Radiologic Anatomy of the Jaws 9781512821185

Table of contents :
Contents
Preface
Illustrations
I. Introduction
II. The Logic in Radiologie Interpretation
III. The Dental Articulation – Gomphosis
IV. Maxillary Intraoral Radiograph Anatomy
V. Maxillary Sinus
VI. Nasal Fossa
VII. Anterior Maxillary Landmarks
VIII. Mandibular Intraoral Radiographic Anatomy
IX. Anatomie Structures in Extraoral Radiographs
X. Landmarks in Panoramic Radiographs
XI. Self-Study Exercises
References
Suggested Reading

Citation preview

Radiologic Anatomy of the Jaws

RADIOLOGIC ANATOMY OF THE JAWS Harrison M. Berry, Jr., D.D.S., M.SC. Professor of Radiology, School of Dental Medicine, University of Pennsylvania

U N I V E R S I T Y O F P E N N S Y L V A N I A PRESS Ι

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philadel

Phia

Design by Lawrence Didona Copyright © 1982 by the University of Pennsylvania Press All rights reserved Library of Congress Cataloging in Publication Data Berry, Harrison M. Radiologic anatomy of the jaws. Bibliography: p. 1. Jaws—Anatomy. 2. Jaws—Radiography. I. Title. [DNLM: 1. Radiography. 2. Metabolic diseases—radiography. W N 200 T236r] QM535.B47 1982 617.6Ό757 82-60263 ISBN 0-8122-7870-4 ISBN 0-8122-113C-8 (pbk.) Printed in the United States of America

To Joseph R.

Ashman

True Friend and teaching teammate in our course "Morphodynamics of the Human

Body'

Contents ι INTRODUCTION

II T H E LOGIC IN RADIOLOGIC INTERPRETATION

III

T H E DENTAL ARTICULATION—GOMPHOSIS

9

13

Periodontal ligament Lamina dura Interdental septum

IV MAXILLARY INTRAORAL RADIOGRAPHIC ANATOMY

27

Pterygoid hamulus Lateral pterygoid ala Coronoid process Maxillary tuberosity Zygoma Malar process (of maxilla) Flexed-cheek shadow

V

MAXILLARY SINUS Normal extensions Septa

39

viii CONTENTS

Bony nodules Nutrient canals Typical " Y "

VI NASAL FOSSA

57

Conchae Nasal septum Midpalatine suture Nasolacrimal canals

VII ANTERIOR MAXILLARY LANDMARKS

63

Anterior nasal spine Incisal foramen Premaxillary suture Canine (lateral) fossa Lip Nose Nasal bones

VIII MANDIBULAR INTRAORAL RADIOGRAPHIC ANATOMY External oblique line Mylohyoid ridge Submandibular fossa Inferior border Mandibular canal Mental foramen

77

ix Contents

Sublingual fossa Mental ridges Lingual foramen Genial tubercles Nutrient canals

IX ANATOMIC STRUCTURES IN EXTRAORAL RADIOGRAPHS

91

Mandibular ramus Gonion Antegonial notch Mandibular condyle Temporomandibular joint Glenoid fossa (temporal bone) Eminentia articularis External auditory meatus Mandibular (sigmoid) notch Mandibular foramen Vertebrae Styloid process Hyoid bone Epiglottis

X LANDMARKS IN PANORAMIC RADIOGRAPHS 97 Vertebrae " G h o s t " shadows Soft palate Tongue Oropharyngeal space

χ CONTENTS

XI SELF-STUDY EXERCISES

109

REFERENCES AND SUGGESTED READING

121

Preface Ever since Dr. O t t o Walkoff exposed the first dental radiograph (a glass photographic plate, wrapped in black paper and covered with rubber dam, and exposed for 25 minutes!) only 14 days after Professor Roentgen had announced his epochmaking discovery of χ rays, the dental profession has attempted to produce radiographs yielding the highest degree of diagnostic information with the least expenditure of radiation. Our current name for this concept is "radiographic quality assurance." No matter how perfect the radiograph may be, the art of interpreting the images registered in the emulsion rests primarily upon a thorough understanding of the appearance of normal anatomic landmarks. Determination of the region depicted on the film depends upon recognition of normal landmarks, and also an understanding of the range of normal known to exist for each structure. O n c e this has been learned, and only then, can deviations of form, structure, and density be recognized, and their nature, extent, stage, and severity be assessed. An attempt has been made to enhance the straightforward description of normal landmarks in both text and illustrations by reference to clinical situations in which their incorrect recognition could lead to serious consequences. Citations in the text relate to a carefully selected group of references revealing important and/or unusual appearances of normal structures. Welcome to the fascinating world of radiologic interpretation! Your introduction will be enhanced by the inspired art work and photography of Elissa Berardi and David Sullivan, respectively, to whom the author is deeply indebted.

Illustrations FIGURE

PAGE

1A

3

R a d i o g r a p h o f w a t e r (ice)

IB

3

R a d i o g r a p h o f w a t e r (ice)

2

5

R a d i o g r a p h o f fat

3

5

R a d i o g r a p h o f fat; m u s c l e

4

6

Radiograph of bone

5

6

Radiograph of b o n e and muscle

6

7

Radiographs of bone; bone and muscle

7

15

Gomphosis: the dental articulation

8

16

Hypercementosis; calculus

9

17

L a m i n a dura

10

19

Developmental crypts

(Figures 1-6, courtesy of Dr. James £

Phillips)

11

20

Developmental crypts

12

21

W i d e i n t e r d e n t a l s e p t a ; a n g u l a r crests

13

22

Frail i n t e r d e n t a l septal crests; b o n e a r c h i t e c t u r e

14

23

P o i n t e d vs. flat i n t e r d e n t a l s e p t a l crests

15

24

C e r v i c a l b u r n o u t ; residual root

16

25

R e l a t i o n s h i p o f o b j e c t q u a n t i t y to r a d i o g r a p h i c

17

29

density Hamular process; developmental crypt

18

31

Posterior maxillary landmarks

19

32

Posterior maxillary landmarks

20

33

Posterior maxillary landmarks

21

35

Posterior maxillary and mandibular landmarks

22

37

Posterior maxillary landmarks

23

41

Alveolar and tuberosity extensions of the maxillary sinus

24

43

Alveolar, tuberosity, and palatine extensions of

25

45

Palatine e x t e n s i o n s o f the maxillary sinus

26

46

M a x i l l a r y sinus septum;

27

47

B o n y nodule (osteophyte) on maxillary s i n u s wall

the maxillary sinus flexed-cheek

shadow

xiv ILLUSTRATIONS

FIGURE

PAGE

28

49

Nutrient canal

29

50

Nutrient canal

30

51

F l e x e d - c h e e k s h a d o w ; gingival tissue

31

53

Illustration of the superimposition of structures in t h e third dimension (depth) in t h e maxillary molar region

32

55

Typical " Y " landmark

33

59

Landmarks visualized in a maxillary midline occlusal radiograph

34

60

Anterior maxillary landmarks

35

61

Anterior maxillary landmarks

36

65

Anterior maxillary landmarks

37

66

Anterior maxillary landmarks

38

67

Premaxillary suture

39

69

M o v e m e n t of incisal foramen image

40

71

Nasolacrimal canal; supraorbital ridge

41

73

D i a g r a m m a t i c illustration relating maxillary anatomic structures to their radiologic images

42

75

Diagrammatic

illustration relating

maxillary

a n a t o m i c structures to their radiologic images 43

79

External o b l i q u e line; m y l o h y o i d ridge

44

81

Illustration of undercut potential o f m y l o h y o i d

45

83

M a n d i b u l a r canal

ridge 46

85

Mental foramen

47

86

M e n t a l ridges

48

87

Lingual f o r a m e n

49

88

Genial tubercles

50

89

Genial tubercles

51

90

Nutrient canals

52

93

T e m p o r o m a n d i b u l a r j o i n t ( T M J ) , transcranial projection !Courtesy Dr. Robert fV. Beidemanj

XV Illustrations

FIGURE

PAGE

53

95

54

101

C o n t i n u o u s cycle panoramic radiograph

55

103

L e f t half of interrupted cycle panoramic radiograph

56

105

Interrupted cycle panoramic radiograph

57

107

Continuous cycle panoramic radiograph demonstrating " g h o s t " s h a d o w phenomenon !Courtesy Dr. Edward P. Henefer and Dr. James E. Phillips)

Landmarks seen in lateral extraoral projection of the left mandible

I Introduction

2 RADIOLOGIC

ANATOMY

OF THE

JAWS

As in any discipline, radiology in general and dental radiology in particular has its own terminology. T h e broad term radiology is defined as the science of radiant energy; however, in our area of usage it refers to the particular science of ionizing radiation as produced in an x - r a y tube. Ionizing radiation consists of short-wave, high-frequency radiant energy which has the ability to cause three basic effects: 1.

