en th e lm packet sh ou ld be posit ion ed on th e tongu e in th e m id dle of th e oral cavit y ( Fig. 9.25). After w ard s, th e operator ch ecks to m ake sure th at th e im age receptor is com p letely cushion ed by th e tongu e an d th at n o h ard or sh arp edges are causing pain an d discom for t . Th e h older is th en align ed orth ogon ally. It is p ivoted m ore dist ally for m olars an d m ore m esially for prem olars. With m an dibu lar periap icals, pressu re can be exerted w hen th e tongue is u sed . Th e posit ion of th e im age receptor is cru cial: th e plan e of th e lm packet m ust be t an gen t ial to th e tooth u n der invest igat ion .

Mandibular Incisors and Canines Placem en t of th e film packet on th e tongu e is also recom m en d ed for m an dibular in cisors an d can in e p eriapicals. Th is creates m ore space to accom m odate th e w idth of th e film p acket an d to ach ieve parallelism ( Fig. 9.26).

The bisecting-angle technique of periapical radiography was designed for use in cases w here it is not possible to achieve parallelism bet ween the film and the teeth, ow ing to either anatom ical constraints or the lack of a suitable film -holder. It is an alternative m ethod of obtaining anatom ically correct intraoral radiographic im ages of the teeth. In prin ciple, th e lm packet is rm ly placed again st th e tooth un der invest igat ion , w ith ou t ben ding. Th is form s an angle bet w een the long axis of th e tooth an d th e lm . Th e cen t ral ray is aim ed perpen dicular to th e im agin ar y bisector (th e plan e th at bisect s th e lm an d th e tooth ). Th e bisect ing-angle tech n ique provides an atom ically correct im ages of th e teeth , based on sim ple rules of geom et r y. Th is geom et ric con gurat ion correspon ds to an isosceles t riangle ( Fig. 9.27 an d Fig. 9.28). The patient’s thum b or index nger can be used to stabilize the lm packet in the m outh, by gently pressing it against the palatal or lingual side of the upper or lower arch. Especially in th e m axillar y arch , th ere are an atom ical st ruct ures th at can in crease th e angle bet w een th e tooth an d th e lm to as m uch as 45 degrees. In th e m an dibu lar arch , th e lm can th eoret ically be pressed far en ough in to th e oor of th e m ou th th at th e tooth an d th e lm are n early p arallel ( Fig. 9.29). Geom et rically accurate im ages of single-rooted teeth can easily be ach ieved by correct vert ical angulat ion of th e X-ray beam . Mult i-rooted teeth are m ore problem atic. In m any cases, correct ver t ical angulat ion is n ot possible becau se th e roots of th e tooth are n ot parallel to each oth er. Th e larger volum e of th e prem olars an d m olars also h as an un favorable e ect on th e project ion s. Th e bisect ing-angle tech n ique m ay result in m ore or less im age distort ion , ow ing to tech n iqu e-related factors. Especially w h en using a sh or t con e (10 cm ), im age distor t ion is par t icularly problem at ic because of in creased beam divergen ce. Distor t ion m ay be readily apparent; for exam p le, th ere m ay be con sp icu ou s elongat ion of palat al roots in th e m axillar y posterior region , or crow n s m ay be cu t o at an angle ( Fig. 9.30 an d Fig. 9.31).

9

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Practical Dent al Radiography

Apical projection

Axial projection

Limbal projection

Fig. 9.29 Bisecting-angle technique: projection geom etry for m axillary anterior radiographs. (From : Schwenzer N, Ehrenfeldt M, eds. Chirurgische Grundlagen. 4th ed. Stut tgart: Thiem e; 2008.)

Coronal projection Long axis of the film

Occlusal plane

9 Fig. 9.30 Bisecting-angle technique: radiograph of the right m axillary teeth of a phantom head.

Fig. 9.31 Paralleling technique: radiograph of the right m axillary teeth (sam e as in Fig. 9.30).

Because of tech n iqu e-related factors an d th e gen eral lack of posit ion ing d evices, th e bisect ing-angle tech n iqu e h as m any disadvan t ages. It gen erally requ ires larger vert ical angu lat ion , w h ich m akes it h arder to ach ieve or th ogon al p roject ion geom et r y ( Fig. 9.32). Th e zygom at ic bon e often project s on to th e ap ices of th e m olar root s, ow ing to excessive vert ical angu lat ion ( Fig. 9.33). Moreover, it is n ot alw ays easy to h it th e bisector correctly. In correct ver t ical angu lat ion result s in elongat ion ( Fig. 9.34) or foresh or ten ing of th e im age ( Fig. 9.35).

Fig. 9.32 Radiograph acquired with nonorthogonal projection geometry (angle too steep).

68

9.1 Intraoral Radiography

a

b

Fig. 9.33a, b Projection of the zygom atic bone. a Zygom atic bone. b Projection in the molar apical region.

a

b

9 Fig. 9.34a, b Bisecting-angle technique: too shallow an angle results in elongation of the teeth. (a from : Pasler FA. Zahnärztliche Radiologie. 5th ed. Stut tgart: Thiem e; 2008; b from: Schwenzer N, Ehrenfeldt M, eds. Chirurgische Grundlagen. 4th ed. Stut tgart: Thiem e; 2008.)

Fig. 9.35a, b Bisecting-angle technique: too steep an angle results in foreshortening of the teeth. (a from : Pasler FA. Zahnärztliche Radiologie. 5th ed. Stut tgart: Thiem e; 2008; b from: Schwenzer N, Ehrenfeldt M, eds. Chirurgische Grundlagen. 4th ed. Stut tgart: Thiem e; 2008.)

a

b

69

Practical Dent al Radiography Film or p late b en d in g can also result in im age distort ion . Th is occu rs du e to excessive pressu re during h andling or from th e lm being p ressed again st th e palate or oor of th e m ou th . Radiograp h s acquired using th e bisect ing-angle tech n iqu e h ave geom et rically correct size equ alit y bu t are n ot t rue to scale ( Fig. 9.36).

Object

a

Excessive ver t ical angu lat ion is also n ot recom m en ded for reason s of rad iat ion p rotect ion , because a larger port ion of th e beam w ou ld irrad iate th e t ru n k of th e body. There is a risk of exposing oth er part s of th e pat ien t’s body to prim ar y radiat ion , even if a radiat ion -protect ion apron is correctly placed.

Fig. 9.36a–c Radiographic distortion caused by bends in the lm . a Bisecting-angle technique (schematic diagram): there is great divergence of the beam and bending of the exible im age receptor ( lm and image plate) in the apical region, near the palate. (From : Pasler FA. Zahnärztliche Radiologie. 5th ed. Stut tgart: Thiem e; 2008.) b Note the elongation of the root- lled tooth. The apex is not visualized on the im age. This problem occurred because the angle of incidence is too shallow and the lm is bent in the apical region. c The paralleling technique was used for this radiograph. All important areas are visualized without distortion.

Focus

Long axis of the film

9

b

c

a

b

Fig. 9.37a–c Comparison of three periapical radiographs. a Bisecting-angle technique: too steep an angle result s in foreshortening of the teeth. b Paralleling technique: geom etrically correct im age of the teeth. c Bisecting-angle technique: too shallow an angle result s in elongation of the teeth.

70

c

9.1 Intraoral Radiography Moreover, use of th e bisect ing-angle tech n iqu e decreases radiograp h ic reprodu cibilit y. Th e rep rod u cib ilit y of radiograp h s is a ver y im port an t elem en t of radiograph ic d iagn osis. To be com parable, radiograph s m u st sh ow th e t arget an atom ical st ruct ures in th e sam e m an n er. Reprodu cibilit y facilitates th e iden t i cat ion of di eren ces, regard less of w h eth er th ese are n orm al varian t s or path ologic ch anges ( Fig. 9.37).

Note The bisecting-angle technique does not conform to the rules of projection geom etry because the X-ray beam, including the central ray, is not oriented perpendicular to the lm and the long axis of the tooth. Moreover, the use of a short cone results in considerable beam divergence and im age distortion. Only those X-rays near the central ray are likely to form im ages without m ajor geom etric unsharpness. This problem resulted in the developm ent of so-called apical, coronal, and m arginal projections, in which the central ray was aim ed at the center of the apex, the crown, or the alveolar ridge, depending on the clinical question, in an at tempt to im age these regions without distortion. However, these m ethods were never able to produce intraoral radiographs of the entire tooth in a single exposure without distortion. The bisecting-angle technique is only recom m ended for use in certain exceptional cases. Furtherm ore, the use of a short cone is no longer permit ted today: an FOD of at least 20 cm is required for reasons of radiation protection. Otherwise, the X-rays responsible for image form ation would not be perpendicular to the im age receptor, resulting in im age distortion.

a

b

9

On first glan ce, th e bisect ing-angle tech n ique m ight seem to be easy to u se, bu t it is n ot easy to learn . Even experienced radiograph ers som et im es h ave problem s correctly calcu lat ing th e im agin ar y lin e th at bisects th e im age receptor an d th e long axis of th e tooth an d aim ing th e cen t ral ray p erp en d icu lar to th e bisector ( Fig. 9.38).

Bisecting -angle Technique : Methodology Th e bisect ing-angle tech n iqu e is u su ally p erform ed w ith ou t a film -h older or aim ing device (e. g., aim ing ring an d in dicator rod). Th erefore, th ere are m any m ore factors to con sider th an w ith th e paralleling tech n ique. For exam p le, th e h ead posit ion ing is m ore im p or tan t for th e bisect ing-angle tech n iqu e th an for th e paralleling tech n iqu e. Th e occlusal plan e m ust be align ed st rictly h orizon t al an d p arallel to th e oor. Th is m ean s th at th e h ead m u st be t ilted sligh tly for w ard for m axillar y radiograp h s, an d sligh tly backw ard for m an dibu lar radiograp h s. Correct h ead posit ion can be ch ecked again st th e posit ion of th e tooth axes, w h ich sh ould be perpendicu lar to th e oor.

c Fig. 9.38a–c Bisecting-angle technique: both vertical angulation of the beam and orthogonal projection geometry m ust be considered. Vertical angulation adjustm ents can result in three possible outcom es: a Too steep an angle (perpendicular to the lm ). b Correct angle (perpendicular to the bisector). c Too shallow an angle (perpendicular to the tooth).

71

Practical Dent al Radiography For an atom ical reason s, th e lm is placed in th e oral cavit y at an angle, p ressed again st t h e tooth . Th is con gu rat ion m akes it h ard to ch eck th e p osit ion of th e lm for correct n ess. W h en t h e p at ien t h old s th e lm w it h a nger, it is u su ally n ot p ossible to d eterm in e w h et h er th e p osit ion of th e lm ch anged u n t il after lm d evelop m en t . Th e posit ion of th e bisector is d i eren t for each p at ien t becau se of th e in dividual n at ure of each person’s an atom y an d th e resu lt ing lm posit ion . In pract ice, it is u su ally easy to m en tally bisect th e angle form ed by th e lm and th e long axis of th e tooth an d aim th e cen t ral ray perpen dicu lar to th e im agin ar y bisector. If th is is don e correctly, th e vert ical angle is u su ally correct . W hen centering, the edge of the cone should be as parallel as possible to the visible edge of the lm . W hen the lm is positioned correctly ( Fig. 9.39), the central ray sh ould be perpendicular to the im aginary plane that bisects the angle form ed by the lm and the long axis of the tooth.

Fig. 9.39 Correct position of the lm packet in the lower arch. (From: Pasler FA, Visser H. Zahnmedizinische Radiologie. 2nd ed. Stuttgart: Thieme; 2000. Farbatlanten der Zahnmedizin; Band 5.)

9.1.5 Right-angle Technique Th e righ t-angle tech n iqu e is u su ally con sidered to be th e sam e as th e p aralleling tech n iqu e. How ever, th e on ly th ing th e t w o tech n iqu es h ave in com m on is th at a film h olding device is u sed to direct th e cen t ral ray of th e beam perpen dicu lar to th e film . As in th e paralleling tech n ique, th e im age receptor is posit ion ed in th e m iddle of th e oral cavit y, in order to obtain parallelism bet w een th e im age receptor an d th e long axis of th e tooth . Th e differen ce is th at th e righ t-angle tech n iqu e is p erform ed w ith out a bite block ( Fig. 9.40). In stead, th e h old er is m ou n ted on a spacer con e. Ow ing to th e lack of a bite block, th e righ t-angle tech n iqu e is a com bin at ion of th e paralleling tech n iqu e an d th e bisect ing-angle tech n ique. In th e paralleling techn ique, th e ver t ical angle is determ in ed by th e bite block, w h ereas in th e righ t-angle tech n iqu e, th e ver t ical angle is determ in ed an d set according to th e law s of th e bisecting-angle tech n iqu e ( Fig. 9.41). Th e m ain disadvan t age of th e righ t-angle tech n ique, w h ich w as in t roduced by Hielsch er an d m odi ed by Pasler, is th at it is n ot alw ays reliable for visualizing th e apical region ( Fig. 9.42). Parallelism bet w een th e long axis of th e tooth an d th e im age receptor sh ou ld be ach ieved in th e righ t-angle tech n iqu e, bu t if th e p at ien t h as a sh allow p alate, th e upper edge of th e lm m ay fall below th e ap ical region . Th is result s in th e apical region being cu t o th e lm . Th e bisect ing-angle tech n iqu e m ust be u sed in th is sit u at ion . Oth er disadvan t ages of th e righ t-angle tech n iqu e in clu de th e follow ing: ● Th e lm -h old er m u st b e m ou n ted on t h e sp acer con e: th is m akes th e righ t-angle tech n ique m ore difcu lt to p erform an d result s in low accept an ce by pat ien t s.

9

72

Fig. 9.40 Right-angle technique: lm -holder without a bite block is m ounted on the cone. (Adapted from : Pasler FA, Visser H. Zahnmedizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.)

Fig. 9.41 Ideal parallelism bet ween the lm and the tooth (in the upper arch).

9.1 Intraoral Radiography ●

Th e h old er p osit ion in g is n ot rep rod u cible: w h en t aking follow -u p rad iograph s (e. g., after im plan t surger y), th e h older posit ion in th e m ou th ch anges, ow ing to th e lack of a bite block.





Parallel p osit ion in g of t h e lm is arbit rar y: con sequ en tly, th e root t ip s m ay be cu t o th e radiograph . Su per im posit ion du e to lm posit ion ing er rors m ay occu r: if the lm is placed in a slanted m esial or distal position, the tooth axes w ill be radiographed at an angle, and interproxim al superim position artifacts m ay occur.

9.1.6 Bitew ing Radiography

Fig. 9.42 Right-angle technique: radiograph of the maxilla.

Bitew ing radiography w as in t rodu ced by Rap er in 1925. It is th e m ost im por tan t radiograph ic tech n iqu e for diagn osis of caries. Bitew ing radiograp h s sh ow th e alveolar ridge w ith out distort ion . Th ey dem on st rate salivar y ston es w ell an d are useful for evaluat ing th e m argin al in tegrit y of crow n s an d fillings ( Fig. 9.43). Bitew ings sh ould alw ays be obt ain ed supplem en t ar y to th e clin ical exam in at ion in cases w h ere th e m esial an d distal con t act areas can n ot be evaluated by visual in spect ion . Approxim al caries is usually overlooked w h en bitew ing radiograph s are n ot m ade supplem en t ar y to th e clin ical exam in at ion . Th is is especially t rue in cases w h ere

9

Fig. 9.43a–d Bitewing radiographs. a Right m olars. b Right prem olars. c Left prem olars. d Left molars.

73

Practical Dent al Radiography invasive caries t u n n els th rough th e in terp roxim al en am el to th e d en t in an d u n derm in es th e en am el. In diagn ost ic radiography, early detect ion of den t al caries is st ill on e of th e m ain st rategies for p rom ot ing den tal h ealth in broad segm en t s of th e popu lat ion . Size 3 × 4 cm lm is gen erally u sed for bitew ing radiograp hy. Long an d n arrow lm (2.7 × 5.4 cm ) is n o longer recom m en ded, for t w o reason s: rst , it is n ot alw ays possible to ach ieve or th ogon al im aging of all m olars an d prem olars in a single project ion an d, secon d, th e lm is too sh ort to capt u re th e alveolar crest .

Bitew ing Radiography: Methodology Becau se bitew ings are u sed for evalu at ion of in terproxim al areas, a film -h older an d aim ing ring sh ou ld alw ays be u sed in bitew ing radiography ( Fig. 9.44).

9.1.7 Radiographic Measurement Techniques Radiographic m easurem ent techniques are used to determ ine the working length of root canals ( Fig. 9.45). Since these radiographs m ust be taken w ith root-canal instrum ents and a rubber dam in place, technical difficulties m ay occur. Ideally, they should be obtained using the paralleling technique, but this is not possible w ith conventional film holders. The Endo-Holder was designed to sim plify the radiographic m easurem ent of root-canal working length ( Fig. 9.46). Its raised basket-like bite block m akes it possible to take the X-rays w ith root-canal instrum ents and a rubber dam in place. As in the parallel technique, the Endo-Holder has an aim ing ring and indicator rod, and the X-rays are directed perpendicular to the im age receptor. This m akes it possible to obtain reproducible working length m easurem ents in endodontic applications.

9.1.8 Occlusal Radiography

9

Fig. 9.44 Bitewing lm -holder. (With the kind perm ission of Dentsply Rinn.)

Fig. 9.45 Radiographic measurem ent of the working length of a root canal.

74

Occlusal film is screenless film . Com pared w ith bitew ing film , the only difference is that occlusal film is larger; the standard size is 7.5 × 5.5 cm ( Fig. 9.47). Its size m akes occlusal film very versatile. Occlusal radiographs can supplem en t or replace oth er intraoral radiographic exam inations. Ph osph or storage plates are th e on ly t ypes of digit al im age receptors available for occlusal radiography. Occlusal radiography is n ot lim ited to th e use of large lm : th e 3 × 4 cm size can also be u sed . Th e lm packet is placed in the m outh parallel to th e occlusal surfaces of th e teeth . Th ere sh ould be an angle of 90 degrees bet w een th e lm an d occlu sal p lan e. Th e t w o m ain tech n iqu es used for occlusal radiography are: ● Bisect ing-angle tech n iqu e ● Axial p roject ion tech n iqu e.

Fig. 9.46 Dentsply Rinn Endo-Holder for radiographic m easurement.

9.1 Intraoral Radiography

Occlusal Radiography: Bisecting -angle Technique Th e bisect ing-angle tech n ique m ust be u sed in occlusal radiography. As m any as ve teeth can be dep icted on a single posterior occlu sal radiograp h w h en large lm is u sed. An terior an d can in e occlu sal radiograp h s sh ow th e teeth an d large segm en ts of th e bon e. Man dibular occlusal radiograp h s sh ow th e en t ire m an dibu lar arch , in clu ding th e cort ical bon e. Den tal radiograph s taken using larger lm form ats gen erally p rovide m ore in form at ion by vir t ue of th eir larger size ( Fig. 9.48). Occlusal radiography is

som et im es possible in cases w h ere oth er in t raoral radiograph ic tech n iques can n ot be perform ed, for exam ple, in sit uat ion s w h ere pan oram ic radiography or oth er tech n iques of in t raoral radiography can n ot be perform ed successfu lly becau se of physical con st rain ts. Because of th e ease of lm placem en t , occlusal radiography is especially useful for th e assessm en t of an terior tooth t raum a in ch ildren .

Bisecting-angle Technique: Methodology Th e film packet m ust be posit ion ed in th e pat ien t’s m outh on th e occlu sal su rfaces of th e teeth , such th at th e outer edge of th e film packet is parallel to th e crow n s of th e teeth of in terest . Th is edge form s th e t angen t lin e th at th e cen t ral ray m ust in tersect at righ t angles for proper orth ogon al im aging ( Fig. 9.49 an d Fig. 9.50).

Fig. 9.47 Occlusal lm (left) versus bitewing lm (right).

9

Fig. 9.49 Correct lm positioning for m axillary posterior occlusal radiographs.

Fig. 9.48 This maxillary anterior occlusal radiograph obtained using the bisecting-angle technique shows a large area of osteolysis.

Fig. 9.50 Occlusal radiograph of the m axillary posterior teeth.

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Practical Dent al Radiography

Occlusal Radiography: Axial Projection Technique In th e axial project ion tech n iqu e of occlu sal radiography, th e axial project ion of th e beam result s in a secon d plan e th at can provid e a spat ial im age im pression w h en com bin ed w ith oth er radiograph s. Film posit ion ing is differen t from th at of th e bisect ing-angle tech n iqu e. Because th is project ion is u sed to iden t ify p ath ological ch anges in th e bu ccolingu al dim en sion , th e m an dible m u st alw ays be posit ion ed in th e cen ter of th e film , as parallel to th e edges of th e film packet as possible ( Fig. 9.51). Th e cou rse or dislocat ion of m an d ibu lar fract u res can th en be view ed in a secon d plan e in supplem en t to pan oram ic radiograph s ( Fig. 9.52 an d Fig. 9.53). Th e axial p roject ion tech n iqu e can also be used to visualize im p acted teeth or sp ace-occupying lesion s. Becau se of radiat ion -protect ion an d im age-qu alit y st an dards, th e axial p roject ion tech n iqu e of occlu sal radiography sh ou ld be used for evalu at ion of t h e m an d ib le on ly. Moreover, CBCT n ow p rovides im ages in m u lt iple plan es an d w ith bet ter diagn ost ic qu alit y th an can be ach ieved w ith th e axial project ion tech n ique of occlusal radiography. Visu alizat ion of sialolit h iasis in th e du cts of th e su b m an d ibu lar glan d is a special in dicat ion for th e axial pro ject ion tech n iqu e of occlusal radiography. Th e exposu re t im e m u st be redu ced sign i can tly to detect radiopaqu e object s such as sialolith s ( Fig. 9.54).

9

Fig. 9.52 Axial projection technique of occlusal radiography used to show a second dim ension, to identify the spatial position of fractures.

76

Fig. 9.51 Correct positioning for occlusal radiography of the m andibular posterior teeth using the axial projection technique.

Fig. 9.53 Axial projection technique of occlusal radiography used to show a second dimension revealed a cyst.

Fig. 9.54 Occlusal radiograph of the oor of the mouth revealed a sialolith in the duct of the submandibular gland.

9.2 Conventional Tom ography

9.2 Conventional Tomography A conven t ion al radiograph ic im age is th e su m of an infin ite n u m ber of an atom ical slices. It con t ain s coun tless det ails, all of w h ich arise from a single focu s of p roject ion . A single p roject ion th at visu alizes ever y det ail w ith out su perim p osit ion does n ot exist . Th erefore, a sum m at ion

radiograph is on ly capable of depict ing a few st ruct ures opt im ally. In m any cases, th e ch aracterist ic im age feat u res can n ot be adequately visualized on radiograph ic im ages th at on ly sh ow a single plan e. Even if in t raoral radiograph s cou ld reprodu ce th e n est an atom ical st ru ct u res, it w ou ld n ot be possible to display a tooth in it s en t iret y. Su pplem en tar y special in t raoral radiograph ic project ion s (e. g., m esial an d dist al eccen t ric p roject ion s) can som et im es reveal previou sly un recogn izable st ru ct ures w ith out superim posit ion , bu t th e diagn ost ic qu alit y is n ot sat isfactor y. Th e easiest w ay to display cert ain areas w ith out su perim posit ion is to blu r ou t st ruct u res above an d below th e plan e of in terest . Th is is don e by ch anging th e angle of h ead p osit ion as n eeded, to visu alize an isolated asp ect of th e m an dible or m idface, for exam ple, by blurring out th e tem poral bon es from th e m axillar y sin us ( Fig. 9.55). Close-u p im agin g is an oth er w ay to im age region s w ith out superim posit ion . In X-ray im aging, th is is don e using a sh or t con e an d is based on th e prin ciple of geom et ric un sh arpn ess ( Fig. 9.56 an d Fig. 9.57). Th e in t rod u ct ion of tom ograp h y by Bocage in 1922 provided a n ew and bet ter m eth od.

Fig. 9.55 Partial-arch projection showing osteolysis in the horizontal ramus of the m andible. T

Skin

Skin

Angle

Fo cu s Film

9

Short cone FOD > 5 cm

Fig. 9.56 Close-up view of the temporom andibular joint (Parm a projection). FOD: focus-to-object distance. FT

IR

Fig. 9.57 Close-up view of the temporom andibular joint.

Fig. 9.58 Basic principle of tom ography (schem atic): structures in the selected slice, or focal trough (FT), of the object appear in sharp focus while those outside the focal trough appear blurred. The rotational movem ents of the tubehead (T) and im age receptor (IR) are synchronized. Blurring is lowest at the rotation center (red dot). The plane of the rotation center is the in-focus slice. The larger the angle of rotation, the thinner the slice.

77

Practical Dent al Radiography

a

d

Fig. 9.59 Polytom es in m ovement.

In p rin cip le, conven t ion al tom ograp h y con sist s of th ree com p on en t s—th e X-ray t u beh ead (T), im age receptor (IR), and object (O), t w o of w h ich are m obile. In m ost cases, th e t u beh ead an d im age receptor are in m ot ion , w h ile th e object rem ain s st at ion ar y an d m ot ion less ( Fig. 9.58). Because th e m ovem en t of th e t u beh ead an d im age receptor arou n d th e rot at ion cen ter is syn ch ron ized ( Fig. 9.59), on ly th ose st ruct ures located w ith in th e plan e of th e cen ter of rot at ion —th at is, th e im age layer/focal t rough —appear in sh arp focu s, w h ile st ru ct u res ou tside th e focal t rough are blurred. Du ring an d because of t u beh ead rot at ion , st ru ct u res ou tside th e focal t rough are n ot projected on th e sam e sp ot , bu t on d i eren t p oin t s across th e lm , an d th u s ap pear b lu r red on th e im age. Conversely, all object s located w ith in th e focal t rough are p rojected on exactly th e sam e sp ot du ring th e en t ire exp osu re cycle, an d th u s ap pear in sh arp focu s on th e im age ( Fig. 9.58). Tom ograp h ic system s m ay be classi ed according to th e exten t an d t ype of blurring. Th e exten t of b lu r r in g is depen den t on th e angle of rotat ion (φ ), w h ich is determ in ed as th e p oin ts w h ere t ubeh ead m ovem en t begin s an d en ds ( Fig. 9.58). As th e angle of rot at ion in creases, th e d egree of blu rring increases an d th e th ickn ess of th e im age layer (focal t rough ) decreases. Th e t yp e of b lu r r in g is determ in ed by th e geom et r y of th e m ovem en t of th e X-ray sou rce. Th e goal of t u beh ead m ovem en t an d th e resultan t blurring is to m ake st ruct u res th at lie ou t side th e im age layer (focal t rough ) so in dist in ct th at th ey are n o longer recogn izable as st ru ct u res, bu t on ly as h om ogen eous lm blacken ing. Th is en sures th at st ruct ures th at are blu rred ou t do n ot lead to radiograp h ic m isin terpret at ion .

