Infection Control in Primary Dental Care [1st ed.] 978-3-030-16306-8;978-3-030-16307-5

Table of contents :
Front Matter ....Pages i-x
Front Matter ....Pages 1-1
A History of Infection Control (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 3-10
The Microbiology and Pathology of Infection Control in Dentistry (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 11-19
The Regulation of Infection Control (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 21-28
Hand Hygiene and Personal Protection (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 29-41
The Immune System (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 43-50
The Infected Oral Healthcare Worker (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 51-58
Front Matter ....Pages 59-59
The Concept of Decontamination in Dentistry (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 61-63
Cleaning Methods for Dental Instruments (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 65-76
Sterilisation in Dentistry (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 77-88
Local Decontamination Units in the Dental Office (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 89-96
How to Choose Clinical Dental Equipment (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 97-104
Dental Disinfection and Environmental Decontamination (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 105-115
Dental Unit Waterlines (Martin R. Fulford, Nikolai R. Stankiewicz)....Pages 117-122
Back Matter ....Pages 123-130

Citation preview

BDJ Clinician’s Guides

Martin R. Fulford Nikolai R. Stankiewicz

Infection Control in Primary Dental Care

BDJ Clinician’s Guides

This series enables clinicians at all stages of their careers to remain well informed and up to date on key topics across all fields of clinical dentistry. Each volume is superbly illustrated and provides concise, highly practical guidance and solutions. The authors are recognised experts in the subjects that they address. The BDJ Clinician's Guides are trusted companions, designed to meet the needs of a wide readership. Like the British Dental Journal itself, they offer support for undergraduates and newly qualified, while serving as refreshers for more experienced clinicians. In addition they are valued as excellent learning aids for postgraduate students. More information about this series at http://www.springer.com/series/15753

Martin R. Fulford • Nikolai R. Stankiewicz

Infection Control in Primary Dental Care

Martin R. Fulford Wedmore, Somerset, UK

Nikolai R. Stankiewicz East Lydford, Somerset, UK

ISSN 2523-3327     ISSN 2523-3335 (electronic) BDJ Clinician’s Guides ISBN 978-3-030-16306-8    ISBN 978-3-030-16307-5 (eBook) https://doi.org/10.1007/978-3-030-16307-5 © Springer Nature Switzerland AG 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG. The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

We have attempted in this book to summarise the principles of good infection control in a primary care dental environment for all members of the dental team. It should be recognised that the underlying science and engineering principles are constant worldwide. We have tried to give the reader a summary of the background science to enable a better understanding of the reasons for the implementation of certain protocols. There is nothing to suggest that microorganisms change their behaviour as a result of geographical variations, but it must be acknowledged that disease prevalence does differ from area to area as does the susceptibility of the population. It must be recognised, however, that the details of what is considered to be good practice do vary from region to region. Some of the variation is determined by local attitudes to risk aversion, some of it depends on local economics and some of it has evolved through custom and practice over a long period of time. We have therefore not championed any particular guidance as this is the remit of local standard setters and professional bodies. Most of the chapters have a short list of additional resources that the reader may wish to refer to, but we have avoided a fully referenced text to avoid any undue interruption for the reader. Both of the authors have a background in dental practice with additional experience and qualifications in microbiology and infection control. We do recognise the challenges posed by infection control in the safe delivery of dental care and acknowledge this comes with both cost and time pressures. Nevertheless, it is important that appropriate protocols are adopted to safeguard the general health and well-being of both patients and members of staff as far as practically possible. Wedmore, Somerset, UK Somerset, UK  January 2019

Martin  R. Fulford Nikolai R. Stankiewicz

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Contents

Part I Basic Science of Infection Control 1 A History of Infection Control������������������������������������������������������������������   3 1.1 Semmelweis����������������������������������������������������������������������������������������   3 1.2 The Germ Theory of Disease��������������������������������������������������������������   4 1.3 Infection Control in Dentistry Emerges����������������������������������������������   5 1.4 Hepatitis����������������������������������������������������������������������������������������������   6 1.5 The Steam Age������������������������������������������������������������������������������������   7 1.6 HIV/AIDS and a New Era of Infection Control ��������������������������������   7 1.7 Prions��������������������������������������������������������������������������������������������������   9 1.8 Learn from the Past ����������������������������������������������������������������������������  10 Further Reading ������������������������������������������������������������������������������������������  10 2 The Microbiology and Pathology of Infection Control in Dentistry������  11 2.1 Some Examples of Infections that Could Be Transmitted in the Dental Environment������������������������������������������������������������������  15 2.2 Blood-Borne Viruses��������������������������������������������������������������������������  16 2.2.1 Hepatitis B������������������������������������������������������������������������������  16 2.2.2 Hepatitis C������������������������������������������������������������������������������  16 2.2.3 HIV ����������������������������������������������������������������������������������������  16 2.3 Other Viruses��������������������������������������������������������������������������������������  17 2.3.1 Influenza and Other Respiratory Viruses��������������������������������  17 2.3.2 Norovirus��������������������������������������������������������������������������������  17 2.3.3 Mumps������������������������������������������������������������������������������������  17 2.3.4 Ebola Virus������������������������������������������������������������������������������  18 2.4 Bacterial Infections ����������������������������������������������������������������������������  18 2.4.1 Tuberculosis����������������������������������������������������������������������������  18 2.4.2 Neisseria meningitidis������������������������������������������������������������  18 2.4.3 Bordetella pertussis����������������������������������������������������������������  19 Further Reading ������������������������������������������������������������������������������������������  19 3 The Regulation of Infection Control��������������������������������������������������������  21 3.1 Safety for Both Patients and Staff������������������������������������������������������  21 3.2 Regulation ������������������������������������������������������������������������������������������  21 3.3 Standards��������������������������������������������������������������������������������������������  22 vii

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3.4 Cost as a Barrier to Infection Control ������������������������������������������������  23 3.5 The Environmental Impact of Infection Control��������������������������������  23 3.6 Case Studies ��������������������������������������������������������������������������������������  27 Further Reading ������������������������������������������������������������������������������������������  27 4 Hand Hygiene and Personal Protection ��������������������������������������������������  29 4.1 Hands��������������������������������������������������������������������������������������������������  29 4.2 Soap and Water ����������������������������������������������������������������������������������  29 4.3 Alcohol Rub����������������������������������������������������������������������������������������  32 4.4 When to Wash and When to Rub��������������������������������������������������������  32 4.5 Personal Protective Equipment (PPE)������������������������������������������������  34 4.6 Eyes����������������������������������������������������������������������������������������������������  35 4.7 Nose and Mouth����������������������������������������������������������������������������������  35 4.8 Gloves ������������������������������������������������������������������������������������������������  36 4.9 Uniform and Aprons ��������������������������������������������������������������������������  39 4.10 Treatment Considerations ������������������������������������������������������������������  40 Putting on and taking off PPE����������������������������������������������������������������������  40 Putting on PPE ��������������������������������������������������������������������������������������   40 Removing PPE ��������������������������������������������������������������������������������������   40 Further Reading ������������������������������������������������������������������������������������������  41 5 The Immune System����������������������������������������������������������������������������������  43 5.1 Vaccines����������������������������������������������������������������������������������������������  44 5.2 Herd Immunity������������������������������������������������������������������������������������  45 5.3 Vaccines for the Dental Team ������������������������������������������������������������  47 5.4 Hepatitis B������������������������������������������������������������������������������������������  47 5.5 Tuberculosis����������������������������������������������������������������������������������������  48 5.6 Influenza: Seasonal Flu ����������������������������������������������������������������������  49 5.7 Tetanus������������������������������������������������������������������������������������������������  49 5.8 Chickenpox ����������������������������������������������������������������������������������������  50 5.9 Emerging and Regional Risks������������������������������������������������������������  50 Further Reading ������������������������������������������������������������������������������������������  50 6 The Infected Oral Healthcare Worker ����������������������������������������������������  51 6.1 HIV ����������������������������������������������������������������������������������������������������  51 6.2 Hepatitis B������������������������������������������������������������������������������������������  52 6.3 Hepatitis C������������������������������������������������������������������������������������������  53 6.4 Other Infections����������������������������������������������������������������������������������  53 6.5 Sharps Injuries������������������������������������������������������������������������������������  54 6.6 Safer Sharps����������������������������������������������������������������������������������������  56 Further Reading ������������������������������������������������������������������������������������������  58 Part II Decontamination in Dentistry 7 The Concept of Decontamination in Dentistry����������������������������������������  61 7.1 Dental Instruments and Equipment����������������������������������������������������  62

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8 Cleaning Methods for Dental Instruments����������������������������������������������  65 8.1 Principles of Instrument Cleaning������������������������������������������������������  65 8.2 Manual Cleaning��������������������������������������������������������������������������������  66 8.3 Ultrasonic Cleaning����������������������������������������������������������������������������  70 8.4 Automated Cleaners����������������������������������������������������������������������������  73 Further Reading ������������������������������������������������������������������������������������������  76 9 Sterilisation in Dentistry����������������������������������������������������������������������������  77 9.1 Boiling Water��������������������������������������������������������������������������������������  78 9.2 Dry Heat����������������������������������������������������������������������������������������������  78 9.3 Moist Heat������������������������������������������������������������������������������������������  79 9.4 Benchtop Pressure Steam Sterilisers (PSS)����������������������������������������  79 9.5 Type N Pressure Steam Sterilisers������������������������������������������������������  80 9.6 Type B Pressure Steam Sterilisers������������������������������������������������������  81 9.7 Type S Pressure Steam Sterilisers������������������������������������������������������  81 9.8 Water Supply��������������������������������������������������������������������������������������  82 9.9 The Use of Benchtop Steam Sterilisers����������������������������������������������  82 9.10 Validation��������������������������������������������������������������������������������������������  83 Further Reading ������������������������������������������������������������������������������������������  88 10 Local Decontamination Units in the Dental Office ��������������������������������  89 10.1 Why Not Reprocess Instruments in the Treatment Room?��������������  89 10.2 Room Design and Workflow ������������������������������������������������������������  89 10.3 Dirty/Cleaning Area��������������������������������������������������������������������������  92 10.4 Clean/Packaging and Sterilisation Area��������������������������������������������  92 10.5 Services and Surfaces ����������������������������������������������������������������������  93 10.6 Plumbing ������������������������������������������������������������������������������������������  93 10.7 Airflow����������������������������������������������������������������������������������������������  94 10.8 Additional Notes ������������������������������������������������������������������������������  95 Further Reading ������������������������������������������������������������������������������������������  96 11 How to Choose Clinical Dental Equipment ��������������������������������������������  97 11.1 Hollow Instruments��������������������������������������������������������������������������  97 11.2 Burs ��������������������������������������������������������������������������������������������������  98 11.3 Single Use ����������������������������������������������������������������������������������������  98 11.4 Certificate of Conformity������������������������������������������������������������������  99 11.5 Instrument Trays ������������������������������������������������������������������������������ 101 11.6 Repairing and Disposal of Instruments�������������������������������������������� 103 11.7 Numbers of Instruments�������������������������������������������������������������������� 103 Further Reading ������������������������������������������������������������������������������������������ 104 12 Dental Disinfection and Environmental Decontamination�������������������� 105 12.1 Fomites���������������������������������������������������������������������������������������������� 105 12.2 Respiratory and Hand Hygiene�������������������������������������������������������� 105 12.3 Treatment Areas�������������������������������������������������������������������������������� 106 12.4 Disinfectants ������������������������������������������������������������������������������������ 107 12.5 Choosing Disinfectants �������������������������������������������������������������������� 107

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12.6 Spray or Wipe?���������������������������������������������������������������������������������� 109 12.7 Zoning ���������������������������������������������������������������������������������������������� 109 12.8 Suction Lines������������������������������������������������������������������������������������ 109 12.9 Routine Environmental Cleaning������������������������������������������������������ 110 12.10 Portable Electronic Devices as Fomites�������������������������������������������� 111 12.11 Body Fluid Spills������������������������������������������������������������������������������ 112 12.12 Laboratory Work ������������������������������������������������������������������������������ 114 Further Reading ������������������������������������������������������������������������������������������ 115 13 Dental Unit Waterlines������������������������������������������������������������������������������ 117 Further Reading ������������������������������������������������������������������������������������������ 122 Glossary�������������������������������������������������������������������������������������������������������������� 123 Index�������������������������������������������������������������������������������������������������������������������� 127

Part I Basic Science of Infection Control

1

A History of Infection Control

1.1

Semmelweis

In 1847 Ignaz Semmelweis (Fig. 1.1), a doctor undertaking obstetrics in a hospital in Vienna, did an audit much like we would do today. He investigated the postdelivery mortality rates of mothers, with startling results. If a doctor or medical student was to deliver a baby, the chance of the mother dying was as high as 18%, but if a midwife or midwifery student was to deliver the baby, the death rate dropped to 2%. Semmelweis rigorously assessed what factors could explain the different death rates between the two groups and noted that unlike the midwives, the doctors would at times undertake autopsies upon cadavers then as needed go to the maternity ward and deliver babies. Semmelweis concluded that the doctors were becoming contaminated by the cadavers and passing on something deadly to the mothers. So, he came up with a simple solution; he got the doctors to wash their hands. He redid his audit and found the intervention worked, and the death rate for the mothers dropped to 2% when the doctors delivered the babies. Semmelweis demonstrated two important principles: 1. Healthcare has the potential to make people sick. We call this nosocomial infection. 2. Interventions can be undertaken to reduce this risk; we call this infection control. Unfortunately for Semmelweis he was ahead of his time. His superiors did not attribute the handwashing to the improved survival rates, instead crediting the hospital’s newly installed ventilation system. This was because at that point in history infections were thought to be spread by miasma, foul smelling air.

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_1

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1  A History of Infection Control

Fig. 1.1  Portrait of Ignaz Philipp Semmelweis (1818–1865), Hungarian-­ Austrian physician. Credit: Wellcome Collection. https://creativecommons. org/licenses/by/4.0/

1.2

The Germ Theory of Disease

It was not until the work of Louis Pasteur, Jacob Henle and Robert Koch from the 1860s onwards that the paradigm of miasma as the source of infection would be challenged. The germ theory of disease proposed that microorganisms were responsible for infections. Joseph Lister (Fig. 1.2) became aware of Pasteur’s research and with time formulated methods of delivering antiseptic surgery, publishing his initial findings in 1867. Embraced by some, there were still many in the medical establishment that were resistant to Lister’s methods. However, by the end of the nineteenth century, the success of those that did adopt his techniques became too many to ignore. Lister’s research sought to find chemicals that would disinfect not only the wounds he operated on (antisepsis) but also the hands of the operators and the instruments (asepsis). Word spread of Lister’s methods in Europe and America, and this prompted further developments by those enthused by his work. The harsh phenols advocated by Lister in cleaning instruments prompted William Halsted to commission the Goodyear Rubber Company to make rubber gloves, which were then worn by theatre nurses and then his colleague Joseph Bloodgood started using them to undertake surgery.

1.3 Infection Control in Dentistry Emerges

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Fig. 1.2  Joseph Lister, 1st Baron Lister (1827–1912) surgeon. Credit: Wellcome Collection. https:// creativecommons.org/ licenses/by/4.0/

1.3

Infection Control in Dentistry Emerges

In 1891 Willoughby Miller wrote about disinfection of dental instruments in reducing the risk of patient-to-patient transmission of infection, citing examples of spread of syphilis due to dental care. Miller’s recommendations included the boiling of linen and the single use of rubber dam. A salient observation Miller made was that bioburden remaining on instruments reduces the efficacy of chemicals to sterilise instruments, and he recommends they are scrubbed first. Boiling water is cited as the preferred method of instrument reprocessing during this period. The efficacy of boiling surgical instruments had been demonstrated in 1888 by Hugo Davidsohn. A 1902 article by Young describes how a device to boil dental instruments could easily be made. Perhaps one of the most telling and thought-provoking articles to be published around this time was penned by Fossume in 1905 who opined that frequent reasons

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1  A History of Infection Control

dentists were not following infection control measures of the time were time and cost; plus ça change! He goes on to argue that the implementation of infection control is a moral and intellectual obligation of the modern dentist, calling upon the values of professionalism. By 1915  in the USA, there were guidelines on infection control in dentistry issued by the Public Health Service under the auspices of the Hygienic Laboratory, which would later become part of the National Institutes of Health. This guidance by H. E. Hasseltine encompassed asepsis, validation, cross infection, instrument reprocessing including the role of cleaning prior to sterilisation and methods of sterilisation. Whilst autoclaves and Arnold (non-pressure) devices were noted for their role in preparing linen and glassware, boiling water is favoured for instruments. Moist heat was deemed essential by Hasseltine in sterilising instruments, with a jacketed water bath described that maintained a temperature of 80° C. A section was dedicated to reprocessing handpieces and the problems this might pose, something we still are challenged by today. Single-use instruments and equipment were detailed, including endodontic files and paper cups for patients. He highlighted the role dental schools had in educating in infection control. The guidance also encompassed the surgery and dental chair, the maintenance of the cuspidor and the role of protective barriers, albeit linen as compared to the singleuse plastics we use today.

1.4

Hepatitis

McDonald proposed in 1908 that infectious jaundice was due to a virus. It was MacCallum in 1947 who went on to classify viral hepatitis as A (infectious) or B (serum). By the 1940s there was an increasing awareness of viral hepatitis posing a public health problem in many parts of the world. In 1952 an expert panel came together as part of the World Health Organization to address the problems posed by hepatitis. The panel were unsure how hepatitis B might be spread, but they were sure that parental penetration of needles contaminated with blood would transmit the disease. It is worth noting that up until the mid-1950s hypodermic needles and syringes were normally reused. This accounts for why hepatitis epidemics would break out after vaccination programs. Subsequently, dentistry was recognised as being a potential risk in the transmission of hepatitis B. Amongst the panel’s recommendations on invasive surgical instrument reprocessing was that chemical disinfectants should not be used as they could not be relied upon to be effective. It was not until 1963 with the discovery of the Australia antigen (hepatitis B surface antigen) by Baruch Blumberg and Harvey Alter that progress in the understanding of the virus increased at a greater pace. The first commercial vaccination against hepatitis B, developed by Maurice Hilleman, was released in 1981. Papers soon appeared in dental journals recommending its use by the profession. Unfortunately, the uptake of the vaccine by the dental profession remains low in many countries due to a range of factors.

1.6 HIV/AIDS and a New Era of Infection Control

1.5

7

The Steam Age

Charles Chamberland and Pasteur’s invention of the autoclave in 1879 would prove to be an even more effective method of destroying microorganisms than using chemicals. Ernst von Bergmann and his assistant Schimmelbusch began steam sterilisation of surgical dressings in 1885. By the 1890s steam sterilisers were in use in some American hospitals. There were various changes in sterilising machines over the years, but it was in 1933 that the American Sterilizer Company would introduce the first machine that used temperature indicators, rather than just pressure, thereby improving the control and accuracy of the process and heralding what Perkins described as the ‘modern era of sterilisation’. From the mid-1950s onwards, the cost of automatic autoclaves that were quick to run had started to come down in price, making them more affordable and practical for general dental practice. In the late 1950s, articles started appearing in dental journals supporting the use of autoclaves in dentistry to reduce the risk of spreading hepatitis B, especially given that case reports around this time also suggested multiple cases of hepatitis transmission due to dental care. It may come as a surprise for more recent members of the dental team to learn that even in the mid-1980s, boiling instruments in water remained a popular means of reprocessing instruments in the UK, despite only disinfecting them at best. More recent studies have shown that in some developing countries, boiling instruments persists as a method of reprocessing. Spaulding proposed in 1957 that surgical and medical instruments be reprocessed based on the risk of associated infection. Instruments used within body cavities would be classed as critical; those in contact with mucous membranes or non-intact skin would be semi-critical, and those instruments that only touch intact skin would be classed as non-critical. This system is still largely used in dentistry, but for ease semi-critical instruments are often reprocessed as if critical. The problem with the Spaulding’s system is it was based on the available knowledge at the time about microbiology. Since then, it has become evident that there are pathogens that will escape eradication unless the instruments they contaminate are cleaned before sterilization, rather than just disinfected even if classed as semi-critical. In the 1950s, UK hospitals began centralising their sterilisation services. This was done to achieve a uniform standard of reprocessing, better maintenance of equipment and well-trained staff. By the mid-1960s there were advocates of doing the same within general dental practice, rather than undertaking instrument reprocessing in treatment areas. This remains a challenge for many practices that are not located in purpose built premises.