It can cause certain salts to fluoresce.

2.

It can darken photographic emulsions.

3.

It can bring about biologic changes in living tissue.

It accomplishes all of these p h e n o m e n a by displacing electrons (negatively charged particles) from their orbital rings in atoms, to form ions; hence the name ionizing radiation. T h a t certain salts can be made to fluoresce is the basis for fluoroscopy and for the fluorescent intensifying screens employed to intensify the exposure of extraoral films used in cassettes; the darkening of photographic emulsions is the principle used in producing x - r a y pictures, called radiographs or roentgenograms; and the production of biologic effects is the rationale for using high doses of χ rays, gamma rays, and radium to kill malignant cells. T h e latter is also a phenomenon which we strive to minimize in the routine usage of χ rays to produce radiographs. All of these phenomena are covered in greater detail in the standard dental radiology texts. 2 - 4 Since our bodies are composed to a great degree of water, and of muscle, fat, and bone, the concept of radiography can be illustrated by passing χ rays through an ice cube, a piece of meat, a chunk of suet (fat), and a slice of soup b o n e from the

3 Introduction

butcher shop, and recording their images on dental x-ray films. Since water in its liquid state would require a container, and since the container itself would absorb some of the incident radiation, frozen water was used for the example. T h e resulting radiograph, Figure 1A, shows the ice cube as a lighter or gray shadow surrounded by the black borders of the x-ray film. T h e rays which struck the film without passing through the ice cube caused complete blackening of the emulsion and produced a radiolucent image. T h e rays which struck the ice cube were partially absorbed by the H 2 0 molecules; with fewer χ rays reaching the emulsion behind the ice cube, less blackening of the emulsion occurred, producing a lighter, or relatively radiopaque, image. Note also that the image of the ice cube is not of a uniform shade, or density; there is a somewhat round area (m) that is slightly darker (relatively radiolucent) than the rest of the radiopaque cube. T h i s is a spot where the heat of the t h u m b caused a slight melting, or a reduction in quantity, of the ice. W h e n the cube is turned, (Fig. I B ) , the slightly recessed, melted area is visible (m) on the right side of the cube.

A.

With melted spot, m, facing x-ray tube

B.

Ice cube turned to show melted spot, m, on side of ice cube

4 RADIOLOGIC

ANATOMY

Figure 1, then, introduces

OF

THE

JAWS

t h e terminology of radiolucency

(darker images) and radiopacity (lighter images), and t h e concept that these terms are relative in nature; and that t h e y d e p e n d u p o n the quantity of the material or structure t h r o u g h w h i c h t h e y pass. It also introduces t h e concept of t h e p r o d u c t i o n of a two-dimensional radiographic image of a three-dimensional object (ice cube). In Fig. 1A, t h e cube w a s placed u p o n t h e film packet w i t h t h e melted spot (m) at t h e top, or nearer to the x - r a y tube. T h u s , t h e rays passed first t h r o u g h t h e edge w i t h t h e m e l t e d area, t h e n t h r o u g h the rest of t h e cube. T h e melted area, t h e n , w a s superimposed over t h e greater substance of t h e cube, a n d is recognized in the resultant radiograph as a slightly radiolucent (or less radiopaque) r o u n d e d area within t h e m o r e r a d i o p a q u e image of the cube. Each layer, or plane, of t h e ice c u b e that lies perpendicular to the path of the x-ray beam (i.e., the third dimension) is compressed into one flat, two-dimensional image in the film emulsion. In Fig. IB, t h e cube has been t u r n e d so that t h e melted area (m) is on t h e right side, rather t h a n on t h e top surface, and t h e margin of the area (m) is clearly defined. T h u s , t h e concepts of superimposition a n d the passage of rays in a different direction h a v e been introduced a n d illustrated. Figure 2 is a radiograph of a piece of fat (E) placed on t h e film packet. It, too, results in a slightly r a d i o p a q u e (lighter) image, as compared w i t h t h e s u r r o u n d i n g black film e m u l s i o n . N o t e that there is an even more r a d i o p a q u e zone r u n n i n g across it. This w a s produced by a second piece of fat w h i c h w a s laid across t h e first, again s h o w i n g t h a t a greater quantity p r o d u c e s a more radiopaque image. This is because the greater t h i c k n e s s resulted in greater a b s o r p t i o n of x - r a y energy; t h a t is, f e w e r χ rays reached the emulsion to d a r k e n it. (See also Fig. 16.)

5 Introduction

Ε Figure 2. Radiograph of a piece of fat, E. On the left side there is a second piece of fat overlaying the large piece. Figure 3 shows a piece of fat (E) and a piece of meat (M) side by side. Note that the meat is slightly lighter (more radiopaque) than the fat. This illustrates the principle that the degree of radiopacity is influenced also by the density of the object, as well as by the quantity.

Figure 3.

Radiograph of pieces of fat, E, and muscle, Μ

6 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 4 is a radiograph of a section of long bone. Note the very radiopaque, homogeneous band of cortical bone along one edge, and the finely detailed radiopaque trabeculae and adjacent radiolucent medullary spaces. Figure 5 is a radiograph of a second section of bone with a piece of muscle (meat) attached. The relative radiopacity of bone indicates that bone is more dense than muscle tissue. Figure 6 (right) shows the section of bone that was seen in Figure 4, but on the left is another section of bone covered by muscle. Note that the image of the muscle-covered bone shows far less detail than the bare bone. The absorption (scattering) of χ rays in the muscle has

7 Introduction

obliterated much of the bony detail, illustrating how superimposition of tissues can detract from detail.

Figure 6. Section of bone with muscle superimposed on left, section of bone alone on right. Note difference in bone detail. With this knowledge of the production of radiolucent and radiopaque images, and of the influence of quantity and density of the object, and of the effect of quantity, density, and superimposition of tissue layers upon detail, we may now proceed to the radiographic appearance of normal anatomic structures of the jaws. It must be kept in mind that each successive layer of skin, fat, and muscle of the cheek, the oral mucous membrane, the bone, and the teeth which are situated within the path of the χ rays will be compressed by superimposition into one final image on the film. (See Fig. 30.) From this final image composed of varying degrees of radiographic density (radiolucency-radiopacity), the radiologist must draw his/her interpretation of the shape, density, and position (spatial relations) of the structures which produced it.

II The Logic in Radiologie Interpretation

10 RADIOLOGIC

ANATOMY

OF T H E

JAWS

Disease conditions depicted in radiographs represent alterations of tissues from their normal state. It goes without saying, therefore, that a thorough understanding of normal radiologic anatomy must precede a study of pathologic conditions. Stated differently, intelligent radiologic diagnosis cannot be attempted without knowledge of the normal appearance of the anatomic structures involved. Treatment decisions must be based upon accurate diagnosis, which depends upon the patient's history, clinical and laboratory examination, and radiologic interpretation. Only when these are carried out in an orderly process can the accurate diagnosis be achieved. A contribution to such an orderly procedure was devised by the author in 1963 to provide a radioLOGIC interpretation. 1 This is a progression of steps from the first glance at the radiograph to its final interpretation, and thence to its incorporation into the diagnosis: localization of the anatomic area depicted; Observation of the images of normal, malformed, or pathologic structures in the radiograph; General consideration of the meaning of the observations; /nterpretation of the radiographic images; Correlation of radiologic interpretation with history, clinical examination, and laboratory findings to arrive at a Diagnosis. (C may also cause one to reflect upon the Consequences of a faulty interpretation, which could lead to an inaccurate diagnosis and improper treatment!)

11 The Logic in Radiologic Interpretation

Radiographic interpretation is difficult at best, but impossible if carried out in haphazard fashion, with improper viewing conditions, or with preconceived ideas which can lead to reading error into the film. A prominent light or dark shadow tends to command attention, often at the expense of other important images. To avoid such errors, the diagnostician must use a good source of even, diffused light of proper intensity, and be certain that the films are mounted correctly for right or left sides, and for maxillary or mandibular arches. When teeth are present, such L ocalization is relatively easy, but for edentulous areas an expert knowledge of anatomic landmarks is essential. This requires attentive Observation of the radiographic images which delineate these structures: their presence or absence, their density (radiopaque or radiolucent?), their size and relative positions, their shape (normal or altered?). Just as there are variations in the size and shape of individuals, so are there variables in the radiographic appearance of normal anatomic landmarks. Furthermore, a person who displays all the radiographic landmarks to be discussed in this book would be a distinct rarity. Therefore, the absence of one or several landmarks in the radiographs of any individual should not be considered abnormal. The scope of this book is limited to the recognition of normal anatomic landmarks, and does not cover the field of diagnostic radiology; that is left to other publications. 2 ^ 1 Thus, we shall deal here with the recognition of normal anatomic landmarks upon which interpretation, diagnosis, and treatment depend.