9

78

b

c

e

Fig. 9.60a–e Blurring pat terns in conventional tom ography. a Linear. b Circular. c Elliptical. d Hypocycloidal. e Spiral.

Fig. 9.61 Tomographic im age of the m axillary sinuses.

On e-dim en sion al (lin ear) an d m ult i-dim en sion al or plan ar (circular, spiral, an d hypocycloidal) b lu r r in g m ovem en t s are w ell kn ow n ( Fig. 9.60). Gen erally speaking, on e can say th at th e m ult i-dim en sion al m ovem en t s blur bet ter an d th us are also bet ter for th e diagn ost ic evaluat ion of bony st ru ct ures of th e facial skeleton ( Fig. 9.61). Lin ear blurring usually causes blurring sh ad ow s th at frequen tly can n ot be dist inguish ed from path o logical processes. Th e large t radit ion al tom ograph ic im aging system s h ad a blurring angle of alm ost 50 degrees an d a spiral or hypocycloidal blu rring m ot ion , result ing in th e gen erat ion of im ages w ith slice th ickn esses of ~1 m m w ith ou t in terferen ce sh ad ow s. Th e on ly disadvan t age of th ese im ages w as th eir relat ively low con t rast .

9.3 Panoram ic Tom ography

9.3 Panoramic Tomography Th e origin s an d cou rse of developm en t of p an oram ic tom ography are com pletely d ifferen t from th ose of th e con ven t ion al tom ography tech n iqu e as con ceived by Bocage. Becau se of th e com plex an atom y of th e den t al arch es an d facial skeleton , it is di cu lt to depict th ese st ru ct ures in th eir en t iret y on a single radiograp h . Most of th ese st ru ct u res are circular, oval, or arcuate, an d h ardly any of th eir bony m argin s are sit uated at righ t angles to each oth er. To obt ain diagnost ically u seful radiograph s of th e den t it ion , th e teeth h ave to be visu alized on in dividu al int raoral radiograp h s. Diagn ost ic assessm en t of th e ent ire facial skeleton by conven t ion al radiography (e. g., by using radiograph s of th e m axillar y region ) is also di cu lt , ow ing to th e rou n d sh ape an d close proxim it y of several relat ively sm all an d often duplicate st ruct ures ( Fig. 9.62).

Th e prin ciples of pan oram ic radiography for den t al ap plicat ion s w ere rst described in a U. S. paten t led by A. F. Zulauf in 1922. Pan oram ic im ages w ere gen erated using long lm w h ich , sim ilar to bitew ing lm , w as placed in th e pat ien t’s m outh to obt ain separate exposures of th e m axillar y an d m an dibular arch . Th e key to success w as th e use of a ver y n arrow ver t ical slit collim ator ( Fig. 9.63). Th is device m ad e it p ossible to produ ce im ages of th e m axillar y an d m an dibular teeth in t w o separate exposu re cycles. Zulauf m erely led a paten t for th e prin ciple of den t al pan oram ic radiography in 1922, w h ereas Num at a (1933) an d Paatero (1946) w ere th e rst to act u ally build a m ach in e capable of p rod u cing pan oram ic im ages u sing a slit collim ator (see Fig. 1.6).

9.3.1 Panoramic Radiography w ith a Slit Collimator Th ese problem s prom pted several in dep en den t den t al research ers to invest igate th e qu est ion of h ow to gen erate pan oram ic radiograph s th at provided scout im ages of th e en t ire den t it ion or, bet ter yet , of th e en t ire facial skeleton . Th e basic idea w as to develop a m eth od of producing p an oram ic scou t im ages th at t akes th e rou n d to oval st ru ct u res of th e facial skeleton in to accou n t w h ile en abling sim u lt an eou s an d com plete rep rod u ct ion of th e teeth , jaw s, tem p orom an dibular join ts, an d basal m axillar y sin u ses.

9 Fig. 9.63 Slit collim ator.

Fig. 9.62 Panoram ic photom ontage according to Pasler.

79

Practical Dent al Radiography W h ile Zulau f, Paatero, an d Nu m at a focu sed on panoram ic im aging of th e teeth , th e radiologist Heckm an n develop ed a m eth od for th e produ ct ion of pan oram a-like radiograph s of su per cial st ru ct ures of th e en t ire facial skeleton u sing ext raoral lm , w h ich h e in t rod u ced in 1939.

9.3.2 Panoramic Radiography w ith an Intraoral Source Pan oram ic rad iography w ith an in tern al source w as con ceived as a con cept in w h ich th e an ode is p laced in t raorally, in order to direct th e beam s of X-rays from in side to ou t side th e m outh , to produ ce p an oram ic im ages of th e teeth . Th is radiograph ic tech n iqu e, w h ich is n ow ob solete, em ployed a special rod-sh aped X-ray t ube th at w as placed in th e pat ien t’s m outh ( Fig. 9.64; see also Fig. 1.8). Th e lm w as con t ain ed in a exible casset te, w h ich w as posit ion ed on th e u p p er or low er arch , to allow sep arate exposures of th e m axilla or m an dible, depen ding on th e direct ion of th e an ode. Th e Fren ch m an Bou ch acou r t w as th e rst to propose th e con cept of pan oram ic radiography of th e jaw using a specially design ed in t raoral X-ray t ube, in 1898. Paten t s led by Koch an d Sterzel in Germ any in 1943 an d by Ot t in Sw it zerlan d in 1951 lau n ch ed th e developm en t of th is tech n ology.

9

Focus

Film

Fig. 9.64 Placement of the X-ray tube in panoram ic radiography with an intraoral source.

80

In 1961, th e rst system for pan oram ic radiography w ith an in t raoral source w as in t rodu ced in pract ice. If used correctly, th e m ach in e produced sat isfactor y pan oram ic im ages of th e m axillar y an d m an dibu lar teeth , respect ively. Th e best diagn ost ic qualit y w as ach ieved in th e an terior region becau se im age m agn i cat ion occu rred tow ard th e posterior region (see Fig. 1.9). Pan oram ic radiography w ith an in t raoral source h as n ot been u sed for decades. Becau se th is tech n ology u ses a ver y sm all FOD, it em it s ion izing radiat ion above th e level prescribed by regulat ion . Con sequen tly, it is n ow classied as a p roh ibited radiat ion sou rce.

9.3.3 Rotational Panoramic Radiography Th e con cept of pan oram ic im aging w as a crucial step forw ard in den t al radiology con sidering th at , w ith out th is tech n ology, on ly in t raoral radiograph s of th e teeth an d ext raoral radiograph s of par t s of th e m an dible w ere available. It w as n ot possible to produce diagnost ic qualit y radiograph s of th e m axillar y an d m an dibu lar arch es an d th eir associated st ruct ures un t il th e adven t of pan oram ic radiography w ith a rotat ing ext raoral source of radiat ion . Paatero in t rodu ced th e basic con cept of in t raoral p anoram ic radiography in 1948. As long in t raoral lm proved to be ver y im p ract ical, h e exp erim en ted w ith ext raoral lm . Th is allow ed h im to produce pan oram ic im ages of th e super cial layers of th e m idface th at w ere ver y sim ilar to th ose produced by Heckm an n ( Fig. 9.65). Paatero m ade th e n ext decisive step tow ard ach ieving tom ograp h ic im ages, by devising a system in w h ich th e pat ien t an d th e lm sim ultan eously m oved on syn ch ron ized path s aroun d a cen ter of rotat ion , w h ile th e X-ray beam , w h ich w as n arrow ed to a blade by a vert ical slit collim ator, rem ain ed st at ion ar y ( Fig. 9.63). The narrow beam passed through the rotational axis and cen ter of both th e object and the lm , w hich w as at tached to a round lm -holder. If t wo points on the sam e radius m ove at the sam e velocit y, they w ill alw ays be at rest rela-

Fig. 9.65 Panoramic radiograph of the im age without the tomographic e ect.

9.3 Panoram ic Tom ography

ω

r'

Film /screen com bination

Fig. 9.66 Principle of rotational panoram ic radiography (see text for explanation). ω: angular velocit y; r: radius.

ω

r

Focal trough

tive to each other. If one of the points is part of the object of interest and the other is part of the lm , then that part of the object w ill alw ays appear in sh arp focus on the lm . Th is tech n iqu e w as fu rth er re n ed an d, in 1955, a pan tom ograp h bu ilt in Helsin ki w as put in to operat ion in Lon don .

Principle of Rotational Panoramic Radiography Th e prin ciple of rot at ion al pan oram ic radiography can be exp lain ed as follow s: t w o adjacen t rot at ing disks w ith th e sam e radiu s (r) are rotat ing in opp osite direct ion s at th e sam e angu lar velocit y (ω) as th e X-ray beam passes th rough th eir cen ters of rotat ion ( Fig. 9.66). Th e object of in terest (in th is case, th e tooth ) m oves on radiu s r of th e first disk, w h ile th e film m oves on radiu s r′ of th e secon d disk. Becau se th e radii are equ al (r′ = r), th e object an d th e film m ove at th e sam e velocit y on th eir respect ive disks. If th e cen t ral ray is lim ited to a ver y n arrow (1 m m ) vert ical beam by a n arrow slit collim ator, an d th e object an d th e film rot ate past th e slit at th e sam e t im e an d are th u s irradiated sim u ltan eously, th en th e object w ill be displayed sh arp ly on th e film . Th is is possible becau se th e radii of th e t w o disks are equ al an d because th e t w o disks rot ate at th e sam e velocit y; con sequ en tly, th e object an d th e film are at rest relat ive to each oth er. If it is p ossible to keep th e radius of th e object an d th e lm equ al th rough out th e en t ire exposure cycle, it is also possible to disp lay arbit rarily sh aped object s (such as th e den tal arch es) in sh arp focu s on den tal lm , or any oth er t yp e of im age receiver.

Adapting the Focal Trough to the Dental Arch If th e den t al arch w ere circu lar, th en it w ould be n o m ajor problem to obtain sh arp im ages of th e teeth in th e focal t rough (im age layer). How ever, sin ce th e t w o den tal arch es are h orsesh oe sh aped, th e radiu s of th e t arget st ruct ures ch anges d u ring th e exposure cycle. Circular m ovem en t of th e film is n ot appropriate for producing sh arp

Slit collimator

r'

Im age layer

r

Im age receiver

Fig. 9.67 Adjusting the focal trough to accom m odate the dental arch (schem atic). r: radius.

9

im ages of th e m axillar y an d m an dibular arch es in a circu lar im age layer (focal t rough ). Con sequen tly, th e posit ion of th e lm m u st be adapted to th e sh ape of th e den tal arch . Because it is di cult to ch ange th e lm radius by m ech an ical m ean s, th e pan oram ic lm velocit y is con t in uou sly in creased an d decreased during the exposure cycle, to accordingly in crease or decrease th e w idth of th e im age layer (focal t rough ) to accom m odate th e sh ape of th e den tal arch . Any arch can be cen tered w ith in th e focal t rough by th is m eth od ( Fig. 9.67 an d Fig. 9.68). Th e sou rce–pat ien t– lm con gurat ion of m odern equ ip m en t h as been m odi ed, su ch th at th e p at ien t rem ain s st at ion ar y w h ile th e t ubeh ead an d lm m ove on syn ch ron ized path s aroun d th e pat ien t’s h ead.

Orthopantomography: Orthogonal Imaging of the Teeth Th e first step tow ard a pan oram ic im aging tech n iqu e th at provided diagn ost ically relevan t in form at ion w as th e developm en t of a m ean s of posit ion ing th e teeth precisely in th e focal t rough . Th e origin al pan oram ic system could n ot ach ieve orth ogon al im aging of all teeth because it on ly h ad on e rot at ing disk. On ly th e an terior crow n region w as sh ow n w ith out su perim posit ion .

81

Practical Dent al Radiography The n ext task was therefore to w ork out how to project th e beam in such a w ay as to irradiate both the anterior and posterior region as orthogonally as possible. The solution was to add m ore rotating disks to the panoram ic m achine.

As in in t raoral radiography, th e cor rect an gle of in cid en ce for each region of in terest m ust be en sured for th e produ ct ion of su perim p osit ion -free im ages in rot at ion al pan oram ic rad iograp hy ( Fig. 9.69). Sin ce or th ogon al im aging of th e m olars can n ot be ach ieved from th e an terior aspect , addit ion al rot at ion cen ters w ere n eeded for rotat ion al pan oram ic radiography. Th ese cen ters of rot at ion m ust be posit ion ed such th at parallel rays st rike th e posterior teeth orth ogon ally as th e t ubeh ead revolves aroun d th e pat ien t’s h ead. On ce a system w ith t w o addit ion al rot at ion cen ters for th e posterior region w as built , it n ally becam e possible to ach ieve or th ogon al pan oram ic im aging of th e m olars an d prem olars. Th is feat w as accom plish ed by Paatero, w h o presen ted a sm all protot ype of a pan oram ic m ach in e called th e orth opan tom ograph , in 1957.

Fig. 9.68 Focal trough adjusted to accommodate the dental arch.

9

CSCEPHPAN

Fig. 9.70 If there are at least three rotation centers (ideally, “ ying” rotation centers that continuously change positions during the rotation cycle), the narrow beam will strike the image receptor and all teeth in the entire arch orthogonally. B

E

+

C



PH

+

C

PAN

+

C

S

+

A –

Fig. 9.69 Direction of incidence during the rotation cycle of rotational panoramic radiography. The X-ray tube and lm rotate clockwise around rotation centers A, B, and C, around the patient’s head. Because orthogonal projection geom etry m ust be ensured, a separate rotation center (e ective focus of projection of the narrow beam ) is needed for each segment of the arch. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thieme; 2000. Farbatlanten der Zahnm edizin; Band 5.)

82

1 mm

5 mm

Fig. 9.71 Slit collimator widths available for various view options (schematic representation). Currently, only a slit width of 1 mm tends to be used. A wide slit width of 5 mm is needed for thin layers. CEPH: cephalometric; CS: cross-sectional; PAN: panoramic.

9.3 Panoram ic Tom ography To accom plish th e goal of or th ogon al im aging of all of th e teeth , th e origin al single-d isk p an tom ograp h w as m odi ed to accom m odate th ree rot at ing disks ( Fig. 9.70). Th e develop m en t w as com p leted in 1959 an d th e rst Orth op an tom ograp h becam e com m ercially available for u se in den t al pract ice in 1961.

Image Layer Thickness and Blurring Mechanism In con t rast to conven t ion al tom ograp hy, th ere is n o tom ograph ic angle in rot at ion al p an oram ic radiography. Th e slit collim ator assum es th e role of th e tom ograph ic angle. Most slit collim ators u sed in p an oram ic im aging are 1 m m in w idth . Slit collim ators w ith a w ider apert ure (5 m m ) can be u sed for special program s. As beam w idth is proport ion al to th e tom ograph ic an gle, th e u se of a n arrow -slit collim ator is associated w ith a sm all tom ograp h ic angle an d th us w ith low blu rring. Th erefore, th e im age layers used in rotat ion al pan oram ic radiography are also relat ively th ick (10–25 m m ). A slit collim ator w idth of 1 m m correspon ds to a tom ograp h ic angle of ~10 degrees. Zon ograp h y is a tom ograph ic tech n ique using a n arrow exp osu re angle of less th an 10 degrees. Un der favorable an atom ical con dit ion s, a collim ator w idth of 5 m m h as an e ect sim ilar to th at of a tom ograph ic angle of 15 to 20 degrees an d an im age layer th ickn ess of 1 to 2 m m ( Fig. 9.71). Th e p roject ion radiu s, de n ed as th e d ist an ce bet w een th e rot at ion cen ter an d th e cen ter of th e im age layer, is th e secon d factor th at in u en ces th e th ickn ess of th e im age layer. Th e rot at ion cen ter con st an tly ch anges posit ion du ring th e exposure cycle, becau se th e p roject ion direct ion con stan tly ch anges to m ain tain or th ogon al p roject ion geom et r y. As th e m oving rotat ion cen ter t ravels a predeterm in ed p ath from th e posterior to th e an terior region an d back, th e project ion radiu s, an d th u s th e im age layer th ickn ess, also ch anges con stan tly. Th e im age layer is n arrow er in th e an terior region an d w id er in th e posterior region ( Fig. 9.72): ● 10 m m in th e an terior region (because th e radius is sm aller) ● 20 to 30 m m in th e posterior region (because th e radiu s is larger).

Characteristics of Imaging Geometry Tw o d ifferen t t yp es of p roject ion s are u sed in rot at ion al pan oram ic radiography: project ion in th e vert ical p lan e an d project ion in th e h orizon t al plan e.

Fig. 9.72 Unlike conventional tom ography, the slice thickness of rotational panoramic radiography is not determined by the tom ographic angle, but rather by the radius and the width of the slit collimator (see Fig. 9.71). The radius (arrow) is the distance from the rotation center (e ective focus of projection) to the im age layer (focal trough).

Projection in the Vertical Plane As th e t ubeh ead w ith th e ver t ical n arrow X-ray beam revolves in lin ear m ot ion arou n d an im agin ar y rot at ion cen ter located w ith in th e m outh , th e posit ion of th e rot at ion cen ter ch anges con st an tly during th e rot at ion cycle. Th e n arrow beam act s like th e cen t ral project ion in in t raoral radiography. Th e beam path is n ot pu rely h orizontal, but m oves in ferior to superior at a project ion angle of –4 to –7 degrees ( Fig. 9.73).

9

Projection in the Horizont al Plane All of th e X-rays pass th rough th e respect ive cen ters of rot at ion th rough out th e exposure cycle (see Fig. 9.70). Th e X-rays appear to diverge from th e rot at ion cen ters. Th erefore, th e rot at ion cen ters fun ct ion as th e effect ive focus of project ion ( Fig. 9.74). As th e t ubeh ead rotates arou n d th e pat ien t’s h ead, th e X-rays diverging from th e rot at ion cen ters h ave e ect s on th e h orizon t al dim en sion . Each rot at ion cen ter ser ves as an e ect ive focus of project ion for th e h orizon tal dim en sion of th e im age. Th e rot at ion cen ter h as a ver y large an d usu ally n egat ive in uen ce on pan oram ic im age form at ion . In correct posit ion ing m ay resu lt in geom et ric un sh arpn ess an d distort ion in th e h orizon t al dim en sion of all par t s of th e jaw s, if th e distan ce bet w een th e rot at ion cen ter an d th e jaw is too sm all.

83

Practical Dent al Radiography

a

b

Fig. 9.73a, b Projection geometry and head positioning in panoram ic radiography. a Oblique angle of incidence. b Correct head position.

9

Fig. 9.75 Each panoram ic unit has positioning guides for correct patient positioning.

Advances in Rotational Panoramic Radiography Fig. 9.74 The rotation centers serve as e ective foci of projection.

Th e p r in cip le of rot at ion al p an oram ic rad iograp h y w ill on ly w ork if: ● Th e sh ape of th e focal t rough is opt im ally adjusted to th at of th e den t al arch ● Th e rot at ion cen ters are adju sted as in d ivid u ally as possible ● Th e p at ien t is opt im ally posit ion ed in th e system ( Fig. 9.75).

84

With th e adven t of orth opan tom ography, an im aging system w as in t roduced th at , by virt ue of it s pan oram ic fun ct ion , h as becom e th e m ost im por t an t radiograph ic tech n iqu e in den t al, oral, an d m axillofacial radiology. An orthopantom ogram can ser ve as the basis of furth er exam in ations, such as individual in traoral radiographs for sim ple clinical questions, or CBCT for com plex questions. After recognizing the potential of rotational panoram ic radiography, researchers started to develop additional program s for these m achines in 1975. In the course of these developm ents, panoram ic m achines that could im age not only

9.3 Panoram ic Tom ography the m axillary and m andibular arches and their supporting structures, but also m any other parts of the facial skeleton, were placed on the m arket ( Fig. 9.76; see also Fig. 1.10). Th e Scanora system , for exam ple, can also produce very im pressive pan oram ic im ages. This m ultim odal tom ographic system o ers a com bination of pan oram ic radiography, conventional tom ography, and spiral tom ography. Th e Scan ora w as th e rst system capable of gen erating cross-sect ion al tom ograph ic im ages ( Fig. 9.77). Th is

w as a crucial step tow ard th ree-dim en sion al im aging, as is n ow possible w ith CBCT, th e su ccessor to th e conven t ion al tom ography in den tal radiography. Modern pan oram ic m ach in es w ith th e correspon ding tech n ical capabilit ies o er a w ide range of special program s w ith di eren t fun ct ion s.

Special Programs In part ial-arch project ion s using special program s w ith on e rot at ing disk or w ith th e st an dard pan oram ic program , th e follow ing st ruct ures are of part icular pract ical in terest: ● Par t ial-arch segm en t s ● An terior tooth region ● Alveolar crest an d in terp roxim al m argin s ● Midface ● Tem porom an dibular join t s.

Viewing Partial-arch Segm ent s W h en invest igat ing specific quest ion s, it w ou ld seem logical to invest igate n ot alw ays th e full arch , but on ly th e cu rren t region of in terest . Part ial-arch pan oram ic radi-

9 Fig. 9.76 The Zonarc rotational panoram ic radiography m achine for recumbent patients has several special program s.

Fig. 9.78 Partial-arch view of the left m axilla.

Fig. 9.77 This implant on this cross-sectional tom ographic image is sharply de ned.

Fig. 9.79 Partial-arch view of the m andible.

85

Practical Dent al Radiography ography allow s dose reduct ion relat ive to full-arch panoram ic radiography, but visualizes a larger area th an an in t raoral radiograph ( Fig. 9.78 an d Fig. 9.79).

Viewing the Anterior Tooth Region Special rules apply to an terior pan oram ic radiography. Th e im age qualit y of an terior pan oram ic radiograph s can be en h an ced by u sing a special an terior program w ith a th icker im age layer. An terior program s greatly reduce spin al sh adow s an d geom et ric un sh arpn ess on an terior pan oram ic rad iograp h s ( Fig. 9.80).

Alveolar Crest and Interproxim al (Bitewing) Views Th rough advan ces in digit al tech n ology, m odern pan oram ic m ach in es n ow h ave special program s for areas previou sly reser ved for in t raoral bitew ing rad iograp h s. Because th e project ion angle rem ain s con stan t , m odern pan oram ic m ach in es can gen erate u n iform an d an atom ically correct pan oram ic view s of th e alveolar crest .

9

Fig. 9.80 Owing to the larger radius and adjusted m ovem ent path, the anterior program depicts the anterior region with m uch less geometric unsharpness.

Fig. 9.81 Panoram ic radiography: bitewing program.

Fig. 9.82 Orthophos XG program, showing the temporomandibular joint with the mouth open (outer images) and closed (inner images).

86

9.3 Panoram ic Tom ography Likew ise, bitew ing p rogram s provide in creasingly bet ter su perim posit ion -free in terp roxim al view s of coron al aspect s of th e den t it ion ( Fig. 9.81).

Viewing the Tem porom andibular Joint s Tem p orom an dibu lar join t disorders are u sually of a fun ct ion al n at u re. Th e first qu est ion is h ow th e h ead of th e con dyle is p osit ion ed w ith in th e fossa an d h ow m uch m ou th op en ing is p ossible. Magn et ic reson an ce im aging is u su ally perform ed for fu r th er fu n ct ion al diagn osis. In pract ice, h ow ever, th e stat us of th e tem porom an dibu lar join t w ith th e m ou th closed an d du ring m a xim al op en ing can be assessed in a sim ple m an n er, u sing th e tem porom an dibu lar join t p rogram of a pan oram ic m ach in e ( Fig. 9.82 an d Fig. 9.83).

Th ere are oth er special program s for assessm en t of ch anges in th e bony st ru ct ures of th e tem porom an dibular join t by pan oram ic radiography. Digital volum e tom ography (CBCT) is, h ow ever, th e preferred tech n ique for invest igat ing special quest ion s regarding th e bon e.

Viewing the Midface Before th e adven t of CBCT, orth opan tom ography w as used for radiograph ic visualizat ion of th e m idface region . It p rovided a sim p le an d u sefu l w ay of obt ain ing diagn ost ically u seful in form at ion abou t st ruct ures above th e m axilla ( Fig. 9.84). Th is radiograph ic tech n ique h as also been replaced by CBCT becau se th in -slice im ages in m ult iple plan es are n eeded for su ccessful diagn ost ic im aging of th e m idfacial region .

9

Fig. 9.83 Rotational m ovem ent path for panoramic im aging of the temporomandibular joint. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thieme; 2000. Farbatlanten der Zahnm edizin; Band 5.)

Fig. 9.84 Panoramic radiograph of the m idfacial region.

33 32

16

48 50

51

29

40

8

39 37

9

41

30

Muco ce le

14

42

31 10

11

7

47

36

37

18

37

19

17

38

37

Fig. 9.85 Panoram ic radiographic anatomy of the m andibular and m axillary region. See

Table 9.1 for key to numbers.

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Practical Dent al Radiography 34

33 31

4

16

10

48

30

5

38 52

38

6

1

11 15

53

• 47

50

7

8

15

14

10

29 27

35 13

9

12 28

19

18

45

45 17

20

21

Fig. 9.86 Panoram ic radiographic anatomy, dem onstrated using a head phantom. See

9

88

Table 9.1 for key to num bers.