1.6

HIV/AIDS and a New Era of Infection Control

In 1980 the World Health Organization announced that smallpox had been eradicated. That same year in the USA would see increasing numbers of homosexual men developing unusual opportunistic infections and cancers including

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1  A History of Infection Control

Pneumocystis carinii and Kaposi’s sarcoma, marking the beginning of the acquired immune deficiency syndrome (AIDS) epidemic. By 1984 researchers in France and the USA had identified that AIDS was due to a virus, human immunodeficiency virus (HIV). In the USA by the 1960s, hospitals for infectious diseases had been replaced by isolating patients in wards within general hospitals. The Centers for Disease Control and Prevention (CDC) issued guidance on how to manage infectious patients based on epidemiologic risk factors in 1970, and revised in 1975, including blood precautions. The emergence of AIDS would become a major factor in re-evaluating this methodology, and new guidance was released in 1983, which included guidance on the management of patients’ blood and body fluids. The use of personal protective equipment, including gloves and masks, was highlighted as being important in protecting healthcare workers. A fundamental problem with the 1983 guidance was that it was for managing patients who were known to be infectious. This ignored those in the population who were yet to be diagnosed, healthy carriers or those that failed to disclose an infection. The release of the 1985 guidance, universal precautions, recognised this deficiency and advised that all blood and some body fluids should be considered infected. The response to AIDS by government, health organisations and the public demonstrates the complex nature which societies can respond to infectious disease. The early years of the AIDS epidemic saw governments fail to get to grip with the problem based on political ideology and values. The media created fear and spread misinformation. Various public health measures were wasteful by not specifically targeting those at greater risk. The already marginalised in society were vilified and blamed for the disease, due to the ensuing fearmongering. The momentum behind this did however force dentists to look at their infection control measures, with the adoption of universal precautions. In 1990 an American dentist, David Acer, died of AIDS-related illness. It would emerge that in all likelihood six of his patients had contracted HIV from him. It remains unclear how this happened, with suggestions ranging from poor infection control procedures to it being deliberate. To date, there are no other known cases of patients acquiring HIV from an infected member of the dental team. Regardless, it was enough for the public to fear dental care as a potential route of infection. Furthermore, it would reinforce regulatory bodies putting restrictions on HIV-­ positive members of the dental team in many countries. In the UK, these restrictions were finally revised in 2016 when the guidance acknowledged that the risk of transmission of blood-borne viruses from the dentist to patient was negligible for many dental procedures. The CDC replaced universal precautions in 1996 with standard precautions (Table 1.1). The changes were prompted by the need to unify the CDC-issued guidance on moist body substances (body substance isolation or BSI) that had been introduced in 1987 and the universal precautions. In 2003 the CDC issued its guidelines for dentistry which were a more tailored version of the standard precautions, applicable to the dental setting.

1.7 Prions

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Table 1.1  The body fluids presumed to be infectious under universal precautions and standard precautionsa Body fluid Blood Semen Vaginal secretions Cerebrospinal fluid Synovial fluid Pleural fluid Pericardial fluid Peritoneal fluid Amniotic fluid Saliva in dental procedures Any body fluid visibly contaminated with blood All body fluids in situations where it is difficult or impossible to differentiate between body fluids Urine Faeces Nasal secretion Sputum Vomit Breast milk Saliva other than in dental procedures

Universal precautions ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

Standard precautions ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

Based on the table by the Occupational Safety and Health Administration at: https://www.osha. gov/SLTC/bloodbornepathogens/worker_protections.html

a

1.7

Prions

In 1982 Stanley Prusiner published his findings on what he described as proteinaceous infectious particles, which he termed prions. This research would go on to earn him the Nobel Prize for Medicine. The first case of bovine spongiform encephalitis (BSE), a prion-mediated disease in cows, was noted in the UK in 1984. By 1988 that number had risen to approximately 600. It is likely that the disease spread amongst cows due to the use of recycled animal protein in ruminant feed, following an initial sporadic case. In an enquiry that was led by Lord Phillips some years later, it was revealed that parts of the British government were seemingly more concerned about the impact BSE would have on the beef industry than any possibility that it could be a risk to humans, based on the assumption that this type of disease did not cross species. The first dairy farmer in the UK died of Creutzfeldt-Jakob disease (CJD) in 1992; by 1995 a fourth had died. By the end of 1995, ten cases of young people with CJD had been identified. The government position had remained steadfast that eating British beef was safe and you could not get BSE; that is, until it conceded otherwise in March 1996. Variant CJD (vCJD) is developed by eating beef contaminated with BSE, demonstrating transmission via the oral route. As of 2016 there have been 178 cases of

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1  A History of Infection Control

vCJD identified in the UK.  The identification of vCJD prompted the next major paradigm shift in dental infection control in the UK.  In 2009 the Department of Health issued guidance on infection control in dentistry, commonly referred to by the profession as ‘HTM 01-05’. This resulted in a greater emphasis on single-use instruments and pre-sterilisation cleaning when reprocessing instruments. Having identified pulpal tissue as a possible source of infected tissue, attention turned to mandatory single patient use endodontic instruments. Whilst the UK potentially remains at a greater risk of vCJD than many other countries, it would seem prudent to follow the underlying principles of protein removal and elimination.

1.8

Learn from the Past

Dental infection control guidance has evolved with our understanding of the microbiologic world. From the initial realisation of the role of bacteria in infections to the discovery of viruses and most recently prions, the methods that are employed to deliver safer care have been challenged. From the very earliest days of infection control in dentistry, cost and time have been barriers to compliance. Resources and infrastructure to deliver infection control are also necessary. This may prove a challenge in developing countries. What does remain a constant is that the knowledge we have garnered on infection control must be shared and taught to those in the profession if we are to provide a global effort in delivering the safest care we can.

Further Reading The BSE Enquiry archived online at: http://webarchive.nationalarchives.gov.uk/20060525120000/ http://www.bseinquiry.gov.uk/index.htm Eisenbud L. Serum hepatitis in dental patients. J Dent. 1957;27:177. Fossume FL. A plea for more thorough dental asepsis. Dental Cosmos. 1905;47(6):672–4. Hasseltine HE. The sterilization of dental instruments. Hyg Lab Bull. 1915;101:53. Magner L. A history of infectious diseases in the microbial world. Westport: Praeger Publishers; 2009. Miller WD.  The disinfection of dental and surgical instruments. Dental Cosmos. 1891; 33(7):514–26. Perkins JJ. Principles and methods of sterilization in health sciences. 2nd ed. Illinois: Charles C Thomas; 1969.

2

The Microbiology and Pathology of Infection Control in Dentistry

Microorganisms, including bacteria, viruses and fungi, are ubiquitous and are widespread in the environment, both in the environment where we live and work and in and on our bodies. The human body is composed of about 1014 cells only about 10% of which are mammalian, the remainder are microbial. Only very small proportions of these microbes are parasitic and cause pathological changes in their hosts and thus cause disease. The extent or severity of disease will vary from microbe to microbe and is called virulence, and the ability of a microbe to cause disease is called pathogenicity. No infectious disease is invariably fatal as this is not in the interest of the microbes as they will rapidly run out of hosts to infect. They may, however, cause significant damage to the host and thus are able to spread to new hosts by a process of shedding. This can then lead to cross infection when this occurs in a medical/dental environment. All parasitic microorganisms have a differing ability to infect their hosts, and the number of microbes required to reliably infect an individual is known as the infectious dose and will vary from species to species. For some microbes only a very small number are required to transmit infection; for other microbes it may require many hundreds of thousands of cells or particles to cause disease in the exposed individual. It is therefore very important that in managing the risk of the transmission of infection to ensure that equipment and the environment are regularly decontaminated to reduce the microbial loading of anything that patients or members of staff may be exposed to. The relative risks of the transmission of microbes in the dental environment will not only depend on the pathogenicity of the microbe but also on its ability to survive in the environment. Accordingly, microbes have developed survival mechanisms to ensure their continued existence. Some bacteria will produce spores that will protect them from extreme conditions such as heat, desiccation, lack of nutrients and chemicals such as disinfectants. They are able to survive in this state of inertia for a very long time, in some cases for decades. Once conditions become favourable, they are able to revert to a vegetative state and can multiply rapidly and

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_2

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cause disease. This ability is analogous to plants that produce seeds, and when these seeds are planted into soil, they germinate and become flowers/vegetables once again. The spores may be able to survive temperatures as high as 100oC but will be destroyed at higher temperatures. This is the reason why boiling water has been superseded by high-­temperature steam, produced by a steam steriliser, for the decontamination of dental instruments. An example of spore-producing bacteria that is of medical significance is Clostridium tetani, the cause of tetanus. Some bacteria have a cell wall that is very dense and impenetrable and renders it less susceptible to desiccation or chemical disinfectants and therefore can survive outside of the host, such as in dust in the dental environment, for several months. For example, this is a property of Mycobacterium tuberculosis, the cause of tuberculosis in man. Most viruses survive poorly outside of the host and have a very short period of viability unless they are protected by organic soil such as blood or saliva. For example, hepatitis B viral particles on their own outside the host will have a survival time measured in minutes. If, however, they are present in dried blood, for example, they can remain infectious for up to a week. The risk of transmission of microbes will not only depend on the ability of the microbe to survive in the environment but also on its route of transmission. For some microbes the route of transmission may be by direct contact with another person that is either infected by or asymptomatically carrying and then shedding the infectious agent. This could be a mode of transmission between the operator and the patient, and the risk of transmission can be reduced by the use of personal protective equipment such as clinical gloves. Transmission of infections can also occur via an indirect route such as aerosols. Aerosols can be created either directly such as by sneezing or indirectly by the use of dental equipment such as air rotors or mechanical scalers which produce high-­ energy fine sprays that can pick up microbes from the patient’s oral tissues and distribute them into the environment. Another indirect mode of transmission is via dental equipment or work surfaces; these are known as fomites. Most microbes have poor adherence to the surface of materials such as stainless steel used for dental instruments or smooth plastic materials such as work surfaces. The ability of microbes to adhere to such surfaces, however, is greatly enhanced if these surfaces are contaminated with organic material such as blood, saliva or other bodily secretions. Also the presence of organic material on surfaces may provide a source of nutrients for bacteria which are then able to multiply rapidly and colonise this environment. In this scenario it is possible that the initial level of contamination may have been quite low and been below the threshold where transmission of infection would be likely, but a delay in cleaning the contaminated surface has led to an increase in the number of bacteria present, and therefore the threshold where transmission of infection could occur has now been exceeded. It is therefore a central plank of good infection control that all surfaces that have a risk of contamination should be cleaned regularly and particularly, before and between all patient treatment episodes.

2  The Microbiology and Pathology of Infection Control in Dentistry

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Fig. 2.1  Bacterial cells. The long structures at the end of the cell are flagella providing motility to the cell. The shorter hairlike structures are fimbria which provide a means of attachment to surfaces

Some bacteria are motile and have the ability to ‘swim’ and multiply when in a moist environment (Fig. 2.1). Therefore, there is a risk that any contamination of a surface could spread to adjacent areas in the presence of moisture. It is important, therefore, to ensure that surfaces that are cleaned using liquids are also dried following cleaning and not allowed to remain moist. It is also advisable to ensure that a wider area is cleaned in order that there is a margin of safety around areas that have been contaminated (Fig. 2.1). Most pathogenic bacteria cause the signs and symptoms of disease by the action of toxins on the host’s tissues. Some toxins are produced as a waste product of the bacteria’s metabolic processes and secreted into the environment that the bacteria are multiplying in. These are known as exotoxins and are usually proteins and will have a wide range of effects. For example, some exotoxins may be cardiotoxic and cause damage to the host’s heart, some may be haemolytic and destroy red blood cells and some may be neurotoxic and cause damage in the nervous system. These exotoxins are often strongly antigenic, that is, they stimulate the immune system to produce antibodies. This can then enable a preventative approach to these diseases by the production of vaccines aimed not at the bacteria themselves but at their toxins and thus prevents the effects of infection. Examples of this are tetanus and diphtheria where individuals are given doses of toxoid, which are chemically similar to the toxin but without the toxic effects, and this stimulates the individual to produce antibodies to the toxin which will then inactivate the toxin and prevent the effects of the infection. Exotoxins are usually destroyed or inactivated by heat, and therefore most decontamination processes involving heat will remove the risk of these substances causing ill effects if they contaminate the clinical environment. Some toxins are not secreted by bacteria but are found as constituents of the bacterial cell, in particular the cell wall of certain types of bacteria. These substances are not released into the environment until the cell dies and breaks down. These are known as endotoxins and are usually lipopolysaccharide in nature. Endotoxins are usually heat stable and therefore not destroyed by heat. Endotoxins are often present in low levels in the body and will usually be found in the gut and the mouth as a product of the life and death of the bacteria that normally inhabit

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2  The Microbiology and Pathology of Infection Control in Dentistry

these environments. At higher levels endotoxins will cause effects such as raised temperatures (pyrexia), a feeling of general unwellness, and may impede the healing of wounds. If endotoxin is released into the bloodstream in large amounts, it can cause a condition known as toxic shock and can lead to death. Raised and significant levels of endotoxin can be found in the water reservoirs of surgery autoclaves where the water is allowed to be recycled on numerous occasions. The mechanism of this problem is where the water is contaminated by environmental bacteria and will multiply in the warm conditions found in the reservoir. The water is then used to make steam in the autoclave chamber, and the bacteria in the water are destroyed by the high-temperature steam, releasing endotoxin. This endotoxin is then returned to the reservoir on condensation of the steam at the end of the cycle. If this is allowed to continue repeatedly, then accumulation of endotoxin will occur and may reach significant levels. The endotoxin-laden steam used in this way will result in the dental instruments being coated in endotoxin which could have an adverse effect on the patients that these instruments are used on. This has happened in ophthalmic surgery. The problem can be mitigated by ensuring that the water in the autoclave reservoir is discarded at the end of each working day and the reservoir is refilled with fresh water at the beginning of the next working day. Using an autoclave that has separate clean and used water reservoirs will also reduce the risk of recirculating endotoxins. Viruses are different to bacteria in that they are strict parasites and rely completely on the host’s cells to multiply and survive. Each different virus will have a specific target cell type that it will infect. The virus attaches to specific sites on the surface of the target cell and will gain entry to the cell. Once the virus is inside the cell, it will ‘highjack’ the cell’s own genetic material and will corrupt the cell’s reproductive mechanisms so that instead of producing further copies of itself, the cell is ‘reprogrammed’ to produce copies of the virus. Eventually the cell will be so full of copied viruses that it will burst open releasing large numbers of viruses that will then go on and infect further target cells either in the host or will be shed from the host and will go on to infect further individuals. This process results in widespread destruction of the host tissues causing the signs and symptoms of the disease (Fig. 2.2). Fig. 2.2  An HIV virion budding from the surface of a T cell (a type of white blood cell). The virus is replicated by the host cell with the components gathering at the cell membrane to be assembled into new virus particles. Credit: NIH

2.1 Some Examples of Infections that Could Be Transmitted in the Dental Environment

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Fungi such as some strains of Aspergillus sp. may cause disease by the production of toxins although this is often indirect as they may produce toxins in foodstuffs that are then ingested by humans. Candida albicans is a single-celled fungus that may invade damaged tissues, in particular, oral tissues that have had their normal resident bacterial flora depleted by the administration of antibiotics. The cells of Candida albicans are normally part of a balanced mixed population of microbes on the oral tissues but can become the dominant species once the other microbes have been destroyed. In this scenario it is known as an opportunistic pathogen. Infection of a host will usually result in an immune response with a resultant production of antibodies to the invading microorganisms. This host defence mechanism, however, is not always successful and will not result in the eradication of the invading microbes, and the infection will persist or even worsen. In some infections it is the host’s immune response that is thought to be responsible for most of the damage to the host tissues. For example, this is thought to be the cause of tissue damage in tuberculosis. It is also the cause of the worse effects in some patients with a group A streptococcal sore throat where the antibodies formed against the cell wall of the streptococcus cross-react with the patient’s heart muscle or valves leading to condition known as rheumatic fever. Medicine has also harnessed the immune response as a mechanism for attempting to prevent the occurrence and spread of infectious diseases by means of vaccination. This often uses strains of microbes that have been developed to resemble the disease-causing microbes but are not capable of causing the disease; when injected into the host, they stimulate the production of antibodies, thus preventing infection by the pathogenic strains. In other instances antibodies are harvested from hosts who have recovered from infections and are given to people exposed to pathogenic microbes such as hepatitis B. This is known as passive immunisation. Unfortunately, in some cases vaccination is not always successful as a strategy for preventing disease as some microbes can mutate and not be affected by the antibodies produced. Microbial evolution by means of mutation can happen very rapidly because of the speed at which microbes multiply. Successful microbes can multiply as frequently as every 20 min and thus will evolve at a rate about half a million times faster than a human would in 20 years. Therefore, effective vaccines can become ineffective in quite a short period of time and may need to be redeveloped in the light of microbial changes such as in the case of influenza.

2.1

 ome Examples of Infections that Could Be Transmitted S in the Dental Environment

It would take an entire book to detail all the microbes that could pose a risk of infection in the dental environment. So a few examples of microbial risks will be detailed in the following section. Some of which may be familiar to all members of the dental team, but some may receive less consideration.

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2.2

2  The Microbiology and Pathology of Infection Control in Dentistry

Blood-Borne Viruses

2.2.1 Hepatitis B • Found in the blood of individuals infected with the virus. It has a very low infectious dose, with sufficient viral particles to reliably transmit infection found in about 1 picolitre (10−12 L) of infected blood. Thus, it could be readily transmitted to susceptible individuals with exposure to microscopic amounts of contaminated blood or saliva. • Approximately 257 million people are infected with the hepatitis B virus worldwide (WHO). • Chronic infection with hepatitis B virus occurs in about 5% of those infected and can lead to death from cirrhosis or liver cancer. It causes nearly a million deaths a year worldwide. • The highest prevalence rates are found in the Western Pacific and African regions with just over 6% of the population infected. Prevalence in Europe is about 1.7%, and in America it is estimated at about 0.7% of the population (WHO). • Hepatitis B vaccination is available and will provide good protection in about 95% of individuals.

2.2.2 Hepatitis C • Found in the blood of individuals infected with the virus. It has a very low infectious dose, with sufficient viral particles to reliably transmit infection found in about 10 picolitre (10−12 L) of infected blood. Thus, it could be readily transmitted to susceptible individuals with exposure to microscopic amounts of contaminated blood or saliva. • Approximately 71 million people are chronically infected with the hepatitis C virus worldwide (WHO). • About 60–80% of those infected will develop chronic infection, and of these up to 30% will develop cirrhosis or hepatocellular carcinoma (liver cancer). • Currently there is no vaccine against hepatitis C. • There are antiviral drugs that have a high success rate in curing the disease once it has been diagnosed. It should be noted, however, that hepatitis C infection is often asymptomatic for many years and a diagnosis is not made until late stages and liver failure occurs.

2.2.3 HIV • Found in the blood of infected individuals. It is much less infectious than the hepatitis viruses, and very few cases have been associated with spread in the medical/dental environment. There has, however, been one incident of several patients infected with HIV that was associated with an HIV-positive dentist in the USA, but the mechanism of infection was never firmly established.

2.3 Other Viruses

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• Approximately 25 million people are living with HIV worldwide (WHO). • Effective treatments are available to control HIV infection. • Untreated cases of HIV infection may go on to develop AIDS (acquired immune deficiency syndrome) and be very susceptible to infections with other microbes. In particular, in some parts of the world, the commonest cause of death for patients with AIDS is tuberculosis.

2.3

Other Viruses

2.3.1 Influenza and Other Respiratory Viruses • Respiratory viruses spread very effectively particularly in the winter months. • They are usually associated with aerosol transmission by coughing and sneezing. They could, however, be spread by aerosols generated in dental practice. • For most healthy people, respiratory infections are fairly minor but in elderly or frail people can be life-threatening. In the UK, for example, influenza infection can cause 30,000 excess deaths per annum.

2.3.2 Norovirus • An enteric virus that causes acute diarrhoea and vomiting. • Extremely infectious as the infectious dose is as low as 10–100 viral particles. • Causes very large outbreaks of illness (685 million cases worldwide), particularly in the winter months. During outbreaks it can cause significant hospital ward closures when both patients and staff are infected. This can therefore affect the delivery of healthcare to local populations and is therefore very significant when this occurs even though the infection is relatively minor when it occurs in otherwise healthy individuals. • Transmission of the virus occurs directly from person to person, via food produced by infected individuals or from environmental contamination. Control of outbreaks is facilitated by the adoption of high standards of hand hygiene. Survival of the virus in the environment can be as long as several weeks even on hard surfaces such as work surfaces or door handles.

2.3.3 Mumps • An infection of the salivary glands that could be spread in dental practices via saliva. • Generally seen as a relatively minor disease of childhood but can affect adults where it may cause significant morbidity, for example, 15% of infected adults may develop meningitis.

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2  The Microbiology and Pathology of Infection Control in Dentistry

• In some parts of the world, the incidence of mumps has been controlled by means of vaccination programmes using a combined vaccine, MMR (measles, mumps and rubella). In some countries a health scare involving the use of the combined vaccine resulted in a drop in uptake of the vaccine leading to the re-emergence of these diseases.