III The Dental Articulation— Gomphosis

14 RADIOLOGIC

ANATOMY

OF

THE

JAWS

T h e scientific term for the dental articulation is gomphosis—the fitting of a tooth in a socket (alveolus) in the bone (alveolar process) (Fig. 7). T h e bulk of the tooth is composed of dentin, the crown surface of which is covered by enamel, and the root portion of which is covered by a thin layer of cementum. Enamel is more dense, and hence more radiopaque, than dentin, but cementum is usually too thin to be differentiated radiographically from dentin; the exception occurs in hypercementosis (Fig. 8), in which unusual thicknesses of cementum are laid down, giving the root a bulbous appearance. T h e tooth is attached to the socket wall (lamina dura) by periodontal ligament fibers embedded on one side in cementum and on the other in the lamina dura. 5 - 6 T h e periodontal ligament, being soft tissue, is radiolucent, while the lamina dura, a calcified cribriform plate, is radiopaque. T h e degree of its radiopacity depends upon (1) the density of the plate, which in turn can vary according to the forces applied; (A tooth in overfunction would tend to show a heavier radiopaque image, while the lamina dura of a tooth out of occlusion would be very difficult to visualize. In fact, when a tooth is extracted, the lamina dura atrophies and disappears completely.) (2) the amount and density of alveolar bone superimposed over, and thus obscuring, the lamina dura; and (3) the angle of the x-ray beam through the lamina dura. In the case of the premolar and molar teeth (Fig. 9), the lamina dura lining the mesial or distal side of a socket may be 0.5 cm or more in depth. If the rays are projected directly through the structure, it will appear very radiopaque and well defined, whereas a beam projected obliquely through the lamina dura may show very little evidence of its presence.

15 The Dental

F i g u r e 7.

Articulation—Gomphosis

M a n d i b u l a r left premolar periapical radiograph

CV

cervical burnout areas

LD

lamina dura

MF

mental foramen

NC

nutrient canals carrying neurovascular bundles to the apical foramina of the first molar roots

PS

periodontal space, occupied by the tissues of the periodontal ligament

16 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 8. Maxillary left molar periapical radiograph; third molar is missing. AW anterior wall of the maxillary sinus CL

calculus deposit on second molar

CP

coronoid process of the mandible, the tip being superimposed over the maxillary alveolar bone

ED

embossed dot

TC

fractured cusp tip, simulating a lesion of dental caries

HC

hypercementosis, producing a bulbous root

MP

malar process of the maxilla; a is anterior plate, ρ is posterior plate.

MR

metallic restorations

MSF maxillary sinus floor RM

roof of the mouth (hard palate)

Ζ

lower edge of zygoma

17 The Dental

Articulation—Gomphosis

Figure 9. LEFT: Mandibular right molar periapical radiograph. Notice the clear lamina dura along the mesial root of the first molar, while the lamina dura surrounding the second premolar is barely perceptible. RIGHT: In the right premolar radiograph, a slight change in horizontal tube angulation has rendered unclear the lamina dura along the first molar mesial root, while the lamina dura around the second premolar and along the distal of the first premolar become sharp. (Note, also, the pulpal calcifications, or pulp stones, in the teeth.) EO

external oblique line

MC mandibular canal SB

sclerotic bone formation

18 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Prior to eruption, the teeth develop in chambers within the bone called developmental crypts, the walls of which are sufficiently calcified to present a radiopaque image (Figs. 10, 11). The crests of the interdental septa under normal conditions present a smooth, well-organized appearance, sometimes with a radiopaque border. Patients who possess alveolar processes composed of rugged, quite radiopaque trabeculations usually also show thick, radiopaque margins of their interdental septa (Fig. 12); while individuals with frail, less heavily trabeculated alveolar bone tend to show septal crests of similar density (Fig. 13). The shapes of tooth crowns play a role in the shapes of the interdental septal crests. When the proximal surfaces of the crowns of adjacent teeth are nearly parallel, there is not sufficient space for a great width of bone between the teeth, hence the septa will be thin and the crests will not have great width; in fact, in such instances, between the mandibular incisors the crests will be pointed (Fig. 14, left). On the other hand, with approximating teeth whose crowns flare, the roots will be farther apart and the interdental septa correspondingly wider; the crests in these cases will appear flat or blunt (Fig. 14, right). Under normal conditions the crestal surfaces of the interdental septa run parallel with imaginary lines projected between the proximal cemento-enamel junctions (CEJ) of adjacent teeth. (See Fig. 12.) When two adjacent CEJs are at different levels, "angular crests" result.

19 The Dental Articulation—Gomphosis

BWC

Figure 10. Mandibular left canine periapical radiograph of a patient with mixed dentition BWC bony wall (radiopaque) of the developmental crypts CT radiolucent space occupied by connective tissue forming the pulp and root DCC developmental crypt (radiolucent) around the crowns of the unerupted permanent canine and premolars. The crypts contain the tooth follicles. DCR developmental crypt (radiolucent) around the root of the permanent canine OT overlapping tooth shadows R calcifying root structure of the permanent canine

20 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 11. Left b i t e - w i n g of a patient having a mixed dentition ( s o m e p e r m a n e n t as w e l l as d e c i d u o u s t e e t h are in place). CF

creased film marks

DC

developmental crypt premolar crowns

images

LDC occlusal lesion of dental caries

surrounding

developing

21 The Dental

F i g u r e 12.

Articulation—Gomphosis

Right premolar bite-wing radiograph

AC

angular crests of the interdental septa. The slant of the crests parallels imaginary lines connecting the CEJ's of adjacent teeth.

ED

embossed dot (Note: the crowns flare, creating wide spaces and broad septal crests.)

22 RADIOLOGIC

Figure 13.

ANATOMY

OF

THE

JAWS

M a n d i b u l a r right premolar periapical radiograph

BT

bony trabeculation

D

dentin

Ε

enamel

IS

interdental septum of the alveolar process

LD

lamina dura: the radiopaque line depicting the "hard layer" of bone lining the tooth socket

MD medullary space in the bone MF

mental foramen

MR

metallic restoration

Ρ

pulp chamber (in the crown)

PC

pulp canal (in the root)

PS

periodontal space: dark line surrounding the tooth root, occupied by the periodontal ligament

PST pulp stone: calcification within the pulp

23 The Dental Articulation—Comphosis

Figure 14. Mandibular incisor periapical radiographs LEFT: Proximal incisor crown surfaces are nearly parallel, leaving little space between the roots, and resulting in narrow interdental septa with pointed crests (IS). RIGHT: Proximal incisor coronal surfaces are flared, resulting in wide interdental septa with broad, flat crests (is). Both are variations of normal.

24 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 15. LEFT: Maxillary left canine periapical radiograph showing shadows of cervical burnout on the distal of the canine and the mesial of the first premolar. RIGHT: Maxillary left premolar periapical radiograph showing how the areas of cervical burnout disappear when the χ rays are projected directly (rather than obliquely) along the proximal surfaces of the same teeth. (Note, also, that the crown of the premolar has been prepared for an artificial crown.) BR

buccal root of the premolar

CV

cervical burnout radiolucent areas

MP

base of the malar process of the maxilla

MS

recess of the maxillary sinus

MSF maxillary sinus floor PR

palatal root of the premolar

RR

residual root fragment

25 The Dental

χ rays

Articulation—Gomphosis

I I 11 I 11 i I

object

film

Figure 16. density

3Ü

Relationship of object quantity to radiographic

LEFT: X rays passing through twice as much structure are absorbed to a greater extent and produce a lighter (radiopaque) image than the thinner part. CENTER: The thin edge of the wedge absorbs fewer χ rays than the thick edge, resulting in a darker (radiolucent) image. RIGHT: An elliptical object, such as the cross-section of a tooth root in the cervical region, will produce radiolucent images at the thin edges. Known as cervical burnout, these radiolucencies can mimic carious lesions.