Table 9.1 Panoram ic radiographic anatomy

Table 9.1 (Continuation)

Number

Structure

Number

Structure

1

Anterior nasal spine

28

Mandibular foramen

2

Incisive foramen

29

Zygomatic arch

3

Piriform aperture

30

Articular tubercle

4

Nasal septum

31

External acoustic opening

5

Nasal cavit y

32

Petrous bone

6

Maxillary sinus

33

Orbit

7

Alveolar recess of the m axillary sinus

34

Lateral wall of the orbit

8

Medio-anterior wall of the m axillary sinus

35

Posterior wall of zygom atic bone

9

Inferior wall of maxillary sinus

36

Hyoid bone

10

Posterior wall of the m axillary sinus

37

Im age of the cervical spine

11

Hard palate

38

St yloid process

12

Maxillary tuberosit y

39

Shadow of the nose

13

Pterygoid process

40

Air bet ween the tongue and hard palate

14

Zygom atic bone

41

Ear lobe

15

Coronoid process

42

Soft palate and uvula

16

Infraorbital m argin

43

Pharynx

17

Mental foram en

44

Nasal oor

18

External oblique line

45

Mandible, opposite side

19

Mandibular canal

46

Mastoid process

20

Trabecular bone

47

Pterygopalatine fossa

21

Cortical bone

48

Infraorbital foram en

22

Dentin

49

Sphenoid sinus

23

Root canal

50

Median palatine suture (intermaxillary suture)

24

Periodontal ligam ent space

51

Nasal conchae

25

Lam ina dura

52

Sem ilunar notch

26

Condylar process

53

Skull base

27

Head of the condyle

9.3 Panoram ic Tom ography

Radiographic Anatomy of Panoramic Radiography w ith Special Consideration of Orthopantomography Kn ow ledge of th e relevan t an atom ical st ruct ures is th e cru cial basis for in terpretat ion of any radiograph ic im age. It is n ot p ossible to detect path ological ch anges if on e does n ot kn ow w h at th e n orm al an atom y of th e region of in terest looks like in it s h ealthy state. Th ere are coun tless n orm al an atom ical varian t s of th e facial skeleton , an d even th ese p ose a h igh risk of m isin terpret at ion of radiograp h ic fin dings. As described in Sect ion 6.1, cen t ral p roject ion (an d it s special im age-form at ion ch aracterist ics) is th e m ain reason w hy it is often di cu lt to detect path ological ch anges. Becau se th e p an oram ic view is cur ved, th e in terpretat ion of th e in dividual st ru ct ures is m ore di cult an d th e view itself is n ew an d u n fam iliar. A p h otom on tage by Pasler sh ow s a ver y im p ressive pan oram ic view of th e m axilla, m an dible, an d basal m a xillar y sin us ( Fig. 9.85). For com p arison , an orth opan tom ogram of a sku ll ph an tom is sh ow n , w ith th e key an atom ical st ru ct ures labeled ( Fig. 9.86).

Panoramic Radiology: Methodology and Avoidance of Errors Th e facial skeleton is m ade u p of m any differen t an atom ical st ruct ures. Most of th em are bony in n at ure, but som e are soft-t issu e st ruct ures th at are visible on radiograph s. Th e oral cavit y an d n asoph ar yngeal region con tain m any air-filled spaces th at are also eviden t on den tal pan oram ic tom ograph s. Th e su m of all of th ese st ru ct u res m akes th e pan oram ic radiograph an X-ray im age th at is n ot easy to in terpret or un derst an d. Correct pat ien t posit ion ing is ext rem ely im por t an t , as th is h elps to en su re th at th e m any differen t t ypes of st ru ct ures in th e facial skeleton can be in terpreted correctly.

Positioning and Positioning Errors Each pan oram ic X-ray m ach in e h as a focal t rough th at is in dividually adjusted to accom m odate th e pat ien t’s den tal arch . St an dard focal t rough sh apes can be program m ed, based on st an dard arch form data. Digit al system s allow for opt im al in dividual focal t rough adjustm en t based on pat ien t-specific dat a collected during th e exp osu re. Fu r th erm ore, pan oram ic m ach in es h ave a h ead posit ion er an d oth er m easurem en t tools th at can be ut ilized to gen erate cu stom focal-t rough p rofiles for p at ien tspecific arch form s ( Fig. 9.75).

9 Asce nding ramus o f the mandible

Hard palate/ nasal flo or

Frankfort ho rizontal plane

Fig. 9.87 Correct head position, as evidenced by the horizontal line of the hard palate, which should normally be parallel to the Frankfort horizontal plane.

89

Practical Dent al Radiography Regardless of th e m eth od of focal t rough adaptat ion , th e pat ien t m u st be correctly cen tered in th e adapted focal t rough . Th is en sures th at th e cen t ral ray st rikes each tooth as orth ogon ally as possible an d preven t s th e reduct ion of im age qu alit y due to distor t ion an d geom et ric un sh arp n ess. Er ror s in t h e p osit ion in g of t h e h ead h ave t w o m ain causes: ● Tilt ing of th e h ead ● Disp lacem en t an d rot at ion of th e h ead .

a

Any ch ange in head position m eans th at th e head is no longer exactly in the focal t rough. This results in unw an ted superim position an d distortion in th e h orizon tal dim ension. Superim posit ion is caused by tilt ing of the head, distortion by displacem ent of th e teeth out of the focal trough, and geom etric distort ion by the location of objects in the rotat ion center (effective focus of project ion).

b

Fig. 9.88a, b Head tilted too far forward. a Head tilted too far forward (schem atic diagram). Red line: Frankfort horizontal plane with head tilted too far forward. Blue line: Frankfort horizontal plane with head positioned correctly. Black line: occlusal plane. (From : Pasler FA, Visser H. Zahnm e dizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.) b Patient with head tilted too far forward.

9

Fig. 9.89 Panoram ic radiograph taken with the head tilted forward.

90

9.3 Panoram ic Tom ography

Tilting of the Head It is possible to determ ine w hether the patient’s head is tilted forward or backward, based on the follow ing structures: ● If posit ion ed correctly, th e h ard palate and n asal oor sh ou ld be dep icted as a st raigh t h orizon t al lin e parallel to th e low er border of th e radiograph . ● It is possible to ch eck for correct h ead posit ion w ith respect to th e Fran k for t h or izon t al p lan e: th is referen ce p lan e is an im agin ar y lin e join ing th e extern al au ditor y m eat u s to th e in fraorbit al m argin ( Fig. 9.87).

a

If th e h ead is t ilted too far for w ard , th e t w o posterior en ds of th e h ard palate m ay open superiorly, form ing a blun t or poin ted “V” ( Fig. 9.88 an d Fig. 9.89). If th e h ead is t ilted too far back w ard , th e h ard palate w ill appear as an inver ted “V.” Th ere is a risk th at th e oor of th e n ose an d th e h ard palate m ay be superim posed on th e apices of th e m axillar y teeth . Th e visual e ect is w iden ing of th e en t ire im age, w h ich m ay result in th e h eads of th e con dyles being cu t o ( Fig. 9.90 an d Fig. 9.91).

b

9

Fig. 9.90a, b Head tilted too far backward. a Head tilted too far backward (schem atic diagram). Red line: Frankfort horizontal plane with head tilted too far backward. Blue line: Frankfort horizontal plane with head positioned correctly. Black line: occlusal plane. (From : Pasler FA, Visser H. Zahnm e dizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.) b Patient with head tilted too far backward.

Fig. 9.91 Panoram ic radiograph taken with the head tilted backward.

91

Practical Dent al Radiography Lateral t ilt in g d oes n ot a ect im age qu alit y as m u ch as anterior an d posterior t ilt ing. Never th eless, th is h am pers com parison w ith previous radiograph s, m aking it m ore di cult to in terpret th e a ected radiograph ( Fig. 9.92 an d Fig. 9.93).

Displacem ent and Rot ation of t he Head out of the Focal Trough If th e pat ien t’s h ead t ilt s in th e ver t ical plan e, th e m axilla an d m an dible st ill rem ain largely in th e focal t rough . On ly excessive t ilt ing h as an effect on th e im age, n am ely, w iden ing in th e an terior region . If h ead displacem en t or rot at ion occurs, th e dist an ce to th e rot at ion cen ter ch anges, result ing in geom et ric un sh arpn ess an d w iden ing or n arrow ing of th e jaw s on th e im age. Because of a rotat ion center located in the anterior oor of the m outh, anterior or posterior displacem ent of the an terior teeth out of the focal trough results in geom etric unsharpness. The further backw ard the teeth are positioned relative to th e cen tral plane of th e focal trough , the w ider they appear on the im age. The further forw ard the teeth are posit ion ed, the n arrow er th ey appear on th e im age.

Fig. 9.92 Head slanted to the side. (From : Pasler FA, Visser H. Taschenatlas der zahnärztlichen Radiologie. Stut tgart: Thiem e; 2003.)

9

Poster ior d isp lacem en t of t h e an ter ior teet h : If th e pat ien t’s h ead is t ilted too far back, th e an terior teeth are displaced posterior of th e focal t rough , an d th e distan ce to th e rotat ion cen ter decreases. Con sequen tly, th e an terior teeth are irradiated in th e zon e of in creasing beam divergen ce, an d visible w iden ing of th e an terior teeth occu rs on th e im age ( Fig. 9.94 an d Fig. 9.95).

Fig. 9.93 Panoram ic radiograph taken with the head slanted to the side.

92

9.3 Panoram ic Tom ography

IR

Focal trough

Fig. 9.94 Schem atic of posterior displacem ent. If the teeth are located posterior to the focal trough, they appear wider on the radiograph. IR: im age receptor. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnmedizin; Band 5.)

Result

Fig. 9.95 The further the anterior teeth are located posterior to the focal trough, the wider they appear on the radiograph.

9 Wide Norm al Narrow

Practice To avoid such positioning errors, it is crucial to ensure that the anterior teeth are properly aligned in the m iddle of the focal trough. ● A bite-rod positioning device m ust be used in dentate patients. Modern panoram ic m achines also have correction options that should be used for these cases. ● In edentulous patients, close at tention to proper positioning is especially important. In the case presented in Fig. 9.96, a bite rod was not used because tooth 21

was missing. This resulted in improper alignment of the anterior teeth and marked widening of the maxillary and mandibular anteriors. Consequently, there was a signi cant decrease in anterior image qualit y. It is also evident that no bite rod was used in this case. In the repeat exposure, correct anterior alignment was achieved ( Fig. 9.97), that is, the anterior teeth were correctly positioned within the focal trough. As is clearly visible on the repeat radiograph, this resulted in signi cant improvement of diagnostic image qualit y.

93

Practical Dent al Radiography

Fig. 9.96 Posterior displacement: because the patient was positioned posterior to the focal trough, the images of the anterior teeth appear wider.

9

Fig. 9.97 In the repeat radiograph (sam e patient as in correctly.

94

Fig. 9.96), the patient was positioned correctly and the teeth are depicted

9.3 Panoram ic Tom ography

Fig. 9.98 In this panoramic radiograph of a patient with an edentulous anterior m axillary and m andibular arch, the anterior region appears extrem ely widened.

9

Fig. 9.99 On a later radiograph of the sam e patient, there was m uch less anterior widening.

In p ar t ially an d fu lly ed en t u lou s p at ien t s, th ere is a h igh er ch an ce th at th e an terior teeth w ill n ot be correctly posit ion ed in th e focal t rough . Th e reason is th at th ese pat ien t s are su bopt im ally im m obilized in th e focal t rough , ow ing to th e lack of appropriate posit ion ing gu ides ( Fig. 9.98 an d Fig. 9.99).

95

Practical Dent al Radiography

IR

Focal trough

Result

Fig. 9.100 Schematic of anterior displacement of the head. The teeth are positioned anterior to the focal trough. IR: image receptor. (From : Pasler FA, Visser H. Zahnmedizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.)

9

Fig. 9.101 In this panoram ic radiograph, taken with the head tilted forward, there is apparent narrowing of the anterior teeth.

An ter ior d isp lacem en t of t h e an ter ior teet h : According to th e gen eral prin ciple of tom ograph ic blurring, if th e an terior teeth are displaced too far for w ard an d lie out side th e focal t rough , th ey appear blurred an d n arrow and are n ot sh ow n com pletely on th e im age ( Fig. 9.100 and Fig. 9.101).

96

9.3 Panoram ic Tom ography Rot at ion of t h e h ead ou t of t h e m ed ian p lan e: If th e h ead is rot ated sligh tly to th e side, st ru ct u res ap pear distor ted an d w id er on on e side th an on th e oth er, because a rot at ion cen ter is located in th e posterior region . Th is is m ore or less ap paren t on th e pan oram ic radiograph , depen ding on th e degree of h ead rotat ion ( Fig. 9.102 an d Fig. 9.103).

Other Factors In uencing Im age Qualit y and Diagnostic Qualit y In addit ion to posit ion ing errors, oth er factors th at affect th e qu alit y of den tal p an oram ic im ages, som et im es ver y st rongly, m u st be t aken in to con siderat ion during radiograph ic in terpret at ion an d diagn osis. Th ese in clude su perim posit ion s, soft-t issue sh adow s, an d gh ost im ages (rad iograp h ic ar t ifact s th at appear on pan oram ic film w h en a radioden se object is pen et rated m u lt ip le t im es by th e X-ray beam ). Com m on gh ost im ages an d soft-t issue sh adow s in clude: ● Gh ost im ages of th e cer vical sp in e ● Gh ost im ages of m et allic object s an d an atom ical st ru ct u res ● Gh ost im ages of objects located in th e rot at ion cen ter ● Soft-t issue sh adow s an d superim posit ion s ● Air w ay sh adow s from th e oral cavit y, n asal cavit y, an d ph ar yngeal areas.

Fig. 9.102 Schem atic dem onstrating rotation of the head out of the median plane. (From: Pasler FA, Visser H. Zahnmedizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.)

9

Fig. 9.103 In this panoram ic radiograph, taken with the head rotated out of the median plane, the left side appears m uch wider than the right.

97

Practical Dent al Radiography

Fig. 9.104 Panoramic radiograph showing ghost im ages of the cervical spine, projected three tim es.

9

Fig. 9.105 The t wo diagonal radiolucent lines at the level of the apex of teeth 12 and 22 are projected from the spine.

Ghost Im ages of the Cervical Spine Ow ing to th e m ovem ent path and project ion geom etr y, the X-ray beam penet rates th e cer vical spine t w ice laterally (on th e right an d left side of the im age) and once in the m idline (in th e cen ter of the im age), producing ghost im ages. Th e lateral im ages generally cause no in terference, but th e cen tral gh ost im age is a m ore or less annoying artifact

98

that can—or rather used to—com plicate anterior diagnosis trem endously. Modern panoram ic m achines have special program s to com pensate for ghost im ages of radiodense struct ures such as th e spin al colum n ( Fig. 9.104). Th e atlas, th e rst cer vical ver tebra, is com m on ly seen on radiograph s as a con spicuously sym m et rical st ruct u re associated w ith th e spin al colum n ( Fig. 9.105).

9.3 Panoram ic Tom ography

Fig. 9.106a, b The radiolucent lines in the anterior apical region are projected from the atlas. a Joint space of the rst cervical vertebra (arrow). b Panoram ic appearance of the radiolucent lines (arrow).

9

It ap pears as a sym m et rical, sh ort obliqu e brigh t lin e in th e ap ical areas of th e an terior teeth . Alth ough often m isin terp reted as an an terior p eriapical radiolu cen cy, it s sym m et r y is m ore suggest ive of an an atom ical st ru ct ure. Tw o radiolu cen t lin es arise from th e join t sp ace bet w een th e rst an d secon d cer vical vertebrae, as sh ow n on th e CBCT im age of th e atlas ( Fig. 9.106).

99

Practical Dent al Radiography

Ghost Im ages of Met allic Object s in the Head and Neck Region All m et allic object s in th e n eck region m ust be rem oved prior to exp osu re of th e p an oram ic radiograp h becau se th ey are located in th e path of th e beam . Met al ar t ifacts are m ost com m on ly cau sed by lead ap ron s (if p laced too h igh ) an d n ecklaces.

If placed too h igh at th e back of th e n eck, lead ap ron s cause m et al art ifact s th at often obscure large areas of th e an terior m an dible an d cause un n ecessar y radiat ion exposure by m aking it n ecessar y to repeat th e radiograph ic exam in at ion ( Fig. 9.107). Par t s of a n eck lace located at th e back of th e n eck produce gh ost im ages in th e m an dibular an terior region ( Fig. 9.108).

9 Fig. 9.107 Lead apron artifact projected on the anterior region of a panoramic radiograph.

Fig. 9.108 Ghost im age of a necklace appearing in the anterior region of a panoram ic radiograph.

100

9.3 Panoram ic Tom ography

Mandibular and Maxillary Dentures All m et al object s in th e oral cavit y, part icularly m axillar y an d m an dibular d en t u res, appear on th e film . Before start ing th e p an oram ic exposu re, th e p at ien t sh ou ld be in st ructed to rem ove all den t u res from both th e m axillar y an d th e m an dibu lar arch , even if on ly on e arch is being invest igated ( Fig. 9.109).

Com plete den t u res w ith n o m et al com pon en ts can be left in th e m outh to bet ter posit ion th e pat ien t in th e m ach ine. How ever, it can n ot be recom m en ded to leave com plete den t u res in th e m ou th du ring a pan oram ic exp osure because th is m eth od is n ot reliable ( Fig. 9.110).

9 Fig. 9.109 Metal clasps of maxillary and m andibular partial dentures.

Fig. 9.110 Maxillary and m andibular complete dentures.

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Practical Dent al Radiography

Ghost Im ages of Anatom ical Structures Gh ost im ages of st ruct u res in th e region of th e angle of th e m an dible m ay appear on th e opposite side of th e film , ow ing to low blurring. Dep en ding on th e degree of h ead t ilt ing, gh ost im ages of the h orizon t al p osterior ram u s of th e m an dible an d part s of th e ascen ding ram u s m ay ap pear as an atom ical st ru ct u res on th e op p osite side of th e lm . Th e in ferior cort ical bon e frequ en tly appears as a w ell-de n ed radiopaqu e lin e ( Fig. 9.111).

In th e gure, a h orizon t al radiopaque lin e th at t u rn s sligh tly upw ard in th e region of tooth 45 appears at th e level of th e hyoid bon e on th e righ t side. On th e left side, th e lin e is located sligh tly h igh er because th e h ead is t ilted sligh tly to th e left . Th is ph en om en on can be dem on st rated by posit ion ing th ree lead sph eres along th e poste rior border of th e ascen ding ram u s of th e m an dible ( Fig. 9.112).

9 Fig. 9.111 The posterior m andible and angle of the mandible project onto the opposite side.

Fig. 9.112 Lead spheres were placed along the left angle of the m andible to dem onstrate the projection of the left mandible and right half of the jaw.

102

9.3 Panoram ic Tom ography

Ghost Im ages of Earrings and other Ear Jewelry Earrings an d oth er m et allic ear jew elr y are th e best kn ow n an d m ost com m on cau se of gh ost im ages in pan oram ic radiograp hy ( Fig. 9.113). Th e in ferior–superior beam p ath an d p roject ion -related m agn ificat ion can be readily iden t ified .

Ghost Im ages and Blurring of Object s Located in the Rot ation Center Objects located directly in a rotation center (effective focus of projection) produce gh ost im ages that con tribute to im age form ation as long as they rem ain in the rotation center.

In th e case exam ple, a barbell-t ype tongue piercing w ith sph erical beads w as at t ach ed on th e top an d bottom of th e tongue ( Fig. 9.114). On th e pan oram ic radiograph , th e beads do n ot appear as circles but as elongated ovals. Th is in dicates th at th ey are located in th e oral cavit y, posterior to th e focal t rough . Th e u pper bead produces n ot on ly an oval ar t ifact , bu t also a brigh t st ripe th at exten ds h orizon t ally across th e lm . Th e on ly explan at ion for th is ph en om en on is th at th e bead w as located in th e rot at ion cen ter an d w as th us im aged th rough out th e en t ire exposure cycle as it rem ain ed in th e e ect ive focus of project ion . In th e subsequen t exposure, th e tongue w as pressed far en ough again st th e roof of th e m outh th at th e

9 Fig. 9.113 Ghost im ages of earrings appear on the respective opposite side.

Fig. 9.114 Ghost im ages: barbell-shaped tongue piercing located in the rotation center for the anterior teeth.

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Practical Dent al Radiography u p per bead of th e tongue piercing projected just below th e n asal oor an d h ard palate; as it w as located in th e rotat ion cen ter, it appears as a long sh adow st rip e exten ding from tooth 15 to tooth 25. Th e diagram in th e righ t pan el of Fig. 9.115 sh ow s an d exp lain s w hy th e u p p er bead located in th e rot at ion cen ter (e ect ive focu s of project ion ) appeared as a brigh t st rip e on th e lm .

Practice Jewelry, piercings, and dentures should be rem oved before a panoram ic exam ination.

If th e h ead is in correctly posit ioned posterior to th e focal t rough (as eviden ced by w iden ing of th e an terior teeth ), th e crow n s of th e m olars an d prem olars m ay sh ift th eir rot at ion cen ter an d produce gh ost im ages th at appear in th e apical region on th e opposite side of th e film ( Fig. 9.116).

Soft -tissue Shadows and Superim positions Many soft-t issue st ruct u res in th e facial region produ ce sh adow s on pan oram ic radiograph s th at m ay lead to un cert ain t y an d m isin terpret at ion .

Fig. 9.115a, b E ect of tongue piercing located in the rotation center of panoram ic radiography. a Ghost im ages of tongue piercing on panoram ic radiograph (cf. Fig. 9.114). b Schem atic explaining the phenomenon (with rotation center).

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a

b

Fig. 9.116 Ghost im ages of right m axillary crowns located in the rotation center.

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9.3 Panoram ic Tom ography W h ile earlobe sh adow s are usually easy to iden t ify an d gen erally cau se n o radiograph ic problem s, ow ing to th eir lateral posit ion , soft-t issu e sh adow s of th e n ose, n asal con ch ae, an d soft palate m ay som et im es lead to con fusion ( Fig. 9.117).

Nasal con ch ae: Th e pan oram ic radiograph is a tom ograph ic im age w ith a relat ively large slice th ickn ess (in th e order of 10–25 m m ). Th erefore, th is X-ray tech n ique is ch ie y in dicated for im aging areas w ith n o st ruct ures th at are sit uated close togeth er. Th is m ain ly applies to th e m an d ibu lar arch , bu t also ap p lies to th e m a xilla.

Fig. 9.117 Soft-tissue shadows of the nose and ear lobe on a panoram ic radiograph.

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a

b Fig. 9.118a, b Shadows caused by the nasal conchae. a Marked right nasal concha. b Extension of the nasal conchae. The oval m arks the right nasal concha. The double-ended arrow shows the shadow of the left nasal concha extending in the frontal and anterioposterior direction.

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Practical Dent al Radiography Pan oram ic im age qu alit y becom es crit ical in part s of th e m axilla su p erior to th e h ard palate an d n asal oor, w h ere th e n asal cavit y lies in close p roxim it y to th e m axillar y sin u s. Neith er area can be displayed separately on pan oram ic radiograp h s because th e im age layer is n ot th in en ough . Th is is w hy com preh en sive p an oram ic radiograph ic diagn osis of th e sin u s cavit y is n ot p ossible (an d m ay even be dangerous). Basal m axillary sinus shadow s w ith a clearly identi able, ch aracteristic shape (e. g., a m ucocele or odontogen ic cyst) and location on th e oor of th e m axillary sinus can be diagnosed w ith a high degree of con dence. More superi-

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orly located lesions or changes cannot be reliably detected or interpreted by panoram ic radiography ( Fig. 9.118). Overlapp ing st ru ct u res on th ick-layer p an oram ic im ages can be in terpreted w ell by m agn et ic reson an ce im aging, w h ich can be u sed for separate assessm en t of th e n asal cavit y an d m axillar y sin u s ( Fig. 9.119). Soft -t issu e sh ad ow of t h e n ose: If th e focal t rough is too far an terior, or for an atom ical reason s, th e n ose m ay appear as a soft-t issue sh adow in th e m axillar y an terior region th at can n ot im m ediately be in terpreted w ith certain t y ( Fig. 9.120).

Fig. 9.119a, b Nasal conchae and m axillary sinuses. a Maxillary sinus. b Nasal conchae.

Fig. 9.120 Soft-tissue shadow of the nose in the upper anterior region of a panoramic radiograph.

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9.3 Panoram ic Tom ography Soft p alate: Th e pan oram ic appearan ce of th e soft palate is variable. Th e on ly w ay it can be iden t i ed is by th e presen ce of air from th e n asoph ar yn x an d oral cavit y along its borders. It can usu ally be iden t i ed as an elon gated soft-t issu e st ru ct u re th at exten ds sligh tly dow n w ard. Ow ing to tongu e an d sw allow ing m ovem en t s, th e sh ape of th e soft p alate m ay var y or it m ay n ot be visible at all ( Fig. 9.121).

Ton gu e sh ad ow : Because th e tongue is posit ion ed in th e low er par t of th e oral cavit y, th ere is an air- lled space bet w een th e dorsum of th e tongue an d th e h ard palate. Th is air- lled space m ay appear as a black eld of in terferen ce on panoram ic radiograph s, exten ding from th e soft palate from th e righ t side to th e left . Th is m ay com pletely obscure th e root s of th e m axillar y teeth . If obscu red by th e tongu e “sh adow,” th e roots can n o longer be m ade visible, especially w h en digital system s are used.

9 Fig. 9.121 Panoramic appearance of the soft palate as rectangular shadow on the left, and as a sausage-shaped shadow on the right.

Fig. 9.122 Correct tongue position for panoram ic radiography (schematic). The tongue should be pressed against the roof of the m outh during the exposure. (From: Pasler FA, Visser H. Zahnmedizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.)

Fig. 9.123 The tongue is clearly seen on this lateral cephalogram .

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Practice It is therefore of utm ost importance to ensure that the patient’s tongue is pressed well against the nasal oor and hard palate during the exposure cycle. Because of its m uscle m ass, the tongue acts as a lter, and more radiation is absorbed ( Fig. 9.122 and Fig. 9.123).

If th e tongu e is n ot p osit ion ed again st th e roof of th e m outh , a radiolucen t zon e w ill ap pear th at m ay p ar t ial-

ly or com pletely obscure diagn ost ic in form at ion ( Fig. 9.124). On th e repeat radiograph , successful im aging of th e m axilla w as ach ieved becau se th e tongue w as rm ly pressed again st th e roof of th e m outh ( Fig. 9.125). Because th e pat ien t forgot to press th e tongu e again st th e palate at th e begin n ing of th e exposure, a con spicuous black air ar t ifact appeared in th e left m a xillar y region . Later, as th e righ t side w as being exposed, th e pat ien t pressed th e tongue again st th e roof of th e m outh ( Fig. 9.126).

9 Fig. 9.124 Tongue shadow due to improper tongue positioning is clearly seen on this panoram ic radiograph.

Fig. 9.125 There is no tongue shown on this panoram ic radiograph because the tongue was properly positioned against the roof of the m outh during the exposure.