2.3.4 Ebola Virus • Ebola disease is caused by a haemorrhagic virus which has a very high average mortality rate of 50%, with a range of 25–90%, in previous outbreaks. • Outbreaks of the disease may occur by human contact with animals carrying the disease which then spreads by human to human contact. • Has previously occurred in small clusters of cases in rural areas in West Africa. Increasing urbanisation has now increased the risk of contact with disease sufferers and caused much larger outbreaks of the disease. • Infection spreads by contact with bodily fluids from infected persons, and it is extremely infectious. • A small number of cases have occurred in healthcare workers outside of West Africa by contact with travellers who are incubating the disease. • In the right circumstances, it is possible that cross infection could occur in a dental environment.

2.4

Bacterial Infections

2.4.1 Tuberculosis • Bacterial infection associated with Mycobacterium tuberculosis is usually pulmonary (lung infection). The bacteria are found in the sputum of infected individual, and therefore this will contaminate the mouth. • It is the world’s most common infectious disease and currently is estimated that some 1.7 billion people are infected with the bacterium. • Many strains of the bacterium are acquiring resistance to the drugs commonly used to treat the disease. • The bacterium may survive in the environment for months. • Workers in healthcare may be more exposed to the risk of tuberculosis than members of the general public. It is important therefore that members of the dental team are vaccinated using the currently available BCG vaccination.

2.4.2 Neisseria meningitidis • Also known as meningococcus. • May cause bacterial meningitis with significant mortality and morbidity rates, particularly in the young.

Further Reading

19

• Often found in the upper respiratory tract of asymptomatic carriers. Ten percent of adults may be carriers and up to 25% of teenagers. Therefore, there is a risk of transmission in the dental environment.

2.4.3 Bordetella pertussis • The cause of whooping cough and found in the mouth and upper respiratory tract of infected individuals. • May cause severe disease in children but can infect adults as well. • In some countries re-vaccination of adults in ante-natal clinics may be used to reduce the risk of spread to newborn babies.

Further Reading World Health Organization (WHO): www.who.int. Nash A, Dalziel R, Fitzgerald J., Mims’ pathogenesis of infectious disease. London: Elsevier/ Academic Press; 2015. ISBN: 9780123971883.

3

The Regulation of Infection Control

3.1

Safety for Both Patients and Staff

Patients have a reasonable expectation that the care they receive and the environment it is performed in are safe. All those working within a dental practice should also expect a level of safety in the workplace. It can be reasonably argued that dental healthcare workers may have a higher risk of acquired infection in the workplace based on their increased exposure to this environment rather than patients whose exposure is considerably less. Dentists and other dental healthcare workers have professional, ethical and legal obligations they must meet. In addition to this, business owners will have further obligations to their staff, patients who attend their practice and the public. If any dental healthcare worker has concerns about the infection control standards in their workplace, they should raise them. This may be, in the first instance, by raising concerns with the person responsible for setting the standards within the practice. If this approach fails to result in an appropriate response within a reasonable timeframe, then it may be necessary to raise concerns with, for example, local or national regulators of infection control or professional standards. Whilst this may seem to be a rather drastic step, it is not sustainable to ignore issues that may adversely impact upon the general health and wellbeing of those people that may encounter an unsafe environment.

3.2

Regulation

Governments regulate dentistry to protect the public. Laws are set by governments, and the regulations set by government agencies then specify how these laws are met. Guidelines contain the technical details needed to help with both compliance and understanding of associated laws. Where guidelines are followed by the dental team, they can expect to meet their legal requirements.

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_3

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3  The Regulation of Infection Control

Whilst guidelines may not always be compulsory under the law, there will be circumstances where contracts between dental practices and third-party providers might specify following set guidelines as a condition of a contract. Anyone who fails to follow guidelines must be able to provide appropriate reasons why they have taken this course of action and be prepared to justify this. They may thus find themselves the subject of public criticism or even prosecution, and their professional reputation called into question.

3.3

Standards

Contemporary infection control guidelines have their roots in the CDC guidance that started with blood and body fluid guidance in the 1970s and early 1980s in response to hepatitis. It was the emergence of HIV/AIDS that would make a significant re-evaluation of infection control in dentistry with the adoption of universal precautions in the mid-1980s. Standard precautions (1996) now forms the backbone of all current guidelines around the world and is endorsed by the FDI World Dental Federation (Table 3.1). Standards are criteria that set what is expected of a product or process, as agreed by experts in the relevant discipline. There are national, regional (e.g. Europe) and worldwide bodies that set and advise formal standards for many aspects of infection control. By adopting these standards and procuring equipment that meets them, the dental team can have a level of confidence that they are meeting their obligations. Minimum acceptable practice, also termed essential practice, sets a baseline for what is required in infection control. Practices not meeting these criteria would be failing in their duties and might be considered not to be safe. Good practice is used to describe how to achieve a set of goals effectively that are based on the latest evidence-based research and expert opinion, and this principle can be applied to infection control. Best practice describes the superior way of achieving this goal. Quality assurance in infection control seeks to maintain a level of quality at all stages of the processes involved. It can be confusing when undertaking infection control that there is scope for essential, good and best practice. If the role of infection control is to protect people, how do we reconcile that there are measures beyond the level of essential practice Table 3.1  Standard precautions set by the CDC Hand hygiene PPE use Respiratory hygiene Safer sharps Safe use of injectable medicaments Sterile equipment Clean and disinfected environment These are accompanied by transmission-based precautions which identify those patients who are known to be acutely ill with infections that are readily transmitted. These patients should be rescheduled for care when they have recovered or referred to hospital for specialised care

3.5 The Environmental Impact of Infection Control

23

that are not being undertaken? Furthermore, what risks are people being exposed to where best practice is not being achieved and how do we decide this is acceptable? This is an ethical conundrum that must be seen in the wider context of how dental care is practiced, funded and the availability of resources. Essential requirements are based on the knowledge at the time they are set, but infection control is not a static discipline. With research and new technologies, there will be aspects of infection control that offer improvements, and this is where both good and best practice will change with time whilst the minimum standards may remain valid. Of course, minimum standards can change too. Infection control must be practical and economically viable. It should be considered that availability of resources, principally money, will have a bearing on what is achievable. Infection control is an exercise in risk management. Risk assessments are based on both scientific principles and expert opinion. Whilst it may prove frustrating, it must be accepted that we simply do not know how likely some risks are. Nor do we know to what extent some of the interventions we undertake reduce these risks. It is likely that dental nosocomial infections are under-reported, but it also seems that where infection control procedures are followed, the risk of transmission is low.

3.4

Cost as a Barrier to Infection Control

Cost is an important part of infection control, and it must be considered when deciding what steps are reasonable. Most risks from contaminated re-usable instruments in dentistry would be solved instantly if everything that was used was single use, but this would simply not be financially viable when we consider certain equipment like dental handpieces. Cost can certainly be a barrier but must not be used as an excuse for poor infection control. It seems reasonable to expect that there should be a level of financial commitment that is expected, based on the availability of resources, within the country that dentistry is practiced. Healthcare-acquired infections are a global problem, but resources are not shared equally. Many countries simply do not have the financial resources and infrastructure that others have. This is where national and local dental organisations have a key role in setting the standards their members should be meeting as they will be able to form a consensus as to what is reasonable. International efforts may be needed to help raise standards, an example being the WHO/UNICEF WASH strategy is aimed at addressing the sanitation and hygiene in healthcare needs of those parts of the world that need help.

3.5

The Environmental Impact of Infection Control

Sustainability in healthcare, including dentistry, is a global imperative. In many countries, there is a legal obligation to address climate change and the role of carbon emissions and other greenhouse gases. Sustainability is approached through optimised resource management and making systems better for the environment.

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3  The Regulation of Infection Control

There are certainly ways infection control can be improved to address sustainability, but not without some challenges that are yet to be overcome. The environmental impact of infection control includes the roles of energy, toxic chemicals and waste. Electricity and gas use contribute about 15% of the carbon footprint in dental care. Examples where this can be reduced include turning off autoclaves and automated cleaning machines when not in use, not using water that is too hot to wash hands and using reverse osmosis-generated water rather than distilling it on-site. The hierarchy of waste prioritises the ways waste is managed (Fig.  3.1). Separating instrument wrapping for recycling before it becomes contaminated can avoid it being incorporated in waste streams that result in incineration or going to landfill. Technologic advancements are creating ways of reducing dental waste. Radiographic waste chemicals and film lead can be recycled, but by moving to digital radiography, they can be eliminated. Intraoral scanners that take optical impressions eliminate the generation of waste from both impression materials and gypsum. Gypsum waste emits hydrogen sulphide gas when mixed with organic waste, which is both toxic and an environmental pollutant. Single-use plastics are an environmental concern because they do not biodegrade but persist in the environment when thrown away. Extensive contamination of parts of the world’s oceans has raised public awareness of this problem in the last few years. Single-use items are an important part of infection control because many items cannot be reliably cleaned. It is not appropriate to lower infection control standards to address this. There is scope for improvement in the materials

Redesign the product to make it more sustainable

Most favoured

Reduce the amount of waste produced

Reuse products

Recycle Recover energy from heat when waste is incinerated*

Landfill

Least favoured

*It is not clear cut that energy recovery is preferable to landfill

Fig. 3.1  The hierarchy of waste

3.5 The Environmental Impact of Infection Control

25

manufacturers use, looking at viable alternatives, incorporating recycling, how items are packaged and where they are made. Examples include suction tips made from paper and three-in-one tips made using recycled plastics (Figs. 3.2 and 3.3). At present, it does not seem possible to further recycle single-use plastic items that are contaminated. In the surgery, disposable plastic barriers placed on surfaces that are easily cleaned could be considered unnecessary. Some waste facilities will reprocess medical waste as flock, which can be used as a fuel. Ash recovered from incinerated waste can be used as an aggregate, e.g. for making asphalt roads. Fig. 3.2  The tips for air/water syringes are an example of the tension that arises when addressing sustainability in infection control. Metal tips can be re-used which avoid waste, but successive studies have demonstrated they are not readily cleaned due to their narrow lumens and for this reason are not advised; single-use tips should be used. The tip depicted is made from 30% recycled plastic, demonstrating how some manufacturers are seeking to address the issues associated with single-use items. Courtesy of EcoBee, Inc

Fig. 3.3  With heightened awareness of the role of plastic waste, the public has an expectation that industries look to alternatives. At the time of writing, the manufacturers of dental consumables have been slow to move in this direction, but there are those that have innovated and brought alternatives to the market. This is exemplified by the paper high volume ejector/suction tip pictured here. Courtesy Practicon, Inc

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3  The Regulation of Infection Control

Reducing toxins released into the environment can be achieved in several ways. Australia and New Zealand have actively sought to reduce disinfectant chemicals used in dentistry by advising the use of detergents to clean hard surfaces in the treatment area. Countries who are signatories to the Minamata Convention are committed to reducing their use of dental amalgam. The use of amalgam separators in the dental suction systems reduces the levels of amalgam waste that can contaminate water ways (Fig. 3.4). Using a waste contractor that allows for the disposal of extracted teeth that contain amalgam separate from other clinical waste is advised too.

Fig. 3.4  In Europe, amalgam separators are compulsory under EU regulation 2017/852 and should meet the standard set by EN ISO 11143:2008

Further Reading

3.1

27

Case Studies

Case Study: The Role of Resources in Shaping Standards

It is reasonable to assume that the dentistry undertaken and the patients seen in England and Scotland are not dissimilar, presumably with the same infection control risks associated with their care. However, these two countries have different guidelines on infection control and, furthermore, different essential standards. In Scotland, the use of a thermal washer disinfector is considered essential practice, whereas in England it is best practice. This difference in part is accounted for by a smaller number of dental practices in Scotland and accompanying government grants for some practices that helped meet this standard. Lack of a willingness by government to provide resources for state funded dentistry in England in part may account for a difference in standard.

Case Study: The Gap Between Essential Practice and Best Practice

It was not routine for many dental practices to process handpieces in an autoclave until the mid-1990s. The profession was forced in part to change this due to public scrutiny following media features that scared the public they were at risk of getting HIV from handpieces at their dentist. Multiple bodies including the WHO now consider it essential that handpieces are reprocessed, including in an autoclave after use. There is a good body of evidence that demonstrates that handpieces reprocessed in a non-vacuum autoclave may not be sterile. For sterility assurance handpieces must be reprocessed in a vacuum autoclave, representing best practice. Whilst there is a considerable difference in running cost between the two types of autoclave and a small body of evidence to support the actual risk to patients, it is unlikely that vacuum autoclaves will become essential for all handpieces in the near future worldwide. It is reassuring to note that in some parts of the world, such as Australia and possibly elsewhere, surgical handpieces must be reprocessed in a vacuum autoclave.

Further Reading Healthcare-associated Viral and Bacterial Infections in Dentistry Laheij AMGA, Kistler JO, Belibasakis GN, Välimaa H, de Soet JJ, European Oral Microbiology Workshop (EOMW) 2011. J Oral Microbiol. 2012;4 https://doi.org/10.3402/jom.v4i0. Molinari JA. Infection control: its evolution to the current standard precautions. J Am Dent Assoc. 2003;134(5):569–74. Oosthuysen J, Potgieter E, Fossey A. Compliance with infection prevention and control in oral health-care facilities: a global perspective. Int Dent J. 2014;64(6):297–311.

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Links https://www.cdc.gov https://www.fdiworlddental.org https://www.unicef.org/wash/

3  The Regulation of Infection Control

4

Hand Hygiene and Personal Protection

4.1

Hands

Semmelweis demonstrated the importance of hand hygiene in 1847, and it remains the single most important intervention in infection control. This is because so many diseases are transmitted by our hands. Potential pathogens will be amongst the transient flora residing on our hands; the microbes loosely attached to the outer layers of our skin, picked up from touching parts of our body; contact with other people; handling pets and other animals; and contact with surfaces like door handles and other fomites. These can then be passed onto people we contact, e.g. patients, and deposited on fomites, or we can self-inoculate ourselves, e.g. touching our mouth and nose. Hand hygiene aims to remove these harmful microorganisms and stop their spread. Unfortunately, hand hygiene is frequently not well done in healthcare, and dentistry is no exception. To help with compliance, the infection control lead should establish and enforce a practice hand hygiene policy; ensure regular staff training; put up posters that demonstrate how hands should be cleaned; and ensure hand hygiene facilities are suitable. It seems people need constant reminders and feedback to improve and maintain good hand hygiene compliance.

4.2

Soap and Water

Hands can be cleaned using either soap and water or an alcohol-based hand rub. Soap and rubbing the hands whilst washing them will lift contaminants off the skin, which are then carried away by water (Fig. 4.1). The temperature of the water should be comfortable; the heat of the water is not going to kill the microorganisms on the hands, it only needs to carry them away. If water is too hot, it may burn, and if the temperature isn’t comfortable, people may rush and not wash long enough. Excessive water temperature also impacts on sustainability, as unnecessary energy

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_4

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4  Hand Hygiene and Personal Protection

1

2

Wet hands with water

3

Apply enough soap to cover all hand surfaces

4

Rub hands palm to palm

5

Right palm over left dorsum with interlaced fingers and vice versa

6

Palm to palm with fingers interlaced

Backs of fingers to opposing palms with fingers interlocked

Fig. 4.1  How to hand wash. The procedure should take 40–60 s. Reproduced with permission of the World Health Organization. Based on the WHO Hand Hygiene Poster http://www.who.int/ gpsc/5may/How_To_HandWash_Poster.pdf?ua=1 © World Health Organization 2009. All rights reserved

4.2 Soap and Water

7

31

8

Rotational rubbing of left thumb clasped in right palm and vice versa

Rotational rubbing, backwards and forwards with clasped fingers of right hand in left palm and vice versa

10

9

Rinse hands with water

11

Dry hands thoroughly with a single use towel

12

Use elbow to turn off tap

Fig. 4.1 (continued)

Your hands are now safe.

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4  Hand Hygiene and Personal Protection

is being expended. Soap should be in liquid form rather than a traditional bar. This is because bars of soap may be potential reservoirs for microbes, acting as a fomite. Once washed, hands should be dried to reduce recolonisation of bacteria. Furthermore, moist gloved hands will be more prone to irritation. Disposable paper towels are recommended for dentistry as hand dryers are noisy and have the potential to blow droplets containing any transient flora not washed away into the air.

4.3

Alcohol Rub

Alcohol hand rub is advised for routine hand hygiene other than where soap and water are indicated (Fig.  4.2). This is largely due to ease of use and the need to encourage compliance in hand hygiene, which has been found to be better when alcohol rubs are made available (rather than handwashing alone). They have a good broad antimicrobial range of activity. Quick evaporation also leaves the hands dry before donning gloves and reduces the amount of paper waste. Not all hand rubs are equal, with varying alcohol content and other additives which can affect how quickly they dry out and how comfortable they are to use. They should contain at least 60% alcohol. The addition of humectants like glycerol and emollients makes them less irritating to the skin. For hand rub to be optimally effective, it must be used for 20 to 30 s, so it is important that the rub does not evaporate too quickly. Evaporation time can be moderated by the addition of thickeners.

4.4

When to Wash and When to Rub

It is prudent that hands are washed with soap and water at the start and end of the session, where visibly dirty, after contact with body fluids and after using the toilet. However repeated handwashing with soap and water can dry out the skin leading to dermatitis. Alcohol hand rubs reduce the chance of irritant dermatitis compared with soap; however they cannot clean dirt off hands, and they don’t kill all microorganisms. Alcohol attacks the lipid envelopes of viruses, but certain gastric viruses like Norovirus do not have this cellular feature so it isn’t very effective. Therefore, washing hands with soap and water is preferable after going to the toilet. The use of a moisturiser at the end of the session will help reduce drying out of the hands. Moisturisers act as a barrier keeping water within the skin layers. They shouldn’t be used prior to putting on gloves as they may compromise the integrity of the glove material. Soap, alcohol rub and moisturiser should be contained within single-use dispensers or cartridges. This is because microorganisms can accumulate within refillable containers. By purchasing alcohol rub that conforms to EN 12791, you should have some reassurance that it is suitable. Alcohol hand rub should be stored safely and away from points of ignition as it is flammable. Where practices have dispensers for public use in non-clinical areas, ensure that they are not above carpet, which can soak up drips, or by fire exits.

4.4 When to Wash and When to Rub

33

Fig. 4.2  How to hand rub. The procedure should take 20–30 s. Reproduced with permission of the World Health Organization. Based on the WHO Hand Hygiene Poster http:// www.who.int/gpsc/5may/ How_To_HandRub_Poster. pdf?ua=1 © World Health Organization 2009. All rights reserved

Apply a palmful of the product in a cupped hand, covering all surface

Rub hands palm to palm

Palm to palm with fingers interlaced

Right palm over left dorsum with interlaced fingers and vice versa

Backs of fingers to opposing palms with fingers interlocked

Rub hands the same way as for hand washing, step 3 through 8

Your hands are now safe.

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4.5

4  Hand Hygiene and Personal Protection

Personal Protective Equipment (PPE)

All members of the dental team should expect to work under safe conditions. Risks to safety should always be eliminated or reduced as much as possible; we call this risk management. The contemporary method of assessing risk management is to use a hierarchy of hazard controls (Fig. 4.3). Eliminating a safety risk is the most desirable control measure, but may not always be possible. The dental team is at risk of injury from infections, primarily those carried by the patients under their care. Blood and saliva can transmit a range of pathogens, and the dental team are potentially exposed to copious amounts of both during the working day. By placing our fingers in patients’ mouths, using and cleaning sharp instruments and generating aerosols via high-speed handpieces and ultrasonic tools, we are putting ourselves at risk. The areas particularly vulnerable when providing dental care are the face and hands. Our eyes, nose and mouth are all potential routes pathogens may pass through to infect us. Therefore, it makes sense to use physical barriers to reduce the chance of this happening. These barriers are called personal protective equipment (PPE) and form part of the recommendations of standard precautions. Many countries regulate and legislate the use of PPE, and it is employers’ obligation to supply it. PPE is an essential component of risk management, but users should pay heed that it is the least effective way of controlling a risk.

Most effective

Hierarchy of Controls Physically remove the hazard

Elimination

Substitution

Replace the hazard

Engineering Controls

Isolate people from the hazard

Administrative Controls PPE

Change the way people work Protect the worker with Personal Protective Equipment

Least effective

Fig. 4.3  Hierarchy of controls in risk management. Credit: National Institute for Occupational Safety and Health

4.7 Nose and Mouth

4.6

35

Eyes

Dental procedures place eyes at risk of infection and mechanical and chemical injury. Infections can be spread via blood and saliva splashes. Tooth and dental materials are dispersed about when drilled. Chemicals including etchant on teeth and disinfectants used to clean hard surfaces of the surgery may be splashed too. Subsequently eye injury is a potential hazard when treating patients and undertaking decontamination. Glasses that offer side protection and conform closely to the face or face shields/visors are advised to protect the eyes. Eyewear that conforms to regional standards (e.g. ANSI Z87.1-2003  in the USA; European standard BS EN166:2002; Australian and New Zealand standard AS/NZS 1337.1; SANS404 in South Africa) is recommended (Fig. 4.4). In the event of the eye being contaminated or injured, first aid protocols should be in place. Material safety data sheets will also help in the immediate management of chemical splashes to the eye. An eye wash kit or station is essential in every dental practice, and staff should be aware of its location.