26 RADIOLOGIC

ANATOMY

OF THE

JAWS

O n the proximal surfaces of the teeth, between the CEJ and the alveolar bone crest, the cervical edge of the tooth may appear radiolucent, often mimicking a lesion of cervical (or cemental) dental caries. T h i s radiolucent area, called cervical burnout (Fig. 15), or cervical radiolucency, is produced by (1) the relative radiolucency of the dentin appearing darker, in contrast to the adjacent lighter enamel on one side and bone on the other, and (2) the passage of χ rays through the thin edge of the root, (Fig. 16) where relatively less absorption of radiant energy takes place than through the adjacent internal portion of the root, where the bulk of dentin is greater.

IV Maxillary Intraoral Radiograph Anatomy

28 RADIOLOGIC

ANATOMY

OF

THE

JAWS

T h e most posterior anatomic landmark seen in intraoral radiographs of the maxilla is the hamular process (Figs. 1 7 - 2 0 ) of the medial pterygoid plate of the sphenoid b o n e . 7 - 1 1 This plate, lying against the posterior surface of the maxilla, terminates in a small bony process which appears directly behind the maxillary tuberosity. When thin, it has the appearance of a bony spicule; occasionally it may be thicker and in some cases may have a rounded, bulbous end. A ligament of the tensor palati muscle glides around the hamulus; thus the hamulus functions somewhat as a pulley for this muscle. Long hamular processes have on rare occasions caused swelling and pain. O n e case has been reported of fractures of both medial pterygoid plates (above the level of the hamulus) in an automobile accident, without accompanying fractures through the posterior walls of the maxillary sinuses. 1 0 T h e duct of the parotid gland, called Wharton's duct, lying superficially and laterally to the plane of the pterygoid hamulus, has on occasion contained a salivary stone (sialolith) which has appeared in periapical radiographs directly over the hamular process, and which has been interpreted as being a part of it. Since they are some distance apart, however, taking a second radiograph with the rays projected in a slightly different horizontal direction will usually separate the shadows of the sialolith and the hamulus. T h e wing of the lateral pterygoid, plate sometimes may be visualized radiographically as a small, fairly broad, often diffuse, triangular radiopacity, running off the upper posterior corner of the film (Fig. 18). Because it is situated farther from

29 Maxillary Intraoral Radiographic Anatomy

F i g u r e 17.

Left m o l a r b i t e - w i n g radiograph

DC

developmental crypt surrounding the crown of the unerupted third molar

ED

embossed dot

HP

hamular process of the medial pterygoid plate

LDC lesions of dental caries

30 RADIOLOGIC

ANATOMY

OF T H E

JAWS

the periapical film than the hamulus, it presents a less sharp image. The lower posterior corner of maxillary molar periapical films often includes the image of the coronoid process of the mandible (Figs. 1 8 - 2 1 ) . 1 2 - 1 5 Usually triangular in shape, it most often presents the homogeneous structure of cortical bone, but occasionally may also show internal trabecular patterns (Fig. 20). The coronoid tip may be pointed, blunt, or rounded. Its image is often seen superimposed over the molar alveolar bone and must be distinguished from a residual root of a molar tooth (Figs. 21-22). The appearance of the coronoid process in maxillary molar radiographs results from the forward and downward position of the mandible when the mouth opens (Fig. 21, top). Therefore, the coronoid processes need not be unusually long to appear radiographically, but large processes can present quite dramatic images. 16 It is generally thought that bilaterally enlarged coronoids are normal variants, while a unilateral enlargement probably represents a tumor, e.g., osteoma. Strange as it may seem, several reports in the literature describe misplaced teeth which have grown in the coronoid process. 13 · 14 Studies also show that 1 - 2 % of facial fractures include those of the coronoid process, even though it is sheltered beneath the zygomatic arch. Several cases of iatrogenic fractures have been reported, the coronoid process being fractured during the extraction of maxillary and mandibular third molars. 15

31 Maxillary Intraoral Radiographic Anatomy

Figure 18.

Maxillary right molar periapical radiograph

CP

coronoid process of the mandible

ED

embossed dot

HP

hamular process of medial pterygoid plate

MP

malar process of the maxilla; a is the anterior plate, ρ is the posterior plate.

MSF maxillary sinus floor MSS maxillary sinus septum MT

maxillary tuberosity

PW

pterygoid wing of lateral pterygoid plate

RR

residual root fragment of the extracted second molar, the third molar having migrated anteriorly into the second molar space

Ζ

lower border of the zygomatic arch

32 RADIOLOGIC

Figure 19.

ANATOMY

OF

THE

JAWS

Maxillary left molar periapical radiograph

AW

anterior wall of the maxillary sinus

AX

alveolar extension of the maxillary sinus

CP

tip of the coronoid process of the mandible, superimposed over the maxillary tuberosity

MP

malar process of the maxilla; a is the anterior plate, ρ is the posterior plate.

MS

deep recess of the maxillary sinus

MT

maxillary tuberosity

NFF nasal fossa floor, which is also the roof of the hard palate PT

wing of the lateral pterygoid plate

PW

posterior wall of the maxillary sinus

Ζ

inferior border of the zygoma

33 Maxillary Intraoral Radiographic Anatomy

Figure 20.

M a x i l l a r y left m o l a r periapical r a d i o g r a p h

AW

anterior wall of the maxillary sinus

CP

coronoid process tip; note that this particular coronoid process shows trabeculated (cancellated) bone in its interior, with cortical bone on the surface. Many do not show cancellated structure.

ED

embossed dot

HP

hamular process of medial pterygoid plate

MP

malar process of the maxilla; a is the anterior plate, ρ is the posterior plate.

MR

metallic restoration

MSF maxillary sinus floor PW

posterior wall of the maxillary sinus

Ζ

lower border of zygomatic arch

34 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 21. Combination of a maxillary left molar periapical radiograph (top), left molar bite-wing (center), and mandibular left molar periapical radiograph (bottom), illustrating the continuity of posterior anatomic landmarks BWTbite-wing tab CP

coronoid process of the mandible

EO

external oblique line

HP

hamular process of medial pterygoid plate

IB

inferior border of the mandible

MC

mandibular canal border

MP

malar process of the maxilla; a is the anterior plate, ρ is the posterior plate.

MSF maxillary sinus floor PW

wing of the lateral pterygoid plate

RA

ramus of the mandible

35 Maxillary Intraoral Radiographic Anatomy

36 RADIOLOGIC

ANATOMY

OF

THE

JAWS

The rounded bony posterior termination of the maxillary alveolar process is known as the tuberosity (Fig. 18). 1 7 It may be occupied by the third molar, 1 8 by trabecular bone, and/or by a tuberosity extension (See Fig. 23) of the maxillary sinus. Fracture of the tuberosity is a complication to be avoided during the extraction of certain third molars, or even of first or second molars, when deep alveolar and tuberosity extensions of the sinus exist. In these cases the alveolar bone, although lacking in quantity, is strong and heavily mineralized. In such cases the thinnest and weakest area of the bone is the buccal plate at approximately the level of the root apices, and it is here that fracture may occur. This can generally be prevented by careful interpretation of the radiograph and proper surgical technique. The prominent bone of the cheek is the zygoma, the temporal process of which extends posteriorly to meet the zygomatic process of the temporal bone, thereby forming the zygomatic arch. The zygoma and its temporal process lie laterally to the maxilla but nevertheless within the path of the x-ray beam when maxillary molar periapical film exposures are made. Because of its increased distance from the film, the zygoma thus projects a broad, somewhat hazy radiopaque band extending posteriorly across the upper portion of the radiograph (Figs. 20, 22). When the rays can be projected with a flat vertical angle (nearly parallel with the occlusal plane), the zygomatic arch image may not appear on the film, or may be visible only along its upper edge. With steeper vertical angles, however, it will be projected closer to the middle or even to the lower border of

37 Maxillary Intraoral Radiographic Anatomy

Figure 22. Maxillary right molar periapical radiograph. T h e molar region is e d e n t u l o u s ( w i t h o u t teeth). AW anterior wall of the maxillary sinus CP coronoid process of the mandible, the tip superimposed over the maxillary alveolar process ED embossed dot G faint shadow of the gingival tissue MP malar process of the maxilla; a is the anterior plate, ρ is the posterior plate of the process MR metallic restoration (crown) on a premolar MSF maxillary sinus floor NTC nutrient canal (or channel) in lateral wall of the maxillary sinus Ζ lower border of the zygoma

38 RADIOLOGIC

ANATOMY

OF THE

JAWS

the radiograph; in these instances its shadow will tend to obscure the molar root images. The anterior portion of the zygoma is marked radiographically by a radiopaque V- or U-shaped image, which is actually produced by the zygomatic (or malar) process of the maxilla. (See Figs. 18, 19, 20, 22.) This process juts out laterally from the surface of the maxilla above the first molar and consists of slanted anterior and posterior plates of cortical bone; the space between the plates is hollow and occupied by the zygomatic extension of the maxillary sinus. The plates, extending as they do approximately at right angles to the midsagittal plane, are in the same plane as the x-ray beam, when molar and premolar periapical films are being made. Since the rays pass directly through a centimeter or more of these cortical plates, they register as heavy radiopaque images on the film. To identify the area of the mouth seen in edentulous films, recognition of landmarks is essential. In posterior maxillary films the tuberosity, the coronoid process, and/or the hamular process will identify the posterior side of the radiograph. Additionally, the hazy radiopaque band of the zygoma always swings posteriorly from the V-shaped malar process (Fig. 22).