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9.4 Cone Beam Com puted Tom ography

Fig. 9.126 Because the tongue was not positioned against the roof of the m outh at the beginning of the exposure, a black stripe ap peared in the left maxillary region of the panoram ic radiograph. Later, when the beam scanned the right m axillary region, the tongue was properly positioned against the hard palate.

Practice

in spect ion , fun dam en tal di eren ces in th e in tern al tech n ology of th e t w o system s becom e eviden t .

To be able to press the tongue against the palate correctly, the patient m ust be told how to do so just before each exposure. To avoid fault y radiographs and unnecessary radiation exposure, the correct tongue position should be practiced before the patient is positioned in the m achine. This takes a lit tle m ore tim e but certainly helps to improve diagnostic im age qualit y.

9.4.1 Technique and Image Formation in Cone Beam Computed Tomography

9.4 Cone Beam Computed Tomography CBCT, also kn ow n as d igit al volu m e tom ography, is th e first fully fledged tom ograp h ic tech n iqu e design ed specifically for th e field of den t al, oral, an d m axillofacial radiology th at w as capable of providing opt im al tom ograph ic im ages of osseou s st ru ct u res of th e facial skeleton . CBCT can be con sidered th e d irect su ccessor to conven t ion al tom ography based on th e blurring prin ciple. Un like conven t ion al tom ograp hy, CBCT is readily available for den tal, oral, an d m axillofacial radiology. Because of its cu t t ing-edge tech n ology, CBCT h as a m u ch larger im aging sp ect ru m th an tom ography based on th e blurring prin ciple. In th e late 1990s, th e New Tom becam e th e rst CBCT system available for in -o ce u se. Th e New Tom CBCT un it m ay look ver y sim ilar to a conven t ion al com puted tom ograp hy (CT) m ach in e on th e out side but , on closer

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Technical Developments from Computed Tomography to Cone Beam Computed Tomography CT w as in depen den tly in t roduced by Godfrey N. Hou n sfield an d Allan McCorm ack in 1972, as a tech n ique capable of producing tom ograph ic im ages by a m eth od th at w as com pletely differen t from conven t ion al tom ography based on th e blurring prin ciple. In CT, th e X-ray t ube an d th e digit al detector array revolve aroun d th e pat ien t in a circular m ovem en t (to gen erate cross-sect ion al [slice] im ages u sing a n ely collim ated, fan -sh aped X-ray beam ). Modern th ird- an d four th -gen erat ion CT scan n ers use a sign i can tly en larged fan -beam . Th is apert ure en largem en t ser ves to en sure m ore e cien t u t ilizat ion of X-rays. How ever, becau se on ly a sm all area of skin is exp osed, m u lt ip le rot at ion s of th e t ubeh ead aroun d th e pat ien t are n eeded to expose a given volum e of t issue. By using a larger collim ator aper t ure, th e X-ray t ube can be m oved con t in uously w ith out lin ear displacem en t . Th is result s in a subst an t ial reduct ion of rot at ion t im e.

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Start of spiral computed tomography scanning Focal path of continuously rotating X-ray tube

z (m m) Direction of continuous table motion

t (s)

a Fig. 9.127a, b Spiral computed tom ography. a Schem atic. z: slice thickness; t: time. (From : Pasler FA, Visser H. Zahnm edizinische Radiologie. 2nd ed. Stut tgart: Thiem e; 2000. Farbatlanten der Zahnm edizin; Band 5.) b Orthophos XG 3D cone beam m achine with com bined digital CBCT and panoramic im aging capabilities.

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Spiral CT, in t roduced by Willi Kalen der in 1989, w as a sign i can t advan ce in CT tech n ology. In spiral CT, th e pat ien t lies on a m otorized t able, w h ich is con t in u ously advan ced th rough th e gan t r y w h ile th e X-ray t u be an d detectors revolve arou n d th e pat ien t . Alth ough m u lt iple rotat ion s of th e X-ray t u be are st ill requ ired to im age th e area of th e body being invest igated, th is tech n iqu e produces a con t in u ou s im age w ith ou t gaps bet w een slices ( Fig. 9.127a). Th e n ext advan ce in CT tech n ology w as th e in tegrat ion of an addit ion al collim ator ap er t u re an d u t ilizat ion of th e fu ll beam for th e acqu isit ion of a com plete dat aset . Th ese m ach in es, w h ich h ave a con e-sh aped beam an d fan sh aped detector array, basically rep resen t an oth er n ew gen erat ion of CT scan n ers. Becau se of th e large volu m e of th e X-ray beam , th ey can im age th e en t ire volum e of an organ in on ly on e rot at ion . Cu rren tly, th is tech n iqu e can on ly be u sed to im age sm all an atom ical st ruct ures, ow ing to equ ipm en t size con st rain t s an d th e ver y com plex im aging geom et ries. Th is sp ecial CT im aging procedure is par t icularly w ell suited for im aging th e facial skeleton —th e focu s of den t al, oral, an d m axillofacial radiograph ic diagn ost ics.

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A n ew digit al volum et ric CBCT system developed speci cally for den t al applicat ion s w as in t roduced by Mozzo an d colleagu es in 1998. Th is m arked th e start of th e developm en t of digital volu m et ric CBCT an d its u se in den tal, oral, an d m a xillofacial radiology ( Fig. 9.127b).

Data Reconstruction and Image Formation W h en an X-ray beam t ravels th rough t issues, all st ruct ures in th e p ath of th e beam at ten u ate th e beam to differen t d egrees, resu lt ing in a greater or lesser degree of blacken ing of th e film or im age receptor. Th e degree of blackn ess is th e sum (of radiograph ic den sit ies) of all irradiated st ruct ures. A single exposure does n ot provide en ough data to determ in e th e exact locat ion w h ere a given am ou n t of absorpt ion took place. To determ in e th e spat ial dist ribu t ion , a su fficien tly large n um ber of exposu res m ust be t aken from m any differen t angles. Th erefore, scan n ers take at least 200 exposures per rot at ion aroun d th e pat ien t’s h ead. Pulsed radiat ion is gen erally used, but con t in uous radiat ion m ay be used for sm all-volum e scan n ing, to im prove im age qualit y an d to ach ieve sh orter rotat ion t im es.

9.4 Cone Beam Com puted Tom ography Absorpt ion valu es for each project ion can be m ath em at ically back-calculated to precise spat ial posit ion s of a given slice. Each absorpt ion value can th us be m apped back to th e exact sp at ial p osit ion w h ere th e absorpt ion took place w ith in th e irradiated t issu e. In CT, a t w o-dim en sion al dat aset is gen erated as an axial tom ograph ic im age. Th e com puter soft w are t ran sform s th e t w o-dim en sion al axial slice im ages in to a th ree-dim en sion al im age, w h ich ideally sh ou ld n ot con t ain any gap s bet w een slices. In spiral CT, th e in dividual slices are com bin ed w ith ou t gaps, so th at th ree-dim en sion al volum et ric dat asets can be acquired. CBCT system s can directly gen erate th ree-dim en sion al volu m et ric datasets, ow ing to th e con e-beam geom et r y. Most CBCT system s u se at p an el detectors, bu t som e use im age in ten si ers. Th e detectors con sist of ch arge-coupled device (CCD) or com plem en t ar y m et al oxide sem icon du ctors (CMOS) im age sen sors. Im age in ten si ers use ph osp h ors su ch as cesium iodide. Im age form at ion is by prim ar y an d secon dar y recon st ru ct ion .

Prim ary Reconstruction Several steps are involved in t ran sform ing raw dat a in to a recon st ru cted im age by m apping th e at ten u at ion coefficien t s (absorpt ion ch aracterist ics, gray-scale valu es) of th e in dividu al volu m es of irradiated t issu e. Mapp ing of th e precise sp at ial dist ribut ion of th e at ten uat ion coefficien t s is of crit ical im port an ce for diagn ost ic im age qualit y. Th e m ath em at ical fou n dat ion for th e recon st ru ct ion of CT im ages w as laid by th e Boh em ian m ath em at ician Joh an n Radon , w h o, in 1917, p roposed a CT recon st ru ct ion algorith m u sing th e at ten uat ion coe cien t s as th e basis of calcu lat ion . His m ath em at ical m eth od of ltered back p roject ion an d di eren t m odi cat ion s of it are st ill used for CT im age recon st ruct ion today. Filtered back project ion is also used in CBCT im age recon st ru ct ion . Becau se of it s con e-beam geom et r y, CBCT is a m ath em at ically m ore ch allenging back-project ion prob lem th an conven t ion al fan -beam CT, w h ich involves less volu m et ric data. Radon’s ltered back project ion alon e is n ot su cien t for CBCT im age recon st ru ct ion . Th erefore, th e Feld kam p algorith m , p roposed in 1984, is also com m on ly u sed for CBCT im age recon st ruct ion today. Th e volu m et ric dat aset con sists of a grid of cubic volu m e elem en ts, or voxels, in th ree-dim en sion al sp ace. Th e voxel is th e th ree-d im en sion al varian t of th e p ixel. Each voxel is assign ed a gray-scale n u m ber (represen t ing th e degree of at ten u at ion of th e X-ray beam by th e m aterial w ith in th e voxel). Each p osit ion of th e object is assign ed an exact gray-scale n u m ber in th ree-dim en sion al space

Fig. 9.128 Result of a CBCT reconstruction. After primary reconstruction, various secondary reconstructions (e. g., axial, sagit tal, and coronal views) can be perform ed.

by m ean s of back p roject ion . From th e su m of voxels in th e irradiated region , secon dar y recon st ruct ion is perform ed to create a recon st ructed CBCT im age th at , to a great degree, re ect s th e an atom ical an d p ath ological con dit ion s w ith in th e region ( Fig. 9.128).

Secondary Reconstruction Th e processed volum et ric dat aset can be u sed to gen erate im ages of any desired cross-sect ion al slice of th e scan n ed object . In addit ion to th e t ypical sagit t al, coron al, an d axial view s used in cran ial diagn ost ics, it is also possible to recon st ruct cross-sect ion al view s adapted to th e specific quest ion s addressed in den t al, oral, an d m a xillofacial radiology ( Fig. 9.129, Fig. 9.130, Fig. 9.131). Th e diverse possibilit ies to recon st ruct basically any slice plan e from th e volu m et ric dat aset m akes CBCT so especially in terest ing for den tal, oral, an d m axillofacial radiology. Th e an atom y of th e facial skeleton is ver y com plex. Th is applies n ot on ly to bony st ruct ures of th e face, but also, an d equally, to th e teeth an d th e adjacen t bony st ruct ures of th e m axilla an d m an dible. Preform ed st an dardized slices h ave proved u n sat isfactor y for visu alizat ion of th e sm all in dividual an atom ical st ruct ures in th e den t al eld. CBCT m ust provide th e opport un it y to create a custom slice for each region . Th e in t raoral or pan oram ic radiograph is a n ish ed radiograph w h ose project ion geom et r y can n ot be ch anged. In CBCT, on th e oth er h an d, th e pract it ion er m ust in divid ually select th e slice th at is m ost appropriate for th e clin ical quest ion . Th is is precisely th e area w h ere th e problem s an d th e diverse diagn ost ic possibilit ies of CBCT lie close togeth er ( Fig. 9.132 an d Fig. 9.133).

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Fig. 9.129 Orthopantogram showing radiolucencies of unclear etiology in the lateral mandible.

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Fig. 9.131 The normal variant is clearly identi able in the axial view (cf. Fig. 9.130). Fig. 9.130 This secondary coronal reconstruction shows a normal anatom ical variant of the mandible. Because of the low thickness, hypodense areas appear in the lateral view.

9.4.2 Limitations of Computed Tomography and Cone Beam Computed Tomography CT is th e stan dard im aging m odalit y u sed to an sw er m ost clin ical qu est ion s across th e en t ire field of m edicin e. It is capable of p rod u cing th ree-dim en sion al im ages w ith ver y good im age qualit y. Tw o d isadvan t ages associated

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w ith CT are ar t ifact s caused by filtered back project ion , an d relat ively h igh rad iat ion exp osu re.

Artifacts Met al ar t ifact s are am ong th e easiest ar t ifacts to spot on CT im ages. Th ey occur w h en an object produces such st rong absorpt ion of radiat ion that it can n ot be com pen sated by back project ion . Par t ial volu m e ar t ifact s are an oth er m ajor t ype of art ifact to look out for. Th ey m an ifest as ext in ct ion effect s in recon st ruct ion s w ith large con t rast differen ces bet w een th e target object an d it s

9.4 Cone Beam Com puted Tom ography

Fig. 9.132 Secondary reconstruction corresponding to an orthopantogram .

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Fig. 9.133 In contrast to the classical orthopantogram , views of the m axillary sinus can also be reconstructed from the dataset.

su rrou n dings. Mot ion ar t ifact s play a m in or role in CT, bu t m ay becom e sign ifican t as th e irradiated volum e in creases. CBCT is also su bject to m et al art ifact s, but to a m uch lesser exten t . Volu m e art ifact s m ay also occu r. Mot ion art ifacts can be con sidered a m ajor disadvan t age of CBCT ( Fig. 9.134).

Fig. 9.134 Motion blur on a CBCT scan.

Radiation Exposure A m ajor advan tage of CBCT is th at radiat ion exposu re is sign ifican tly low er th an th at w ith conven t ion al CT. Th e m ain reason is th at th e th ree-dim en sion al volum et ric dat aset is acqu ired in a single rot at ion of th e beam an d scan n er. In addit ion , m uch low er m illiam pere levels are n eeded for CBCT scan s. According to th e guidelin es for CBCT, th e e ect ive dose is sign i can tly low er th an for conven t ion al CT.

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Practical Dent al Radiography According to literat u re sou rces, e ect ive doses for con ven t ion al CT range from 180 to 2,100 µSv, w h ile th ose for m ost CBCT system s range from 11 to 674 µSv. In pract ice, h ow ever, e ect ive doses of on ly 11 to 96.2 µSv are u sed, especially for den tal im p lan t plan n ing. Th e ICRP 2007 recom m en dat ion s p rovide th e follow ing e ect ive doses for rou t in e den tal p rocedu res: ● Ceph alom et ric radiograph : 5.6 µSv ● Pan oram ic rad iograph , digital: 2.7 to 24.5 µSv ● In t raoral rad iograph : 34.9 to 388 µSv ● CBCT: 11 to 674 µSv ● CT: 180 to 2,100 µSv. Act u ally, th e on ly “p rice” for th e low er radiat ion dose is that CBCT is u n su it able for soft-t issue im aging. How ever, this is n ot n eeded for m ost of th e clin ical qu est ion s p osed in d en t al, oral, an d m axillofacial radiology.

9.4.3 Volume Size Sin ce all dat a for CBCT are collected in a single rot at ion , th e volu m e size for a given clin ical qu est ion m u st alw ays be selected before st art ing th e scan . Th e rst digital CBCT m ach in es h ad large volum e sizes ( eld of view : 15–18 cm ) th at could provide a com plete pict u re of th e w h ole facial skeleton in it s en t iret y. Over t im e, CBCT system s w ere developed th at h ad sm aller volu m es of arou n d 5 × 5 cm to 8 × 8 cm . Large volum es con t in u e to be u sed p arallel to th e sm aller volum es. Con sidering th e size of th e jaw region , a volum e size of ~8 × 8 cm sh ou ld be qu ite su cien t for m ost in d icat ion s. Tw o m ain advantages of using sm aller volum es are lower radiation doses and sh orter recon struction tim es. Because sensor size also determ ines th e price of a CT system , CBCT system s also cost less than conventional CT system s. Furth erm ore, m uch higher im age qualit y can be achieved by using sm aller volum es. Am ong other th ings, this has led to an expansion of clinical indications for CBCT because m odern CBCT system s can depict even ver y sm all an atom ical struct ures in excellen t detail ( Fig. 9.135 and Fig. 9.136).

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9.4.4 Clinical Indications for Cone Beam Computed Tomography Th ree-dim en sion al im aging is n ecessar y w h en conven t ion al t w o-dim en sion al im ages fail to provide sufficien t in form at ion to an sw er th e clin ical qu est ion . Su p p lem en tar y th ree-dim en sion al radiograph ic im aging sh ould con t ribu te to su pp ort ing th erap eu t ic decision -m aking. Th e pu rpose is to provide a bet ter over view for su rgical an d oth er t reat m en t plan n ing. Th e n eed for su p plem en t ar y diagn ost ic p rocedu res is st rongly depen den t on th e experien ce of th e clin ician . Ult im ately, th e ju st ifying in dicat ion determ in es w h eth er CBCT is n ecessar y.

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Basic Rules for the Generation of Individual Reconstructions Diagn osis based on cross-sect ion al CBCT im ages requ ires proper applicat ion of th e kn ow n ru les of in t raoral an d ext raoral pan oram ic radiography. Th e product ion of an atom ically correct view s of th e upper an d low er jaw an d teeth is of cen t ral im port an ce. Th e m ost basic r u le is th at th e beam m ust be perpen dicu lar to th e long axis of th e teeth for or th ogon al im aging. Proper applicat ion an d use of th e tools supplied w ith each respect ive CBCT system is th e prerequisite for ach ieving th is goal. Sim ilar to pan oram ic radiography, th e slice t h ick n ess an d p osit ion of CBCT recon st ruct ion s can be varied. Th ese t w o p aram eters m u st alw ays be con sidered w h en taking cross-sect ion al im ages. Th e ch oice of slice posit ion is of m ajor im por t an ce. Th e slice plan e sh ould alw ays be posit ion ed at righ t angles to th e an atom ically relevan t axes of th e m axilla an d m an dible an d to th e axes of th e diagn ost ically relevan t teeth . Correct adjust m en t of th ese param eters requ ires an exact kn ow ledge of th e an atom y an d a good spat ial im agin at ion . If th ese basic rules are ign ored or follow ed in correctly, th en th ere is a risk th at th e an atom ical sit uat ion an d/or any path ological ch anges th at m igh t be presen t w ill be m isin terpreted. Arbit rar y plan e select ion result s in a lack of com parabilit y an d in creases th e risk th at im port an t details w ill be overlooked. It is im por tan t to en su re th at th e cen ter of th e slice is exactly parallel to th e object it passes th rough ( Fig. 9.137). All oth er slices m u st be at a righ t angle to th e object . If th e slice axis deviates by several degrees, th en th e im age of th e scan n ed st ruct ures w ill n ot be an atom ically correct ( Fig. 9.138).

Indications for Cone Beam Computed Tomography Clin ical in dicat ion s for CBCT h ave developed in all areas of den tal, oral, an d m axillofacial radiology over th e years. In th e begin n ing, CBCT w as m ain ly used for plan n ing den tal im plan t s, w h ich is st ill th e m ain in dicat ion for th e exam in at ion . Over t im e, h ow ever, in dicat ion s for CBCT h ave developed over th e en t ire field of den t ist r y. CBCT sh ould on ly be used if th e th ree-dim en sion al im ages w ill provide im port an t n ew in form at ion th at is n eeded to an sw er th e clin ical quest ion . Th e im plicat ion s for t reat m en t sh ould alw ays be t aken in to accoun t w h en con sidering a referral for CBCT. If a p an oram ic or in t raoral radiograp h alon e does n ot provide su cien t diagn ost ic in form at ion , a CBCT exam in at ion is gen erally just i ed.

9.4 Cone Beam Com puted Tom ography Experien ce h as sh ow n th at in previously un clear cases, CBCT can provide reliable im ages, even aroun d th e root s of th e m axillar y posterior root , result ing in a sign i can t im provem en t of diagn ost ics.

Fig. 9.135 Panoramic reconstruction with a spherical volum e of 16 cm .

9 Target w indow

Target w indow

Fig. 9.136 Bilateral arteriovenous m alform ation visualized by panoram ic image reconstruction.

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Practical Dent al Radiography In on e case exam ple, plain lm radiography an d clin ical exam in at ion did n ot p rovide su cien t in form at ion to determ in e w h eth er osteolysis an d root fract u re w ere p resen t in an en dodon t ically t reated tooth 26 ( Fig. 9.139). High -resolut ion m u lt ip lan ar recon st ru ct ion im ages ob tain ed by CBCT w ere n eeded to reveal th e t ru e exten t of in am m at ion ( Fig. 9.140 an d Fig. 9.141).

Fig. 9.139 Intraoral radiograph of endodontically treated tooth 26.

9 Fig. 9.137 Correct position of the im age layer in the upper arch (red and blue lines). The layer thickness is m arked by the yellow line.

Fig. 9.140 CBCT coronal view of tooth 26.

Fig. 9.138 Incorrect position of the im age layer in the lower arch.

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Fig. 9.141 CBCT axial view of tooth 26.

9.4 Cone Beam Com puted Tom ography In a secon d case exam p le, p lain lm radiograph ic n dings w ere equ ivocal for oro-an t ral com m u n icat ion ( Fig. 9.142). Th e oro-an t ral com m un icat ion could be seen un equ ivocally on th e adjun ct CBCT im ages of th e righ t an d left m an dible ( Fig. 9.143 an d Fig. 9.144).

Fig. 9.142 Conventional panoram ic radiography was equivocal for oro-antral com munication.

9

Fig. 9.144 Oro-antral comm unication was unequivocally shown by CBCT (right mandible). Fig. 9.143 Oro-antral com m unication was unequivocally shown by CBCT (left mandible).

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Chapter 10 Anatomy and Topography of the Facial Skeleton

10.1 The Teeth and Tooth-supporting Struct ures

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10.2 The Mandible

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10.3 The Maxilla

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10.4 Panoram ic Radiographic Anatom y

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0

Anatom y and Topography of the Facial Skeleton

10 Anatomy and Topography of the Facial Skeleton A p recise kn ow ledge of radiograp h ic an atom y is essen t ial for th e correct in terp ret at ion of radiograp h s. Com preh en sion of th eir arrangem en t in th ree-dim en sion al sp ace is also of fu n dam en t al im por tan ce.

In con t rast to ph otography, th e diagn ost ic in terpret at ion of radiograph s depen ds n ot on ly on th e visible im age, but also on th e beam path (project ion ) un derlying th e p rocess of im age form at ion ( Fig. 10.1).

10

Fig. 10.1a–c This panoramic radiograph (a) revealed deep vertical bone loss on the distal surface of tooth 22. Periapical radiographs did not show any abnormalities. Transverse (b) and axial (c) views were needed to dem onstrate that a cyst was causing vestibular displacem ent of the endodontically treated tooth.

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10.1 The Teeth and Tooth-supporting Structures Becau se of cen t ral p roject ion , all st ru ct u res of th e t arget object are st ru ck by X-rays an d projected on th e im age. Many an atom ical st ru ct ures con t ribute to im age form at ion th rough su m m at ion . Su m m at ion can be t ricky becau se bony st ru ct u res located ou tside th e target region can con t ribu te to im age form at ion an d, if th ey do, th ere is alw ays a risk of m isin terp ret at ion . Th erefore, th e con gu rat ion s seen on radiograph ic im ages do n ot alw ays accu rately re ect t ru e un d erlying an atom ical con dit ion s. In in t raoral radiography, for exam ple, even th e p resen ce of m ult i-rooted teeth can cau se diagn ost ic di cu lt ies. Su p erim posit ion of th e zygom at ic bon e (ch eekbon e) over th e m axillar y region can also lead to m isin terp ret at ion .

10.1 The Teeth and Toothsupporting Structures Th e teeth an d tooth -su p p or t ing st ru ct u res are am ong th e sm allest an d fin est an atom ical st ru ct u res th at can be visu alized radiograp h ically.

Th e lam in a du ra is of great im p or tan ce for th e iden t icat ion of path ological ch anges in th e alveolar area. Th e lam in a du ra is th e th in layer of com pact alveolar bon e th at lin es th e tooth socket (alveolus). It s th ickn ess varies from 0.1 to 0.4 m m . Becau se it looks like a sieve con t ain ing m any sm all h oles, th e lam in a dura is also referred to as th e “cribriform p late.” It is at tach ed to th e t rabecu lae of th e can cellous bon e. Th e cribriform plate appears as a radiopaque lin e called th e lam in a dura on radiograph s in th e vest ibu lo-oral p roject ion , for exam p le, on bitew ing radiograph s ( Fig. 10.2 an d Fig. 10.3). Nat urally, the in terradicular bon e sept um m u st be in clu ded to evaluate th e bifurcat ion an d th e rich variet y of form s of th e pulp ch am ber an d root can als. Th is push es in t raoral radiography to th e lim it s, an d addit ion al th reedim en sion al im aging st u dies su ch as con e beam com pu ted tom ograp hy (CBCT) m ay be n eeded to add ress diagn ost ic qu est ion s in th is com plex area ( Fig. 10.4). Correct visualizat ion of th e alveolar ridge an d in terden t al bon e sept um on in t raoral radiograph s is h igh ly depen den t on th e radiograph ic tech n ique an d th e X-ray project ion angle. If th e beam is n ot directed at righ t angles to th e alveolar ridge, th ere is a risk of m isrepresen t at ion of th e h eigh t of th e alveolar ridge on th e radiograph . In th is case, th e alveolar ridge seen on th e radiograph usually seem s h igh er th an it really is. Bitew ings, pan oram ic radiograph s (orth opan tom ogram s), or special set t ings for th e alveolar crest in panoram ic radiography m ay th en be n eeded for proper visualizat ion of th e alveolar ridge ( Fig. 10.5).

10

Fig. 10.2 The lam ina dura appears as a thin, solid, radiopaque line surrounding each tooth socket.

Gingiva Fiber bundles Periodontal ligament space Cementum a

b

Fig. 10.3a, b Tooth and tooth-supporting structures. a The anatomical alveolus appears as a thin radiopaque line called the lamina dura. b Longitudinal cross-sectional view of the tooth and supporting structures.

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Anatom y and Topography of the Facial Skeleton

Fig. 10.4a–c Interradicular bone septum , bifurcation, pulp chamber, and root canals. a The exposed bifurcation of tooth 36 is clearly visible. In tooth 37, the oblique line appears at the level of the alveolar ridge as a broad, radiopaque line that project s onto the distal root. b This transverse CBCT im age shows the full extent of bone loss in a second plane. c Fractures in the root region of tooth 16 complicate the diagnosis, but signi cant widening of the periodontal ligam ent space can be seen. Tooth 15 has an incomplete root lling. The llings of tooth 17 show irregularities and the pulp cannot be diagnosed with certaint y. The coronoid process shows anatom ical irregularities in the vicinit y of the m axillary tuberosit y. The pterygoid process ap pears distal to the m axillary tuberosit y. The posterior part of the zygomatic bone appears in the upper part of the X-ray image. The border of the m axillary sinus appears as a thin radiopaque line.