4.7

Nose and Mouth

Face masks can be used to protect the nose and mouth from splatter and aerosols generated by routine dental procedures. Masks may also protect patients from the wearer, but the evidence base for this is weak. It would seem sensible to wear a mask even when using a face shield to provide optimal protection against splatter directed upwards that may go under the shield (Fig. 4.5). Face masks have their limitations and must be used properly if they are to be effective. Firstly, they are single use and should be disposed of after each patient. Touching them mid-treatment, pulling them down and leaving them over the chin and extended periods of wear will compromise the mask. Wicking of moisture in the Fig. 4.4  Safety glasses should extend to protect the sides of the eyes. Courtesy of Hogies Australia Pty Ltd

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4  Hand Hygiene and Personal Protection

Fig. 4.5  A face mask worn under a face shield is advisable to protect against splatter directed upwards

mask will cause it to collapse and become a poor barrier allowing contaminants on the surface to come into direct contact with the wearer. Effective communication is essential in dentistry, and wearing a face mask can hamper this. Rather than pulling the mask temporarily over the chin, potentially with dirty gloves, remove the mask, and after discussion with the patient, put on a new mask. Unfortunately, incorrect mask wearing has become normalised in the dental press where dentists are depicted talking with patients and a face mask pulled down around their chin (Fig. 4.6). The face masks used in routine dental care will not filter out smaller particles that may cause respiratory infections, like tuberculosis or influenza. In some clinical settings where patients with acute respiratory infections are being treated, the use of FFP3 class respirator masks is advisable. This type of respirator is often recommended by public health authorities for clinical staff during influenza epidemics. This style of mask lies outside the scope of this guide.

4.8

Gloves

The pioneering surgeon William Halsted is credited with commissioning the Goodyear Rubber Company to make the first pair of rubber gloves, circa 1890, to protect his future wife Caroline from the harsh chemicals she was being exposed to when scrubbing surgical instruments. Halstead was inspired by Lister to incorporate

4.8 Gloves

37

Fig. 4.6 How not to wear a face mask. The image of the dentist with a face mask around the chin has become a cliché of dental marketing but risks normalising this poor habit

aseptic surgical techniques, but it was his colleague Joseph Bloodgood who first started to wear gloves for his operations, with great success. Following the introduction of universal precautions in 1987, just short of a century after Halstead’s innovative work, examination gloves are now considered mandatory for dental care. They serve to protect the wearer from pathogens and harmful chemicals, and they offer indirect protection to the patient from infections arising from the wearer. It must be considered if gloves have the potential to introduce bacteria into our patient’s mouths. Sterile gloves are used in oral and maxillofacial surgery where there are deep wounds, but are not indicated for routine primary dental care. A small number of studies have not found any difference in post-operative complications where sterile or non-sterile gloves have been worn for the nonsurgical extraction of

38

4  Hand Hygiene and Personal Protection

teeth. The bacterial load found on non-sterile gloves straight out of the box is likely to be too low to cause an infection of the wound site. It is important that the glove box does not become a point of contamination, and this will be reduced by strict adherence to hand hygiene and storing boxes in a way that operative aerosols don’t settle on them. Wall-mounted glove dispensers are a simple way of keeping work surfaces uncluttered. Wearing two pairs of gloves at once is termed double gloving and emerged as a belt and braces response to the fear of contracting HIV from patients in the 1990s. There is evidence to support the use of double gloving for exposure prone surgical procedures as commonly undertaken in orthopaedic surgery, but for routine dental care, this is unnecessary. Double gloving to treat patients simply because they are HIV positive is not indicated and has been identified as a behaviour that stigmatises and discriminates. Some countries regulations demand that HIV-positive dentists double glove when treating patients, although there is no evidence to support this requirement. Examination gloves come in a range of materials, each with their advantages and disadvantages. Those made from latex, nitrile and vinyl are the most popular and are acceptable for dental care if they conform to an acceptable standard, e.g. EN 455, ISO 11193-1. Latex gloves have historically been the first choice due to their lower cost, elasticity and durability. The problem with latex rubber gloves is they contain proteins that some people are allergic to. This can be a life-threatening (type I hypersensitivity) anaphylactic reaction. Powder donning agents, used to help ease gloves on, may absorb latex proteins and should be avoided. The use of powder free gloves will avoid creating an aerosol of latex proteins which could be inhaled, by staff or patients, or transferred beyond the confines of the surgery. The more common reactions to latex, and non-latex gloves, are (type IV delayed hypersensitivity) contact dermatitis reactions. These reactions are commonly due to the chemicals used in the glove manufacturing process called accelerators. There has even been a case report of an allergy to the dye used to colour nitrile gloves. Whilst manufacturing methods have sought to reduce the allergens in latex gloves, there are those that have chosen to make their dental practices latex free. This rationale adopts the risk hierarchy principal of substitution; if a safer alternative exists, use it. Some elastomeric impression materials that are mixed by hand are inhibited by latex gloves, nitrile gloves and donning agents. Sulphur in latex gloves can react with the catalyst chloroplatinic acid found in these impression materials. This disrupts the setting reaction making the impression unreliable. Where a material is not setting as expected, nitrile or vinyl gloves should be worn. The benefits provided by the barrier a glove provides may also contribute to skin irritation (irritant contact dermatitis), as moisture from sweat can accumulate within the glove during prolonged wear, combined with frequent hand hygiene. Prolonged use of gloves may also increase microporosities, reducing their protective effect. For these reasons gloves should be changed during lengthier procedures. Gloves are single use and should be disposed of in the correct waste stream. Wearing gloves does not remove the need for hand hygiene. Multiple reports have identified that gloves are often misused by healthcare workers. Some workers have been found to keep gloves on and continue with other tasks where hand hygiene

4.9 Uniform and Aprons

39

should have been exercised; this can lead to the misuse of gloves spreading infection. Therefore, it is important that their use is limited to clinical wear and that they are removed and hand hygiene performed prior to touching clinical records, pens, etc. Walking out of the treatment area to other rooms in the dental practice whilst still wearing gloves is a poor practice and should not be done. More thoughtful use of gloves can also help practices meet their efforts to improve sustainability. This is done by ensuring everything is in place before undertaking any work where gloves are needed, e.g. materials are out of drawers and radiographs and charts are available to see, thereby reducing the number of glove changes during the patient’s visit. Where instruments are cleaned as part of the instrument reprocessing cycle, examination gloves are too thin to provide protection from sharps and puncture wounds. It is recommended that heavy-duty gloves are used. This is especially important if manual cleaning of instruments is undertaken as it has the greatest potential for those handling the instruments to be injured. They need not be single use, and they should be washed after use and left to dry. If they are damaged, they should be disposed of. It is considered good practice to replace them weekly.

4.9

Uniform and Aprons

The clothes we wear in the surgery can also become contaminated. A uniform should not be considered PPE, but it should be worn to separate it from our regular clothes. Fabrics that can be washed at high temperatures are advisable. Whilst there is no evidence that cleaning uniforms at home is ineffective or a significant risk in transmitting infection, it is advisable to carry uniforms in a plastic bag and clean them separately to other loads. If space allows a washing machine within the practice dedicated to laundering uniform could be considered. It is sensible that uniforms finish at the elbows to maintain good hand hygiene although this might prove to be a cultural/religious issue for some people where modesty is a concern. One study looking at doctors demonstrated no difference in the efficacy of hand hygiene if elbows were bare or not. The concern in dentistry is the type of work undertaken has the propensity to wet sleeves; fabric readily takes up water making it a good environment for bacterial growth. Where being bare below the elbow is a problem, acceptable solutions are full or three quarter sleeves that can be pulled or rolled back when treating patients. Alternatively, single-use disposable sleeves are available. Certain clinical procedures, and when decontaminating instruments, put us at greater risk of getting splashed by body fluids. Disposable plastic aprons provide a simple means of protecting against contamination. Wall-mounted apron dispensers are available. Aprons should only be worn for a single patient. For minor oral surgery (excluding nonsurgical extractions), disposable sterile gloves and gowns are indicated. Not only do they protect the wearer from splashes, but they will reduce the chance of the site of surgery being contaminated by microorganisms falling off the dental team; subsequently they cover the whole arm, with the cuffs covered by sterile gloves.

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4  Hand Hygiene and Personal Protection

4.10 Treatment Considerations When treating patients, efforts that reduce exposure to aerosols are a good idea. The use of high-volume evacuation (HVE) suction and rubber dam where possible may help reduce the spread of microbes around the room. Good ventilation and airflow are essential. Pretreatment mouth rinsing with chlorhexidine mouthwash before using ultrasonic scalers has been suggested as a way of helping reduce potential airborne pathogens. The use of chlorhexidine should be discussed with patients following documented, albeit rare, cases of fatal allergic reactions to it in dental practices.

Putting on and taking off PPE When both putting on and taking off PPE the order it is done is of significance. It is important that “clean” gloves are put on last, after hand hygiene, so contamination is minimised. When removing PPE gloves should come off first, and other barriers are removed in a fashion that does not inadvertently contaminate the wearer.

Putting on PPE 1 . Where indicated, put on single use apron first. 2. Fit face mask. 3. Fit eye protection. 4. Undertake hand hygiene. 5. Put on gloves.

Removing PPE 1. Remove gloves by pulling them inside out. If the hands become contaminated at this point, they should be washed. 2. If worn, remove the apron by breaking at the back of the neck and folding it inwards by gathering it on the clean side that rests against the body. 3. Face masks are either unhooked from the ears or the ties broken and the mask removed away from the face whilst holding the outer edge where least likely to be contaminated. 4. Eye protection is then removed. 5. All disposable items should be placed in the appropriate waste stream. 6. Hand hygiene is performed. Face shields and safety glasses will need to be cleaned or disposed of where damaged.

Further Reading

41

Further Reading Moodley R, Naidoo S, Wyk JV. The prevalence of occupational health-related problems in dentistry: a review of the literature. J Occup Health. 2018 Mar 27;60(2):111–25. WHO. WHO guidelines on hand hygiene in health care: first global patient safety challenge clean care is safer care. Geneva: World Health Organization; 2009.

5

The Immune System

Pathogenic organisms use our bodies to replicate, grow and survive. Their activity on and within us, and how our bodies respond to this, results in the signs and symptoms of disease. To protect ourselves from the myriad of possible threats, we have a system of defences, the immune system. This compromises an incredibly complex interplay of chemicals and cells that interact to isolate, destroy and remove potential threats. The immune system needs to be able to differentiate ourselves (self) from potential threats (non-self). Antigens are the parts of non-self that are recognised by the immune system. Antigens on the surfaces of microorganisms mostly take the form of proteins or polysaccharides. The immune system has an innate response and an adaptive response to antigens (Fig. 5.1). These responses are mediated by both cells (cellular response) and chemicals within body fluids (humoral response).

Immune system

Innate

Physical barriers

Natural post infection

Adaptive

Internal defenses

Active

Artificial post immunisation

Passive

Natural maternal transfer

Artificial antibody transfer

Fig. 5.1  The elements of the immune system

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_5

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5  The Immune System

The innate response is immediate and not specific, with cells including macrophages and the complement cascade within fluids becoming activated when antigens are detected. Some innate immune cells have pattern recognition receptors (PRRs) that recognise specific pathogen-associated molecular patterns (PAMPs) that are not in humans but are found on the surfaces of viruses, bacteria, fungi and protozoa; this allows for immediate recognition that these are non-self and therefore should be eradicated. Whilst the immediate response is broad and quick acting, not targeting specific threats means that there will be those pathogens that are resistant to this first line of defence due to their own innate and adaptive mechanisms of self-preservation. The adaptive response is specific to a single antigen. Antigens are taken up by dendritic cells within tissues and presented to the lymphocytes in lymphoid tissue, but this means there is a delay in the time between exposure to the antigen and the response. The innate response is critical during this time in providing protection. Antigen-­ specific lymphocytes within the lymphoid tissue become activated and proliferate. These cells and the antibodies they produce will then attack the pathogens with the associated specific antigens. Most of these defensive cells will die off after they have performed their defensive role, but some will remain in the form of memory cells. Memory cells allow a quicker response should the same threat be met again, rapidly producing antigen-specific antibodies.

5.1

Vaccines

By taking advantage of the adaptive immune response, vaccines can be administered to immunise against infections and toxins (Fig. 5.2). Vaccines capitalise on the immune response targeting specific antigens and forming a memory for these antigens. If an antigen can be presented to our immune system stripped of the accompanying threat of a pathogen, then the adaptive response will be able to make memory (T and B) cells that will be quickly activated should the pathogen that antigen is associated with be encountered. Vaccines have been developed that use live bacteria or viruses that have been weakened (attenuated), inactivated and parts of bacteria and viruses (fractions). Researchers are currently exploring methods of directly changing host immune cells via DNA and recombinant vector vaccines. Whilst the principal of tricking our immune system with antigens is straightforward, the reality is far more complex. Unfortunately, making vaccines is not a simple affair. This is because many pathogens mutate (e.g. the common cold); invade and damage immune cells thereby evading detection or destroying our defences (e.g. HIV); or have a complex life cycle (e.g. malaria) to name but a few barriers. The route of administration and the site of injection can also influence the efficacy of a vaccine; this is why some are injected, and others are inhaled or swallowed.

5.2 Herd Immunity

45

Invading microbe

Vaccine

Antigen on antigen presenting cell

B cells T cells Memory

B blasts

Secondary lymphoid organs

Memory T blasts

Plasma cells

Antibodies

T cells Cell mediated immunity

Fig. 5.2  Active adaptive immunity

5.2

Herd Immunity

There have been many successes in vaccine development, and vaccines are an important tool in infection control with the World Health Organization estimating between two and three million lives saved each year. Immunisation protects members of the dental team and vulnerable patients under their care and may also contribute towards herd immunity. Herd immunity is the protective effect of halting the transmission of an infection within a population due to a critical number of people being immune and unable to pass an infection onto those who are not immunised. Herd immunity is important in protecting those in the community who cannot be vaccinated (Fig. 5.3). When the threshold of protection is not reached due to too few people being immunised, infections can spread. This has been repeatedly seen in communities where the uptake of the MMR triple vaccine has diminished below the 93–95% threshold and measles outbreaks occur. It is worth noting that the MMR vaccine has come under much scrutiny following the now discredited and retracted publication of a paper that proposed a link between the development of autism and MMR. It is important that the dental team is clear in its understanding that there is no such link.

46

5  The Immune System = Not immunized but still healthy

= Immunized but healthy

= Not immunized, sick, and contagious

No one is immunized.

Contagious disease spreads through the population.

Some of the population gets immunized. Contagious disease spreads through some of the population.

Most of the population gets immunized. Spread of contagious disease is contained.

Fig. 5.3  Herd immunity occurs when enough of the population is immunised against an infection. Credit: National Institute of Allergy and Infectious Diseases

As expected from our understanding of the innate immune response, common responses to be expected following vaccination may include the symptoms of inflammation, mild shivering, fatigue, muscle and joint pains and headache. Rare outcomes are febrile seizures and anaphylaxis.

5.4 Hepatitis B

5.3

47

Vaccines for the Dental Team

Mandatory vaccination has been a contentious issue since the mid-nineteenth century with the introduction of the Vaccination Act of 1853 in the UK. It continues to challenge us today when faced with considering the rights of the individual versus that of society and the communities in which we live. Further questions arise when we ask if healthcare workers, the dental team included, have an ethical and moral obligation to be immunised against various diseases regardless of their personal choice because of the need to protect the patients under their care. Many authors have concluded that healthcare workers do have a moral imperative to be immunised against infections which pose a threat to their patients.

5.4

Hepatitis B

Regardless of the regulations under which the dental team work, hepatitis B vaccination should be considered essential even if it is not mandatory to practice dentistry. Hepatitis B has a very low infectious dose, meaning you need only be exposed to a small amount of the virus to become infected. The virus persists primarily in the blood but also saliva of those infected, making it a potential occupational hazard when undertaking dental care. Unfortunately, for many underdeveloped parts of the world, the uptake of hepatitis B vaccination by the dental team remains unsatisfactorily low. This is a concern as these tend to be the areas where the virus is endemic. Hepatitis B vaccine has been available since 1982 and is credited as the first vaccine to help prevent a cancer (hepatocellular carcinoma). The hepatitis B vaccine contains the protein hepatitis B surface antigen (HBsAg), a component of the virus’s lipid envelope. The surface protein is sourced from the plasma of those chronically infected or produced using recombinant insertion of genetic material using plasmids into cells (yeast or mammalian). The protection afforded by the hepatitis B vaccine will depend upon sufficient levels of the antibody ‘anti-HBs’. The hepatitis B vaccine is administered in three doses, usually at least 4 weeks apart. The longer the duration between doses, the higher the final antibody titre may be, but it will not improve seroconversion. A blood test is used to verify if a person is protected, and a titre above 10 mIU per ml will protect against both acute and chronic infections (Fig. 5.4). A titre of at least 100 mIU per ml is desirable, and below this is considered a weak response, and a fourth dose is indicated. It has about a 95% success rate, but not all recipients of the vaccine will seroconvert. A second three-dose course is undertaken where there has been an insufficient response. Even then there will be a small number who do not seroconvert. Variables that may reduce seroconversion are age (>40), smoking, obesity, alcohol intake, advanced liver disease and acute hepatitis B. For those that are unable to seroconvert, occupational health guidance should be sought. The ability to undertake routine dental care and decontamination duties may need to be reassessed and a risk assessment made. Access to hepatitis B immunoglobulin in the event of a needlestick injury should be in place, and periodic testing for hepatitis B infection may be required based on regional regulations. Hepatitis B

48

5  The Immune System

Fig. 5.4  An example of a report to check seroconversion following hepatitis B immunisation

immunoglobulin contains antibodies against HBsAg that have been extracted from donor plasma and is administered as a form of passive immunisation. Passive immunisation against hepatitis B is short lived and does not lead to the formation of immune memory against the infection. Some countries recommend that after 5 years a top-up (booster) dose of hepatitis B vaccine is given to replenish the memory cells. Whilst the level of anti-HBs that is circulating in an immunised individual might diminish with time, the current evidence does not support the need for a booster dose of hepatitis B vaccine for most people. This is because the memory (via B and T lymphocytes) against hepatitis B persists even when levels of anti-HBs drop. The decision to get a booster should be made by consulting an occupational health team or doctor, although it would seem prudent after known exposure to the virus. Other vaccines recommended for the dental team include the following: • • • • •

Routine vaccines: tetanus, polio, pertussis and diphtheria Measles, mumps and rubella (MMR) Chickenpox (unless already immune) Tuberculosis Influenza

5.5

Tuberculosis

The aerosol spread of droplets of pulmonary tuberculosis (TB) makes it a potential hazard to the dental team. Acutely infected patients rather than those with chronic latent infections are potentially infective. In 1921, the Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine was introduced against tuberculosis. It provides only partial protection against pulmonary tuberculosis that strangely diminishes the

5.7 Tetanus

49

closer you live to the equator. Whilst TB prevalence may be low in many countries, it certainly remains a problem throughout the world. Migration and changing population demography may lead to regions in otherwise low prevalence countries having a higher risk, as seen in London, UK. Despite the BCG vaccine not being fully effective, it is a sensible precaution that the dental team get it.

5.6

Influenza: Seasonal Flu

Influenza A and B viruses are the cause of flu for many thousands of people each year, normally during the winter months. Seasonal influenza is a challenge for vaccinologists as the viruses responsible are always evolving. Therefore, vaccines must be developed each year that attempt to predict what strain may come with the winter months based on events in the opposing hemisphere. This means that the vaccine will only provide protection if the correct strains have been predicted, and the effect will only be for that season. Yearly vaccination is highly advised for healthcare workers, the dental team included, as it may reduce the spread of the infection from the dental team to vulnerable patients (children, immunocompromised patients and the elderly). Uptake of the flu vaccine by healthcare workers has been historically low; the promotion of seasonal flu vaccination within practice could be championed by the infection control lead. Occasionally new strains of influenza emerge that rapidly spread and infect significant numbers of people around the world; this is called a pandemic. These pandemics can occur out of the winter season and have the potential to cause high mortality rates (Table 5.1). As well as vaccinating against influenza, a business continuity plan that anticipates what measures might be needed in the event of a pandemic would seem wise.