ν

40 RADIOLOGIC

ANATOMY

OF THE

JAWS

Through the process of pneumatization the b o d y of the maxilla becomes hollow, the chamber being k n o w n as the maxillary s i n u s . 1 9 - 2 2 It presents as a radiolucent shadow with radiopaque borders, which represent the walls and floor o f the sinus. (See Figs. 18, 19, 20, 22.) As a rule of thumb, t h e floor o f the sinus in dental radiographs will be seen at approximately the level of the floor of the nasal fossa around the age of puberty; subsequently, the sinus may extend in any or all of five directions: alveolar, tuberosity, zygomatic, palatine, and

infra-

orbital. A comparative study of aging skulls showed that paranasal sinuses increase in size over a lifetime. 2 0 T h e alveolar extension is recognized by the close proximity of the sinus floor to the roots of the molar, often the premolar, and occasionally the canine teeth; indeed, in many cases the floor of the sinus may seem to " f l o w " over the root apices and down along roots to the cervical regions of the teeth (Figs. 20, 23). Following extraction of such teeth and subsequent resorption of the alveolar process, the floor will appear at the very edge of the alveolar margin. T h e alveolar extension can be seen only in maxillary molar and premolar (and in rare cases, canine) periapical radiographs, not in incisor films. Rosen and Sarnat demonstrated that the extraction of a dog's teeth adjacent to the maxillary sinus caused the sinus to increase in size from 4 . 6 % to 2 7 % . 2 2 T h e y suggest, therefore, that if, at the time of extraction of molar teeth, an alveolectomy may be predicted as a future possibility in preparation for dentures, the alveolectomy should be performed in c o n j u n c tion with the extractions. If alveolectomy is done at a later date, after excessive pneumatization of the alveolar process has

41 Maxillary

Sinus

Figure 23. M a x i l l a r y left m o l a r periapical radiograph illustrating alveolar and tuberosity extensions of the maxillary sinus AX CP

a l v e o l a r e x t e n s i o n of maxillary sinus anterior border of coronoid process of the m a n d i b l e , superi m p o s e d o v e r the t u b e r o s i t y and the sinus

HP

h a m u l a r process of medial p t e r y g o i d plate

M S S m a x i l l a r y sinus s e p t u m MT

maxillary tuberosity

OE

o v e r l a p p i n g e n a m e l of molars

TX

t u b e r o s i t y e x t e n s i o n of maxillary sinus

42 RADIOLOGIC

ANATOMY

OF

THE

JAWS

taken place, surgical correction may not be possible for fear of breaking into the maxillary sinus. Large alveolar and tuberosity sinus extensions may also negate treating a patient with endosteal implant (e.g., "blade-vent") prostheses. 2 3 - 2 4 The tuberosity extension fills the alveolar bone posterior to the second and third molars and extends to the posterior border of the maxillary tuberosity (Figs. 23, 24). It can be visualized only in molar periapical or specially angled occlusal radiographs. The tuberosity extension seldom occurs without a deep alveolar extension as well, and must be recognized prior to tooth extraction to prevent fracture of the entire tuberosity. It would be helpful at this point to perform Self-Study Exercise 1. The zygomatic extension is a hollowing of the zygomatic (or malar) process of the maxilla, between the plates which form the V- or U-shaped image previously discussed. Its lateral extent can be visualized best in maxillary occlusal films (Fig. 33). The palatine extension usually accompanies very large sinuses which have extensions in all five directions. It is characterized by an extension of the sinus toward the midline (Fig. 25), and is visualized in anterior periapical radiographs and midline occlusal projections (Fig. 41). It must be understood that although the sinuses are usually somewhat similar in size and shape on both the right and left sides of the face, such is not always the case, and that different

43 Maxillary Sinus

Figure 24. Maxillary periapical radiographs of a patient exhibiting exceptionally large maxillary sinuses bilaterally, with large tuberosity extensions, deep alveolar extensions, and the suggestion of palatine extensions in the central incisor radiograph. See fig. 25, an occlusal radiograph of the same patient, showing the extent of the palatine extensions, especially on the patient's left side.

44 RADIOLOGIC

ANATOMY

OF THE

JAWS

sizes per se are not a valid reason for inferring that one side is pathologic. Occasionally a maxillary sinus is of a uniform depth and will therefore present a uniformly

radiolucent

image, but more often the walls have ridges and depressions which result in some recessed areas being more or less radio lucent than others. Frequently the sinuses are traversed vertically by thin bony septa, recognized in the radiograph as sharp radiopaque spines which appear to divide the sinus into separate chambers (Fig. 2 6 ) . 2 5 Not infrequently bony nodules (osteophytes) arise from the floor or walls of the sinus and are revealed as radiopaque objects (Fig. 27). Since they are covered with the same dense bone as that which forms the sinus walls, some nodules may resemble tooth apices. However, the inner substance of a bony nodule nearly always shows trabecular bone beneath the outer layer of dense cortical bone; this contrasts with a fractured tooth root, 2 6 which presents the homogeneous (nontrabeculated) density of dentin (and may also show a root canal). Additionally, the base of a bony nodule blends into the sinus wall so that a complete outline cannot be visualized, whereas a root fragment will show a complete, sharp border around its entire periphery. The maxillary sinus walls are also traversed by canals, channels, or grooves which carry neurovascular bundles to supply the sinus lining, the teeth, bone, and gingivae. These radiolucent vascular markings are called nutrient canals. 2 -

27-29

(See

Fig. 22.)

It would be helpful at this point to perform Self-Study Exercise 2.

45 Maxillary Sinus

Figure 25. Maxillary midline occlusal radiograph; same patient as the maxillary periapical radiographs in fig. 24. There are bilateral palatine extensions of the maxillary sinus, the one on the patient's left side extending nearly to the midline. ANS CC IF LW MPS MS PX

anterior nasal spine cone-cutting (edge of the cone of radiation) incisal foramen lateral wall of the nasal fossa median palatine suture maxillary sinus medial wall of palatine extension of the maxillary sinus

46 RADIOLOGIC

F i g u r e 26.

ANATOMY

OF

THE

JAWS

M a x i l l a r y left premolar periapical radiograph

AW anterior wall of maxillary sinus AX

alveolar extension of maxillary sinus

FL

flexed-cheek

MS

deep recess of maxillary sinus

shadow

MSS maxillary sinus septum NFF nasal fossa floor (Note the extent to which the premolars are rotated.)

47 Maxillary

F i g u r e 27.

Sinus

Maxillary right premolar periapical radiograph

AW anterior wall of maxillary sinus AX

alveolar extension of maxillary sinus

BN

b o n y nodule (osteophyte) on wall of maxillary sinus

MP

malar process, posterior plate

MSF maxillary sinus floor MSS maxillary sinus s e p t u m NFF nasal fossa floor Ζ

lower edge of zygoma

48 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Prominent foramina of large nutrient canals are commonly seen in radiographs as round radiolucent spots near the apices of maxillary canines and second incisors. When they appear directly above the root apices they must not be misinterpreted as apical rarefactions of a pathologic nature, and where they appear over the root itself, they must be differentiated from internal resorption (Fig. 28). In both cases the observer must look for the canal which leads to the foramen to make the differential interpretation. Taking a second film using a slightly different horizontal and/or vertical tube angle may help to separate the nutrient foramen shadow from the tooth, if, indeed, there is any anatomic distance between them. When it has been determined that the foramen is actually in close proximity to the tooth, special care must be exercised if that tooth is to be extracted, for the vessels contained therein may be torn and severe bleeding may ensue (Fig. 29). Occasionally a faint, radiopaque shadow may be seen superimposed over the maxillary premolars or canine, its sharp anterior edge slanting posteriorly from the upper edge of the film, in oblique fashion. This is the shadow of the side of the upper lip, stretched when the cheek is flexed to accommodate the periapical film and its holder apparatus. The flexed-cheek shadow (Figs. 26, 30) is more often seen when the premolar region is edentulous, when the tooth images are not present to overwhelm the soft tissue shadow of the cheek. Ennis has emphasized the importance of that anatomic landmark created by the confluence of the lateral and anterior walls of the nasal fossa with the anterior wall of the maxillary sinus. 2

49 Maxillary

F i g u r e 28.