10 a

b

Fig. 10.5a, b Anatom ically correct representation of the alveolar ridge can only be achieved when a parallel beam of incident radiation is highly perpendicular to the m andible and image receiver. These conditions are best achieved in panoram ic radiography and vertical bitewing radiography. a Bitewing radiograph acquired using a panoram ic radiography m achine (Orthophos XG). b Vertical bitewing radiograph (intraoral).

Cer vical bu r n ou t : An oth er radiological ph en om en on is cer vical bu rn ou t , w h ich app ears as a radiolu cen t area in th e cer vical region of a tooth . Th is di use brigh ten ing is caused by an atom ical factors. Becau se th e en am el t apers tow ard th e root , th ere is decreased X-ray absorpt ion at th e cem en to-en am el jun ct ion , m aking th e area appear darker.

Note Fig. 10.6 The dark areas appearing at the necks of teeth 16 and 15 could be mistaken for cervical caries, but their shape and structure is indicative of cervical burnout. The enamel dam age seen on the distal surface of tooth 35, on the other hand, is indicative of caries.

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Cervical burnout is sim ilar in appearance to root caries. Therefore, care m ust be taken to avoid m isinterpretation of cervical burnout as caries ( Fig. 10.6).

10.2 The Mandible

10.2 The Mandible On ly a few an atom ical st ru ct u res in th e m an dibu lar region are of part icu lar in terest in den t al radiography. In th e p osterior m an dibu lar region , th e obliqu e lin e (obliqu e ridge) gen erally project s to th e root region of th e w isdom teeth an d secon d m olars. Th e obliqu e lin e of th e m an dible (lin ea obliqu a) appears as a sligh tly cur ved,

th in radiopaque lin e w ith a w idth of 1 to 2 m m . It m ay cause diagn ost ic problem s if it exten ds to th e apical region ( Fig. 10.7). Th e m en tal foram en is usually visible on ly on panoram ic radiograph s. Th e m an dibular n er ve can al appears as a rad iolu cen t ban d bet w een t w o p arallel radiop aqu e lin es. In m ost cases, it can be easily iden t i ed on radiograph s.

Fig. 10.7a–c Depending on its shape and on the radiographic projection, the oblique line appears at the level of the alveolar crest and projects to the root area of the wisdom tooth and second m olars.

Fig. 10.8a–c Pathologic process or normal anatomical variation? a This lateral view shows a sharply de ned, hypodense, oval area resem bling a cystic lesion. b Marked thinning of the m andibular cortex is seen on this radiograph. c The symm etrical pat tern of thinning of the m andibular cortex can be seen in this plane. This thinning is the cause of the questionable hypodense oval area observed in (a).

a

10

b

c

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Anatom y and Topography of the Facial Skeleton Th e incisive can al, w h ich varies in an atom ical w idth an d size, appears on m axillar y an terior radiograph s as a radiolu cen t ban d bet w een t w o parallel radiopaque lin es th at exten d vert ically.

Caution In som e cases, the nerve canal cannot be visualized on either conventional or panoram ic im ages. If this is the case, even greater caution is needed when perform ing surgical procedures in this region.

Caution

An atom ical var iat ion s: Th ere are m any variat ion s of the n orm al an atom y of th e m an dible. Th e cross-sect ion al an atom y of th e m an dible can lead to m isin terpret at ion of radiograph ic im ages. If, for exam ple, th ere is radio lucen cy of u n clear origin , side-to-side com p arison is alw ays n ecessar y to di eren t iate bet w een n orm al variat ion s of the m an dibu lar an atom y an d p ath ological processes. If in dou bt , addit ion al CBCT st udies can h elp determ in e w h eth er a qu est ion able area of radiolucen cy is due to a path ological p rocess or a n orm al an atom ical varian t ( Fig. 10.8).

10.3 The Maxilla Th e m axillar y region con t ain s sign ifican tly m ore st ruct u res of in terest (besides th e teeth an d th e alveolar ridge) th an th e m an dible.

In the presence of a nasopalatine cyst, the incisive canal may be widened and rounded. However, this sign alone is not reliably indicative of a cystic lesion.

The m edian palat in e su t ure an d, in m any cases, th e an terior n asal sp in e, also ap pear on m axillar y an terior radiograph s. Th e soft-t issu e sh adow of th e n ose superim poses on th e m axillar y an terior region . In in t raoral radiography, this often m akes th e root region seem den ser th an it act ually is. How ever, th e soft-t issu e sh adow of th e n ose can be easily iden t ified on m ost in t raoral radiograp h s as th e cur ved lin e correspon ding to th e cur vat ure of th e n ost rils ( Fig. 10.9). Above th e m axillar y can in es, th e radiopaqu e lin es form ed by th e m edioven t ral bord er of th e m axillar y sin u s and by th e n asal oor in tersect , form ing an “inverted Y.” A brigh ter, den ser area can be seen m esial to th e can in es; as in th e m axillar y an terior region , th is is caused by th e soft-t issue sh adow of th e n ose ( Fig. 10.10).

Ante rior nasal spine

10

Incisive forame n

Soft-tissue shadow of the nose Inte rmaxillary suture

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Fig. 10.9 Maxillary anterior region and radiographically relevant (generally identi able) anatom ical structures.

10.4 Panoram ic Radiographic Anatom y

Fig. 10.10 X-ray im age of tooth 13 (canine), showing the border of the m axillary sinus (distal), oor of the nasal cavit y (cranial), and soft-tissue shadow of the nose (m esial).

Medioven t rally, the border of th e m axillar y sinus ap pears as a fain t , th in radiopaqu e lin e th at t yp ically exten ds across th e h ard p alate/n asal oor. Th e h ard p alate/n asal oor appears as a st raight h orizon tal radiopaque lin e th at , unlike th e radiopaque line of th e border of th e m axillar y sinus, is alw ays readily iden t i able ( Fig. 10.11). Th e alveolar recess is a part of th e m axillar y sin us th at appears posterior to th e h ard palate/n asal oor. It m ay cause diagn ost ic p roblem s if it ap p ears as a radiolu cen t area resem bling a cyst . In th e p osterior m axillar y region , th e bony border of th e m axillar y sin us alw ays appears as a ver y th in , cur ved (con cave) radiopaque lin e in th e area of th e m olar an d prem olar root s ( Fig. 10.12). In subject s w ith a at h ard palate, th e radiopaque lin e of th e zygom at ic bon e can “m igrate” posteriorly (e. g., w hen using th e bisect ing-angle tech n ique) an d superim pose on th e m olar ap ices ( Fig. 10.13). Th e coron oid process of th e m an dible can som et im es be seen on ver y distal view s ( Fig. 10.14).

10.4 Panoramic Radiographic Anatomy

Fig. 10.11 High palate: only a small portion of the oor of the nasal cavit y appears as a radiopaque line above the maxillary molars.

Because it covers a larger area, pan oram ic radiography, or or th opan tom ography, n at urally sh ow s m ore an atom ical st ruct ures th an in t raoral radiography. W h ile th e an atom ical st ruct ures in th e m an dibular region are usually clearly visualized an d iden t ified, th ose in th e m a xillar y an d bifacial region frequen tly presen t diagn ost ic ch allenges. Tw o m ain reason s for th is are th e th ickn ess of th e im age layer (up to 25 m m ) an d superim posit ion of a variet y of di eren t an atom ical st ru ct u res in th e im age layer ( Fig. 10.15).

10

10.4.1 The Mandible

Fig. 10.12 Molar region with small root fragm ents at the level of the alveolar ridge. The posterior m argin of the alveolar process appears as a thin radiopaque line. The posterior part of the zygom atic bone appears in the upper part of the X-ray im age.

Th e m an dibular canal is usually w ell visualized on radiograp h s, as are th e m en t al foram en an d th e m an dibu lar foram en . Th e m an dibu lar can al is ext rem ely variable in locat ion an d sh ap e an d sh ou ld alw ays be assessed by left– righ t com parison . Th e an atom y of th e so-called ascen ding bran ch of th e m an dible, in clu ding th e m an dibu lar angle, is ch aracterized by th e n er ve can al th at open s superiorly in to th e

Fig. 10.13a, b In both radiographs, the zygomatic bone is very low. a The zygom atic bone covers the apex. b The zygom atic bone projects to the root region.

a

b

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Anatom y and Topography of the Facial Skeleton fossa of th e m an dible. Th e coron oid process, th e m an dibu lar n otch , an d th e cap u t an d collu m of th e m an dible are usually clearly visu alized on radiograph s. How ever, diagn ost ic problem s m ay arise in th e area, ow ing to soft-t issu e st ru ct u res, w h ich cau se an atom ically in duced problem s su ch as th ose n orm ally seen on ly on p an oram ic radiograph s. Becau se th ese soft-t issu e sh adow s (an d air sh adow s) di er greatly from on e in d ivid u al to an oth er, radiograph ic diagn osis in th is region is part icularly m ore ch allenging th an in oth er areas. Radiograp h ic sh adow s of th e opposite jaw, th e soft palate, an d th e t u be of air from th e m ou th an d th e n asal cavit y gen erally project on th e ascen ding bran ch of th e m an dible. Th e t w o sh adow s m eet at th e ph ar yn x, form ing di eren t sh ap es th at project on th e ascen ding bran ch of th e m an dible. Th ese radiograph ic sh adow s can easily be m isin terp reted. Th e m axillar y t u berosit y is located at th e p osterior en d of th e m axilla. It is clin ically relevan t w h en t uberosit y fract u res occur du ring tooth ext ract ion . Th e poste-

rior border of th e m axillar y sin us exten ds cran ially as a th in radiopaque lin e. A secon d, th in , vert ical radiopaque lin e exten ds posteriorly. Both lin es m ark th e borders of th e pter ygopalat in e fossa. Th e pter ygoid process or plate is n ot alw ays visible radiograph ically, an d th e pter ygoid h am ulus is rarely visible. Th e st yloid process can be m ore clearly iden t i ed as a m ore or less th in radiopaque lin e th at exten ds posteriorly an d can be ver y long in th e presen ce of calci cat ion . Pan oram ic radiography sh ow s th e soft-t issue sh adow of th e auricle (pin n a) of th e ear, in addit ion to th at of th e n ose. Th e ch aracterist ic sh ape of th e ear aps gen erally leaves n o room for m isin terpret at ion . Th e soft palate, w h ich exten ds as a relat ively th ick, den se soft-t issue st ruct ure from th e en d of th e h ard palate to th e ph ar yn x, is m ore problem at ic. Th e soft palate is iden t i ed by th e air th at surroun ds it . Th is air com es from th e n asal cavit y an d from th e posterior oral cavit y, w h ich u n ite in th e ph ar yn x. Problem s in assessm en t of th e soft palate m ay arise, ow ing to th e fact th at th e soft palate can assum e m any d i eren t sh ap es as a resu lt of tech n iqu e-related im aging factors. Th e tongu e is an oth er im port an t soft-t issue sh adow to be con sidered in den t al radiography in gen eral, but in pan oram ic rad iograp hy in p art icu lar. Th e m ost im port an t an atom ical st ru ct ures in den t al radiography are sh ow n in Fig. 10.16 (I), Fig. 10.17 (II), Fig. 10.18 (III), Fig. 10.19 (IV).

Fig. 10.14 Tooth 17, with a view of the coronoid process of the m andible.

10

Fig. 10.15 Panoramic radiograph obtained with an X-ray sensor, showing a complete view of the upper and lower jaw, the basal m axillary sinus, and the bony joint surfaces.

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10.4 Panoram ic Radiographic Anatom y

Exte rnal acoustic me atus

Soft palate

Soft-tissue shadow of the no se Hard palate/nasal flo o r

Ear lo be

Hyoid bo ne

The alve olar re ce ss is lo cate d caudal to the nasal flo or

Fig. 10.16 Panoramic radiography: anatom ical structures I.

Articular tube rcle

Orbit

Late ral atlanto -axial joint

Sphe no id sinus

10

Collum

Radiopaque line fo rme d by the de nse poste rior compact bo ne of the oppo sing jaw

Stylo id proce ss Oblique line

Fig. 10.17 Panoramic radiography: anatom ical structures II.

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Anatom y and Topography of the Facial Skeleton

Pte ryg o palatine fossa

Nasal cavity

Nasal se ptum

Infe rio r nasal concha

Se milunar notch

Condyle

Hyoid bo ne

Me ntal fo rame n

Mandibular canal

Fig. 10.18 Panoramic radiography: anatom ical structures III.

Infrao rbital canal

Maxillary tube rosit y

Zyg omatic bo ne

10

Zygomatic arch

Pharynx

Ce rvical spine

Ang le of the jaw

Compact bo ne of the mandible

Fig. 10.19 Panoramic radiography: anatom ical structures IV.

10.4.2 The Maxilla and Midface Th e m id face is con n ected to th e m axilla. Th e zygom at ic bon es are th e m ost com m on ly im aged m idfacial st ruct u res in rad iograp hy. Depen ding on th e angle of in ciden ce

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of th e beam , th e zygom at ic bon es m ay appear as den se, V-sh aped, radiop aqu e lin es. Th e sh ap e an d exten t of th e rem ain ing p art s of th e zygom at ic bon es are som et im es clearly iden t ified on radiograph s.

10.4 Panoram ic Radiographic Anatom y

Fig. 10.20 The zygom atic bone, coronoid process, m axillary sinus, and nasal cavit y superimpose on each other in the lateral m axillary and m idfacial region. This m akes radiographic diagnosis di cult, if not impossible. Blue : zygomatic bone; yellow : hard and soft palate; green: m axillary sinus; brow n: orbit; red: coronoid process.

b

10

a

c Fig. 10.21a–c Visualization of the posterior and lateral walls of the maxillary sinuses by panoram ic radiography. First, the posterior wall of the m axillary sinus (yellow ) was visualized as a sum mation e ect. Then, a tangential projection along the lateral wall of the m axillary sinus showed a second vertical line (w hite). a Beam path. b Owing to rotation of the tube, the posterior wall is depicted as the rst vertical line (yellow ). c The second vertical line (w hite) appears, owing to summ ation of the lateral wall of the antrum .

Th e m an dible, m axilla, an d m idface are gen erally visualized in pan oram ic radiography. Because th e im age layer th ickn ess in th e m axillar y region is in th e cen t im eter range, th e m axillar y sin u s an d n asal cavit y can n ot be visu alized sep arately. On ly th e alveolar recess is seen

w ith out su perim posit ion . Th e in ferior t u rbin ates project from th e h ard palate/n asal oor to th e m a xillar y sin us. Th ey can be iden t i ed as relat ively h om ogen eous, elon gated soft-t issu e sh adow s th at exten d from th e an terior to p osterior w all of th e m axillar y sin u s.

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Anatom y and Topography of the Facial Skeleton For tech n ical reason s, st ru ct u res w h ose an atom ically correct posit ion is posterior are posit ion ed laterally on pan oram ic radiograph s. Pan oram ic im aging provides a ver y good over view, bu t m akes correct an atom ical iden t i cat ion an d diagn osis m ore di cu lt . Proceeding tow ard th e eye socket (orbit), th e th in radiopaque lin e of th e m axillar y sin u s often project s on to th e orbit . Ow ing to th e fun n el sh ape of th e eye socket , cran ial areas of th e m axillar y sin u s su p erim p ose on p art s of th e orbit .

a

10

Th e in fraorbit al can al often appears on radiograph s as a pair of parallel radiopaqu e lin es at th e level of th e in fraorbit al ridge. Th e in fraorbital foram en , if visible, appears in th e vicin it y of th e m axillar y sin us. Th e posterior–lateral par t of th e m axillar y sin us is a radiograph ically ch allenging an atom ical region . Th e h igh ligh ted lin es in Fig. 10.20 sh ow h ow m any di eren t st ruct ures superim pose on each oth er an d th eir un usual ap p earan ce resu lt ing from th e p an oram ic e ect .

b

Fig. 10.22a, b Visualization of the lateral walls of the m axillary sinuses by panoramic radiography. a Beam path. b The lateral wall of the m axillary sinus is bounded dorsally by the yellow line at the posterior boundary and ventrally by the w hite line.

Fig. 10.23 A round, convex soft-tissue m ass consistent with a m ucocele appears in the region of the oor of the right m axillary sinus. The area superior to the nasal oor cannot be assessed.

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10.4 Panoram ic Radiographic Anatom y To u n derst an d h ow pan oram ic im ages of th e posterior an d lateral w alls of th e m axillar y sin uses are form ed, it is alw ays n ecessar y to con sider th e beam path an d th e fact th at th e X-ray t u be m oves arou n d th e p at ien t in a circular fash ion ( Fig. 10.21). Th e area bet w een th e t w o lin es in Fig. 10.21 represen t s th e lateral w all of th e m axillar y sin u s, as sh ow n in Fig. 10.22. Ow ing to an atom ical an d tech n ical lim it at ion s, pan oram ic rad iograp hy is n ot a reliable procedu re for diagn ost ic evalu at ion of th e m axillar y sin u s. Th e on ly st ruct ures th at can be reliably assessed by pan oram ic radiography are th e alveolar recess an d th e posterior w all of th e m axillar y sin u s ( Fig. 10.23).

Note Anatom ical relationships superior to the hard palate/ nasal oor prohibit the use of panoramic radiography for diagnostic evaluation of the m axillary sinus. Panoramic radiography can only detect such abnormalities if the alveolar process is the site of origin of the lesion. The posterior wall of the m axillary sinus can also be assessed.

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Chapter 11 Radiographic Findings and Diagnosis

11.1 System atic Im age Analysis and Interpret ation 134

1 11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes 136

Radiographic Findings and Diagnosis

11 Radiographic Findings and Diagnosis 11.1 Systematic Image Analysis and Interpretation Many requ irem en t s m ust be m et for opt im al in terpret at ion of den t al radiograph s: ● Th e t arget st ru ct ures m ust be com pletely visible an d clearly iden t i able on th e radiograph . ● Stan dard radiograp h ic tech n iqu es an d p roject ion s m u st be u sed to en sure com parabilit y an d reproducibilit y. Th is is th e on ly w ay to produce radiograph s th at can be com p ared w ith previou s rad iograp h s. Th e com p arison of cu rren t radiograph s w ith previous rad iograp h s obtain ed from th e sam e pat ien t en ables th e clin ician to bet ter recogn ize d eviat ion s associated w ith path ological p rocesses. ● To ach ieve th ese object ives, it is crucial to follow a system at ic radiograph ic procedu re. This is th e on ly w ay to en su re th e com parabilit y of radiograph s t aken by a speci c in dividu al w ith th ose t aken by an oth er p erson .

Note Two basic rules to rem em ber: ● Always take only as m any X-rays as absolutely necessary, keeping all exposures as low as reasonably achievable (ALARA principle). ● Always ensure that the system provides the speci ed image qualit y (established in acceptance testing) with the lowest dose possible.

11.1.1 Film and Monitor View ing Conditions 11

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A su it able ligh t sou rce is requ ired for p rop er film view ing. A m on itor th at can correctly display ver y fin e an atom ical st ru ct u res is n eeded to view digit al X-ray im ages. Th e m on itors u sed in den t al radiograp hy m u st m eet ver y h igh qu alit y st an dards. A darken ed room is n eeded for both lm view ing an d m on itor view ing. Proper diagn ost ic evaluat ion is n ot p ossible in a brigh tly lit t reat m en t room . Ligh t boxes or m on itors in a w ell lit room are for guidan ce on ly, bu t n ot suitable for diagn ost ic assessm en t . Th e clin ician sh ou ld assess th e qu alit y of th e radiograp h ic im age before st ar t ing th e process of im age an alysis an d in terpretat ion . First , th e radiograph sh ould be evaluated for proper opt ical den sit y. Th is also ap p lies, albeit to a lesser exten t , to digit al X-rays. Alth ough digital rad iograp hy system s h ave w id e exposure lat it ude, it is n ot possible to com pen sate for gross u n der-exposure. Th e n ext step is to evalu ate th e visualized t arget region for com pleten ess, t aking care to en su re th at a m argin

ten ding aroun d th e en t ire useful radiat ion eld is seen on large-form at lm s. Fin ally, th e qualit y of th e radiograph ic set t ings an d posit ion ing of th e pat ien t , lm , an d X-ray t ubeh ead is ch ecked. After th is qualit y con t rol ch eck, a m eth odical exam in at ion of all region s of th e radiograph for th e presen ce of lesion s or ch anges can begin . A thorough an d system at ic approach is required, part icularly w h en view ing pan oram ic radiograph s an d con e beam com puted tom ography (CBCT) im ages. Th e view ing of pan oram ic radiograph s proceeds from on e quadran t to th e n ext , st art ing w ith th e teeth an d proceeding to th e alveolar process an d m a xillar y region , in cluding th e oor of th e m axillar y sin us. Th e n ext step is to in spect th e en t ire m an dible, in clu ding th e con dylar h ead s. Th e size an d clin ical relevan ce of lesion s or ch anges determ in e th e length an d scope of th e w rit ten rep or t . Th e w rit ten repor t m ust provide a clear an d com plete descript ion of th e radiograph ic n dings.

11.1.2 Steps from Findings to Diagnosis Th e path to a possible diagn osis is a m u lt i-step process. Th e first t ask is to en sure th at all fin dings (lesion s, ch anges) h ave been detected.

Identi cation of Pathological Changes Th e exam in er m u st detect any ch ange or deviat ion from th e n orm al or h ealthy con dit ion on first view ing a radio graph . All part s of th e radiograph th at deviate from th e n orm al m ust be iden t ified. A prelim in ar y assessm en t of radiograph ic qualit y is crucial to en sure th at n othing is overlooked. In addit ion to correct exposure, oth er factors th at play an im por tan t role—p ar t icu larly in p an oram ic an d in t raoral rad iography—in clude pat ien t posit ion ing (in pan oram ic tom ography) an d posit ion ing of th e im age receptor (in in t raoral radiography).

Caution Experience shows that even m inor errors in radiographic set tings can lead to m ajor di erences in radiographs, owing to the complex nature of the dental/facial anato my and the t ypes of radiographic techniques used. This is equally true for both intraoral and panoramic radiographs.

11.1 System atic Im age Analysis and Interpret ation

Radiographic Findings Suggestive of Lesions or Changes In prin ciple, path ological lesion s or ch anges can ap pear as an in crease or decrease in bon e substan ce. Th is applies to in flam m at ion s, cysts, an d t um ors, but n ot to fract u res, w h ich st ill can u sually be diagn osed reliably an d w ith out difficu lt y. Th e p resen ce of a break in con t in u it y of th e bon e is h igh ly in dicat ive of a fract ure.

Diagnosis Th e probabilit y of correlat ion bet w een radiograph ic fin dings an d diagn oses varies. A defin it ive diagn osis can n ot be m ade un less th e agreem en t bet w een th e radiograph ic fin ding an d th e diagn osis is u nequ ivocal, for exam ple, in th e case of a fract u re. In m ost oth er cases, on ly a ten t at ive diagn osis can be est ablish ed.

Writ ten Report of Radiographic Findings

Description of Radiographic Findings All lesion s or ch anges discovered m u st be carefu lly described . A p rop er descript ion is essen t ial for evalu at ing w h eth er a radiograph ic fin ding is in dicat ive of a path o logical or a n orm al varian t . Radiograp h ic feat ures th at sh ould be described in clu de th e follow ing: ● Locat ion /site: left m an dibular, tooth 18, periapical, radicu lar, coron al, lateral, m edial, posterior, etc. ● Sh ap e: rou n d, oval, ellipt ical, clou dy, m ult icyst ic, etc. ● Mar gin s: w ell-de n ed, poorly de n ed, irregular, etc. ● Size: size relat ive to th at of adjacen t st ru ct u res an d exact exten t (from … to …), in m et ric un its such as m illim eters, if possible ● In ter n al st r u ct u re: h om ogen eou s, in h om ogen eou s, sept ate, bow l-sh ap ed, etc. ● Den sit y: com p arat ive descript ion s, su ch as bon e-, softt issu e-, tooth -, m et al- or lling-den se, are often h elp fu l ● Relat ion sh ip to adjacen t st r u ct u res: adjacen t teeth , m axillar y sin u s, m an dibular n er ve canal, oor of th e n ose, etc. ● E ect on adjacen t st r u ct u res: in lt rat ion , displacem en t , th in n ing, etc.

Evaluation of Radiographic Findings On ce all p oten t ial lesion s or ch anges iden t ified h ave been docu m en ted in w rit ing, th e evaluat ion process can begin . If, on fu rth er evalu at ion , th e radiograph ic n ding ap pears clearly d evian t , th e probabilit y th at th e iden t i ed st ru ct u re is a path ological p rocess in creases. How ever, th e possibilit y th at th e n ding m ay also be a n orm al varian t m u st alw ays be t aken in to con siderat ion . It is often di cu lt to di eren t iate bet w een th e range of n orm al ap pearan ces an d path ological processes. Th is t akes pract ice an d requ ires com p arison of th e cu rren t n dings w ith previou s n d ings seen in th e course of on e’s radiological experien ce.

Th e w rit ten repor t of radiograph ic fin dings forces th e person w rit ing th e repor t to focus on th e essen t ials. It h as con siderable im pact an d relevan ce in clin ical an d foren sic pract ice.

Radiological Report Th e radiological report con t ain s a descript ion of th e exam in at ion procedure, th e clin ical quest ion s posed, an d th e respon ses to th ese quest ion s. Th e st ruct ure an d conten t of radiological report s sh ould com ply w ith local st an dards. A radiological report sh ould alw ays in clude th e pat ien t det ails an d in form at ion regarding th e radiograph ic tech n iqu e.