5.7

Tetanus

Tetanus is a disease due to the exotoxin released by the bacterium Clostridium tetani. This is a widespread bacterium that is extremely hardy due to its ability to form spores. It is often found in soil and faecal matter of livestock. Mass vaccination started in 1961, and for the most part, it is a rare but potentially fatal disease. It would be unusual for a member of the team not to already be protected, but there will be those colleagues that come from poorer countries where vaccination programs are not optimal. There are still a few case reports of tetanus following tooth extraction and from bites, both human and animal. It is important that following Table 5.1  Influenza pandemics of the twentieth century Year 1918 1957 1968

Virus Influenza A—H1N1 Influenza A—H2N2 Influenza A—H3N2

Name of pandemic Spanish flu Asian flu Hong Kong flu

Estimated global deaths At least 50 million 1.1 million 1 million

50

5  The Immune System

dental trauma the clinician checks tetanus immunisation status as the resulting wounds may be dirty. The tetanus vaccine is intriguing as it stimulates an immune response to the tetanus toxoid rather than the bacteria.

5.8

Chickenpox

Chickenpox is due to the varicella zoster virus. It is a highly contagious virus that is airborne, but also spreads through contact with surfaces and via the hands. For many members of the dental team, it will have been a childhood infection that subsequently conferred immunity, although the virus may remain dormant in nerve ganglia and be reactivated as shingles in later life. Those that are not immune will be vulnerable to infection from both those with chickenpox and those with shingles. They also pose a hazard to pregnant patients, new born children who may be brought to the practice and the elderly or immunocompromised under our care. These risk groups may suffer severe morbidity and even die if infected. Therefore, any members of the dental team who have not had chickenpox should be immunised against it.

5.9

Emerging and Regional Risks

Air travel has made many diseases a global problem due to the ease in travelling to most parts of the world in a short period. However, it is recognised that some regions may have a greater burden of certain diseases than others. This might necessitate variations in the recommended vaccinations on a regional basis. Dental workers who move to new areas for work, either temporarily or permanently, should ensure they meet both the regulatory requirements of the jurisdiction they move to and the public health advice of their homeland and destination. Immunisation is an important tool in dental infection control, but it is not an excuse for complacency. As with PPE, immunisation is a lower-order means of risk control (Fig. 4.3). Not all vaccines will offer complete protection against disease, but by using them the risk is reduced to both the dental team and the patients under our care.

Further Reading Clough S, Shaw A, Morgan C.  Tuberculosis and oral healthcare provision. Br Dent J. 2018;224(12):931–6. Jamrozik E, Handfield T, Selgelid MJ. Victims, vectors and villains: are those who opt out of vaccination morally responsible for the deaths of others? J Med Ethics. 2016;42(12):762–8. Ramsay M, editor. Immunisation against infectious disease. London: Public Health England; 2017. Taylor LE, Swerdfeger AL, Eslick GD. Vaccines are not associated with autism: an evidence-based meta-analysis of case-control and cohort studies. Vaccine. 2014;32(29):3623–9.

6

The Infected Oral Healthcare Worker

What risk does the dental team pose to patients when they are infected with a chronic blood-borne disease? Are the standard precautions enough to protect patients from infected members of the dental team or should their range of clinical duties be modified or even stopped?

6.1

HIV

When faced with this dilemma at the beginning of the HIV/AIDS epidemic, different regulatory bodies took varying approaches. In the UK, a hard-line approach was initially taken, and members of the dental team had to cease clinical work immediately. By 1987 the UK had convened an advisory panel that set the ruling that dentists could undertake a significantly reduced number of clinical duties, pretty much limited to making full dentures only. This rationale in part was based on the supposition that teeth are sharp and could result in the infected worker cutting themselves and bleeding into the patient’s mouth. No such restrictions were imposed on the dental team in the USA or Canada. HIV prompted a paradigm shift in dental infection control, part of which was driven by public perception, expectations, fear and misunderstanding. However, healthcare policy should be framed by a sound evidence base, not fear. The 6th World Workshop on Oral Health and Disease was held in Beijing in 2009. At this conference the evidence for the risk of transmission of HIV from the dental team to patients was analysed. From this emerged a four-point strategy for HIV-positive oral healthcare workers called the Beijing Declaration. 1. The team member receives continued care by a suitable HIV healthcare professional. 2. The team member remains aware of their health status and acts accordingly. 3. Standard infection control is practised. 4. HIV transmission scientific evidence is reviewed. © Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_6

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52

6  The Infected Oral Healthcare Worker

Table 6.1  Examples of exposure and non-exposure prone dental procedures as defined by the UK Advisory Panel for Healthcare Workers Infected with Blood-Borne Viruses Non-exposure prone procedures Removable prosthodontic procedures including impressions Using ultrasonic scalers Routine examination Taking radiographs (both extra- and intraoral)

Exposure prone procedures Administration of local anaesthetic Using hand scalers Extraction of teeth The preparation of teeth using a high-speed handpiece Root canal treatment

(From Challacombe SJ (2011) Beijing Declaration 2009, Adv Dent Res 23(1):6)

The evidence does not support the blanket banning of the HIV-positive dental team member. Nor does it support the restriction of duties to the edentulous mouth. An exposure prone procedure entails the gloved hands of a clinician not being fully visible at all times during surgical procedures, where the use of both sharp instruments and potentially sharp body tissues could cut the clinician (Table 6.1). This could then result in bleeding into the open wound of the patient. Classifying teeth as a potentially sharp body tissue would make a lot of dental care an exposure prone procedure. The evidence does not support this, and the risk of a cut to the gloved hand from a patient’s tooth that bleeds and then infects the patient is negligible. Despite the outcome of the Beijing Declaration, there remains significant variation throughout Europe in the way HIV-positive dental team members are treated. In some countries, all treatment is banned, others rule exposure prone procedures are prohibited, some require the individual to double glove and others have no restrictions or obligations to report their HIV status at all. It was a welcome relief, albeit too late for some, that the scope of duties the HIV-positive dentist could undertake in the UK was revised in 2016 with the ability to treat dentate patients.

6.2

Hepatitis B

Hepatitis B is far more infectious than HIV, requiring fewer viral particles to establish an infection. Less than 5% of adults who contract hepatitis B will become chronic carriers although children are at a much higher rate (as much as 80%). All the dental team are advised to get hepatitis B vaccination at the start of their training if they have not already done so; not all do so. There will be team members who already have chronic hepatitis B prior to their training and those who become infected once they have started, with a higher risk in resource-poor regions of the world and where hepatitis B is endemic. There have been, albeit rare, cases of dentist-­to-patient transmission of hepatitis B virus; therefore it is important to risk assess and manage members of the dental team who are infected. Where hepatitis B virus DNA levels are sufficiently low (below 200  IU/ml) and the person is HBeAg negative, it would seem the risk from undertaking exposure prone incidents is negligible. Regional rules will of course dictate what duties and tasks infected members of the dental team can undertake, if at all regardless of the current evidence.

6.4 Other Infections Fig. 6.1 Disease progression of viral hepatitis

53 Up to 90% recovery

Hepatitis B

Acute hepatitis

Hepatitis C

Up to 30% recovery

Chronic hepatitis 20-50 years

Cirrhosis

Hepatocellular carcinoma

Death

6.3

Hepatitis C

Hepatitis C is an insidious infection that may present with similar or milder symptoms to hepatitis B. Unlike hepatitis B, the chance of becoming chronically infected is as high as 80% (Fig. 6.1). Clinician-to-patient, patient-to-patient and patient-to-­ clinician transmissions of hepatitis C have all been documented in healthcare. In 2013 a dental clinic in the USA was forced to close after hepatitis C was transmitted between patients most probably via contaminated multi-use vials of medicine for intravenous sedation. Cases of transmission from the healthcare worker to patient have been associated with two groups: infected surgeons who do exposure prone procedures and those undertaking invasive procedures without wearing gloves. Whilst there is no vaccine (yet) against hepatitis C, there are antiviral medicines that are very effective. The efficacy will depend upon the strain of the virus and may require the use of multiple drugs for an extended period. Treatment does not confer immunity, so the risk of reinfection remains after treatment.

6.4

Other Infections

Acute childhood viruses and respiratory and gastrointestinal infections can easily be spread to the community. Where a member of the dental team is acutely ill, they should remain at home until they have recovered. This will protect both other staff members and patients. Sickness presenteeism is a neologism that describes those that are unwell but come to work anyway. Motivation for attendance may be due to the expectations of the management culture of the business. Acutely infectious staff

54

6  The Infected Oral Healthcare Worker

should not be working, and this should be reflected in the way dental practices are run as businesses too.

6.5

Sharps Injuries

There is no shortage of sharp instruments in a dental surgery that have the potential to cut those handling them. Where the skin is cut by a dirty sharp instrument, it is called a sharps injury. Of concern are used hollow-bore needles, as they have the potential to contain infected blood or body fluids which may result in transmission of the disease to the injured person. This is also referred to as a needlestick injury. The primary concern (but not limited to) following a sharps injury is inoculation with HIV and hepatitis B or C. These viruses have different likelihoods of successful infection. HIV has 1 in 300 chance, hepatitis C 1 in 30 chance and hepatitis B 1 in 3 chance of being transmitted from contaminated blood in a needlestick injury. As most members of the dental team should be immunised against hepatitis B, this

Fig. 6.2  A sharps injury poster should be sited in each treatment room and the local decontamination unit. It is a good idea to write on it the contact numbers of the local hospital’s accident and emergency department and the occupational health contact used by the practice. Courtesy of Daniels Healthcare Limited

6.5 Sharps Injuries

55

makes hepatitis C the most likely virus to result in an infection if it is in the contaminated sharp. A sharps injury is potentially a medical emergency. It is imperative that all staff know what to do in the event of a sharps injury and that there is a protocol in place that outlines the management for such an event. Advisory posters that simply and clearly outline sharps first aid management should be in every dental practice (Fig. 6.2). Four simple measures used on many advisory posters in the UK are: 1. 2. 3. 4.

Bleed it. Wash it. Cover it. Report it.

The wound site should be gently squeezed to encourage bleeding whilst also washing it under running water and cleaning the site with soap. These measures aim to reduce contamination at the wound site, potentially lowering the number of infectious particles below the threshold of transmission of infection. Covering the wound with a bandage protects the area from secondary infection. Multiple studies indicate that sharps injuries are under-reported. Within an organisation this may result in risks not being identified and appropriately controlled. For the injured worker, it might mean that the best care has not been sought and may pose problems with insurance and legal claims in the event of infection but no documentation of the incident. Algorithms have been developed to assess how a sharps injury should be managed after first aid has been administered. For a high-risk injury, time is imperative, and seeking advice should not be delayed. It is therefore prudent to have the contact numbers on a sharps poster for both an occupational health service and the closest hospital that provides emergency care. Where a sharps injury has been determined to be high risk, then post-exposure prophylaxis (PEP) treatment should be sought. PEP protocols should be in place and set by local health organisations and care providers. First aid kits should have suitable dressings for a sharps injury. Eyewash should also be available in the event of a body fluid splash in a team member’s eyes. The mucosal membranes of the eyes are a potential route of entry for the spread of infection. Copious flushing of the eyes aims to dilute any contamination. Healthcare workers are only too aware of the potentially life-altering consequences acquiring a blood-borne infection will have following a sharps injury. It is worth noting that some studies have identified healthcare workers who have developed post-traumatic stress disorder following a sharps injury, even though they have not become infected. In the UK, the greatest morbidity factor associated with a sharps injury is probably anxiety, yet this is a region where the risk of blood-borne infections is relatively low. Employers and colleagues should be mindful of this as there might be the need to offer both emotional and psychological support.

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6.6

6  The Infected Oral Healthcare Worker

Safer Sharps

Several regions and countries have legislated on the use of safer sharps. The USA’s Needlestick Safety and Prevention Act of 2000 was brought in to mandate the use of engineering controls to reduce the risk of sharps injuries to healthcare workers. Engineering controls are considered a reasonably effective way of risk management (Fig. 4.3). Sharp instruments and devices with safety features that aim to reduce the likelihood of injury are termed safer sharps (Fig.  6.3). Likewise, EU Council Directive 2010/32/EU on the use of safer sharps became mandatory in 2013 for member states. This law was a recognition of the risk sharps injuries posed to numerous healthcare workers, including the dental team. A key element of this change was to mandate the use of safer sharps where possible. For dental care, this not only includes safer syringe/needle systems for local anaesthesia but also scalpels and cannula for IV sedation. Under no circumstances should needles be recapped with two hands. Where a safer system is not in use, recapping aids should be used or, at worst, a single-handed scoop method to recap the needle. Too many dental nurses will have experienced a sharps injury when clearing up after patient treatment. Clinicians have a responsibility to ensure a safe working environment for both themselves and their colleagues. The simple principle that the person who generates the sharp disposes of the sharp should be followed and be part of the practice written protocols. Single-use sharps are a hazardous waste that must be disposed of in approved containers that are suitably sited (Fig. 6.4). A sharps container should meet an established standard that gives confidence that the contents won’t be able to pierce through or leak out (e.g. BS EN ISO 23907, AS4031). Containers must be kept off the floor and out of the reach of children. Where the surgery layout allows, wall mounting the sharps container close to the clinician is a good choice as the sharps can then be disposed of without moving around the room. Some safer syringe systems are relatively large compared with traditional hub-style needles and may readily fill a sharps container, so be mindful not to overfill containers as this may not allow correct closure of the sealing lid posing a risk to anybody handling the full container. Fig. 6.3  An example of a safer dental syringe/needle system. Note the safety sheath is retracted to expose the needle and then pushed back after use and prior to disposal

6.6 Safer Sharps

57

Fig. 6.4  A wall-mounted sharps container close to where sharps are generated allows the clinician to dispose them safely

Other measures to reduce the risk of sharps injury include not using wire-bur brushes to decontaminate instruments. Bur brushes are ineffective at cleaning burs, and the sharp wire bristles expose staff to an unnecessary hazard. The use of non-­ foaming detergent when manually cleaning instruments ensures staff can see what they are doing. Instrument cassettes which reduce handling of contaminated instruments and using automated cleaning instead of manual scrubbing (an ultrasonic bath or thermal washer disinfector) also reduce the risk by using engineering controls and safer alternatives (Fig. 6.5). There is evidence to suggest that most sharps injuries to dentists are from dental burs, so clinicians should be mindful of dirty burs remaining in handpieces which sit on delivery units (Fig. 6.6). Likewise used ultrasonic scaler tips left pointing upwards after use are a hazard too. These instruments all have the potential to scrape and injure the clinician’s arms or hands.

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Fig. 6.5 Instrument cassettes loaded in a thermal washer disinfector

Fig. 6.6  Dirty burs in handpieces can be a potential sharps hazard when resting in the delivery unit

Further Reading Bagg J, Roy K, Hopps L, Black I, Croser D, O’Halloran C, Ncube F. No longer ‘written off’ – times have changed for the BBV-infected dental professional. Br Dent J. 2017;222(1):47–52. Pereira MC, Mello FW, Ribeiro DM, Porporatti AL, da Costa S Jr, Flores-Mir C, Gianoni Capenakas S, Dutra KL.  Prevalence of reported percutaneous injuries on dentists: a meta-­ analysis. J Dent. 2018;76:9–18. Pozzetto B, Memmi M, Garraud O, Roblin X, Berthelot P. Health care-associated hepatitis C virus infection. World J Gastroenterol. 2014;20(46):17265–78. Riddell A, Kennedy I, Tong CY. Management of sharps injuries in the healthcare setting. BMJ. 2015;351:h3733.

Part II Decontamination in Dentistry

7

The Concept of Decontamination in Dentistry

The environment and equipment used in the provision of primary care dentistry should be made as safe as is reasonably practical, and this will include the risk reduction of the transmission of infections. It is neither possible nor likely that the risks can be reduced to nil because of the presence of human beings in the premises along with an atmosphere that will contain microorganisms. Therefore, a risk reduction strategy should be implemented that will reduce the level of risk to an acceptable level where it is unlikely that the transmission of pathogenic microorganisms will occur. The term sterile is an absolute term where there are no viable cells or viral particles present in the environment or on an item of equipment; the presence of a single viable cell will mean that the item cannot be described as sterile. It is not appropriate to describe anything as ‘almost sterile’ or ‘partially sterile’. It is not possible, therefore, to render the environment in a dental surgery sterile. Disinfection is a process which is intended to kill or remove pathogenic microorganisms but will not kill spores. It is not a process that should be considered adequate or appropriate for instruments used in the practice of dentistry. It is, however, the only practical method that is appropriate for treating the environmental items in the dental surgery in order to make them safe for the treatment of patients and a safe environment for staff to work in. Decontamination should be considered as the application of a range of appropriate processes that will render an item safe for use during dental procedures. The range of processes used will depend on the nature of the item to be processed. For example, reusable dental instruments will need to be cleaned and then sterilised, whereas surfaces in a dental surgery that may be contaminated with microorganisms are cleaned and disinfected. The details of the sterilisation and disinfection processes and protocols are dealt with in the chapters on sterilisation and disinfection. It is important to consider the relative risks posed by various items in the dental surgery when determining the appropriate decontamination processes to be used to make them safe. Alongside this it is important to consider the effect of the processes © Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_7

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7  The Concept of Decontamination in Dentistry

on the construction of the item. For example, some plastic materials are unable to withstand the effect of heat; some materials may be denatured by the use of certain chemicals or may be unable to withstand other physical processes such as the action of ultrasonics.

7.1

Dental Instruments and Equipment

Before deciding on appropriate measures to decontaminate reusable dental instruments and equipment, it is helpful to classify them according to the potential risk they may pose to the patient. Instruments can be classified as critical, semi-critical or noncritical, and this classification can inform the process by which they should be decontaminated. This classification scheme was proposed by Dr Earle H Spaulding in 1957 and has been updated and accepted by most worldwide authorities. Critical instruments—these are defined as instruments that will penetrate soft tissues, contact bone or will enter into or contact the bloodstream or other normally sterile tissues. Examples of this type of instrument are surgical instruments, periodontal scalers, scalpel blades and surgical burs. Semi-critical instruments—these are defined as instruments that will contact mucous membranes or non-intact skin but will not normally penetrate soft tissues, contact bone or enter into or contact the bloodstream or other normally sterile tissues. Examples of this type of instrument are dental mouth mirrors, restorative hand instruments, reusable impression trays and dental handpieces. Noncritical instruments—these will only contact intact skin. Examples of this are radiography head/cone, blood pressure cuff, pulse oximeter, operating light handles and bib chain. Critical and semi-critical reusable instruments must be sterilised between uses to reduce the risk of cross infection occurring. It may be considered advisable that critical instruments should be sterile at the point of use. Semi-critical instruments may not necessarily be sterile at the point of use but will have been sterilised; thus all microbiological traces of the patient that the instrument was previously used on have been removed and inactivated. In the original Spaulding classification, it was deemed adequate to subject semi-critical instruments to high-level disinfection, but in the light of current knowledge, in respect of some microorganisms resistance to some chemical disinfectants, it is now considered necessary to sterilise, where possible, these instruments. Noncritical instruments can be decontaminated by disinfection. Alternatively, it may be preferred to use a disposable barrier on a noncritical piece of equipment to reduce the need to disinfect the item particularly if they may be adversely affected by chemical disinfectants (Fig. 7.1). It is important to understand the difference between the terms ‘sterile’ and ‘sterilised’. The use of the term ‘sterile’ when applied to an instrument or piece of equipment refers to its state at the point of use. It will therefore be sterilised inside a sealed package which will prevent the penetration of microbes from the

7.1 Dental Instruments and Equipment

63 Spaulding Classification semi-critical & critical

non-critical

Cleanability Easy

Chemical resistance Yes

Loss of function No

Reprocess

Cleanability Easy

Difficult

Single use

No

Single use

Yes

Difficult

Heat resistance at 134ºC Yes

Loss of function e.g. sharpness No

Reprocess

Single use

No

Single use

Yes

Single use

Single use

Fig. 7.1  Spaulding decision tree

environment during storage and will allow the operator to be confident that the item is sterile until the seal on the package is broken. The term ‘sterilised’ refers to the fact that an item has been subjected to a sterilisation process after it has been used but may not be stored inside sterile packaging. Provided the instruments are stored in a safe manner that would prevent the instruments from becoming significantly contaminated by microorganisms from the environment, they would not pose a significant risk to the patient or operator. Some of the instruments, particularly some critical instruments, used in dentistry may either provide significant difficulties in terms of effective decontamination or may have reduced functionality when re-used and should be considered as disposable single-use instruments. This will be considered in more detail in Chap. 11. It is important to put the risks posed by the dental environment into perspective. There is no evidence that suggests that a sterile environment is either necessary or achievable in a dental surgery. The oral environment which is the gateway to both the alimentary and respiratory systems and as has already been noted is heavily colonised with microorganisms. The mouth is constantly exposed to environmental microorganisms when individuals breathe, eat and drink usually without any ill effects, and provided the surgery environment is maintained in a clean state, it should be no different to the general environment. The procedures carried out in a primary care dental surgery are significantly different to those performed in a general hospital operating room and does not involve sterile body cavities. Unlike an operating room in hospital where air is filtered and there are standards specified for changes of air volume, there are no agreed standards for air quality in a dental surgery. Similarly there are no specified quality standards for water supplies used in dental practice for routine dental procedures beyond the need to ensure the water used is of a potable (drinking) quality. These standards are usually specified in national drinking water standards and will vary slightly from country to country. Where surgical procedures requiring irrigation are carried out in a dental practice, it should be considered necessary to use a sterile solution provided by an independent supply. Further considerations of water systems and water quality are covered in Chap. 13.