Sinus

Maxillary left second incisor-canine radiograph

ED

embossed dot

MS

maxillary sinus

NTC nutrient canal and foramen overlying the apical portion of the second incisor. This situation may o f t e n simulate internal resorption of the root.

50 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 29. Maxillary left canine periapical radiograph; a postoperative view of the extraction site where there was profuse bleeding from vessels in the nutrient canal traumatized during the extraction procedure. AW

anterior wall of the maxillary sinus

IW

lateral wall of the nasal fossa, which is also the medial wall of the maxillary sinus

MS

maxillary sinus

NTC nutrient canal NTT nutrient foramen SK

socket of the extracted canine

51 Maxillary

Sinus

Figure 30. Flexed-cheek shadow cutting obliquely across edentulous alveolar process in a maxillary left premolar periapical radiograph ED

embossed dot

FL

edge of flexed-cheek shadow, which imparts a slight radiopacity to the alveolar bone posterior to it

G

s h a d o w of gingival tissue (Note chunks of calculus on mesial surface of molar and distal of canine.)

52 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 31. Illustration of χ rays passing from cone (left) through posterior right maxilla into film (f) placed in midsagittal plane. After processing, film (F) reveals the images of the anatomic structures. Note that the third dimension (depth), seen in the anatomic section, is not recorded as such on the radiograph. Rather, the several structures from buccal to palatal are superimposed over each other in the film. AP

alveolar process of the edentulous maxilla

BN

bony nodule (osteophyte)

CP

coronoid process of the mandible

GV

gingival tissue

HP

hamular process of medial pterygoid plate of sphenoid bone

MP

malar process of the maxilla; a is the anterior plate; ρ is the posterior plate

MS

maxillary sinus

NF

nasal fossa

NS

nasal septum

NTC nutrient canal PW

wing of lateral pterygoid plate of sphenoid bone

Ζ

zygoma

53 Maxillary Sinus

NF NS

54 RADIOLOGIC

ANATOMY

OF THE

JAWS

T h e s e three radiopaque lines create the capital letter " Y , " a n d he has named it the " t y p i c a l Y . " T h e base of the " Y " is the lateral wall of the nasal fossa, the two arms are the anterior wall of the nasal fossa (not really a wall, but a ridge which runs beneath the nares to the anterior nasal spine) and the anterior wall of the maxillary sinus. T h u s the " Y " opens anteriorly under normal circumstances, and the structure is visualized best in canine periapical films and anterior occlusal film projections (Fig. 32). Should a cyst arise at the canine or premolar apex, the radiolucent cystic cavity would be seen adjacent to the radiolucent maxillary sinus, and one could be hard pressed to m a k e a correct radiographic interpretation as to whether a cyst does exist, or w h e t h e r the area is a chamber of the maxillary sinus. B y fluid pressure within its lumen, a cyst expands and destroys surrounding bone; if it encroaches on the front wall of the sinus, the cystic pressure has the capability of remodeling the wall as if indenting it, and b y doing so an inverted " Y " is eventually created, which opens posteriorly. W h e n this is encountered in a radiograph, one k n o w s that the anterior sinus wall is not normal and that a lesion such as a cyst has distorted it.

It would be helpful at this point to perform Self-Study Exercise 3.

55 Maxillary

Sinus

Figure 32. Maxillary right canine periapical radiograph, illustrating the typical "Y" A . AW

anterior wall of the maxillary sinus

BR

buccal root of first premolar

LW

lateral wall of the nasal fossa ( w h i c h is also the medial wall of the maxillary sinus)

MS

maxillary sinus

NF

nasal fossa

NFA

anterior wall of the nasal fossa

NTC

nutrient canal in the wall of the maxillary sinus

PR

palatal root of first premolar

"y"

the typical " Y "

B. The typical "Y" outlined

58 RADIOLOGIC

ANATOMY

OF THE

JAWS

Midline occlusal radiographs reveal the entire nasal fossa, bounded on both sides by the lateral walls (Fig. 33) which separate the maxillary sinuses from the nasal fossa. At approximately the level of the second molar roots, bilateral round or ovoid radiolucencies are often visualized. T h e s e are the nasolacrimal canals (Figs. 33, 40), which run from the inner canthus of each orbit to their exits in the inferior meati on the lateral nasal walls. 3 0 W h e n appearing radiographically near the molar root apices, they may be misinterpreted as dental root cysts. Occlusal radiographs will also reveal the radiopaque images o f the three nasal conchae on the medial sides of the right and left lateral nasal walls. Usually these are superimposed over each other, but occasionally the inferior turbinates may be distinguishable as bony "fingers," often covered by a thick layer of soft tissue (Fig. 34). In the midline of the palate is seen a radiopaque structure, the nasal septum (Figs. 3 3 - 3 5 ) , formed by the ethmoid and vomer bones. O f t e n it is thick and shapeless, due to deviation, but occasionally it may be straight and sharp. W i t h i n this radiopaque structure may often be seen the midpalatine suture, a thin radiolucent line which zigzags its w a y posteriorly from the region of the anterior nasal spine. (See Fig. 25.) Between the radiopaque nasal septum in the midline and the radiopaque nasal conchae on the lateral nasal walls appear radiolucent tracts running anteroposteriorly.

They

are simply

empty

spaces of the nasal cavity; the nasal floor and palatal roof are often so thin that no bone can be visualized, and these radiolucencies may seem almost to have the shape of canals (Figs. 34, 35).

59 Nasal Fossa

Figure 33. AN

M a x i l l a r y midline occlusal radiograph

aid of the nose (soft tissue)

A N S anterior nasal spine AW

anterior wall of the maxillary sinus

BP

buccal plate of cortical bone

CN

conchae, superimposed over each other

MP

malar process (anterior plate)

MS

maxillary sinus

MSS maxillary sinus septum NE

nares, external (nostril)

N F A anterior w a l l of the nasal fossa NIC nasal aperture of the incisal canal NLC walls of the nasolacrimal canal NS

nasal s e p t u m (bony)

PX

medial wall of palatine extension of the maxillary sinus

SC

cartilagenous septum of the nose

UM

unerupted third molar c r o w n

60 RADIOLOGIC

Figure 34.

ANATOMY

OF

THE

Maxillary central incisor periapical radiograph

ANS anterior nasal spine AS

air space

FB

gold of fixed bridge pontic

LDC lesion of dental caries NF

nasal fossa

NFA anterior walls of nasal fossa NS

nasal septum

RCF root canal filling material TB

JAWS

turbinate b o n e (inferior c o n c h a )

61 Nasal Fossa

Figure 3 5 .

Maxillary incisor periapical radiograph

ANS anterior nasal spine AS

air space between turbinate bone and nasal septum, giving the false appearance of a canal

NFA anterior wall of the nasal fossa NS

nasal septum

PR

premaxillary suture

TB

turbinate bone (inferior concha)

TP

tip of the soft tissue of the nose

Anterior Maxillary Landmarks

64 RADIOLOGIC

ANATOMY

OF

THE

JAWS

T h e lateral walls of the nasal fossa appear radiographically to curve medially as they progress anteriorly and meet in the midsagittal plane at a point, the anterior nasal spine (Figs. 33, 35). As mentioned in the discussion of the typical " Y , " the so-called anterior wall of the nasal fossa is actually a ridge of bone lying beneath the external nares. Above and between the roots of the first incisors is a round or ovoid radiolucent structure, the incisal foramen (Fig. 36). Occasionally its canal, the nasopalatine canal (Fig. 37), which slants upward and backward to the floor of the nasal cavity, may be seen as a radiolucent tract extending posteriorly and opening with radiolucent foramina on either side of the anterior terminus of the nasal septum image. Anatomically the incisal canal may be a single canal or may be divided into two or four canals. W h e n multiple canals are present, the two medial canals carry the name of Canals of Scarpa, but these are difficult to distinguish in most radiographs. Extending anteriorly in the midline from the anterior nasal spine and the incisal foramen is the anterior extension of the midpalatine suture. However, since this actually unites the premaxilla, it is more correctly called the premaxillary suture (Fig. 38). This suture line, which can usually be visualized throughout life, must not be misinterpreted as a fracture line. As mentioned before, the incisal foramen may be seen in the midline above and between the roots of the first incisors. However, this is true only when the central ray passes straight through the midline, because the foramen is anatomically situated on the palatal surface at some distance from the tooth apices. When the rays are projected at an angle to the midsagit-

65 Anterior Maxillary

Figure 36.