Challenging Radiographic Findings in Routine Dent al Practice In den t al pract ice, som e radiograph ic fin dings are ver y com m on an d recurren t , w h ile oth ers are un com m on an d con t in ually ch allenging. In den tal radiography, at ten t ion is focused on th e teeth an d adjacen t st ruct u res. W h ile th e diagn osis of path ological ch anges in th e teeth th em selves sh ou ld be rou t in e, diagn ost ic un cert ain t y st art s w h en th e focus sh ifts to th e periapical area an d adjacen t bon e st ruct ures of th e m an dible. Par ts of th e oor of th e m axillar y sin us are also difcu lt to assess, par t icularly if an area superior to th e n asal oor is to be evaluated. Th e m ost com m on clin ical qu est ion s posed in clude caries diagn osis, apical an d m argin al period on t al d iseases, an d th e range of di eren t den se an d usu ally ben ign sh adow s, m ain ly in th e m an dibular region . Cyst ic lesion s; displaced, su p ern u m erar y, an d im p acted teeth ; an d osseous lesion s in th e tem porom an dibular join t are less com m on but gen erally do n ot cau se diagn ost ic di cult ies. Conversely, radiolucen cies of un clear et iology cause diagn ost ic problem s. Th ey are frequ en tly in terpreted as osteolysis because th ey h ave poorly de n ed m argins an d cou ld be in dicat ive of a m align an t p rocess. W h en view ing radiograph s, it is crucial to n ot overlook any path ological ch ange, but to en su re th at all h ave been detected an d iden t i ed.

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135

Radiographic Findings and Diagnosis Any irregu larit y could be du e to an error in radiograp h ic tech n iqu e. In p an oram ic radiography, in part icu lar, m any sh adow s an d radiolucen cies occur as a result of tech n iqu e-related factors an d posit ion ing errors alon e.

Note There are m any variations of the normal anatomy of the facial skeleton. Side-to-side comparison helps to exclude pathological processes.

If su spiciou s fin dings can n ot be at t ributed to tech n iquerelated factors an d n orm al varian t s, th en a d etailed descript ion of th e ch ange is n eeded for d iagn ost ic evaluat ion . Th e oth er steps are less di cult but require a cert ain level of experien ce. A th orough an d system at ic approach to th e descript ion of n dings is th e prerequisite for correct radiograp h ic diagn osis. In case of dou bt , th e radiograph s sh ou ld be su bm it ted to an experien ced den tal radiologist for in terp ret at ion . This can h elp to p reven t m isin terp ret at ion . Th e p at ien t shou ld n ot be referred to a specialist before th is is don e, to rule ou t th e possibilit y th at th ere is n o path ological n d ing.

11.2 Assessment and Diagnosis of the Most Common Pathological Changes 11.2.1 Carious Lesions

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Caries is th e m ost com m on disease of th e den tal h ard t issues. Failu re to detect an d t reat den t al caries early can resu lt in a loss of vit alit y of th e affected tooth an d lead to in flam m at ion (u su ally periapical in flam m at ion ). Bitew ing radiograp hy, in t rod u ced by Raper (1925), is th e radiograp h ic tech n iqu e of ch oice for th e d iagn osis of ap proxim al caries. Alth ough it h as som e sh or tcom ings, bitew ing radiograp hy is st ill su p erior to all oth er m eth ods available for th e diagn osis of in it ial caries (p rim ar y caries). Th e exten t an d locat ion of caries an d th e selected tech n iqu e are cru cial factors. Approxim al caries can be diagn osed at an earlier st age th an ssure caries an d caries of vest ibu lar an d oral tooth surfaces, ow ing to th e direct ion of th e beam in in t raoral radiography. Early detect ion of in terp roxim al caries is possible becau se of th e beam d irect ion an d t angen t ial e ect . Conversely, su m m at ion e ect s associated w ith the superim posit ion of in tact tooth su bst an ce on tooth surfaces im pede th e early diagn osis of ssu re caries.

Practice Holders with a position-indicating device and the paralleling technique should always be used.

The radiograph ic con dit ion s for bitew ing radiography are m u ch m ore favorable th an th ose for periapical radiography. Th e im age receptor can u su ally be p laced p arallel to th e crow n of th e teeth being radiograp h ed . As in all den t al radiograph ic tech n iques, errors in th e execut ion of bitew ing radiography are a m ajor w eak poin t . Ideally, on e radiograph per side sh ou ld be su cien t for u n equivocal diagn osis of th e various st ages of caries. How ever, a m ore reliable diagn osis is obt ain ed by taking t w o radiograph s per side: on e of th e prem olars and on e of th e m olars. Th is correspon ds to th e procedu re for evaluat ion of periodon t al st at us. With th e cu rren t st ate of tech n ology, conven t ion al an d digital bitew ing radiography system s provide im ages of equal qualit y. How ever, th e u se of a sen sor or storage phosph or plate results in relat ively large diagn ost ic gain , ow ing to im age-processing capabilit ies. Th erefore, preferen ce sh ould be given to digital bitew ing radiograph s. Moreover, th e use of sen sors cut s th e pat ien t’s dose in h alf com pared w ith th e exposure rates associated w ith th e u se of im aging p lates an d E- an d F-speed lm . Th ere are p red ilect ion sit es for caries occu rren ce. Ch ildren an d adolescen ts often h ave a bilateral an d sym m etrical pat tern of caries occu rren ce. Th e m axillar y arch is m ore com m on ly a ected th an th e m an dibular arch . Caries of th e m axillar y can in es is less com m on th an caries of th e in cisors, w h ile th e reverse u su ally app lies to th e m an dibular can in es an d in cisors. Th e m axillar y an d m an dibu lar six-year m olars are alw ays m ore com m on ly a ected by caries th an th e oth er m olars an d prem olars. Oth er predilect ion sites in clude in terproxim al n ich es, w h ich can be m ade in accessible an d h ard to clean by an om alies of tooth posit ion , an d th e cem en to-en am el jun ct ion of th e secon d m olars in pat ien ts w ith m esially t ilted, h alf-im pacted w isdom teeth . Th e accum u lat ion of plaqu e below the con tact poin ts can quickly lead to approxim al caries. Periodon t al pockets can resu lt in cem en t um caries at th e cem en to-en am el ju n ct ion . If cavit ies are n ot carefu lly prep ared, residu al caries can develop below llings. If th ere is poor m argin al seal, secon dar y caries can occu r in th e in terden tal sp aces, as a resu lt of poor d en t al hygien e. After reach ing a cert ain size, caries appears on radiograp h s as a clearly iden t i able, rou n dish , w edge-sh ap ed lesion w ith variably w ell-de n ed m argin s. Large cariou s lesion s app ear as irregu larly sh ap ed defect s.

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes Radiograp h ically, p r im ar y car ies is divided in to four t ypes, based on t issu e involvem en t . Radiograp h ic classicat ion t yp es C1 to C4 correspon d to clin ical t ypes D1 to D4 ( Fig. 11.1): ● D1: su p er cial caries (lim ited to th e en am el) ● D2: m oderate caries ● D3: deep caries ● D4: deep com plicated caries.

Examples of Carious Lesions Superim posit ion -free visualizat ion of the approxim al su rfaces is required for opt im al caries diagn osis ( Fig. 11.2). C1: Su per cial car ies: Super cial caries (en am el caries) appears as a w edge-shaped defect that involves the enam el layer but has not yet penetrated the dentin ( Fig. 11.3). C2: Mod erate car ies: Th e cariou s lesion h as spread to th e in n er en am el region an d h as p en et rated u p to th e den t in an d spread t w o-dim en sion ally ( Fig. 11.4).

D3

D2

D1

D4

Fig. 11.1 Stages of caries progression (approximal caries). D1: lesion in the outer half of the enamel; D2: lesion in the inner half of the enam el; D3: lesion in the outer half of the dentin; D4: lesion in the inner half of the dentin. (From: Weber T. Mem orix Zahnm edizin. 3rd ed. Stut tgart: Thieme; 2010.)

C3: Deep car ies: Deep st ruct ural defect th at involves th e en t ire den t in th ickn ess up to th e den t in layers close to th e pu lp ( Fig. 11.5). C4: Deep com p licated car ies: Caries h as led to open ing of th e pulp ( Fig. 11.6). Radiograph ically, caries lesion s on occlu sal su r faces are m ore difficult to diagn ose th an th ose on approxim al surfaces. Un equ ivocal radiograph ic diagn osis of occlu sal caries is n ot p ossible u n t il caries h as sp read to th e in n er h alf of th e d en t in ( Fig. 11.7). Radiograph ic diagn osis of st age C3 is p ossible on ly if th ere is exten sive spread. Radiograp h ic diagn osis of recu r ren t or secon d ar y car ies is n ot alw ays possible.

11 a

b

c

Fig. 11.2a–c Regardless of whether acute or chronic, initial caries generally is not detectable radiographically or, if so, only in conjunction with the ndings of clinical exam ination.

Fig. 11.3a–c a Distal part b Distal part c Distal part

Super cial caries: note the defects in the enam el. of tooth 35. of tooth 35. of tooth 13.

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Radiographic Findings and Diagnosis

a

c

b

Fig. 11.4a–c Moderate caries. a On the distal part of tooth 46, caries has progressed to the dentin. b There is greater dentin involvem ent on the m esial aspect of tooth 15. c A carious radiolucency is readily identi able in the deeper layers of dentin on the distal part of tooth 16.

a

b

c

Fig. 11.5a–c Deep caries: in all three cases, caries has spread to the dentin layers very close to the pulp.

Fig. 11.6a–c Deep complicated caries: in all three cases, there is extensive caries involvem ent in all segment s of the crown.

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D3 D4

In t raoral radiograph s are th e product of th e t w o-dim en sion al superim posit ion or sum m at ion of sh adow s from th ree-dim en sion al an atom ical st ru ct ures. Addit ion and subt ract ion e ect s can lead to ar t i cially in creased radiopacit y an d radiolucen cy. Depen ding on th e in ten sit y of th e su p erim p osed st ru ct ures, defect s m ay appear sm aller an d in dist in ct on radiograph s, ow ing to th e addit ion e ect , or th ey m ay be brigh ter an d ext inguish ed, ow ing to th e su bt ract ion e ect .

Caution

Fig. 11.7 Occlusal caries stages: radiographic diagnosis of D1 to D2 occlusal caries in the enamel is not possible. D3: carious lesion in the outer half of the dentin; D4: carious lesion in the inner half of the dentin. (From: Weber T. Memorix Zahnm edizin. 3rd ed. Stut tgart: Thieme; 2010.)

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In the case of caries, the addition e ect m eans that the extent of the initial caries lesion is underestim ated on the radiograph, owing to the superimposition of intact enam el and dentin on the carious area.

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes Cariou s lesion s th at h ave in filt rated th e den t in gen erally h ave p oorly defin ed m argin s; in th e case of deep caries, th ey are often separated by a den se react ive zon e of endangered an d ret racted pulp. Ow ing to th e tangen t ial e ect of th e X-ray beam , radiograp h ic detect ion of d evelopm en tal defect s, such as p it s an d irregu larit ies on th e en am el surface of th e crow n , is n ot p ossible u n less th ey are located on th e ap proxim al surfaces of th e teeth . If th ey appear as a radiolucen t area w ith w ell-de n ed m argin s, th ey can som et im es be di eren t iated from in it ial caries. Such radiolucen cies m ust be m on itored at least on ce a year becau se it is im p ossible to radiograph ically dist inguish in it ial caries from develop m en t al defects in th e en am el su rface, or from dem in eralizat ion d isorders begin n ing at th is st age.

Recu r ren t car ies ben eath radiopaque crow n s an d llings can be im possible to visualize properly. Di cult ies also arise in digit al radiography if th ese lesion s are too st rongly processed by lters. Th e m et allic m argin s of den tal crow n s an d llings often appear as th in radiolucen t ban ds, cau sing art ifact s th at m ake radiograph ic diagn osis of caries di cult to im possible in th ese region s. Early ch ild h ood car ies is a special form of caries th at a ect s th e prim ar y den t it ion . Dest ruct ion of th e rem ain ing teeth can occur in th e advan ced st age associated w ith ap ical in am m at ion . To keep rad iat ion exposu re as low as reason ably ach ievable, sen sor system s sh ould alw ays be u sed in pediat ric pat ien t s. Sm all sen sors produce radiograp h s of good diagn ost ic qu alit y in ch ild ren ( Fig. 11.8 an d Fig. 11.9).

11.2.2 Horizontal Bone Loss w ith Vertical Bone Defects

Fig. 11.8 Note the approximal caries on tooth 74 and the discrete radiolucency on the mesial surface of tooth 75.

Th e h eigh t of th e alveolar crest decreases over t im e, an d th e rate of decrease varies from on e in dividu al to an oth er. Gen eralized h orizon tal bon e loss is often accom pan ied by vert ical bon e d efect s an d, in th e advan ced st ages, by exposed bifurcat ion s. As a baselin e exam in at ion , pan oram ic radiography is su it able for visualizat ion of th e alveolar crest . Ow ing to sign i can t im provem en ts in im age qu alit y in recen t years, an d th e con stan t angles of in ciden ce of th e X-ray beam ,

11 a

b

c

Fig. 11.9a–c Large carious lesions in the prim ary dentition.

a

b

c

d

Fig. 11.10a–d Vertical bitewings provide a view of the crowns and alveolar bone.

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Radiographic Findings and Diagnosis

Fig. 11.11 Generalized horizontal bone loss and sm all vertical bone defects in the rem aining m axillary and m andibular dentition.

11

Fig. 11.12 Advanced generalized horizontal bone loss and marked vertical bone defects. Periapical widening of the periodontal ligam ent space of tooth 26 and a large carious lesion on the m esial surface of tooth 46.

pan oram ic radiography allow s h igh ly correct visu alizat ion of th e m an dible an d m axilla. Pan oram ic radiograph s sh ou ld be su pp lem en ted w ith in t raoral radiograp h s on ly in isolated cases. How ever, reliable assessm en t of all teeth in th e crow n region is n ot possible in m ost cases, ow ing to th e su p erim posit ion of st ruct ures. Bitew ing radiograp h s are m ore su it able for th is th an X-rays of th e w h ole tooth . Ver t ical bitew ing radiograph s p rovide an oth er opt ion to visualize n ot on ly th e crow n region bu t also th e alveolar ridge, w ith h igh resolu t ion an d w ith ou t d istort ion ( Fig. 11.10).

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Pan oram ic radiograp h s u su ally en able a com preh ensive an d good assessm en t of bon e con dit ion s in th e m axilla an d m an dible ( Fig. 11.11 an d Fig. 11.12). In t raoral rad iograp h s can provid e m ore precise im ages, w h ich are n eeded for clari cat ion of par t icularly un usual n dings ( Fig. 11.13). Tom ograp h ic im aging tech n iques provide a broader over view. In recen t years, CBCT, also kn ow n as digit al volum e tom ography, h as proved ver y u sefu l for th is. Tran sverse an d axial view s are n eeded for a com plete an alysis of bony periodon t al defect s.

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

Fig. 11.13a–c These intraoral radiographs clearly show the extent of vertical bone defects. a Vertical bone defect on tooth 15. b Vertical bone defect on tooth 15. c Di cult situation on fractured tooth 16.

11.2.3 Apical Periodontitis Pu lp it is, p u lp n ecrosis, failed root-can al t reat m en t , an d t rau m at ic den tal inju ries can lead to apical periodon t it is an d advan ced form s of m argin al periodon t it is. Acu te an d ch ron ic form s of apical periodon t it is are gen erally dist ingu ish ed. Th e severit y of th e disease is determ in ed by th e virulen ce of th e causat ive path ogen an d th e st at u s of th e h ost’s im m u n e system .

Acute and Chronic Apical Periodontitis Even if acu te clin ical sym ptom s are p resen t , radiograph s can n ot dem on st rate in flam m ator y respon ses if n o ch anges h ave occurred th at affect th e in tegrit y of th e p eriapical st ru ct u re. Th ere is a laten cy p eriod before acu te in t raosseou s in flam m at ion can be radiograph ically detected. Precise visu alizat ion of th e apical region is n eeded to detect any ch anges in th e lam in a du ra as early as p ossible. Radiograph ically, acu te in flam m at ion th at in filt rates beyon d th e ap ical foram en is ch aracterized by w iden ing of th e p eriodon t al ligam en t space an d diffu se periapical radiolu cen cy. Any loss of con t in u it y of th e lam in a du ra arou n d th e ap ex of th e affected tooth in dicates th e presen ce of a periapical in flam m ator y process. Ch ron ic apical period on t it is is ch aracterized by loss of th e periodon tal ligam en t sp ace, w h ich en ds as a p eriap ical radiolu cen cy. A gran u lom a is a ch ron ic m ass of gran u lat ion t issu e th at form s in resp on se to in flam m at ion . It is ch aracterized by fu sion of th e lam in a dura w ith th e den se m argin s of th e gran u lom a, cau sing m argin al discon t in u it y an d rad iolu cen cy at th e ap ex of th e involved tooth .

Fig. 11.14 Widening of the periodontal ligam ent space suggestive of acute apical periodontitis.

Radiographic Features of Apical Periodontitis ●





Acu te ap ical p er iod on t it is u su ally h as a radiograp h ically n orm al ap p earan ce bu t som et im es p rodu ces discrete apical w iden ing of th e periodon t al ligam en t space ( Fig. 11.14). Ch ron ic ap ical p er iod on t it is appears as w iden ing of th e periodon tal ligam en t sp ace an d variable, di u se, periapical radiolucen cies ( Fig. 11.15). If th e in am m at ion persist s, th e apical t issu e t ran sform s in to gran ulat ion t issue, th e radiolucen cy becom es su rrou n ded by a den se sclerot ic m argin , an d ch ron ic gran u lom atou s ap ical p er iod on t it is develop s ( Fig. 11.16).

11

141

Radiographic Findings and Diagnosis

Fig. 11.15a–f Di use periapical radiolucencies. a Tooth 31. b Tooth 22. c Tooth 42. d Tooth 48. e Tooth 47. f Tooth 37.

11

Fig. 11.16a–c Endodontically treated tooth (a), carious tooth (b), and residual root (c) with periapical radiolucencies dem arcated by a thin radiopaque m argin; the ndings are suggestive of a chronic process. a Endodontically treated tooth 45. b Carious tooth 47. c Residual root of tooth 12.

142

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

11.2.4 Cystic Lesions Cysts are defin ed as path ological cavit ies that are lin ed by epith eliu m an d filled w ith flu id, sem i-fluid or gaseous con ten t s. Cyst s are st ill classified according to th e World Health Organ izat ion (W HO) classificat ion of 1992; t w o t yp es of ep ith elial cyst s are dist inguish ed: ● Odon togen ic epith elial cyst s of developm en t al origin ● Non odon togen ic ep ith elial cyst s. Keratocyst s are an oth er t yp e of odon togen ic cysts. According to th e W HO classificat ion of 2005, th ey are n o longer con sid ered to be developm en tal cyst s bu t are n ow classified as od on togen ic t u m ors. Radiologically, th e m ost im p or tan t odon togen ic cyst of develop m en t al origin is th e follicu lar cyst (den t igerous cyst). By d e n it ion , a follicu lar cyst is a cyst th at surrou n ds th e crow n of an u n eru pted tooth an d at t ach es at the cem en to-en am el jun ct ion . It develops due to th e accu m u lat ion of u id bet w een th e en am el ep ith eliu m an d th e tooth crow n , or in th e layers of th e en am el epith elium it self, an d slow ly in creases in size, ow ing to osm ot ic in tern al p ressu re. Follicular cyst s usually occur in associat ion w ith im p acted m an dibular th ird m olars an d m axillar y can in es, but in frequ en tly involve th e m axillar y th ird m olars an d th e m an dibu lar prem olars. After th e radicu lar cyst , th e follicu lar cyst is th e secon d m ost com m on cyst of th e jaw. Radiograp h ically, it appears as a roun d to oval radiolucen cy su rrou n ded by a th in radiop aqu e lin e. Th e clin ician sh ou ld alw ays ch eck to determ in e w h eth er th is radiopaqu e lin e en ds at th e cem en to-en am el ju n ct ion . If th is is n ot th e case, th en th ere is a st rong su spicion of a keratocyst ic od on togen ic t u m or.

Like all cyst s, follicular cyst s displace th e surroun ding st ruct ures. In th e m an dibular region , th e teeth , as w ell as th e m an dibular n er ve can al on th e a ected side, are displaced an d n o longer sh ow sym m et r y w ith th e opposite side ( Fig. 11.17 an d Fig. 11.18). Th e n asop alat in e d u ct cyst , alth ough n ot ver y com m on , is a n on odon togen ic epith elial cyst th at m ust be con sidered w h en th e in cisive can al is path ologically enlarged. On radiograph s, it appears as a cyst ic m ass th at is posit ion ed exactly m idlin e an d com p letely en closed w ith in th e in cisive can al.

Practice Panoram ic radiographs do not provide adequate visualization of nasopalatine duct cysts, especially not to distinguish whether a suspicious ndings is actually a cyst or not. CBCT is the im aging technique of choice in cases where there is clinical and radiographic suspicion of a nasopalatine duct cyst. Tomographic images in multiple planes are needed for proper visualization of this di cult part of the m axillary anterior region ( Fig. 11.19).

Th e secon d group of cyst s con sist s of th ose th at develop from th e ep it h elial cell rest s of Malassez because of in flam m at ion . Because th eir grow th is t riggered by pulp n ecrosis, a n onvital tooth is th e prerequ isite for th e developm en t of radicular cyst s. Th e rad icu lar cyst (also term ed periapical cyst) is th e m ost com m on cyst ic lesion of th e jaw, com p rising 90 % of all jaw cyst s. It involves th e m axilla m ore frequ en tly th an the m an dible. Radiograph ically, th is odon togen ic cyst , like all cyst s, appears as a roun d or ovoid radiolucen t area

11

Fig. 11.17 Note the follicular cyst arising from an impacted and dislocated wisdom tooth 48; the cyst m argin is at tached to the cem ento-enamel junction. Tooth 37 shows no signs of root resorption.

143

Radiographic Findings and Diagnosis

Fig. 11.18 Follicular cyst arising from impacted and dislocated wisdom tooth 38; the cyst m argin is also at tached to the cem entoenamel junction. Tooth 37 also shows no signs of root resorption.

11

Fig. 11.19a, b The ndings are suggestive of a nasopalatine duct cyst. a An indistinct circular radiopaque line in the m axillary anterior region is the only nding on the panoram ic radiograph. b This additional occlusal radiograph shows a very large cystic process suggestive of a nasopalatine duct cyst in the vicinit y of the incisive canal.

surrou n ded by a th in rad iopaqu e m argin . If in fected, th e radicu lar cyst m ay h ave an in terru pted radiop aqu e m argin an d resem ble a t um or-like m ass, depen d ing on th e severit y of in fect ion . Radicu lar cysts are un ilocu lar cyst ic lesion s th at can becom e ver y large, dep en ding on th e durat ion of th e ph ase of cyst en largem en t ( Fig. 11.20 an d Fig. 11.21). If such expan sion h as occurred, th ey lose th eir sph erical sh ap e an d can t ake on a variet y of irregu lar sh apes.

144

Practice Dental panoram ic radiography is used for prim ary diagnosis, but m ulti-dim ensional tom ographic im aging is recom m ended once the cysts reach a certain size.

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

Fig. 11.20 Very large radicular cyst in the left m andible, arising from tooth 35.

11

Fig. 11.21 A round cystic radiolucency arising from the residual root of tooth 17 can be seen in the right mandible and m axillary sinus. It is a radicular cyst whose origin is the residual root of tooth 17, which projects into the cyst. The radiopaque line that surrounds the radiolucency is also suggestive of a cyst.

11.2.5 Malignant Lesions Cancer of the Floor of the Mouth Carcin om a of th e oral m u cosa is th e m ost com m on t yp e of can cer of th e oral cavit y. Squ am ou s cell carcin om a of th e floor of th e m outh involves th e lingu al cor t ical bon e of th e m an dible; it can in filt rate an d dest roy th e alveolar p rocess an d even th e en t ire m an dible in th e advan ced

st ages. A p an oram ic den t al X-ray sh ould be perform ed to carefully evaluate th e alveolar ridge for sign s of osteolysis, especially in elderly an d eden t ulous pat ien t s. If th ere is gen eralized h orizon t al bon e loss, cases w h ere th e m argin s of th e alveolar ridge are n o longer sm ooth but h ave breaks in con t in uit y in dicat ive of in filt rat ion by a carcin om a of t h e floor of t h e m ou t h are som et im es overlooked ( Fig. 11.22 an d Fig. 11.23).

145

Radiographic Findings and Diagnosis

Fig. 11.22 On side-to-side comparison, a discrete, tub-like osseous depression in the alveolar ridge can be detected on the right side. There is a risk of misinterpretation of this radiographic nding as norm al in amm atory bone loss. On closer inspection one can see that the m argin of the alveolar ridge is irregular, which is indicative of a destructive process.

11

Fig. 11.23 In this case, m arked osteolysis was visible not only in the right m andible, but also in the right m axilla. In the maxillary arch, destruction of the alveolar ridge extends into the right maxillary sinus.

Osteolysis of th e lingu al cort ical bon e can n ot be detected by pan oram ic radiography. Tom ograph ic im ages in m u lt iple plan es are n eeded for visu alizat ion of th is region . How ever, CBCT is n ot sat isfactor y for detect ion of

146

soft-t issue involvem en t or, in part icular, lym ph n ode in volvem en t from carcin om a. Com p u ted tom ography an d m agn et ic reson an ce im aging are th e im aging tech n iqu es of ch oice in th ese cases.

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

Fig. 11.24 Am eloblastom a of the right mandible with resorption of the roots of teeth 46 and 47.

Odontogenic Tumors Odon togen ic t u m ors or t um or-like lesion s th at arise from th e tooth -form ing st ruct ures are rare. Th eir radiograp h ic appearan ce can be m ore or less t yp ical. Th erefore, w h en ever a t u m or-like lesion is detected on a radiograph , regardless of w h eth er it is presum ed to be ben ign or m align an t , a h istological exam in at ion is alw ays n ecessar y to con firm th e diagn osis.

Note Radiographic im ages only provide inform ation and clues of variable accuracy. Ultim ately, a reliable diagnosis cannot be established based on radiographic im ages alone. The choice of radiographic images can increase the reliabilit y of the diagnosis, but radiographs alone can never provide a completely reliable diagnosis of tum ors and tum or-like lesions.

W HO revised an d re n ed it s classi cat ion of odon togen ic t u m ors in recen t years. Radiograph ically, th ey are st ill divid ed in to t w o m ain groups: ● Path ological ch anges th at appear as cyst ic lesion s ● Path ological ch anges th at arise from m esen chym al t issu es an d bon e.

Solid and Multicystic Am eloblastom as Th e conven t ion al am eloblastom a can occu r in all par ts of th e m axilla an d m an dible. Th e am eloblastom a is th e secon d m ost com m on t ype of odon togen ic t u m or after th e keratocyst ic odon togen ic t u m or, w h ich w as p reviously referred to as th e odon togen ic keratocyst .