8

Cleaning Methods for Dental Instruments

As already alluded to, it is essential to ensure that reusable dental instruments are scrupulously clean as a first step in the decontamination process. Any residual soil on the surface of equipment creates a risk that will prevent steam, generated during sterilisation, from condensing on the surface of the instrument and raising the temperature to that required to ensure sterilisation. Further, most microorganisms will struggle to attach to the surface of a clean instrument. Adherence of microorganisms to the surface of an instrument that is contaminated with organic soil or the irregular surface of residual dental materials is likely to be greatly enhanced. It is therefore important to ensure that residual dental materials are removed from the surface of instruments, at the point of use, before they are allowed to set. It is also important to ensure that the methods used to clean dental equipment do not damage the instrument. Any method that has the potential to scratch the surface of an instrument and therefore make it more difficult to clean should be avoided. Aggressive cleaning can lead to removal of the passivation layer, the chromium-rich layer that prevents corrosion occurring, formed on the surface of instruments made from stainless steel. If corrosion forms on the surface of an instrument, the surface becomes roughened and possibly stained. Surface staining can then be difficult to differentiate from other stains or marks caused by retained biological soil. Corrosion on the surface of an instrument will make the effective cleaning of the surface more difficult and therefore corroded or stained instruments should be discarded.

8.1

Principles of Instrument Cleaning

When selecting methods for cleaning instruments, the following factors should be considered: • Effectiveness • Safety of the operator

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_8

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• Cost • Reliability Effectiveness—Will the method remove the materials that are likely to soil the instrument, particularly bioburden? Safety—Is the method inherently safe for the operator? Are there risks that can be avoided? Cost—Is the relative cost of the method within the resources available to the practice? Reliability—What is the likelihood that the method will give consistent results? Can a system of quality assurance be devised to measure the reliability of the method? These factors will be considered when looking at the relative merits of the commonly available choices for cleaning dental instruments. There are fundamentally three different methods available for dental practices to use to clean reusable instruments prior to sterilisation.

8.2

Manual Cleaning

This is the oldest and traditional way of cleaning dental instruments but is not without its disadvantages and is possibly the least effective way of reliably cleaning instruments. It is important that operators carrying out this process are adequately protected. It is therefore highly recommended that they should be provided with and use a range of personal protective equipment. Heavy-duty rubber gloves should be worn to provide a level of protection for the operator’s hands from contaminated sharp instruments. It is important to ensure that the operator does not have a history of allergy to latex; if so it may be necessary to select a non-latex-containing material. Heavy-duty domestic latex or nitrile gloves will have a limited lifespan and should be discarded and changed regularly. If there are any signs of damage or leakage, then at that point they must be discarded. It is not recommended that clinical gloves are used when manually cleaning instrument as they are not considered to provide an adequate level of protection. The operator’s eyes must be protected by use of safety spectacles, a visor or goggles. When manually cleaning instruments, it must be appreciated that there is a significant risk of contaminated splashes or aerosols being generated that can enter the operators eyes. It should be noted that potentially contaminated splashes that enter the eyes should managed in the same way that a contaminated sharps injury would be. As there is a risk that splashes or spatter could contaminate the facial area, then a mask or visor should be worn. In order to protect the operator’s clothing from the risk of contamination during manual cleaning, a disposable plastic apron should be worn. To protect the operator’s feet from the risk of a penetrating injury from a dropped contaminated instrument, footwear should be enclosed substantial shoes.

8.2 Manual Cleaning

67

Manual cleaning should be carried out in two sinks, one of which should be designated as a ‘dirty’ sink and other should be designated a ‘clean’ sink. If only one sink is available, a separate bowl should be used for rinsing instruments. The ‘dirty’ sink is used to contain the contaminated instruments where they are scrubbed to remove the contaminated soil. The equipment required to manually clean the instrument should include an appropriate detergent solution and a long-handled nylon bristle brush to keep the operator’s hand at a safe distance from the working ends of the contaminated instruments. The use of a brush that could cause damage to the surface of the instruments, such as metal ‘bur’-type brushes, should be avoided. The detergent used should be a detergent that has been formulated specifically for cleaning surgical instruments of which there are a wide range on the market and are relatively inexpensive. A detergent that is aimed at the domestic market for cleaning cutlery and crockery should not be used. The operator must follow the manufacturer’s instruction for use which will include the working concentration of the solution and the temperature range of the water with which it is diluted. To facilitate this it is helpful to mark the inside of the sink with a line to indicate a known volume of water and then have a measure to add a known amount of detergent to arrive at the appropriate final dilution. A digital thermometer should be available to measure the temperature of the final solution. The temperature must not exceed 45 °C because proteins will coagulate onto instruments above this temperature, making their removal difficult. Once the ‘dirty’ sink has been filled with the detergent solution, the contaminated instruments should submerge below the level of the detergent. The use of a non-foaming detergent allows the operator to see what they are doing. The instruments should then be scrubbed, keeping them submerged to reduce the risk of creating contaminated splashes or aerosols. Each instrument should be cleaned individually rather than bunched together as a group in order to ensure that all surfaces of each instrument are cleaned. The cleaned instruments are then placed in the ‘clean’ sink where they are rinsed to remove the detergent solution in fresh potable water. When rinsing dental instruments, it should be adequate to use water supplied through the public mains water supply as this should be of potable quality and should be regularly tested for quality by the public authorities. If the practice is supplied with water from a private water supply, such as well or borehole, it should not be used unless it has been recently tested to assure quality. If there is no readily available supply of fresh water of known quality, it may be necessary to purchase fresh water for instrument decontamination. Once the instruments have been scrubbed and rinsed, they must be inspected to ensure that they are visibly clean. Before the instruments are inspected, they should be dried using a suitable clean non-linting cloth or a disposable paper towel. This needs to be done to ensure that there are no drops of water on the surface of the instruments that may hide any remaining soil on the surface. It is also important if instruments are being sterilised in a vacuum-type steriliser as, during a cycle, drops of water can flash off as steam which may be detected as an air leak by the steriliser and lead to a failed cycle indication. Visual examination of the cleaned instruments should be carried out under good lighting conditions using

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magnification. Any instruments that appear to have retained soil should be cleaned again before sterilisation. Following the cleaning of a batch of instruments, both of the sinks should be drained and a fresh detergent solution and fresh rinse water used for the next batch of instruments. This must be done to prevent carryover of soil removed from one batch of instruments to another (Figs. 8.1, 8.2, 8.3, 8.4, and 8.5). In summary, manual cleaning of instruments is a low capital cost method but is very labour intensive and is very operator dependent and difficult to quality assure meaningfully. It requires the operator to follow the protocol fastidiously to ensure that each instrument is thoroughly scrubbed. Quality assurance relies on visual inspection to provide quality assurance, and it should be borne in mind that not all biological soil is coloured to aid visual detection, for example, saliva. Its biggest drawback, however, is it is inherently an unsafe method of cleaning instruments from the operator’s perspective. The risk of ‘sharps’ injury is high and has been shown to be the single biggest cause of such injuries in dental practice. Fig. 8.1  Manual cleaning 1: Sink containing detergent solution at correct temperature

Fig. 8.2  Manual cleaning 2: Instruments immersed in detergent solution and scrubbed whilst fully immersed

8.2 Manual Cleaning Fig. 8.3  Manual cleaning 3: Scrubbed instruments placed in clean rinse water

Fig. 8.4  Manual cleaning 4: Rinsed instruments dried using clean cloth

Fig. 8.5  Manual cleaning 5: Dried instruments inspected for cleanliness before sterilisation

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8.3

8  Cleaning Methods for Dental Instruments

Ultrasonic Cleaning

The use of ultrasonic cleaning baths has been in common use in dental practice for several decades. Ultrasonic cleaning baths use ultrasonic waves generated by transducers fitted to the base of the chamber. The sound waves that travel through the cleaning solution can remove soil from the surface of objects by a process known as ‘acoustic cavitation’. This involves the formation of cavities in the solution on the surface of the object being cleaned. As these cavities in the solution collapse, they generate high temperatures (up to 5000 °C), and large forces are created in localised areas. The cumulative effect of millions of these events happening within a very short space of time causes disruption of soil in these areas. Cavitation occurs wherever there is fluid in contact with the surface of the object; therefore it is important to ensure that there is no air trapped within the object. It is also important that instruments are not in contact with each other in the chamber as damage can occur where they touch. In use, the ultrasonic bath must be filled with an appropriate detergent solution, and the chamber must not be overloaded. Therefore, there should be a single layer of instruments, and each instrument must not be in contact with its neighbour. Hollow instruments, where there is risk of air being trapped in the cavity of the instrument, should not be cleaned in an ultrasonic bath. The time of a cleaning cycle will be advised by the manufacturers of the ultrasonic bath and will be determined by the power generated by the transducers fitted and should be carefully followed. The detergent solution used in the chamber must be regularly changed so that contamination with biological soil is not allowed to build up and risk contaminating subsequent batches of instruments. Some authorities recommend that the solution should be changed at the end of each working session, but it is not apparent if this advice is based on any scientific evidence. Ideally, the solution should be changed after each cycle, and there are some machines available that automatically drain the solution after each cycle. Before using a fresh detergent solution, it is important to degas it—this entails running a cycle with no instruments present in order to drive off any dissolved air that might interfere with cavitation. It is essential to ensure that the lid is placed on the chamber when the machine is running to prevent the dissemination of contaminated aerosols into the atmosphere. The chamber basket, supplied with the machine, must be used to place the instruments in because if the instruments are just placed in the chamber and allowed to contact the bottom or sides of the chamber, this can prevent the generation of ultrasonic waves (Fig. 8.6). There are a wide range of ultrasonic baths available and should be selected on the requirements of each individual practice. In particular the size of the chamber will be important and should be selected on the requirement of the workflow it is expected to process. It is important to ensure that the equipment is working properly and therefore should be tested or validated regularly to ensure that the noise produced by the machine reflects its effectiveness. There are two main methods that can be used to validate ultrasonic baths. The most commonly used method is the foil ablation test—this uses strips of foil that are suspended in a fresh detergent solution that has

8.3 Ultrasonic Cleaning

a

71

b

Fig. 8.6 (a) Ultrasonic bath basket incorrectly loaded. (b) Ultrasonic bath basket correctly loaded Fig. 8.7  Foil ablation test strips

been degassed. The foil strips are suspended at various points in the chamber; a normal cycle is then run. Once the cycle is complete, the foil is removed from the chamber, labelled to indicate their position in the chamber and examined for pitting and perforation indicating satisfactory performance. There are good videos available online demonstrating foil ablation testing, e.g. https://youtu.be/8M8ve3k6Lls. The treated strips should be retained to provide a comparison for subsequent tests and evidence of the efficacy of the equipment (Fig. 8.7). The other method that can be used to validate an ultrasonic bath is to use a probe or wand designed to measure ultrasonic energy. This would be placed in different but consistent locations in the chamber to measure activity across the whole area of the chamber. This is quite an expensive piece of equipment and is not widely used in dental practice but may be used by a specialist engineer. In order to test the cleaning efficacy of equipment, it may be helpful to use a soiled test piece. These are small pieces of metal or plastic that are soiled with an approved test soil of which there are several recognised formulations. Most of these will contain animal blood as part of the formulation and are applied to the test piece, allowed to dry on the surface and then placed in the cleaning chamber, and the equipment is then challenged to remove the layer of test soil. These can be

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purchased as either pre-soiled by the manufacturer, or the test soil can be purchased independently and applied to the user’s own instruments (Figs. 8.8, 8.9, and 8.10). In summary, ultrasonic cleaning can be an effective method for cleaning instruments provided the equipment has been validated and an appropriate cleaning solution is used. Its main advantage is that it is inherently safer than manual cleaning as the contaminated instruments require less handling, and therefore the risk of ‘sharps’ injury is reduced. Its main disadvantage is that the cleaning solution is usually used several times for successive batches of instruments, and therefore there is a risk of carryover of soil from one batch of instruments to the next. It is therefore inconsistent as the treatment of one batch of instruments is different to the next as the cleaning solution may have been previously used. Some authorities may advocate residual protein testing, but this is difficult to recommend because of the reuse of the cleaning solution.

Fig. 8.8 Commercially available test soil

Fig. 8.9  Test soil applied to instruments

8.4 Automated Cleaners

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Fig. 8.10  Pre-soiled test pieces

8.4

Automated Cleaners

In clinical practice this equipment is usually in the form of an automated washer/ disinfector. This piece of equipment is similar in form to a domestic dishwasher and is available as either a small ‘benchtop’ design or a much larger floor standing design that will fit underneath a regular bench top. Much larger machines are available, but these will tend to be found in hospital departments that have a much higher workflow than that required in a dental practice. The best choice for each dental practice will need to be determined having regard to the size of the practice and the required workflow. It is often a better option for a dental practice to consider purchasing several smaller models rather than a single large machine as this strategy gives more flexibility for the user. This gives a degree of built-in redundancy in the event of a machine breaking down, and cycle times can be staggered to increase the speed of turnover through the decontamination cycle (Figs. 8.11 and 8.12). The cycle of a washer/disinfector once the machine has been loaded and the cycle started begins with a cold rinse that is designed to remove any gross soiling. Cold water is used to prevent the coagulation of proteins onto the surface of the instruments. The next part of the cycle is a hot wash using a detergent that has been specifically developed to effectively remove biological soil. The temperature and time of this part of the cycle will vary from manufacturer to manufacturer but will be set to conform to a range of these parameters in published standards. The next part of the cycle is a final rinse to remove any residual detergent and loosened soil. The final part of the cycle is a drying phase that can be either a passive phase relying on the residual heat in the machine or an active phase using filtered hot air generated by the machine. Once the cycle is complete, the chamber is emptied of its contents, and each instrument can then be inspected for visual cleanliness before sterilisation.

74 Fig. 8.11 Washer disinfector benchtop design

Fig. 8.12 Washer disinfector under-bench design

8  Cleaning Methods for Dental Instruments

8.4 Automated Cleaners

75

The fundamental differences between a domestic dishwasher and a medical washer disinfector are the sophistication of the control and monitoring systems for each phase of the cycle and the type of detergent used. The consistency and repetitive nature of the cycles make this method of instrument cleaning one that lends itself to a high level of reliability and a means of providing quality assurance and validation. To validate the performance of the washer disinfector, it is recommended that an instrument that is a representative example is removed from a load after cleaning and is then tested for residual protein. This is relatively easily carried out using test kits that are available commercially; these contain a swab contained in a tube that has a reagent which when it detects traces of protein changes colour. This test should be carried out at regular intervals, such as weekly, to demonstrate that the machine continues to function as intended. In addition to protein testing, the performance can also be tested using a soiled test piece as described in the section on ultrasonic cleaning (Fig. 8.13). In summary, the use of a washer/disinfector is the most consistent method for cleaning dental instruments as the control system is very accurate and each phase of each cycle has the parameters accurately measured and recorded. Because the machine is consistent from cycle to cycle, validation tests become more meaningful. The detergent solution and the rinse water are only used for a single cycle and then discarded, so contamination carryover risk is eliminated. Like ultrasonic cleaning, it is inherently safer than manual cleaning as the contaminated instruments require less handling, and therefore the risk of ‘sharps’ injury is reduced. Its main disadvantages are that it is the most capital expensive method of cleaning dental instruments and the energy and water volume requirement is also greater. Extended cycle times may mean more instruments might be required in stock to meet clinical workflow demand (Table 8.1). a

b

c

Fig. 8.13 (a) Residual protein test device (b) Test instrument is swabbed (c) Swab placed in reagent, colour change indicates protein detected Table 8.1  Relative merits of cleaning methods Effectiveness Operator safety Cost Reproducibility

Manual Variable/Poor Poor Low Poor

Ultrasonic Variable/Moderate Good Moderate Moderate

Washer/disinfector Good Good High Good

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Further Reading BS EN ISO 15883-1:2006. Washer-disinfectors. General requirements, terms and definitions and tests. 2006. BS EN ISO 15883-2:2006. Washer-disinfectors. Requirements and tests for washer-disinfectors employing thermal disinfection for surgical instruments, anaesthetic equipment, bowls, dishes, receivers, utensils, glassware, etc. 2006. https://youtu.be/8M8ve3k6Lls

9

Sterilisation in Dentistry

Sterilisation, as previously discussed, is a process that kills all viable microorganisms including resistant bacterial spores. It is impossible, however, to guarantee that every single microbe that is exposed to a particular sterilisation process has been destroyed. It is realistic, nonetheless, to define sterilisation as a process that gives an acceptably low chance, about one in a million that any microorganism will survive. Cycle parameters recommended for different methods of sterilisation have been calculated using tests carried out under strictly controlled conditions. This takes into account the rate of biocidal action, initial contamination level and the level of sterility assurance. There are several different methods that are in common use for sterilising equipment used in medicine and dentistry. It should be noted, however, not all of these methods are suitable for use in a busy dental practice. Some methods are only of practical use in a commercial manufacturing environment (Table 9.1). Table 9.1  Common methods of sterilisation and applications Method of sterilisation Steam Irradiation Ethylene oxide

Load Metal and heat resistant instruments Dressings Plastic single-use items Dressings Delicate items including electronic equipment Dressings Heat labile items

Gas plasma (hydrogen peroxide) Chemiclave Metal and heat resistant instruments Filtration Liquids only

Commercial or on-site methodology On-site Primary care and secondary care facilities Commercial

Comments

Commercial On-site secondary care

Items require degassing

Commercial and on-site secondary care On-site primary and secondary care Commercial and on-site secondary care

No degassing required Toxic—utilises formaldehyde

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_9

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Heat sterilisation is traditionally the commonest form of sterilisation used both historically and currently in dental practices. Heat sterilisation can be classified as either dry heat or moist heat. When heat is used as a method of sterilisation, it works by causing death of microorganisms as a result of physical or chemical changes that cause the denaturation of major cell constituents, such as proteins or nucleic acids.

9.1

Boiling Water

This is probably one of the oldest methods that was regularly used in dental practice for the ‘sterilisation’ of dental equipment. A boiling water bath was regularly found in dental practices in the 1940–1950s. Dental instruments, including hypodermic needles used for the administration of local anaesthetics, were submerged in boiling water for varying amounts of time before being reused. This method was routinely discontinued in about the 1960s when it was realised that this method did not provide conditions that would sterilise instruments and would only provide conditions that would disinfect equipment as bacterial spores are not destroyed by water at 100 °C.

9.2

Dry Heat

For a short period of time, dry heat replaced boiling water for the sterilisation of reusable equipment in dental practice. The most common form of dry heat sterilisation is using hot air produced in an oven designed for the purpose. The design of the oven is very important in its effectiveness. Many ovens that were used in dental practice were merely convection ovens that would have a temperature gradient in the chamber, and therefore the temperature at the top of the oven chamber would be different (hotter) to the temperature at the bottom of the chamber (cooler); variations of between 9 and 28  °C could occur. Fan ovens that had mechanical air circulation would provide more uniform temperatures. Many ovens that were in common use did not have doors provided with locks that were interlocked with a cycle timer control, and therefore the cycle could be interrupted thus invalidating the process. The time and temperature required to achieve sterilisation was recommended as 60 min at 160 °C to ensure adequate conduction of the heat by the instrument. This method fell into disuse because of the time taken and also because of concerns about the effect of the high temperatures on the structure of the instruments. Other common uses of dry heat used to be by means of a glass bead ‘steriliser’ which used glass beads heated to a very high temperature in a small receptacle. It was once commonly used to ‘sterilise’ endodontic files and reamers. It fell in disuse because the process was uncontrolled and had an adverse effect on the tempering of the steel that the file was constructed from.

9.4 Benchtop Pressure Steam Sterilisers (PSS)

79

Table 9.2  Temperature and time for sterilisation of medical instruments Temperature °C °F 121 250 126 260 134 273

9.3

Minimum holding time (minutes) 15 10 3

Pressure bar 1.03 1.38 2.07

kPa 103 138 207

psi 15 20 30

Moist Heat

The most effective method of sterilising equipment is by the use of moist heat at a temperature above 100  °C.  In order to raise the temperature of saturated steam above 100 °C, it is necessary to raise the pressure above atmospheric pressure. In order to ensure that the temperature of saturated steam is consistent, it is important to ensure that the water vapour is free from any other gases, e.g. air (Table 9.2). The biocidal activity of saturated steam depends on moisture content, heat content and penetration. Saturated steam has a relative humidity of 100% which is the optimum conditions necessary for the destruction of bacterial spores. Steam has greater heat than water at the same temperature. When steam condenses on a piece of equipment, it rapidly gives up its latent heat, and the condensate remains at the same temperature thus raising the temperature of the item rapidly to the chamber temperature within the vessel. Penetration of steam is particularly important for effective sterilisation of partly enclosed cavities of hollow instruments where it is essential to remove air from the cavity. In order to utilise moist heat for the sterilisation of medical and dental equipment, pressure steam sterilisers also known by some as autoclaves have been developed and are in widespread use.