Landmarks

M a x i l l a r y incisor p e r i a p i c a l r a d i o g r a p h

CG

prominent cingula on central incisors

IF

incisal foramen, lateral borders

MPS median palatine suture, running posteriorly from the incisal foramen NF

nasal fossa

NFA anterior wall of the nasal fossa TR

temporary restorations (sedative cement)

66 RADIOLOGIC

Figure 37. graph

ANATOMY

Maxillary

OF

THE

JAWS

right lateral incisor periapical

radio-

AW

anterior wall of m a x i l l a r y sinus

IC

incisal canal; drawn f r o m the midline to the first incisor apex b y the o b l i q u e horizontal t u b e angle. (For f u r t h e r e x p l a n a t i o n , see fig. 3 9 . )

LF

lateral fossa, due to t h i n b o n e around lateral incisor root apex

LW

lateral wall o f nasal fossa

MS

maxillary sinus

NF

nasal fossa (right side)

NFA anterior wall of nasal fossa OT

overlapped t o o t h i m a g e s

"Y"

the typical " Y " ( N o t e the h e a v y marginal ridges on the c a n i n e and second incisor.)

67 Anterior Maxillary Landmarks

Figure 38. Two maxillary incisor periapical radiographs, illustrating variations in the appearance of the premaxillary suture OE

overlapping enamel (right lateral incisor and canine)

OT

overlapping teeth (roots of left central and lateral incisors)

PR

premaxillary suture

TP

tip of the nose (soft tissue)

UC

unerupted left canine crown, with surrounding developmental crypt

68 RADIOLOGIC

ANATOMY

OF

THE

JAWS

tal plane, for instance, when a lateral incisor or canine film is being taken, one can expect to see the foramen (and canal) positioned over the apex of the first (or perhaps the second) incisor on that side (Fig. 39). In such cases it may be misinterpreted as an apical radiolucency of a pathologic nature; when in doubt, one should take a second film with the rays projected through the midsagittal plane, which will return the incisal foramen image to the midline where it properly belongs. Medial to the canine root, and encompassing the apex of the second incisor, a slight radiolucency is occasionally seen. This is due to an anatomic depression in the region known as the canine fossa, also known as the lateral fossa (Fig. 37). When the fossa is quite deep, it may present a radiolucency which must be carefully distinguished from an apical abscess. T w o soft tissue shadows are commonly visualized in periapical and occlusal radiographs of the anterior maxilla. These are the upper lip (a slightly radiopaque band extending laterally across the incisors) and the soft tissue shadow of the nose. The latter is usually seen in periapical films as a rounded, sharply marginated radiopacity over the central incisor roots (Figs. 35, 38). In maxillary occlusal films the entire fleshy portion of the nose may be seen projected anteriorly to the incisors, showing right and left alae, external nares (Fig. 33), cartilagenous septum, and nose tip (Fig. 41). In severely angled occlusal films the nasal bones may actually be made to project anterior to the incisor crowns (Fig. 42). In fact, otorhinolaryngologists use this technique to demonstrate

69 Anterior Maxillary

Landmarks

Figure 39. Maxillary incisor periapical radiographs. W h e n the horizontal angulation of the x-ray beam is directly through the midsaggital plane, as in the center film, the incisal canal ( i c ) and foramen (IF) will register properly in the midline. For lateral incisor projections, however, when the horizontal angle is directed obliquely to the midsaggital plane, the incisal canal and foramen image will be " p u l l e d " toward the side through which the rays have entered. In such instances the canal and foramen will appear superimposed over the first incisor. (See another example in fig. 37.)

70 RADIOLOGIC

ANATOMY

OF T H E

JAWS

fractures of the nasal bones. Additionally, if the point of entry for the occlusal projection is above the bridge of the nose (nasion), the radiopaque image of the supraorbital ridge may be superimposed over the posterior portion of the film (Fig. 40). It would be helpful at this time to perform Self-Study Exercises 4 and 5.

71 Anterior Maxillary

Figure 40. IF

Maxillary midline occlusal radiograph

walls of incisal foramen

NLC nasolacrimal canal SR

supraorbital ridge

Landmarks

72 RADIOLOGIC

ANATOMY

OF

THE

JAWS

Figure 41. Frontal diagram of maxillary midline occlusal film projection. Rays enter at 65° through the bridge of the nose (nasion) through the midsagittal plane and are recorded on the film (f) in the occlusal plane. The processed images are recorded as seen on film (F). This demonstrates the relationship of the anatomic structures to the position of their images on the radiograph. ANS anterior nasal spine A V B alveolar bone AX

alveolar extension maxillary sinus

BP

buccal plate

CK

cheek

CN

conchae

IF

incisal foramen

MP

malar process; a is anterior plate; ρ is posterior plate

MPS median palatine suture NE

nares, external (nostril)

NLC nasolacrimal canal NS

nasal septum

PR

premaxillary suture

PX

palatine extension maxillary sinus

SC

cartilagenous septum of nose

TP

tip of nose

Ζ

zygoma

ZX

zygomatic extension of the maxillary sinus

73 Anterior Maxillary

Landmarks

74 RADIOLOGIC

ANATOMY

OF

THE

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Figure 42. Diagram of sagittal section of maxillary midline occlusal projection of patient's left side, showing the relationship of anatomic structures to their radiographic images on one-half of the occlusal film. The solid lines depict the χ rays projected at the correct 65° vertical angle onto the film (f). When processed, film (F) depicts the images. Note how the rays pass through the nasolacrimal canal (NLC) but cut across the pterygopalatine canal and foramen (PPC), preventing them from being recorded on the film. The dashed line ( ) shows how a vertical angle steeper than 65° can project an image of the nasal bones beyond the dental arch. ANS anterior nasal spine CN

conchae

IF

incisal foramen

MS

maxillary sinus

Ν

nasal bone

NLC nasolacrimal canal PPC pterygopalatine canal and foramen SC

sella turcica

SS

sphenoidal sinus

Ζ

zygoma

75 Anterior Maxillary

IF

ANS

Landmarks

VIII Mandibular Intraoral Radiographic Anatomy

78 RADIOLOGIC

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Mandibular molar periapical radiographs often reveal a radiopaque line (the external oblique line) slanting downward and forward from the ascending ramus across the neck of the third molar (Fig. 43). 3 1 Below this line, near the apices of the molars may be seen another linear radiographic image also slanting downward and forward, the mylohyoid ridge (Fig. 43). 3 2 Whereas the external oblique line is situated on the buccal surface, the mylohyoid ridge lies on the lingual surface, serving as the attachment for the mylohyoid muscle. It actually extends from the third molar area to the midline, but its radiographic presence is usually prominent only in the second molar to second premolar area. Small and moderately sized mylohyoid ridges, which slope gently away from the body of the mandible, may be barely discernible in the radiograph (Fig. 43, lower left), or may be visualized only as a slight radiopacity lacking clear borders (Fig. 43, lower right). But some ridges are more prominent, extending steeply away from the mandible and creating a sharp undercut; these will be visualized radiographically as heavy radiopaque bands with very sharp inferior borders (Fig. 43, upper left and right). Such ridges should be recognized for the undercut problem they may present when impressions are taken and dentures are fabricated for this region of the mouth (Fig. 44). T h e bone architecture beneath the mylohyoid ridge is varied. In this region the mandible is relatively thin buccolingually, and the trabeculations are often sparse and barely visible (Fig. 43, upper right). Additionally, its lingual surface may be somewhat concave in certain individuals to accommodate the

79 Mandibular Intraoral Radiographic Anatomy

MHR

Mill!

figure 43. Molar periapical radiographs illustrating the relationships of the mylohyoid ridge to the external oblique line, as well as the degree of sharpness of the mylohyoid ridge variations. T h e upper right shows the sharpest mylohyoid ridge, followed by the upper left, lower right, and lower left. These appearances would indicate a sharply undercut ridge (anatomically) in the upper right film, slightly less in the upper left, and only moderately protruding ridges in the lower right and left. See also the diagrammatic representation in fig. 44 and the occlusal projection of the mylohyoid ridges in fig. 49. EO

external oblique line

IB

inferior border of the mandible

LDC

lesion of dental caries

MC

mandibular canal

MHR mylohyoid ridge

80 RADIOLOGIC

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submandibular salivary gland, which accentuates the relative radiolucency of the region; this has been termed the submandibular fossa. B e t w e e n the molar roots the trabeculations of alveolar b o n e are often, b y contrast, well mineralized and easily visualized. T h e y may exhibit heavy parallel trabeculations between the roots and occasionally may encircle large, but normal, medullary

spaces,

creating

the

illusion

of

path-

ologic radiolucent bone cavities (Fig. 43, lower left). At the very base of the mandible is a smooth radiopaque band, the inferior border (Fig. 43). A b o v e this lies the mandibular c a n a l , 3 3 - 3 7 recognized radiographically by the parallel radiopaque lines representing its superior and inferior borders (Fig. 45).