Note Whenever a cystic lesion does not clearly originate from the apex of a tooth, follicular cyst, keratocyst (keratocystic odontogenic tum or), and am eloblastom a m ust be considered in the di erential diagnosis.

The m ost com m on site of occurren ce (in 80 % of cases) is the m andibular m olar region , follow ed by th e m an dibu lar prem olar region an d, less com m on ly, th e m an dibu lar an terior region an d m axillar y m olar region . Th e feat u res of am eloblastom a var y—th ey m ay ap pear as u n ilocu lar or m ult ilocular cyst ic lesion s. Am eloblastom a is often associated w ith an im pacted tooth . Th erefore, if a follicular cyst is detected, th e exact site of origin m u st be determ in ed. Am eloblastom as, like cysts, ten d to displace surroun ding struct ures, result ing in thinning an d expansion of the cort ical bone. Displacem en t of th e m andibular ner ve canal is a sign of am eloblastom a expan sion . Resorpt ion of roots of th e involved teeth is an im portan t an d reliable sign of am eloblastom a ( Fig. 11.24, Fig. 11.25, Fig. 11.26). Am eloblast ic brom a, broden t in om a, an d am eloblast ic bro-odon tom a are rare var ian t s of am eloblastom a that are classi ed as ben ign m ixed odon togen ic t u m ors. These m ixed t um ors h ave both epith elial an d ectom esen chym al com pon en ts an d often involve th e den t al h ard t issues. Un like th e pure am eloblastom a, m ixed odon togen ic t um ors are usually m ult ilocular cyst ic lesion s th at are n ot uniform ly st ruct u red.

11

147

Radiographic Findings and Diagnosis

Fig. 11.25 Multicystic ameloblastoma of the left mandible with resorption of the roots of teeth 35, 36, and 38; the third molar (tooth 38) is displaced and tooth 37 is missing.

Keratocystic Odontogenic Tum or Th e keratocyst ic odon togen ic t um or is a ben ign t um or of odon togen ic origin , w h ich , like th e am eloblastom a, m ay ap p ear as a u n ilocu lar or m ult ilocular radiolu cen t lesion . As th e n am e im plies, th e special feat ures of th e keratocyst ic odon togen ic t um or are: ● Parakeratosis of th e ep ith eliu m ● Aggressive an d in lt rat ing beh avior.

11

Fig. 11.26 Multicystic ameloblastoma of the right m andible.

Am eloblast ic brom a an d bro-odon tom a are ver y rare t um ors com p osed of both odon togen ic epith elium and odon togen ic ectom esen chym e, w ith or w ith out involvem en t of den t al h ard t issue ( Fig. 11.27 an d Fig. 11.28).

148

These t u m ors h ave a h igh recurren ce rate an d a ten den cy to form daugh ter cysts. Th ey can be iden t ified based on the bu dding of daugh ter cyst s, w h ich are in it ially roun dish but later converge to form m asses, giving keratocyst ic odon togen ic t u m ors th eir ch aracterist ic scalloped m argins an d dist in ct appearan ce. Radiograph s often u n derest im ate th e exten t of keratocyst ic odon togen ic t um ors becau se of th e d en sit y an d su p erim posit ion of in t act adjacen t bony st ruct u res on th e daugh ter cysts. Th ese sum m at ion effects m ake early an d com plete detect ion of keratocyst ic odon togenic t um ors by in t raoral an d pan oram ic radiography ext rem ely difficult ( Fig. 11.29, Fig. 11.30, Fig. 11.31).

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

Fig. 11.27 Histologically, this am eloblastic bro-odontom a was classi ed as benign, but it s radiographic appearance is suggestive of a m alignant tumor.

11 Fig. 11.28 Am eloblastic broma.

149

Radiographic Findings and Diagnosis

Fig. 11.29 Typical keratocystic odontogenic tum or with an adjacent tooth. The tumor displaces the tooth but is not at tached to it. This t ype of radiographic constellation can easily be m isinterpreted as a follicular cyst.

11

Fig. 11.30 This unilocular, oval cystic lesion in the right angle of the jaw is a variant of a keratocystic odontogenic tum or.

150

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

Fig. 11.31 Unilocular keratocystic odontogenic tum or in the right angle of the mandible. The radiolucent lesion is not clearly at tached to teeth 47 and 48.

11 Fig. 11.32 This complex odontoma appears as a hom ogeneous, sharply demarcated pericoronal radiolucency on tooth 37, which is deeply impacted. The odontom a is preventing the tooth from erupting.

Odontom a Th e odon tom a is a develop m en tal an om aly th at resem bles a t u m or bu t is a h am ar tom a of odon togen ic origin . It con sist s of several large an d sm all tooth -like st ruct u res or a conglom erate of differen t den tal t issues. Tw o t ypes of odon tom a are d ist inguish ed: com pou n d and com plex. ● Th e com p lex od on tom a is a t u m or-like m alform at ion (h am artom a) ch aracterized by th e form at ion of an am orp h ou s m ass of en am el, den t in , an d cem en t um ( Fig. 11.32). It is frequen tly located on an im pacted m olar, w h ich itself m ay be h ardly visible, ow ing to th e su p erim p osit ion of sh adow s from th e lesion .



Th e com p ou n d od on tom a is a developm en t al an om aly (h am ar tom a) th at resem bles a t u m or an d con sist s of several fu lly develop ed sm all teeth or tooth -like den t icles. It s radiograph ic appearan ce varies, depen ding on th e stage of developm en t . It ap p ears as a w elldem arcated area of osteolysis in th e early st ages. In later st ages, slow ly developing tooth elem en t s m ay be surroun ded by a w ide radiolucen t m argin in dicat ive of a grow th zon e ( Fig. 11.33). In th e n al st age, th e den t icles are su rrou n ded by a th in radiolu cen t m argin .

Com poun d odon tom as are u su ally diagn osed before th e age of 20 years. Th ey m ost com m on ly occur in th e an terior teeth , follow ed by th e prem olar region .

151

Radiographic Findings and Diagnosis

11

152

Fig. 11.33a–d Compound odontoma: the CBCT im ages (b, c, and d) clearly visualize the tooth buds. a A round, very dense area surrounded by a thin radiolucent m argin can be seen in the mandibular anterior region on this panoramic radiograph. b Lateral view CBCT im age. c Lateral view CBCT im age. d Axial CBCT im age.

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

Fig. 11.34 Odontogenic myxoma (myxo brom a): The radiograph reveals a large radiolucency that extends from tooth 35 to tooth 46 and contains trabeculae. The teeth appear to be slightly tilted. Resorption of the root s of teeth 34 and 32 cannot be excluded.

Odontogenic Myxo brom a (Odontogenic Myxom a) Th e odon togen ic m yxofibrom a (odon togen ic m yxom a) is an in t raosseou s n eoplasm . Odon togen ic m yxofibrom as are ben ign but locally invasive t u m ors of th e jaw. Th ey h ave a relat ively h igh recu rren ce rate of u p to 25 %. On th e pan oram ic radiograph , th ey appear as a m ult ilocular radiolucen cy associated w ith dest ruct ion of th e m an dible. Th ey often con t ain delicate t rabecu lae, giving th e lesion an irregu lar m u lt ilocular appearan ce ( Fig. 11.34).

Cem entom a (Cem entoblastom a) Ben ign cem en tom a (syn onym : cem en toblastom a) is ch aracterized by th e product ion of a bulbou s m ass of cem en t u m -like t issue th at is at t ach ed to th e roots of th e tooth . It s radiograph ic appearan ce is variable. Cem en tom as u su ally arise in associat ion w ith th e apices of th e m an dibu lar first m olars an d m an dibular secon d prem o lars, an d th ey u su ally occur during th e secon d an d th ird decades of life. Th e cem en tom a grow s slow ly in layers arou n d th e root of th e involved tooth . Becau se it is at tach ed to th e tooth root , ext ract ion m ay be difficu lt . With p rogressive develop m en t an d cem en t u m dep osit ion , th e cem en tom a appears as a radiopaque m ass w ith eith er a m ot tled, occular, m osaic-like appearan ce or a u n iform ly radiop aque appearan ce. It is often , but n ot alw ays, su rrou n ded by a th in radiolucen t border. Th e presen ce of a radiolu cen t border m ay be a sign of a grow th zon e or sequ est rat ion ( Fig. 11.35).

Cem ento-osseous Dysplasia Th e t w o m ain t ypes of cem en to-osseous dysplasia are: ● Periap ical cem en t al dysplasia ● Florid cem en to-osseous dysplasia. Periapical cem en t al dysp lasia m ost com m on ly involves the m an d ibu lar an terior teeth . Radiograp h ically, th e in it ial st age of developm en t is ch aracterized by osteolysis an d fibrosis. Th e secon d st age is ch aracterized by th e st ar t of th e dep osit ion of cem en t um , as reflected by th e app earan ce of den se cem en t um -like radiopacit ies. Pu lp vitalit y test ing in dicates th at n eith er ap ical p eriodon t it is n or radicular cysts are th e cause of th e radiolu cen cies. Radiograph ically, orid cem en to-osseou s dysplasia ap pears as a large radiolu cen cy su rrou n ded by a radiop aqu e m argin ch aracterized by th e deposit ion of cem en t icles in den se con n ect ive t issu e st rom a ( Fig. 11.36).

11

153

Radiographic Findings and Diagnosis

Fig. 11.35 Cementom a (cem entoblastom a): The radiograph reveals a radiopaque m ass that is closely connected to the apex of tooth 43 and surrounded by a radiolucent m argin.

11

Fig. 11.36 Cemento-osseous dysplasia: edentulous spaces 37 and 46 show the t ypical radiographic features of cem ento-osseous dysplasia; cem enticles are deposited in the connective tissue strom a.

154

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

11.2.6 Bone Diseases of the Jaw In addit ion to in flam m at ion s, cysts, an d t u m ors of th e jaw, bon e diseases of th e jaw s are oth er t yp ical p ath ologies th at d o n ot fit in to th e above categories.

Many are n ot detected in rou t in e X-ray exam in at ion s. Im p ort an t bon e lesion s of th e jaw s in clu de osteom yelit is, ossifying brom a, brous dysplasia, cen t ral gian t cell gran ulom a, an eu r ysm al bon e cyst , an d p seu docyst . Osteom a falls in to a special categor y. Osteom a is den ed as a ben ign n eoplasm of m at ure com pact or can cellous bon e bu t is n ot listed as a t u m or in th e W HO classi cat ion .

Osteomyelitis Osteom yelit is is an in fect ion of th e bon e. In p at ien t s w ith a w eak im m un e system , it can occur as a com plicat ion of periapical in fect ion , acute n ecrot izing gingivit is, an d u n t reated op en fract u res. Radioth erapy of th e jaw is also associated w ith a h igh risk of osteom yelit is. Acute osteo m yelit is is ch aracterized by n ecrosis an d th e form at ion of sequest rum (dead bon e) in th e area of in fect ion ( Fig. 11.37).

Ossifying Fibroma Ossifying fibrom a is classified as a ben ign bon e lesion an d a t ru e n eoplasm . It is m ost com m on ly foun d in th e m an dibu lar m olar region . Radiograph ically, th e ossifying fibrom a appears as m ixed radiolucen t-radiopaque, con tain ing variably calciu m -den se st ruct u res w ith t rabecu lae ( Fig. 11.38). It h as a t ypical groun d-glass appearan ce an d is w ell dem arcated from th e surroun dings.

Fig. 11.37 Osteomyelitis with the formation of sequestrum (dead bone) as a complication of open fracture.

11

Fig. 11.38 Osteolysis: note the well-de ned expansile lytic lesion in the right mandible (edentulous spaces 47–48) containing trabecula-like structures.

155

Radiographic Findings and Diagnosis

Fibrous Dysplasia

Central Giant Cell Granuloma

Fibrou s dysp lasia (McCu n e–Albrigh t syn drom e) is a rare, gen et ically determ in ed bon e disease th at m ost com m on ly involves th e m axilla. Fibrou s dysplasia is a slow ly progressive, episodic disease w ith sym ptom -free in ter vals. On ce th e jaw lesion reach es a cer tain size, it cau ses facial asym m et r y. Adjacen t teeth in th e m axilla are som et im es disp laced. Obliterat ion of th e m axillar y sin us m ay also be obser ved ( Fig. 11.39).

Cen t ral gian t cell gran ulom a is a ben ign , gen erally localized but som et im es aggressive proliferat ing osteolyt ic lesion ( Fig. 11.40). React ive bon e form at ion is a t ypical radiograph ic feat u re. Cen t ral gian t cell gran ulom a is an exp an sile an d often m ult icyst ic bon e disease. Adjacen t teeth are often displaced, an d root resorpt ion is p ossible.

Fig. 11.39 Fibrous dysplasia: the radiograph reveals a homogeneous, hyperdense, sharply demarcated shadow in the left maxillary arch, narrowing of the maxillary sinus, and caudal displacement of m olar teeth 26 and 28.

11

Fig. 11.40 Central giant cell granulom a: note the discernible but not sharply dem arcated round radiolucency in the anterior mandibular region, which appears oval as a result of distortion related to the radiographic technique.

156

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

11.2.7 Sialolithiasis Fun ct ion al in tegrit y of th e salivar y glan ds an d proper saliva secret ion are cru cial for a w ide range of differen t physiological p rocesses occurring in th e oral cavit y. Abn orm ally red u ced or in creased saliva flow can result in dehydrat ion of th e oral m u cosa, w h ich can lead to in fect ion s an d oth er p ain fu l con dit ion s. Diagn ost ic im aging of th e salivar y glan ds does n ot act u ally fall in to th e eld of den t ist r y. How ever, sialolith s (salivar y ston es) are frequen tly detected as in ciden t al or

secon dar y n dings on den tal pan oram ic radiograph s in th e d en t al p ract ice ( Fig. 11.41). Shadow s from salivar y stones often project onto the m andible. Therefore, if a radiopaque w hite zone is detected in the lower jaw, the exam iner m ust rst decide if it is located w ithin the bone or on the oor of the m outh. A second radiograph is then needed for localization. Previously, a survey of the oor of the m outh w as used as the second plane to im age the oor of the m outh. How ever, CBCT is now able to provide high -qualit y im ages and exact localization of salivary stones ( Fig. 11.42 and Fig. 11.43).

Fig. 11.41 Sialolithiasis: a salivary stone in the right duct appears as a large, inhom ogeneously radiopaque lesion on the right side of the m andible.

11

Fig. 11.42 This panoram ic CBCT image shows a large sialolith in the bend of the right submandibular gland.

157

Radiographic Findings and Diagnosis

Fig. 11.43a, b Salivary stones in the subm andibular gland. a Axial view. b Coronal view.

11.2.8 Tooth Fractures

11

Radiograp h ic exam in at ion of th e m an dible, m axilla, an d m idface for fract u res is n ot n orm ally perform ed in a den tal pract ice. If su ch st udies are n ecessar y, CBCT can provide com preh en sive im ages of difficult-to-detect m an dibu lar fract u res in m ult iple plan es ( Fig. 11.44). Most of th e fract u res d iagn osed in n orm al den t al pract ice are associated w ith t rau m at ic den t al injuries—in m ost cases, an terior tooth t raum a, w h ich m u st be adequ ately visualized an d diagn osed. Th ree m ain t yp es of t rau m at ic den tal injuries are tooth lu xat ion , in t ru sion , an d fract ure. Th e rad iograp h ic exam in at ion procedure for each t ype is th e sam e. In t raoral radiograph ic tech n iques are u sually recom m en ded for opt im al visualizat ion of t raum at ic den tal inju ries.

Note In patients presenting with tooth luxation, careful examination of the alveolar sockets is recommended, to rule out the possible presence of a fracture in this region.

158

Fract ure diagn osis is gen erally st raigh tfor w ard in singlerooted an terior teeth . Conversely, fract ures in th e m olar region can cause diagn ost ic difficult ies, regardless of w h eth er th ey are of t raum at ic or idiopath ic origin . Again , CBCT can provide precise an sw ers to th ese clin ical quest ion s ( Fig. 11.45). Root fract u res can involve all segm en t s of th e root . Differen t radiograph ic tech n iques an d project ion s are recom m en ded, depen ding on th e t ype of fract ure an d th e angle of th e exposure. If th e pat ien t’s con dit ion allow s, th e paralleling tech n ique sh ou ld alw ays be used for radiograph ic exam in at ion an d diagn osis of tooth fract u res. Th is is th e on ly w ay to en sure th e reproducibilit y of radiograph ic exam in at ion s, w h ich is especially im port an t for fract u re follow -u p ( Fig. 11.46). Tooth fract ures can occur in associat ion w ith fract ures of th e m an dible. Den tal fract ures (usually longit udin al) can also occur as a com plicat ion of den t al in ter ven t ion s. Root resorpt ion often occurs as a com plicat ion of tooth fract ures ( Fig. 11.47, Fig. 11.48, Fig. 11.49).

11.2 Assessm ent and Diagnosis of the Most Com m on Pathological Changes

a

b

c

Fig. 11.44a–c Median m andibular fracture. a This CBCT panoram ic reconstruction shows a thin vertical fracture line on tooth 31, with no signs of dislocation. b The axial view con rm s the diagnosis of mandibular fracture without dislocation at edentulous space 32, as well as a second fracture without dislocation on the right side of the m andible. The second fracture line extends diagonally. c This three-dimensional view obtained by volume rendering also shows only the fracture in the anterior region.

Fig. 11.45a, b Crown fractures. a Crown fracture of tooth 21. b Crown fracture of tooth 42.

a

11

b

159

Radiographic Findings and Diagnosis

a

b

c

d

e

f

Fig. 11.46a–f Multiple transverse root fractures in the maxillary anterior teeth.

11

Fig. 11.47 Mandibular fracture with tooth involvem ent.

160

Fig. 11.48 Longitudinal fracture caused by a screw root.

Fig. 11.49 Root resorption in teeth 21 and 22, induced by anterior tooth trauma.

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Index Note: Page num bers follow ed by f an d t in dicate gures an d t ables, respect ively.

A Accept able level [term ], 55 Accept ance test s, 56 Accident(s), preven t ion of, 55 Act ive pixel sensors (APS), 47 Addit ion, 35–36, 138 Age (pat ien t), and X-ray im age form at ion, 36 Alph a part icles, 8, 11 – ion izat ion den sit y of, 22 – radiat ion w eigh t ing factor for, 22 Alveolar crest , age-related changes in , 139 Alveolar recess, radiograph ic ap pearance of, 125, 127f, 129, 131 Alveolar ridge, 121, 122f Alveolus, 121, 121f Am eloblastom a(s), 147, 147f – m ult icyst ic, 147 – varian ts of, 147–148, 148f Am erican Den tal Associat ion (ADA), St an dards Com m it tee on Den t al Product s, 56 Angle of jaw, 128f Angle of rotat ion (φ ), in tom ography, 78 An ode(s) – angulat ion of, 14, 14f – rotat ing, 13, 14f – st at ion ar y, 13, 13f – of X-ray t ube, 12, 13–14, 13f, 14f – – interact ion s of elect ron s w ith , 15 An terior n asal spin e, 124, 124f An t i-scat ter grids, 36–37, 37f Apoptosis, 27–28 Art icular t ubercle, 127f As low as reasonably ach ievable (ALARA) principle, 134 Atlan to-axial join t , lateral, 127f Atom (s), 9 – elect ron sh ells, 9, 10 Atom ic n um ber, 9, 34 At tenu at ion , 10, 16, 34 Auger e ects, 26f Autom at ic lm processor(s), 42, 43f – w ith dayligh t loader, 42, 43f Axial project ion techn ique, for occlusal radiography, 76, 76f

B Backgroun d fog, 41 Beam -indicat ing device (BID), 17–18 Beta part icles, 8, 11 Beta rays, radiat ion w eigh t ing factor for, 22 Bisect ing-angle tech n ique, 2, 3f, 61, 63, 67–72, 67f, 68f – disadvan tages of, 68–71, 68f–70f

– im age distort ion in , 67–71, 68f, 69f, 70f – m eth odology, 71–72, 72f – for occlusal radiography, 75, 75f – an d paralleling tech n ique, com parison of, 67, 67f, 70f – an d radiat ion protect ion , 70 – an d reproducibilit y, 71 – vert ical angulat ion and, 71, 71f Bite block, an d paralleling tech nique, 62, 62f Bitew ing radiography, 73–74, 73f, 121, 122f – of caries, 136 – m eth odology, 74, 74f, 136 – vert ical, 139f, 140 Blackm an , Sydn ey, 3 Bloom ing, 47 Blurring, in tom ography, 78 – exten t of, 78 – pat tern s of, 78, 78f – t ype of, 78 Blurring out , 77, 77f Bocage, An dré, 2, 77 Boh r, Niels, 9 Bon e, X-ray appearan ce of, 34 Bon e defect s, vert ical, 139–140, 140f, 141f Bon e diseases, of jaw, 155–156 Bon e loss, h orizon t al, 139–140, 140f, 145, 146f Bouch acourt , Léon , 80 Braking radiat ion . See Brem sst rah lu ng Brem sst rah lung, 15–16, 16f, 26f Broadben t , B. Holly, 3

C Calcium t ungst ate cr yst als, 41, 41f Can cer, radiat ion -in duced, 31, 32f Caries – approxim al, 136 – assessm en t and diagn osis of, 136–139 – C1 (super cial), 137, 137f – C2 (m oderate), 137, 138f – C3 (deep), 137, 138f, 139 – C4 (deep com plicated), 137, 138f – cem en t um , 136 – an d cer vical burn out , di eren t iat ion of, 122, 122f – an d developm ent al defect s, different iat ion of, 139 – di erent ial diagn osis, 139 – early ch ildh ood, 139, 139f – en am el, 137, 137f – ssure, 136 – in terproxim al, 136 – occlusal, 137, 138f – predilect ion sites for, 136 – prim ar y (in it ial), 136, 137f – – t ypes of, 137, 137f

– progression , st ages of, 137, 137f – radiograph ic appearan ce of, 136 – recurren t , 137, 139 – secon dar y, 136, 137 Cath ode, of X-ray t ube, 12–13, 13f CCD sensors, 47 CdTe sen sors, 48 Cell death , program m ed, 27–28 Cell fun ct ion , im pairm en t of, 27 Cem entoblastom a, 153, 154f Cem entom a, 153, 154f Cem ento-osseous dysplasia, 153, 154f – orid, 153 Cen t ral gian t cell gran ulom a, 156, 156f Cen t ral project ion , 34, 121 Cephalom et ric radiograph, e ect ive dose for, 114 Cer vical burn out , 122, 122f Cer vical spin e, 128f Cesium iodide cr yst als, 48 Ch aracterist ic cur ve(s) – for digital radiography, 51, 52f – of radiograph ic lm , 40f, 41, 50–51 – – sh ou lder of, 40f, 41 – – toe of, 40f, 41 – for storage ph osph or im aging plates, 51, 52f Ch em ical t rap(s), 48 Cieszyn ski, A., 2 Clin ical in dicat ion s, for radiological exam inat ion , 56 Close-up im aging, 77, 77f CMOS sen sors, 47 Collim ator(s), 17–18, 18f, 19f, 37 – geom et r y of, an d radiograph ic tech niqu e, 18, 19f Collim ator h older, 18 Com parabilit y, of radiograph s, 134 Com pton e ect (Com pton scat tering), 11, 11f, 26, 26f Com puted tom ography (CT) – art ifacts, 112–113 – e ect ive dose for, 113–114 – h istorical perspect ive on , 109–110 – lim itat ion s of, 112–114 – prin ciples of, 109 – radiat ion exposure in , 113–114 – spiral, 110, 110f Cone beam com puted tom ography (CBCT), 5, 5f, 47, 85, 87, 109–117 – art ifacts, 113 – basic rules for, 114 – of bone con dit ion s, 140 – clin ical applicat ion s of, 114– 117, 115f–117f, 121, 122f – data recon st ruct ion , 110–111 – developm ent of, 109–110 – e ect ive dose for, 113–114 – at panel detectors for, 111

– – – –

im age form at ion , 110–111 im age in ten si ers for, 111 of n asopalat in e duct cyst , 143 prim ar y recon st ruct ion, 111, 111f – radiat ion exposure in , 113–114 – secon dar y reconst ruct ion, 111, 111f, 112f, 113f – of sialolith iasis, 157, 157f, 158f – slice posit ion, 114, 116f – slice th ickn ess, 114, 116f – system s, cost of, 114 – of tooth fract ures, 158, 159f, 160f – volum e size for, 114, 115f Con t in uing educat ion , an d radiat ion protect ion, 56 Con t rast . See Film , con t rast; Object cont rast Coolidge, William , 13 Corpuscular radiat ion , 8 Cosm ic rays, 30 Coulom b per kilogram (C/kg), 22 Cribriform plate, 121, 121f Crossover, 42, 42f Curren t in ten sit y, and im age form at ion , 36 Cyst(s), 120, 120f – de n it ion of, 143 – follicu lar (dent igerous), 143, 143f, 144f, 147 – nasopalat in e duct , 124, 143, 144f – non odon togen ic epith elial, 143 – odon togenic epith elial, 143 – radicular (periapical), 143–144, 145f – radiograph ic appearance of, 135 – W HO classi cat ion of, 143

D Dent al radiography, h istorical perspect ive on, 2–5 Dent al X-ray h ead, 3, 3f Dent al X-ray t ube, 12, 12f – design of, 12, 12f, 13f – kilovolt age and, 11, 15 Dent ures, and panoram ic radiography, 101, 101f Derm at it is, radiat ion -in duced, 54 Detect ive quan t um e cien cy (DQE), 50 Determ in ist ic e ect s, 28, 31, 32f Diagn osis, radiographic n dings an d, 135 Diagn ost ic radiology, physics of, 10–11, 11f Digital dent al radiography – advant ages of, 50–51 – dat a storage in , 51 – de n it ion of, 47 – edit ing of, 51