9.4

Benchtop Pressure Steam Sterilisers (PSS)

Early models of steam sterilisers were vertical designs with internally fitted lids that automatically closed under steam pressure and sealed against the rim of the chamber. These designs resembled domestic pressure cookers and were known as ‘autoclaves’. Current designs are usually cylindrical horizontal chambers made from stainless steel to prevent corrosion with a door made of the same material. The chamber and the door are insulated to reduce the heat transfer to the outer surfaces of the machine and reduce the risk of the operator being burnt. The door is sealed to the chamber by means of a replaceable heat resistant gasket. In most modern PSS machines, the steam is generated separately from the chamber although in early models the steam was generated within the chamber by means of an electrical element, similar to that found in a domestic electric kettle. The steam is admitted to the chamber through pipework from the steam generator. At the bottom of the chamber are thermostatic drains that allow steam and condensate to escape from the chamber. Once the thermostatic device senses that the required

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temperature has been reached, the valves are automatically closed to allow the build-up of pressure in the chamber. At the end of a sterilisation cycle, air is admitted to the chamber, and the valve senses a drop in temperature and opens to allow steam and condensate to be discharged. Within the chamber there are also thermocouple devices that measure the temperature at different points in the chamber. These devices allow the sterilisation cycle to be controlled automatically; they also allow the operator to monitor the parameters of the cycle as it progresses. In modern PSS machines, overall control of the sterilisation cycle is by means of an integrated circuit board within the machine, these are connected to accurate temperature sensing devices (thermocouples) installed at various sites within the chamber. In older machines, control was much less accurate as it relied on mechanical valves and timers. Each machine will have a display that includes chamber pressure and a time display which in modern machines are digital. Other important components found in a PSS include a safety valve mounted in the chamber that is designed to release pressure in the chamber if it exceeds a predetermined safe working pressure. There are also automatic locks on the door that prevent opening of the door, whilst there is residual pressure in the chamber. These are very important safety features that prevent the equipment from suffering catastrophic failure as the machine could explode if this was to happen. It is important that these components are regularly checked by a specialist engineer to ensure they are working correctly. As already discussed it is important that air is removed from the chamber to ensure that pure steam is available and can reach its desired temperature. Steam sterilisers are divided into machines that displace the air in the chamber by downward displacement and those machines that mechanically remove the air from the chamber and the load within. The means by which the air is displaced from the chamber gives rise to a classification system with ‘Type N’ allocated to downward displacement machines and ‘Type B’ allocated to vacuum-mediated air removal machines. There is a third type of machine, designated ‘Type S’, that is something of a halfway house between the N and B type machine using either a low vacuum or intermittent pulsing of steam to displace the air. When choosing a benchtop steam steriliser to use in a dental practice, it is very easy to be confused by the wide selection of equipment available. It is important that the purchaser should choose equipment that is fit for purpose, and it is recommended that the purchaser only considers equipment that complies with the appropriate international standards.

9.5

Type N Pressure Steam Sterilisers

These machines displace air in the chamber by admitting steam to the top of the chamber, and gravity pulls the air from the chamber at the bottom of the chamber through the drain valve. Once the thermostatic valve senses that pure steam is flowing through the drain valve, it closes, and pressure is allowed to build up in the

9.7 Type S Pressure Steam Sterilisers

81

chamber until the predetermined pressure has been reached when the steam inlet valve is closed and the sterilisation cycle is started. Once the holding time of the sterilisation cycle has elapsed, the drain valve is automatically opened, and the steam and condensate are discharged through the valve and are allowed to condense fully in the water reservoir. Once the pressure has dropped to that of atmospheric pressure, the door should be opened as soon as possible. Delay increases the wetness of the load and a vacuum, created by cooling of the air in the chamber, causes an inrush of contaminated air from the environment. Type N sterilisers are only suitable for solid instruments and should not be used for hollow instruments or instruments that are wrapped before sterilisation. This is because there is a high risk that air will trapped within the lumen of a hollow instrument or inside a wrapper and not be removed by the passive nature of air removal.

9.6

Type B Pressure Steam Sterilisers

This type of machine displaces air from the chamber by using a vacuum pump to suck air out of both the chamber and the load before steam is admitted. Some designs also use pulsing of steam in addition to the vacuum pumps to improve the efficiency of air removal. Within the chamber there is also an air sensing device that checks the effectiveness of air removal. There is also a leak detection system in the machine to ensure that an adequate vacuum can be achieved. With all the additional equipment in this type of machine, they are much more complex than an N type steriliser. This makes the total cycle time appreciably longer than an N type and maintenance, and validation is also more complex. Type B sterilisers are suitable for all types of load including hollow and wrapped instruments which makes them much more versatile than N type sterilisers.

9.7

Type S Pressure Steam Sterilisers

The method of air removal varies from manufacturer to manufacturer but is usually a more reliable process than that deployed in N type sterilisers. The type of load that these machines are suitable for will be determined by the manufacturer, and therefore the manufacturer’s advice should be followed (Table 9.3).

Table 9.3  Summary of benchtop steam sterilisers and uses Type Non wrapped (N) Big (B) Specified (S)

Vacuum No Yes Yes

Load Solid Solid and porous Solid and manufacturer’s guidance

Wrapped No Yes Manufacturer’s guidance

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9.8

9  Sterilisation in Dentistry

Water Supply

Most modern benchtop steam sterilisers have an inbuilt water reservoir that supplies the steam generator. In some machines there are two reservoirs one of which holds the water that supplies the steam generator and one is used for storing the waste condensate produced at the end of each cycle. The waste water can then be discarded. This is known as a ‘single shot’ water system and ensures that the water is only used once for a single sterilising cycle. There are models of benchtop steam sterilisers that discharge waste water at the end of each cycle directly to a drain and therefore do not require a waste water reservoir. Where a machine has a single reservoir, it is used as both a supply for the steam generator and a means of recycling the condensate at the end of each cycle back into the reservoir where it is used again for subsequent cycles. There is a risk from the single reservoir system that there will be an overgrowth of bacteria in the water stored in the reservoir. Some bacteria have the ability to multiply in the water and will gain entry to the reservoir from the environment. The ability of the bacteria to multiply in the water is enhanced by the warmth of the water and also the presence of organic material that may originate from poorly cleaned instruments that may make up the load within the chamber and may be carried back to the reservoir in the condensate. When water from a contaminated reservoir, in the form of steam, is admitted to the chamber in subsequent sterilisation cycles, the bacteria in the water will be destroyed but may then release endotoxins into the steam generated. This is then carried back into the reservoir at the end of the cycle and remains in the water stored there. As endotoxin is heat stable, the level of endotoxin may build up to clinically significant levels over a period of time; this has been confirmed by in vivo research which demonstrated extremely high level of endotoxin in dental practice benchtop steam sterilisers. This leads to the risk that instruments will be coated with endotoxin when exposed to the contaminated steam and could have an adverse effect on patients exposed to those instruments. This potential problem can be effectively and simply managed by discarding the water stored in the water reservoir at the end of each working day. The manufacturers of steam sterilisers will provide advice on water that may be used in their products, and this advice should be followed. The quality of the water that must be used in the water supply in pressure steam sterilisers should be of a known quality and should be either distilled or reverse osmosis generated water. This will ensure that there will be minimal levels of minerals in the water. Some models of benchtop steam sterilisers will have devices that will measure the quality of water in the reservoir and will abort sterilisation cycles if the water is not of adequate quality. Tap water must not be used in pressure steam sterilisers.

9.9

The Use of Benchtop Steam Sterilisers

In order to maximise the ability of the steam steriliser to perform its function reliably, it must be used appropriately. Firstly, the appropriate cycle should be selected for each particular load to be sterilised. For example, if there are wrapped or hollow

9.10 Validation

a

83

b

Fig. 9.1 (a) Incorrectly loaded steriliser tray. (b) Correctly loaded steriliser tray

instruments to be sterilised, a B type or manufacturer approved S type machine must be used. The definition of a hollow instrument is where a chamber within the instrument is closed at one end and the diameter of the chamber equals or exceeds the length of the chamber. Where there is a lumen in an instrument (open at both ends) it is classed as hollow when then the diameter of the lumen equals or exceeds twice the length of the instrument. If there are no wrapped or hollow instruments, then an N type steriliser will be adequate. In addition to selecting an appropriate cycle, it is very important that the chamber is loaded appropriately to ensure the entire load is exposed to steam. All of the currently available benchtop steam sterilisers are supplied with chamber furniture that will usually include runners or ledges that perforated metal trays are supported on. The trays are perforated to ensure that steam can freely circulate around the chamber and the load and that air can be effectively displaced. Instruments and equipment must be placed on the perforated trays in such a way that steam can circulate around the load and that all surfaces of the instruments are exposed to steam. The steam will then condense on the instruments surfaces and quickly transfer its latent heat to the instrument, rapidly heating it up to the required temperature. The condensation of the steam will reduce its volume and therefore create a vacuum that will attract more steam into the area and again contribute to the rapid heating of the instrument. The chamber must not be overloaded, and all instruments must be placed on the tray so they do not overlap adjacent instruments and must be placed as a single layer on each tray. If the instruments are overlapping each other, then the surfaces that are touching will not be exposed to steam. It is also advised that hinged instruments, such as extraction forceps, are opened to enhance the penetration of the steam into the joint (Fig. 9.1).

9.10 Validation It is vital to ensure that monitoring of the performance of steam pressure sterilisers is regularly carried out to ensure that instruments are reliably sterilised and the machine is safe to use. The need to test steam sterilisers was reinforced following an incident in the UK where there was an incident that led to the deaths of five patients

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who were given an intravenous infusion that had been ‘sterilised’ in a steam steriliser in which incomplete air removal had occurred. This allowed bacteria to survive the process and multiply in the infusion solution. As a result of this incident, recommendations were made that all medical steam sterilisers must be subjected to regular testing and validation. Safety and performance testing of steam sterilisers should be performed by appropriately experienced engineers at least annually. The user of the autoclave should also carry out regular testing on at least a daily basis. Records of maintenance and testing should also be kept by the user. Annual or periodic engineer testing will include a check on the safety systems of the autoclave including safety valve settings, function of door locks and a check on the calibration of the control systems incorporated into the machine. There are different tests that the user can adopt to assure the performance of the steam steriliser in the intervals between engineers’ testing. Each user of the steam steriliser should find out what local regulation and guidance requires and follow these recommendations. These include: Monitoring the parameters of each cycle will enable the user to check that the necessary temperature and holding time (the time that the cycle is held at the required temperature and pressure) are achieved. Modern benchtop steam sterilisers will display this on a digital display and will usually display a message that satisfactory sterilising conditions have been confirmed at the end of each cycle. It does this by comparing the temperatures recorded by at least two thermocouples installed in different positions in the chamber. If there is a variation of temperature between the thermocouples, this may indicate that the steam in the chamber is contaminated with air. The data generated by this process can be recorded by the machine either in the form of a print out from a connected printer or can be held in a digital device known as a data logger containing a programmable chip or data storage card. This chip/card can hold hundreds of thousand temperature and pressure readings as well as the date and time and can be interrogated by a computer to evidence appropriate monitoring. Where the data is provided by a thermal printer that generates a paper copy of the parameters, it may be necessary to photocopy the paper strip as thermal print outs will fade in quite a short period of time. Older benchtop steam sterilisers are not equipped with such sophisticated self-­monitoring systems, and it may be necessary to monitor the cycle by means of a stopwatch and visual monitoring of the temperature gauge. The readings obtained can then be recorded in a log book to provide evidence that appropriate monitoring has been carried out (Figs. 9.2, 9.3, and 9.4). The time that these records should be maintained for will vary from area to area and local regulations, and guidance should be consulted and followed. These records may be important to provide local regulators with evidence that appropriate quality assurance is carried out. It may also be useful in the event that there are allegations made by patients that cross infection may have occurred during dental treatment. The appropriate monitoring of each cycle is very important as it enables any cycle failures to be dealt with immediately and the instruments to be reprocessed before being used again.

9.10 Validation Fig. 9.2 Steriliser integrated printer

Fig. 9.3  Steriliser data logger with data storage card

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Fig. 9.4 Independent printer that can be fitted to a steriliser or washer disinfector that has an appropriate connector (port) fitted

Chemical monitoring of sterilisation cycles is another method of quality assurance that is in widespread use. This entails using thermo-sensitive chemicals that change colour when exposed to different temperatures. These are available commercially in various forms, for example, impregnated in paper strips and in liquid vials, impregnated in adhesive tape used for packing instrument or impregnated into plastic/paper pouches manufactured for wrapping surgical instruments. It is important, however, for the user to understand the limitations of this type of monitoring. For example, conditions in the steriliser chamber may vary if there are small pockets of trapped air, and therefore the indicator strip will only reflect the conditions in the area of the chamber in which it may be placed. This risk can be mitigated if multiple strips are placed in different areas of the chamber. There are different chemical strips that are available to monitor different temperature cycles, and therefore it is important to obtain the correct strip for the cycles used. Some of the chemical indicators, particularly packaging tape, are not temperature specific and therefore will only indicate that the equipment has been exposed to steam but not specific temperatures and therefore should be supplemented with other monitoring methods. It is useful, however, to the user of the instrument as it can reassure them that the instrument has been subjected to reprocessing, although not the quality of the process (Fig. 9.5).

9.10 Validation

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Fig. 9.5  Chemical test strips: Failed test on left, satisfactory result on right

Biological testing is another method that is widely used in some parts of the world. This entails taking spores produced by bacteria that are known to be very resistant to heat, in particular the spores produced by Geobacillus stearothermophilus, impregnating them into paper strips which are then wrapped in glassine envelopes. These are then placed in a load in a steam steriliser chamber and subjected to a sterilisation cycle. The spore strips are then removed from the chamber and sent to an approved laboratory where they are placed in a liquid culture medium and incubated for 3 days. The culture medium is then examined for growth of the bacteria. The failure to detect growth indicates successful sterilisation. The disadvantage of this system of testing is its retrospective nature. How useful is it to know how the steam steriliser was performing 4 days ago? In the opinion of the authors, it could be considered a useful method of validating the steam steriliser if the equipment that was processed since the machine tested was quarantined and not used until the confirmation of a negative test. For B type (vacuum) benchtop steam sterilisers, there are some additional tests that need to be performed. In particular steam penetration tests which will test the ability of the steam to penetrate a hollow or porous load. In most instances the need to sterilise a porous load such as wound dressings is unlikely in most dental practices, and therefore the use of a Bowie-Dick test is not very relevant. The most likely use of a B type steriliser in a dental practice is to sterilise hollow instruments such as dental handpieces. In order to test the ability of this type of steam steriliser to remove air from a hollow instrument, a helix test should be used. This is a helix of narrow bore tubing that leads to a chamber that contains an appropriate chemical indicator. It is placed in the chamber of the steriliser and a vacuum cycle is run, at the end of which the device is removed from the chamber and the chemical indicator is examined for an appropriate colour change. This indicates that all the air has been removed from the tubing and replaced with steam at the appropriate temperature (Fig. 9.6).

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Fig. 9.6  Helix device. The upper indicator strip is unused, and the lower strip has been exposed to steam, and the yellow indicator has changed to a purple colour. The indicator strip is placed in the chamber at the end of the device

It is important that when deciding what sterilisation processes are to be used in a dental practice that attention is paid to local regulation and guidance and is followed carefully.

Further Reading BS EN 556-1:2001. Sterilization of medical devices. Requirements for medical devices to be designated “STERILE”. Requirements for terminally sterilized medical devices. 2001. BS EN 556-2:2003. Sterilization of medical devices. Requirements for medical devices to be designated “STERILE”. Requirements for aseptically processed medical devices. 2003. BS EN 13060:2004. Small steam sterilizers. 2004. BS EN ISO 11607-1:2006. Packaging for terminally sterilized medical devices. Requirements for materials, sterile barrier systems and packaging systems. 2006. BS EN ISO 17665-1:2006. Sterilization of health care products. Moist heat. Requirements for the development, validation and routine control of a sterilization process for medical devices. 2006.

Local Decontamination Units in the Dental Office

10

Reprocessing of dental instruments that are not single use is normally done on an in-house basis. Ideally this is done in a separate room from where the dental treatment is done, the local decontamination unit (LDU).

10.1 W  hy Not Reprocess Instruments in the Treatment Room? Instrument reprocessing can be noisy, especially where ultrasonic baths are used, and autoclaves generate a lot of heat and steam. Operating these devices within the treatment area can make the environment unpleasant to work in and reduce patient comfort and hamper communication. The aerosols created by ultrasonic scalers and dental handpieces have the potential to settle on instruments as they are reprocessed, contaminating them. Whilst a low risk with well-maintained, serviced and modern autoclaves, they are pressure vessels and have an inherent risk of explosion, so their use in clinical areas potentially puts patients at risk. An LDU avoids all these problems.

10.2 Room Design and Workflow The physical layout of the room should allow operatives to reprocess instruments in a spatial direction that follows the reprocessing cycle. A good workflow is essential for an effective LDU as it maintains quality assurance and reduces the chance of mistakes being made. As dirty instruments are received at one end of the room, they should move in one direction to be cleaned, inspected, sterilised and stored (Fig. 10.1). For many dental practices that are not purpose built premises, this can prove difficult due to space limitations. Figure 10.2 demonstrates how room size and shape may influence the layout of the LDU.  This may impact on the number of sinks that can be

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_10

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Set down area

Wash

Rinse

Ultra sonic bath

Instruments ready for storage

Oil or Magnifying Vacuum handpiece Packaging lamp autoclave cleaner

Dirty to clean

Entrance / exit

Hand sink

Thermal washer disinfector

PPE

Waste

Instructional posters

Air flow

Galley

Dirty zone

“L” shape

Workflow

Workflow

Clean zone

Clean zone Workflow Clean zone

Dirty zone

Fig. 10.1  Key elements of a LDU. The spatial arrangement should reflect the stages of the decontamination cycle

Dirty zone

Straight run

Fig. 10.2  Potential LDU layouts demonstrating the flow from dirty to clean. Courtesy of Intrafit. co.uk

installed, the size and number of autoclaves used and the feasibility of using a thermal washer disinfector. It is plausible that as infection control standards become more stringent and demanding, there will be dental practices that no longer find their premises suitable, or they may need to use an external centralised sterilising service. Most practices will opt for a single room for the LDU due to cost and the size of their premises. The room should be secure from the public to maintain safety and quality assurance. The closer the LDU is to treatment rooms, the easier it is to transport contaminated instruments and reduce the risk of accidents en route. The LDU should not open to the outside of the building as this will allow external contaminants to be drawn in. The LDU should have an area where dirty instruments can be set down (Fig. 10.3). The work surfaces need to be made from a durable material that will withstand the heat and chemicals used in decontamination. Worktops of contrasting colours can be used

10.2 Room Design and Workflow

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Key: 1. Set down area for incoming instruments 2. Hand washing sink 3. PPE (heavy duty gloves not pictured) 4. Foot operated bin 5. Thermal washer disinfector 6. Due to limited space this LDU only has one sink for rinsing instruments. A bowl is available for manual scrubbing of instruments in the event of the thermal washer failing. 7. Handpiece cleaner/lubricator 8. Task light with magnification 9. Type B vacuum autoclaves 10. Reverse osmosis water tap

Fig. 10.3  The key components of the LDU. (1) Set down area for incoming instruments. (2) Hand washing sink. (3) PPE (heavy duty gloves not pictured). (4) Foot operated bin. (5) Thermal washer disinfector. (6) Due to limited space this LDU only has one sink for rinsing instruments. A bowl is available for manual scrubbing of instruments in the event of the thermal washer failing. (7) Handpiece cleaner/lubricator. (8) Task light with magnification. (9) Type B vacuum autoclaves. (10) Reverse osmosis water tap

to help differentiate zones between dirty and clean areas of the room. There should be no exposed joins or cracks that would hamper cleaning. Hand hygiene is undertaken with a dedicated sink. Having donned suitable PPE, the operative will need to clean the dirty instruments and discard any single use items in the suitable waste stream. Handsfree opening bins and a wall-mounted sharps container are advised to facilitate this.