It would be helpful at this point to perform Self-Study Exercises 6 and 7. T h e roots of the posterior teeth, particularly third m o l a r s , 3 8 - 4 0 may be very close to, even wrapped around, the canal, and a high degree of surgical skill must be exercised in removal of such teeth. T h e canal courses at a downward slant from the ramus and then assumes a horizontal path to the premolar area, where a branch m a y be seen rising to the mental foramen. 4 1 O f t e n the mental foramen (Fig. 46) is seen slightly below and between the premolar apices, but also may be situated below or posterior to the second premolar apex, and less often near the first molar or first premolar apex. T h e radiographic image of the foramen occasionally appears directly at the apex o f a premolar root (Fig. 46, top, and left center), simulating an apical rarefaction. T o m a k e the differential interpretation b e -

81 Mandibular Intraoral Radiographic Anatomy

BUCCAL

LINGUAL

Egure 44. Cross section of the mandible at the second molar, showing a slightly sloping mylohyoid ridge (MR). A prominent mylohyoid ridge (dotted line) has the potential of creating a sharp anatomic undercut. MC

mandibular canal

MR

mylohyoid ridge

82 RADIOLOGIC

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tween the normal mental foramen and a pathologic lesion, a second radiograph should be made using the same horizontal and vertical tube angles, but positioning the film and the point of entry slightly anteriorly or posteriorly (Clark's technique of localization). Since the anatomic location of the mental foramen is on the buccal surface at some distance from the premolar apex, the second film will project the foramen image away from the root apex. It would be helpful at this point to perform Self-Study Exercise 8. Just above the inferior border of the mandible in the first premolar-canine region one often sees a faint, rounded radiolucency; this is an anatomic depression on the lingual surface which accommodates the sublingual gland and is known as the sublingual fossa. O n the labial surface of the symphysis menti is a bony enlargement, the mental protuberance. T h e upper edges of the protuberance appear radiologically as radiopaque bands slanting upward toward the midline, below or at the level of the incisor root apices, the mental ridges (Figs. 47, 50). In the midline, less than 1 cm above the inferior border is seen a small radiolucent foramen surrounded by a cortical bone; this is the lingual foramen (Fig. 48). At the inferior border of the mandible, in the midline, are the spinous processes known as the genial tubercles; they are best seen in occlusal films of the floor of the mouth wherein the central ray is projected at 90° to the film (Figs. 49, 50). Fractures of the genial tubercles may occur, 4 2

83 Mandibular

Figure 45.

Intraoral Radiographic

M a n d i b u l a r left molar periapical

Anatomy

radiograph

EO

external o b l i q u e line

IB

inferior border o f t h e m a n d i b l e

MC

t h e upper and l o w e r edges of t h e boriy wall that s u r r o u n d s

MR

metallic restoration

the m a n d i b u l a r canal

84 RADIOLOGIC

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usually in combination with symphysis fractures of the mandible, but occasionally as isolated fractures of the genial tubercles. The tongue seems to have a remarkable capacity to accommodate to displacement of these bony origins of the genioglossus muscle, and a number of oral surgeons feel that palliative treatment alone, rather than surgical intervention, is sufficient. Nutrient canals are seen quite frequently in mandibular incisor periapical radiographs. 2 · 4 3 ' 4 4 These rise vertically between and alongside the incisor roots, and exit through foramina lying to the lingual side of the alveolar crest (Fig. 51). When incisor teeth have been extracted and ridge resorption has taken place, these foramina assume a position on the crest of the ridge, and the pressure of a denture on the vessels and nerves exiting from them often causes a syndrome of a feeling of tightness (interference with venous drainage) and of a pin-prick sensation (pressure on nerves). This can be avoided by recognizing the presence of large nutrient canals in preprosthetic radiographs and by providing relief on the models prior to denture fabrication. It w o u l d be helpful at this point to perform Self-Study Exercise 9.

85 Mandibular

Intraoral Radiographic

Anatomy

Figure 46. Mandibular premolar periapical radiographs illustrating the varying radiographic appearances of the mental foramen (MF). (Note, also, the lesions of recurrent caries on the distal of the second premolar and mesial of the first molar, top film; also, the calculus deposits on the teeth in the left center and left lower radiographs.)

86 RADIOLOGIC

Figure 47.

ANATOMY

OF

THE

JAWS

Mandibular incisor periapical radiograph

IB

inferior border of the mandible

LG

small lingual foramen

MR

mental ridges

87 Mandibular Intraoral Radiographic Anatomy

Figire 48. ED

Mandibular incisor periapical radiograph

e m b o s s e d dot

IB

inferior b o r d e r of the m a n d i b l e

L

lip line; vermillion b o r d e r of a p a t i e n t w i t h a very t h i c k lip s u p e r i m p o s e d over the incisor c r o w n s

LG

lingual f o r a m e n

OE

overlapping enamel

88 RADIOLOGIC

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Figure 49. " F l o o r o f t h e m o u t h " o c c l u s a l r a d i o g r a p h o f an edentulous mandible BP

buccal plate of cortical bone

CC

cone-cutting (edge of the cone of rays)

GT

genial tubercles

LP

lingual plate of cortical bone

MF

mental foramen

M H R mylohyoid ridge TN

tongue

89 Mandibular Intraoral Radiographic Anatomy

Figure 50. Mandibular incisor periapical radiograph. Note that the left first incisor is missing, and the radiolucent bone in the area indicates a thin alveolar process. GT

genial tubercles

IB

inferior border of the mandible

LDC lesion of dental caries MR

mental ridges

90 RADIOLOGIC

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Figure 51. Mandibular incisor periapical radiograph. The advanced periodontal bone resportion, of course, is not a normal condition. CL

calculus deposits on the distal of the right first incisor and mesial of the right second incisor

ED

embossed dot

NTC nutrient canals NTF nutrient foramina, situated anatomically on the lingual aspect of the alveolar crests (Note the pathologic widening of the apical periodontal spaces of the two lateral incisors.)

IX Anatomie Structures in Extraoral Radiographs

92 RADIOLOGIC

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Posterior to the area of the mandible included in molar periapical radiographs is the mandibular ramus. T h i s is best visualized in lateral jaw radiographs (Fig. 53) and panoramic films (Figs. 5 4 - 5 6 ) . At the inferior border of the body of the mandible on the anterior side of the gonion (angle of mandible) is a slight concavity variously termed the facial notch or antegonial notch. A prominent antegonial notch may be congenital or acquired; Becker, Coccaro, and Converse discuss several c o n genital dysostoses and familial anomalies, as well as acquired deformities, the latter including infections, trauma, and tumors in and around the temporomandibular joint, which cause interference with the growth centers in the condyle. 4 5 Aneurysm of the facial artery or vein, both of which cross the inferior border of the mandible at this region, may also produce an indentation similar in appearance to the antegonial n o t c h . 4 6 Just posterior to this is the curved angular process of the m a n dible, or gonion. T h e posterior border of the ramus then rises to the condylar neck, above which is the condylar h e a d — t h a t process which forms the mandibular portion of the t e m poromandibular joint ( T M J ) . (See Fig. 5 2 . ) 4 7 T h e socket portion of the T M J is the glenoid fossa of the temporal bone. T h i s lies slightly anterior to the external auditory meatus, which is recognized radiographically as an ovoid radiolucency. T h e a n terior slope o f the glenoid fossa terminates at the rounded eminentia articularis. Radiographs of the normal T M J reveal a radiolucent space between the rounded surface of the condylar head and the curvature of the glenoid fossa, the interarticular space. A c t u -

c ο

0J ν ε

ο Q. -α

Im Ο -4—' "θ

-C

nj