163

Index – en h an cem en t of, 51 – equipm ent for, 46f, 47 – at pan el detectors for, 46f, 47 – h istorical perspect ive on , 46 – im age acquisit ion in , 47 – im age inten si er for, 46f, 47 – im aging plate for, 46f, 47, 48–50 – rapid availabilit y of im age in , 51 – sen sors for, 46f, 47–48, 47f – spat ial resolut ion in, 48 Digit al radiography, h istorical persp ect ive on , 5 Digit al volum e tom ography. See Cone beam com puted tom ography (CBCT) Distort ion, im aging free of, in int raoral radiography, 59, 60f DNA (deoxyribon ucleic acid) – base dam age, 27, 27f – double-st ran d breaks, 27, 27f – radiat ion dam age to, 27, 27f, 31 – – biological e ects of, 27–28 – repair m ech anism s, 27 – single-st ran d breaks, 27, 27f Dose–area product , 23, 23f Dose lim it(s), 55 – m on itoring of, 55 Dose lim itat ion , 17–18 Dose units, 22 Dosim et r y, un it s an d term s for, 22–23 Dynam ic range, 50–51

E Ear lobe, sh adow, on pan oram ic radiography, 105, 126, 127f Edison , Th om as, 2 E ect ive dose, 23 – for CBCT, 113–114 – for ceph alom et ric radiograph , 114 – for CT, 113–114 – for digital pan oram ic radiograph, 114 – for in t raoral radiograph, 114 E ect s of radiat ion. See Radiat ion e ect s Elect ric eld st rength , 8f, 9 Elect rom agn et ic spect ru m , 9, 9f Elect rom agn et ic w aves, 8–9, 8f Elect ron (s), 9 – in teract ions w ith an ode m aterial, 15 – release of, 26, 26f – sh ell-to-sh ell t ran sit ion s, 10 Elect ron beam (s), radiat ion w eigh t ing factor for, 22 Elect ron shell(s), 9, 10 Elect ron t rap(s), 48, 49 En do-Holder, 74, 74f Epith elial cell rest s of Malassez, 143 Equipm en t (den t al X-ray), radiat ion -proof h ousing, 12, 12f Equivalen t dose, 22 Er ythem a, radiat ion -in duced, 31

164

European Atom ic En ergy Com m unit y (EURATOM), 55 European Com m it tee for St andard izat ion , 56 Excit at ion , 10 Exposure. See Radiat ion exposure Exposure t im e, an d im age form at ion , 36 External acou st ic m eat us, 127f

F Feldkam p algorith m , 111 Fibroden t inom a, 147 Fibrom a – am eloblast ic, 147–148, 149f – ossifying, 155, 155f Fibro-odontom a, am eloblast ic, 147–148, 149f Fibrous dysplasia, 156, 156f Film – bending of, errors cau sed by, 65f, 70, 70f – ch aracterist ic cur ves, 40f, 41, 50–51, 52f – cont rast , 37, 50–51 – – an d ch aracterist ic cur ve, 40f – cross-sect ion al st ruct ure of, 39, 39f – for dent al X-ray, ch aracterist ics of, 37–38, 37f – developm ent of, disadvan t ages of, 51 – D-speed, 38 – em ulsion layer, 39, 39f – E-speed, 38 – F-speed, 38 – w ith in ten sifying screens, 41–42, 41f – – disadvant ages of, 42 – – sen sit ivit y of, 41 – norm al exposure of, 40f – for occlusal radiography, 74, 75f – over-exposure of, 40f – packaging of, 39, 39f – processing of, 42, 43f – screen less, 37–38 – – for occlusal radiography, 74 – sh arpn ess (resolut ion ), 37–38, 37f – silver con tent of, 39 – speed (sen sit ivit y), 37–38 – un der-exposu re of, 40f – view ing, con dit ion s for, 134 – w rong-side exposure of, 39f, 41 Film holder – an terior, for paralleling tech niqu e, 65, 65f – for bitew ing radiography, 74, 74f – in sert ion in to m outh , 64–67, 64f–66f – an d orth ogon al project ion geom et r y, 63, 63f – for paralleling tech n ique, 61, 61f – w ith posit ion -in dicat ing device, 136 Filter(s), alum inum , 17 Filtered back project ion, 111

Filt rat ion – by alu m in um lters, 17 – in h eren t , 17 – tot al t ube, 17 – of X-rays, 17 Fin dings (radiograph ic) – challenging an d/or un com m on , 135–136 – den sit y of, 135 – descript ion of, 135 – an d diagn osis, 135 – e ect on adjacen t st ru ct ures, 135 – evaluat ion of, 135 – in tern al st ruct u re of, 135 – locat ion /site of, 135 – m argins of, 135 – an d n orm al varian t s, 135–136 – relat ionsh ip to adjacen t st ru ct ures, 135 – sh ape of, 135 – suggest ive of lesion s/path ological changes, 135 – w rit ten report of, 135 Fit zgerald, F. G., 61 Fluorescence, 41 Focal spot , 13–14, 14f – act u al, 14, 14f – apparent (e ect ive), 14, 14f – size of, 13–14 Focus-to-object dist ance (FOD), for or th odon t ic radiography, 61–62 Food an d Drug Adm in ist rat ion (FDA), and radiat ion protect ion , 56 Fract ure(s). See also Tooth fract ures – m an dibular, 158, 159f, 160f – radiograph ic appearan ce of, 135 Fran kfort h orizon t al plan e, 89f, 91, 91f Free radicals, 27

G Gadolin iu m cr ystals, 41, 41f Galileos digit al con e beam com puted tom ography system , 5, 5f Gam m a rays, 8, 9, 9f, 11 – radiat ion w eigh t ing factor for, 22 Garret son , J. L., 2 Geh ler in tensifying screen , 2 Gen erator(s), m ult i-pulse, 14, 15f Gen et ic defect s, radiat ion -in duced, 31, 32f. See also Mut at ion (s) Geom et ric u nsh arpness, 48 Gh ost im ages, in panoram ic radiography – of an atom ical st ruct ures, 102, 102f – of cer vical spin e, 98–99, 98f, 99f – de nit ion of, 97 – of earrings and other ear jew elr y, 103, 103f – of m etallic object s, 100, 100f – of m olar/prem olar crow n s, 104, 104f

– of object s in rot at ion cen ter, 103–104, 103f, 104f – t ypes of, 97 Gran ulom a, 141. See also Cen t ral gian t cell gran ulom a Gray (Gy), 22 Gray-scale range, 34, 35–36

H Hard palate, radiograph ic appearan ce of, 125, 125f, 127f, 129f Heckm an n , K., 80 Hofrath , H., 3 Holzknech t , Guido, 35 Houn s eld, Godfrey N., 109 Hyoid bon e, 127f, 128f

I Im age an alysis, system at ic, 134 Im age form at ion , 34 – factors a ect ing – – lm -related, 37–42 – – im age receptor-in dependent , 35–37 Im age in terpret at ion, system at ic, 134 Im age noise, 48 Im age qualit y, 17–18 – assessm en t of, 134 Im aging plate(s). See also Storage ph osphor im aging plates – for digital radiography, 46f, 47 – dyn am ic range of, 51, 52f Incisive can al, 124 Incisive foram en , 124f In am m at ion . See also Periodon t it is – of en dodon t ically t reated tooth , CBCT of, 116, 116f – radiograph ic appearan ce of, 135 Infraorbital can al, 128f, 130 Infraorbital foram en , 130 Inten sifying screen(s), 2, 41–42, 41f – disadvan tages of, 42 – speed classes of, 41–42 Interden tal bon e sept u m , 121 Interm axillar y sut ure, 124f Intern at ional Atom ic Energy Agen cy (IAEA), 54, 55 Intern at ional Basic Safet y St an dards (BSS), 56 In tern at ion al Com m ission on Radiological Protect ion (ICRP) – act ivit ies of, 54–55 – collaborators w ith , 54 – goals of, 54 – h istorical perspect ive on , 54 – recom m endat ion s form u lated by, im plem ent at ion of, 55–56 – st an ding com m it tees of, 54 – st ruct ure of, 54 In tern at ion al Organ izat ion for Stan dardizat ion (ISO), Tech n ical Com m it tee 106 Den t ist r y, 56

Index In terradicular bon e sept um , 121, 122f In t raoral radiography – of bon e con dit ion s, 140, 141f – clin ical applicat ions of, 58 – com pleten ess of visualizat ion in , 58, 58f – diagnost ic im age qualit y of, 58, 138 – distor t ion -free im aging, 59, 60f – e ect ive dose for, 114 – full-m outh series, 63, 63f – im age receptor posit ion ing for, 134 – orth ogon al im aging – – project ion geom et r y for, 58–59, 59f – – superim posit ion -free, 58–59, 58f – periapical, 61, 61f – prin ciples of, 58 – qualit y criteria for, 58–59 – reproducibilit y, 59, 60f – st an dards for, 58 – superim posit ion s in , 138 Inverse square law, 36, 36f Ion dose, 22 Ion izat ion, 9–10, 10, 16 – de nit ion of, 8 – direct , 8 – in direct , 8 Ion izing radiat ion, 8 – e ect s of. See also Radiat ion e ect s (biological e ects/e ects in t issu e) – – direct , 27 – – on DNA, 27–28, 27f – – indirect , 27 Isotope(s), radioact ive, 11

J Jaw s. See also Man dible; Maxilla – bone diseases of, 155–156

K Kalen der, Willi, 110 Kells, C. Edm und, 2, 61 Keratocyst s, 143. See also Tum or(s), odon togen ic Kilovoltage, of den tal X-ray m ach in es, 11, 15 Koch an d Sterzel, 80 Kön ig, Walter, 2

L Lam ina dura, 121, 121f Laten t period, 31 Lead lin e grid, 36–37, 37f, 38 Le Master, Collins, 2 Leukem ia(s), radiat ion -in duced, 32f Ligh t – u lt raviolet . See Radiat ion , ult raviolet – visible, 9f, 10

Lin ea obliqua. See Oblique lin e Linear energy t ransfer (LET), 22, 22f Line pairs per m illim eter (lp/m m ), 48 Lum inescen ce, 16, 17f – ph oto-st im u lated, for im aging plate readout , 48, 48f, 49, 50f

M Magn et ic u x den sit y, 8f, 9 Malign ant lesion s, 145–154 Malign ant t ran sform at ion , 31 Man dible – an atom ical variat ion s, 123f, 124 – bone con dit ion s in, assessm en t of, 140, 140f – collum , 126, 127f – com pact bon e of, 128f – con dyle, 128f – coron oid process, radiograph ic appearan ce, 125, 126f, 129f – radiograph ic an atom y of, 123–124, 123f – – panoram ic, 125–126, 126f, 127f, 128f Man dibular (n er ve) can al, 123, 124, 125, 128f, 143 Man dibular foram en , 125 Man dibular fract ure(s), 76, 76f Maxilla – bone con dit ion s in, assessm en t of, 140, 140f – radiograph ic an atom y of, 124– 125, 124f, 128–131, 129f–130f Maxillar y sinus – diagnost ic evaluat ion of, 131 – lateral w all, on pan oram ic radiography, 129f, 130f, 131 – m ucocele in, 130f – posterior w all, on pan oram ic radiography, 129f, 131 – radiograph ic appearan ce of, 124–125, 125f, 126, 129f, 130 – residual root in , 4f – sh adow, on pan oram ic radiography, 106, 106f Maxillar y t uberosit y, radiograph ic appearan ce of, 126, 128f McCorm ack, Allan , 109 McCune-Albright syn drom e, 156 Median palat in e sut ure, 124 Men tal foram en , 123, 125, 128f Met al art ifact s – on CBCT, 113 – on CT, 112 – in pan oram ic radiography, 100, 100f Midface – pan oram ic radiography of, 87, 87f – radiograph ic an atom y of, 128–131, 129f–130f Mon itor view ing, con dit ion s for, 134 Mot ion art ifact s – on CBCT, 113, 113f – on CT, 113

Mou th , oor of, can cer of, 145– 146, 146f Mozzo, P., 110 Mucocele, in m axillar y sinu s, 130f Muller, H. J., 54 Mutat ion (s), 28, 31, 32f, 54 Myxo brom a, odontogen ic, 153, 153f Myxom a, odon togen ic, 153, 153f

N Nasal cavit y, 128f, 129f Nasal conch ae, sh adow s, on pan oram ic radiography, 105–106, 105f, 106f, 128f Nasal oor, radiograph ic appearan ce of, 125, 125f, 127f Nasal sept um , 128f Nat ional Coun cil on Radiat ion Protect ion and Measurem en ts (NCRP), 55, 56 Neut ron (s), 11 – ion izat ion den sit y of, 22 New Tom con e beam com pu ted tom ography system , 5f, 109 Nose, shadow – on intraoral radiograph, 124, 124f – on pan oram ic radiography, 106, 106f, 126, 127f – on radiograph , 124, 124f, 125f Nuclei – st able, 8, 11 – unst able, 8, 11 Nuclide(s), radioact ive, 11. See also Radion uclides Num ata, H., 3, 4f, 79–80

O Object con t rast , 36 Object-to- lm distan ce, and paralleling tech n ique, 62 Oblique lin e, of m an dible, 123, 123f, 127f Occlusal radiography, 74–76 – axial project ion tech n ique for, 76, 76f – bisect ing-angle tech n ique for, 75, 75f – lm for, 74, 75f Odontom a, 151 – com plex, 151, 151f – com pou nd, 151, 152f Opt im izat ion procedures, 56 Oral cavit y, can cer of, 145–146 Orbit , 127f, 129f, 130 Oro-an t ral com m unicat ion , CBCT of, 117, 117f Orth odon t ic radiography, 61–62 Orth ogon al im aging, 81–83 Orth ogon al project ion geom et r y, 58–59, 59f – lm h olders an d, 63, 63f – for m olars, 63, 63f – for prem olars, 63, 63f Or th opan tom ography, 3, 81–83, 84–85, 88f, 89, 112f

Orth ophos XG 3D con e beam m ach ine, 110f Osteom a, 155 Osteom yelit is, 155, 155f Ot t , Walter, 3, 80

P Paatero, Y. V., 3, 4f, 79–80, 82 Pair product ion, 11 Panoram ic radiography, 79–108, 121, 122f, 139–140 – air sh adow s in , 126 – of alveolar crest , 86 – an atom y, 87f, 88f, 88t, 89, 125–131 – of an terior tooth region, 86, 86f – bitew ing view s, 86f, 87 – of bone con dit ion s, 139–140, 140f – of cyst s, 120, 120f, 143, 143f– 145f, 144 – in den tate pat ien ts, bite-rod posit ioning device for, 93 – dent ures an d, 101, 101f – in eden t ulou s pat ient s, posit ion ing for, 93–95, 94f, 95f – e ect ive dose for, 114 – errors in – – an terior displacem ent of an terior teeth , 96, 96f – – h ead displacem en t or rot at ion, 92–97 – – h ead posit ion ing, 90–97 – – h ead rot at ion out of m edian plan e, 97, 97f – – h ead t ilt , 90–92, 90f–92f – – posterior displacem en t of anterior teeth , 92, 93f – w ith ext raoral lm , 80 – focal t rough adjust m en t to den tal arch in , 81, 81f, 82f – gh ost im ages in , 97 – – of anatom ical st ruct ures, 102, 102f – – of cer vical spin e, 98–99, 98f, 99f – – of earrings an d oth er ear jew elr y, 103, 103f – – of m etallic objects, 100, 100f – – of m olar/prem olar crow n s, 104, 104f – – of object s in rotat ion cen ter, 103–104, 103f, 104f – h ead posit ion ing for, 89–90, 89f – – errors in , 90–97 – h istorical perspect ive on , 3–5, 4f, 5f, 79–80 – w ith in t raoral source, 80, 80f – m ethodology, 89–108 – of m idface, 87, 87f – of part ial-arch segm ent s, 85–86, 85f – pat ient posit ion ing for, 84, 84f, 134 – rotat ion al, 80–81, 80f – – advan ces in , 84–85 – – angle of in ciden ce in , 82, 82f

165

Index – – h ead posit ion ing in, 83, 84f – – im age layer th ickness in , 83, 83f – – an d orth ogon al im aging, 81–83 – – pat ien t posit ion ing in, 84, 84f – – principle of, 81, 81f – – projection geom etry, 83–84, 84f – – project ion in h orizon tal plan e, 83, 84f – – project ion in vert ical plan e, 83, 84f – – project ion radiu s in , 83, 83f – – rot at ion cen ters in, 82–83, 82f, 83–84, 84f – – slit collim ator w idths in , 82f, 83, 83f – w ith slit collim ator, 79–80, 79f – soft-t issue sh adow s in , 97, 104–109, 126 – special program s, 85–88 – superim posit ion s in , 97, 104–109 – of tem porom an dibular joint , 86f, 87, 87f Pan oram ic tom ography, 79–108. See also Pan tom ography Pan orex X-ray m ach in e, 3 Pan tom ography, 3, 4f Paralleling techn ique, 18, 61–67, 136 – advan t ages of, 62, 63 – an d bisect ing-angle tech n ique, com parison of, 67, 67f, 70f – bite block an d, 62, 62f – lm h older for, 61, 61f – – an terior, 65, 65f – – insert ion in to m outh, 64–67, 64f–66f – lm posit ion ing in, 63–64, 65f – im age receptor placem ent in, 62, 62f – long-cone tech nique for, 61–62 – m ethodology, 63–67 – – for m andibular in cisors and can ines, 66f, 67 – – for m andibular m olars an d prem olars, 66–67, 66f – – for m axillar y in cisors an d can ines, 65, 65f, 66f – – for m axillar y prem olars an d m olars, 64, 64f, 65f – object-to- lm distan ce an d, 62 – prin ciples of, 61–62 Par t ial volum e art ifacts, on CT, 112–113 Pathology – iden t i cat ion of, on radiograph s, 134–135 – versus n orm al varian ts, 135–136 – an d X-ray im age form at ion, 36 Periapical cem en t al dysplasia, 153 Periapical radiography, 61, 61f. See also Bisect ing-angle tech n ique; Paralleling tech n ique Periodon t it is, apical – acute, 141 – – radiograph ic feat ures of, 141, 141f

166

– ch ron ic, 141 – – radiograph ic feat ures of, 141, 142f – ch ron ic granu lom atou s, radiograph ic feat ures of, 141, 142f – radiograph ic feat u res of, 141, 141f, 142f Ph ar yn x, 128f Ph otoelect ric e ect , 10–11, 11f, 16, 17f, 26, 26f Ph oton(s), scat tering of, 11, 11f, 26, 26f Ph oton en ergy, t ran sfer to m at ter, 10, 26, 26f. See also Excitat ion; Ion izat ion Ph oton radiat ion, 8–9 Ph oto-st im ulated lum in escen ce (PSL), for im aging plate readout , 48, 48f, 49, 50f Pixel bin ning, 48 Pot assium , 30 Price, W. A., 2 Project ion geom et r y – im plem ent at ion of, 59–61, 60f – prin ciples of, 59–61, 60f Proton (s), 8, 9, 11 – ion izat ion den sit y of, 22 Pter ygopalat in e fossa, 126, 128f

Q Qualit y assuran ce, 56 – st an dards for, 56

R Radiat ion . See also Ion izing radiat ion – absorpt ion of, 10, 22. See also X-ray(s), absorpt ion of – alph a, 8 – art i cial, 12 – beta, 8 – cosm ic, 12, 30, 31f – de nit ion of, 8 – elect rom agn et ic, 8–9, 8f – in frared, 8, 9f – an d m at ter, interact ion s bet w een , 9–10, 26, 26f – n at urally occurring (backgrou nd), 8, 30 – scat tered, 37, 37f. See also Scattering – secon dar y, 37, 37f – solar, 30 – terrest rial, 12, 30, 31f – t ypes of, 8 – u lt raviolet , 8, 9f Radiat ion absorbed dose, 22 Radiat ion e ects (biological effect s/e ect s in t issue), 26, 26f – biological ph ase, 26–28, 26f, 27f – ch em ical ph ase, 26, 26f – determ in ist ic, 28, 31, 32f – direct , 27 – in direct , 27 – physical ph ase, 26, 26f – stoch ast ic, 31, 32f

Radiat ion exposu re – art i cial, 30, 31f – nat ural, 30, 30f, 31f – occupat ion al, 30, 31f Radiat ion protect ion , 17–18 – adm in ist rat ion of, 55 – bisect ing-angle tech n ique an d, 70 – historical perspect ive on , 54 – legal an d regulator y fram ew ork for, 55 – m an agem en t of, 55 – an d need/just i cat ion , 55 – opt im izat ion of, 55 – procedures for, 56 – respon sibilit y for, 55 Radiat ion qualit y, 22 Radiat ion risk(s) – an d need/just i cat ion , 55 – reduct ion of, 55 Radiat ion sickness, acute, 31 Radiat ion w eigh t ing factor (W R), 22 Radioact ivit y, 8, 11–12 Radiograph ic m easurem ent, 74, 74f Radioisotopes, 11 Radion uclides, 11 – terrest rial, 30 Radiosen sit ivit y, 23 RadioVisioGraphy system , 46 Radon , Joh an n , 111 Radon gas, 30, 30f, 31f Raper, How ard R., 2, 73, 136 Rare-earth screens, 41, 41f Report , radiological, 135 Reproducibilit y – of im ages in in t raoral radiography, 59, 60f, 71 – of radiograph s, 134 Right-angle techn ique, 72–73, 72f, 73f Risk/ben e t assessm ent , 56 Roen tgenogram , rst , 2 Roen tgen rays, 2 Roller t ran sport system , of autom at ic lm processor, 42, 43f Rön tgen , Wilh elm Con rad, discover y of X-rays, 2 Root canal, w orking length of, radiograph ic m easu rem en t of, 74, 74f Root resorpt ion – w ith am eloblastom a, 147, 147f, 148f – t raum a-in duced, 158, 160f Rutherford, Ern est , 9

S Scanora, 5, 85 Scat tering, 11, 11f, 26, 26f, 37, 37f – in ten sifying screen s and, 42 Sem icon ductor e ect , 16 Sem ilun ar n otch , 128f Sen sor(s), for digital radiography, 46f, 47–48, 47f – act ive pixel, 47 – CCD, 47

– CdTe, 48 – CMOS, 47 – sign al processing w ith , 47, 47f – spat ial resolut ion of, 48 – t ypes of, 47 Sh ell capacit y, 9 Sialolith iasis, 76, 76f, 157, 157f, 158f Siem ens X-ray sph ere, 3, 3f Sievert (Sv), 22, 23 Silver brom ide cr ystals, 38–39, 38f – conven t ion al, 38, 38f – T-grain (t abular), 38, 38f Single-t ank design , 12 Skin cancer, radiat ion -induced, 54 Slit-beam tech niqu e, 3, 4f Slit collim ator – pan oram ic radiography w ith, 79–80, 79f – in rotat ional pan oram ic radiography, 82f, 83, 83f Soft palate, 127f – radiographic appearance of, 129f – shadow, on panoram ic radiography, 107, 107f, 126 Soft rays, 11 Spacer con e(s), 17–18, 18f, 19f Sphen oid sin us, 127f St andard radiograph ic project ion s, 35 St andards – for in t raoral radiography, 58 – for radiat ion protect ion , 56 St at us-X pan oram ic X-ray ap parat us, 4f Stochast ic e ect s, 31, 32f Storage ph osphor im aging plates, 48–50 – characterist ic cur ve for, 51, 52f – dam age-related m arks on , 50, 51f – form ats for, 49, 49f – laten t im age on , 49 – readout , 48, 48f, 49, 50f – scan ners for, 49, 49f – st ruct ure of, 48, 48f St yloid process, 126, 127f Subt ract ion , 35–36, 138 Sum m at ion e ect , 34, 34f, 121, 138

T Tangen t ial e ect , 35, 35f Teeth . See also Tooth – radiograph ic an atom y of, 121–122, 121f, 122f Tem porom an dibular joint (TMJ) – close-u p view of, 77f – pan oram ic im aging of, 86f, 87, 87f Th erm ion ic em ission, 13 Th orium , 30 Th resh old dose, 31, 32f Tissu e(s) – e ect s of radiat ion in . See Radiat ion e ects

Index – radiat ion -induced ch anges in , 31 – X-ray appearance of, 35 Tissue w eigh t ing factor (W T), 23, 23t Tom ography – blurring in, 78, 78f – conven t ion al, 77–78, 77f, 78f – – principles of, 77f, 78, 78f – digital volu m e. See Con e beam com pu ted tom ography (CBCT) – pan oram ic, 79–108. See also Pan tom ography Tongue – posit ion, for pan oram ic radiography, 107, 107f, 109 – sh adow, on pan oram ic radiography, 107–108, 108f–109f, 126 Tongue piercing, an d rotat ion cen ter of pan oram ic radiography, 103–104, 103f, 104f Tooth fract ures, 158, 159f, 160f Tooth lu xat ion, 158 Tooth -support ing st ru ct ures, radiograph ic an atom y of, 121, 121f, 122f

Training, and radiat ion protect ion , 56 Tran sverse pan oram ic tom ography, 5 Traum at ic den tal inju ries, 158, 159f, 160f Tum or(s) – odontogen ic, 147–153 – – ben ign m ixed, 147 – – keratocyst ic, 143, 147, 148, 150f, 151f – – W HO classi cat ion of, 147 – radiograph ic appearan ce of, 135 Turbinates, in ferior, radiograph ic appearan ce of, 129 Type tests, 56

U Ulcer(s), radiat ion -induced, 31 Un ited St ates, organ izat ion s in, respon sible for radiat ion protect ion , 55–56 Updegrave, W. J., 61 Uranium , 30

V Vascular system , radiat ion -induced ch anges in , 31 Voltage, an d im age form at ion , 36–37 Volum e art ifact s, on CBCT, 113 Voxels, 111

W Waggener, D. T., 61 Walkh o , Friedrich Ot to, 2 Water, radiolysis of, 27 Weh n elt cylin der, 13, 13f, 14

X X-ray(s), 8, 9f – absorpt ion of, 10, 22, 34 – – factors a ect ing, 35–36 – ch aracterist ic, 10, 15, 16f – discover y of, 2 – lt rat ion of, 17 – ion izat ion den sit y of, 22

– an d m at ter, in teract ion s bet w een , 9–10, 26, 26f – product ion of, 10 – – in den tal X-ray equipm en t , 12–16 – propert ies of, 16 – radiat ion w eigh t ing factor for, 22 – of teeth , rst , 2 X-ray beam (s), at ten uat ion of, 10, 16, 34 X-ray m ach in e, den tal, rst , 2

Z Zon arc pan oram ic X-ray m ach ine, 3, 5f Zon arc rotat ion al panoram ic radiography m achin e, 85f Zon ography, 83 Zulauf, A. F., 79–80 Zygom at ic arch , 128f Zygom at ic bon e, radiographic appearan ce of, 125, 125f, 128, 128f, 129f

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