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10.3 Dirty/Cleaning Area Ideally an automated cleaning method should be employed; the first choice is a thermal washer disinfector; second is an ultrasonic bath. Use of both could help with the removal of dental materials that have not been cleaned away at chairside, by the ultrasonic bath, prior to thermal disinfection. Using an ultrasonic bath and thermal washer disinfector will increase both the reprocessing time and the running costs. In the event of failure of these methods, and for instrument rinsing, there needs to be at least one (ideally two; one for washing and another for rinsing) sink(s) for manual cleaning. A handpiece cleaner and lubricants for use in undecontaminated handpieces only may be sited at this point too. If a handpiece cleaner is going to be used, it is likely to need a compressed air outlet which can be taken off the practice central supply. The piping for this should be anticipated before installing the worktops and cabinetry. Some manufacturers also recommend a minimum distance these machines are sited away from points of ignition and light switches due to the flammable disinfectants used in them. Illuminated magnification with a task light allows the inspection of the cleaned instruments. This is a highly specific test, but not very sensitive. Whilst the presence of restorative cements and bioburden may be readily assessed and instruments cleaned a successive time, visual inspection does not necessarily correlate with the protein contamination of instruments. Just because you cannot see anything on the instrument does not mean it is clean. In situ protein testing is possible but in its infancy and currently is prohibitively expensive for dental practice. In years to come, it would be no surprise if this were to be part of routine instrument reprocessing where minimal levels of residual protein are checked for. Magnifying glasses have the potential to be fire hazards where daylight is focussed on a spot, so when not in use, covers should be employed, and the light turned off and if necessary move them from direct daylight.

10.4 Clean/Packaging and Sterilisation Area The point at which instruments are packaged will depend upon the autoclave used. For a B-type vacuum autoclave, instruments may be packaged after they have been cleaned and dried and before they are sterilised. Most S-type autoclaves also allow instruments to be packaged prior to sterilisation, but this will be machine dependant and upon the advice of the manufacturer. Where an N-type non-vacuum autoclave or non-vacuum cycle is used, instruments should be dried then packaged after they have been sterilised. Wet packages should be considered compromised and the contents reprocessed as the moisture will allow environmental microbes to permeate in. Packaging provides a physical barrier that allows instruments to be stored and transported without becoming contaminated. The length of time instruments can be stored in their packaging may be influenced by regional regulations, but multiple studies have supported the integrity of instruments stored in packages for a 1 year period. Dating packages with an expiry (or processing) date ensures quality control for storage times. Some practices may adopt a track and trace process whereby unique identifiers are used for each package that corresponds to the autoclave cycle

10.6 Plumbing

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instruments went through. These details are then recorded in patients’ notes at the point of use, providing an audit trail. Where space allows, the use of two rooms provides a room for the receipt and cleaning of dirty instruments, and the second room serves to sterilise and package the clean instruments. A connection between the two allows the transfer of cleaned instruments, ideally using a double door thermal washer disinfector. This premium solution seeks to minimise any contamination of the reprocessed instruments due to the cleaning part of the cycle. The problem with this layout, aside from the cost, is that it hinges on the washer disinfector working. If it fails, then the workflow becomes compromised.

10.5 Services and Surfaces Important aspects of the LDU are the services and surfaces and ensuring they meet the demands of the work undertaken. Flooring should be impervious, non-slip, easily cleaned and ideally coved at the edges to facilitate cleaning up spillages. Contract-grade materials are likely to be more durable than domestic flooring solutions. Due to the heat and moisture generated by autoclaves, a wall paint for bathroom or kitchen use is a simple way of reducing the potential for surface mould. Where wall-mounted cupboards are used that have exposed undersides, protecting them with an acrylic panel can help reduce the risk of steam causing delamination of the wood coating. Push latches on cupboard doors can eliminate handles, reducing surfaces that are harder to clean. Ensure there are sufficient power points for the equipment needed and possible future apparatus, and that the building wiring can handle the load. Manufacturers and suppliers will often be able to provide preinstallation assessment checklists that can be used to ensure their equipment will work, and importantly, fit! Benchtops should be deep enough for the footprint of intended appliances and don’t forget to allow sufficient clearance for the doors of autoclaves and thermal washer disinfectors to swing open and how that impacts upon the ergonomics of working within the LDU. Manufacturers will also often specify the minimum recommended space that must be left around their machines to ensure adequate airflow, to avoid overheating.

10.6 Plumbing Water is an integral part of decontamination and good plumbing is essential. The plumbing in the LDU should be given careful consideration in the early planning stages. In the same way that the modern dentist plans for failure in restorative treatment, the same principles can be applied to the plumbing supply. Anticipate what can go wrong and how these risks can be mitigated. An isolation tap in the event of a leak is a simple measure to reduce the chance of flooding. Where thermal washer disinfectors are to be used, consider the hardness of the water supply and whether a softener is required; some models can use both a hot and cold water feed, rather than just cold; ensure the waste pipes can handle the volume and temperature of the water, especially if more than one are being used at the same time. The flow pressure of cold water to the thermal washer disinfector may need to be regulated.

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Fig. 10.4  An RO unit occupies a significant amount of space. The filters in an RO unit need replacing so ensure the device is sited in an accessible location

If a reverse osmosis (RO) unit is to be used, ensure there is sufficient space for it, and check if it needs a power supply (Fig. 10.4). Ensure the reverse osmosis unit can output water that is of suitable quality as some autoclaves have a total dissolved solids (TDS) meter that will reject water above a certain threshold. As the filters age, the TDS levels will rise, so it can be prudent to purchase a simple TDS meter (unless already incorporated in the RO Unit) to monitor this and have spare filters to hand for when they need replacement. Where equipment has a cold-water feed, including RO units, thermal washer disinfectors and water softeners, it is important that they have check valves or air gaps that meet the relevant building regulations as these devices are potential cross connections. A check valve stops contaminated water flowing back into the practice and neighbouring buildings’ drinking water supply. Check valves may not necessarily be integrated within equipment and will require a plumber to fit them.

10.7 Airflow Airborne particles have the potential to contaminate reprocessed instruments, but this can be mitigated by suitable ventilation and considering how air flows within the LDU.  Furthermore, due to the heat and moisture generated in the LDU,

10.8 Additional Notes

95

adequate ventilation is essential for staff comfort. A working temperature between 18 and 22 °C and a relative humidity of 35–60% are considered comfortable. Air should flow in the direction from the clean zone to the dirty zone of the room. By maintaining a good airflow, the levels of contaminants within the air are reduced and not dragged across instruments that have just been reprocessed. The UK Health and Safety executive recommends airflow does not drop below 5–8 L/s, per occupant of an enclosed space. Where resources permit, mechanical ventilation with filtration allows for best practice, but for many this might be a financial barrier or simply not possible due to the constraints of the premises. Benchtop fans are not appropriate as they will not give controlled airflow and may spread contaminants around the room.

10.8 Additional Notes The dirty instruments brought to the LDU, and the clean instruments that leave, need to be suitably transported. It is advisable to use rigid plastic leakproof containers with sealed lids. These should be clearly labelled as clean or dirty, and colour coding can help with this. Dirty instruments should be held in a suitable wetting media (water is not ideal as it will rust and corrode metal instruments) in the transport container if they are not immediately reprocessed after use. This is to reduce the chance of proteins becoming fixed to the instruments if left to dry out, which makes them harder to clean off. The dirty transport containers should be disinfected after use. No matter how good the LDU, if it is going to work properly, there must be a lead member of staff to take charge of the validation and maintenance of the equipment. No staff should undertake instrument reprocessing without suitable training (Table 10.1). Table 10.1  Training/induction checklist for the LDU Occupational health checks PPE Hand hygiene Instrument transport Waste Cleaning

Inspection Packaging Autoclave Storage

Staff are immunised against hepatitis B Correct size of PPE available How to put on and take off the PPE Trained how to correctly clean hands How lid is secured How to lift and carry, avoiding overloading Where to set down instruments How waste is sorted and where it is disposed How to manually clean How to use ultrasonic bath (if applicable) How to use thermal washer disinfector (if applicable) What to do if an automatic method fails How to check instruments are clean Which instruments are packed and how this is done How to load and unload the autoclave How to run the cycle What to do if it fails Where to keep reprocessed instruments

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Further Reading Smith AJ, Lockhart DE, McDonald E, Creanor S, Hurrell D, Bagg J. Design of dental surgeries in relation to instrument decontamination. J Hosp Infect. 2010;76(4):340–4.

How to Choose Clinical Dental Equipment

11

Instruments used in primary dental care need to be fit for purpose. This includes the ability to be reprocessed adequately where they are not single use. This is essential if patient-to-patient transmission of infection is to be avoided. Although a wide range of disposable dental hand instruments and even handpieces are available, for most dental practices, the cost of this option is not financially viable. Therefore, a careful choice must be made about which instruments will be purchased as single use and which will be reusable. One of the major factors that should be assessed when making this choice will be the ease of cleaning of the instrument; so, the architecture of the instrument should be carefully examined. Hollow objects and the topology of dental burs are good examples of what is meant. For complex instruments with several parts to them, it can be very helpful if they can be dismantled into their component parts for decontamination purposes. For example, some designs of amalgam carrier can be very soil retentive, particularly the internal springs, and should be dismantled in order to remove any soil from each component before sterilisation.

11.1 Hollow Instruments Hollow instruments pose two challenges; cleanability and sterilisation assurance. The ability to clean inside a hollow instrument will be dictated by the diameter of the space and its length and whether available methods can reliably clean this internal surface. Hollow objects risk having air trapped within them unless reprocessed in a vacuum autoclave. A good example of a product sold as either multiple use (metal) or single use (plastic) is the air/water syringe tip. These instruments contain an extremely fine lumen and are virtually impossible to clean effectively and cannot be inspected for cleanliness. The same type of challenges also apply to suction or aspirator tips; although the lumen is somewhat larger and may be more accessible for cleaning using a ‘bottle-type’ brush, the length of the lumen makes accurate

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_11

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Fig. 11.1  Dimensions of hollow instruments

Open at both ends

x

Equal to or greater than 2X

Open at one end

Equal to or greater than Y

Y

inspection for cleanliness difficult, and the need for sterilisation in a vacuum steriliser remains. The labour-intensive nature of cleaning this type of instrument negates the cost savings over disposable instruments and makes the choice of reusable instruments of this type difficult to justify (Fig. 11.1).

11.2 Burs Instruments that have pronounced undercut areas such as some designs of dental burs are also difficult to clean reliably and may be made of carbon steel that will readily corrode when reprocessed. Not only will they corrode but will rapidly lose their cutting edge after use and reprocessing. Considering the cost of reprocessing and the low cost of purchase, then it appears to make good sense to consider steel burs to be single use.

11.3 Single Use Some instruments will be designated by the manufacturer to be single use and therefore should not be reused. Each area of the world will have its own rules in respect of single-use instruments, and users should be aware of and follow these rules. For

11.4 Certificate of Conformity Fig. 11.2  Medical Devices Directive single-use symbol

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2

example, across Europe there is a directive issued by the European Economic Community that specifies rules that govern all aspects of medical devices and includes a requirement that designated single-use devices must not be reused. In the event that single-use devices are reprocessed by a user, then the user is not only responsible for the safety of the device in respect of the risk of cross infection but is also responsible for the structural integrity of the device. The manufacturers of such devices must label the device or its packaging with a specified single-use symbol as illustrated below (Fig. 11.2). In addition to area-wide rules or legislation, there may also be country-specific rules that supplement or supplant these requirements. In Scotland, for example, matrix bands used in restorative dentistry and endodontic files and reamers have been mandated by local guidelines to be single use irrespective of manufacturer’s requirements. Reuse of designated single-use items, if identified, is likely to lead to action against the individual(s) by regulators as well as attracting adverse publicity. Where single-use items are supplied in a sterile state by the manufacturer, the packaging will be labelled with the method by which it was sterilised, the expiry date, a certificate of conformity symbol with the code number of the organisation that tested the product and a single-use symbol (Fig. 11.3).

11.4 Certificate of Conformity Many of the dental instruments available are readily amenable to safe and predictable methods of decontamination. In particular, simple, solid instruments made from surgical grade stainless steel should provide little challenges to satisfactory decontamination. To achieve this, the instruments’ manufacturer’s instructions for reuse must be followed. In Europe, it is a requirement to achieve a certificate of conformity (CE mark) that the manufacturers must comply with the Medical Devices Directive. The Medical Devices Directorate stipulates that not only must the manufacturers supply information on cleaning, disinfection, packaging and, where appropriate, sterilisation to allow reuse of the device. There is the same requirement if the device is supplied non-sterile and it requires sterilisation prior to use. The instructions provided must also have been validated to demonstrate that

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Fig. 11.3 Instrument package labelling

these instructions are effective. Guidance on the content of these instructions is found in the form of an International Standard ISO 17664(2017). This standard specifies requirements for the information to be provided by the medical device manufacturer so that the medical device can be processed safely and will continue to meet its performance specification. Requirements are specified for processing that consists of all or some of the following activities: • • • • • • •

Preparation at the point of use Preparation, cleaning, disinfection Drying Inspection, maintenance and testing Packaging Sterilisation Storage

Unfortunately, and unhelpfully, many of the products available on the dental market do not comply with this requirement and yet still achieve a CE mark. This makes it difficult for the user who then must decide how decontamination of these devices will be achieved, and often then the user has to rely on generic protocols. When procuring instruments, it is sensible to choose those compatible with the standard decontamination protocols used in the practice. By adopting this strategy, the need for multiple different decontamination processes can be avoided which in turn reduces the risk that an inappropriate process could be used by a member of staff for a particular instrument. For example, if the use of a washer disinfector is

11.5 Instrument Trays

101

Fig. 11.4 Handpiece markings

used as the primary means of cleaning instruments, then it is prudent to ensure that any new equipment purchased is compatible with this. For example, some dental handpieces can be processed in a washer disinfector and should be labelled to indicate their compatibility with, in particular, the detergent used and the temperature at which it may be sterilised (Fig. 11.4).

11.5 Instrument Trays It is convenient to use trays to place instruments on when carrying out procedures; this reduces the amount of surface area that may need to be cleaned between patients. It may be convenient to line these trays with disposable coverings to further reduce the need for cleaning between patients. Some dental practices find it convenient to store instruments as procedure sets inside the trays that are used chairside and further the instruments are sterilised inside these trays. In these circumstances the trays should be of a perforated design in order to allow steam to penetrate the trays and reach the instruments. If adopting this system of instrument storage, there is still a requirement to make up the sets of instruments following cleaning and before sterilisation which is a repetitive, labour-intensive method of working. This system of instrument storage can be further refined by using open cassette style trays in which the instruments can be processed without removing them from the trays. This requires that the instruments are cleaned in a washer disinfector and that the steriliser chamber is large enough to accept the cassette trays. The advantage of this system is that the instruments are retained as sets of instruments and do not have to be repeatedly reassembled during each decontamination cycle, thus saving substantial amounts of staff time. Once processed the instrument sets can be stored aseptically inside suitable packaging (Figs. 11.5, 11.6, 11.7 and 11.8).

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Fig. 11.5  Open-type instrument cassettes Fig. 11.6 Washer disinfector with open-type instrument cassettes

Fig. 11.7  Steriliser with open-type instrument cassettes

11  How to Choose Clinical Dental Equipment

11.7 Numbers of Instruments

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Fig. 11.8 Aseptically packed instrument set

11.6 Repairing and Disposal of Instruments Any instrument that requires service or repair and needs to be sent away must be fully decontaminated before sending via post or a public carrier to an authorised repairer. The instrument should be accompanied by a declaration that confirms that this has been done. In some countries this requirement is reflected in postal regulations. When simple hand instruments are damaged, they should be disposed of in a safe manner. For single instruments they can simply be placed in an approved contaminated sharps box without decontamination. If a practice has several instruments for disposal, it may be worth contacting the manufacturer to see if they have a metal recycling scheme that will accept them for disposal in an environmentally friendly manner. In this instance the instruments must be fully decontaminated prior to returning them by post or carrier.

11.7 Numbers of Instruments Practices should ensure they have sufficient number of instruments to ensure that they have an adequate stock of decontaminated instruments to meet the normal workflow. Each practice will be different, and an assessment must be made of the

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11  How to Choose Clinical Dental Equipment

number of patients seen in each session, the range of procedures carried out and the time taken to decontaminate the instruments before they are recycled back into use. A reasonable margin should be allowed to cover expected and unexpected contingencies, for example, the number of dental handpieces in stock should allow for service and repair periodically.

Further Reading BS EN ISO 11607-1:2006. Packaging for terminally sterilised medical devices. Requirements for materials, sterile barrier systems and packaging systems. 2006. Directive 93/68/EEC [CE Marking]. ISO 17664:2017. Processing of healthcare products—information to be provided by the medical device manufacturer for the processing of medical devices. Medical Devices Directive Council Directive 93/42/EEC.

Dental Disinfection and Environmental Decontamination

12

12.1 Fomites Some microbes can survive for extended periods of time on inanimate surfaces (fomites) with the potential to be picked up and transmitted. Viruses tend to only survive for hours or at most days, but some bacteria can remain viable for weeks to months without a host. MRSA has been found to remain viable for over 70 days and E.coli for 16 months. Persistence of microbes on surfaces including door handles and bedding has been identified as a source of the spread of infections in hospital settings. Environmental contamination in healthcare is not limited to the hospital setting, and dental practices are no exception. Decontamination seeks to remove and kill the microbes that are potential hazards through cleaning and disinfection. This must be proportionate, effective, safe, practical and financially viable. The dental surgery is not as high-risk environment as a hospital, but there is still a real risk of the transmission of infections. Subsequently, there is a need to address decontamination of all areas of a dental practice.

12.2 Respiratory and Hand Hygiene Contamination of the dental practice’s environment may come from the dental team and patients, most likely via their hands or poor respiratory hygiene. It is essential to encourage and support hand and respiratory hygiene. Simple measures including availability of tissues, bins and routine environmental cleaning help to control these risks. Many practices now provide alcohol rub dispensers for patients and non-­clinical staff use to improve hand hygiene. Signs prompting hand washing in both staff and patient toilets can also be strategically placed to improve compliance with hygiene too. Less than 20% of the world’s population are thought to wash their hands with soap and water after going to the toilet, albeit many simply lack the infrastructure to do so. Even where facilities are available to wash, hand hygiene remains suboptimal.

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_12

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12.3 Treatment Areas The primary area of concern in the dental practice will be the work surfaces in the treatment area as this is where most potential contamination of the environment will occur, although it must be said that the risk of transmission of infections from work surfaces is thought to be low. As with contaminated dental instruments, cleaning to remove bioburden that can protect and nourish microbes is an important part of environmental decontamination. Cleaning is achieved with physical scrubbing using a detergent or disinfectant. How, and with what, surfaces are cleaned within treatment areas is a matter of some debate. There are those that advocate the use of detergents alone to remove any bioburden left on surfaces. Others state that chemical disinfectants are needed to ensure eradication of potential pathogens. Disinfectants have an environmental impact, can damage surfaces and may be harmful to the staff handling them; detergents largely avoid these problems. Advice on surface decontamination tends to come from research based in (non-dental) hospital settings. Whether the dental treatment area is of a comparable risk is not clear. On one hand the general population is healthier than would be expected in hospitals, but in dental practices there is the problem of aerosols and gloved hands touching both body fluids and the hard surfaces at chairside. The protocol adopted to decontaminate surfaces in the treatment area will largely be driven by the need to follow national guidance. Table 12.1 gives examples of regional variations.

Table 12.1  Examples of variations in national guidance on cleaning of clinical areas Country Australia England

France

New Zealand

USA

Guidance ‘Working surfaces in the contaminated zone must be cleaned after every patient by wiping the surface with a neutral detergent’ ‘The use of disinfectant or detergent will reduce contamination on surfaces. If there is obvious blood contamination, the presence of protein will compromise the efficacy of alcohol-based wipes’ ‘Cleaning centres on simple techniques using disposable cloths wetted with clean water and a detergent’ ‘This operation can be carried out in three stages: cleaning with a detergent product, rinsing, application of a disinfectant product or in one step, using a detergent-­ disinfectant product. In the latter case, a disposable cloth soaked in detergent-­ disinfectant is applied to the surfaces (chair, medical devices nearby). These products do not require rinsing’ ‘Clean work and equipment surfaces in the contaminated zones with a suitable clinical detergent—use in accordance with manufacturer’s instructions, and dry surfaces with a low-lint cloth or disposable paper towel’ ‘When effective disinfection can be achieved it may be used between patients and/ or at the beginning and end of a treatment session or day. Disinfection of work and equipment surfaces in the contaminated zone, following effective cleaning between patients is not routinely required’ ‘…clinical contact surfaces should be barrier protected or cleaned and disinfected between patients. EPA-registered hospital disinfectants or detergents/disinfectants with label claims for use in health care settings should be used for disinfection’

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The authors view bioburden removal essential in decontaminating surfaces in the treatment area, and effective cleaning is the priority. Wipes pre-soaked with a neutral detergent are a convenient way of cleaning surfaces within the treatment area.

12.4 Disinfectants Where disinfectants are chosen to decontaminate hard surfaces, it is important that they meet the needs of the dental environment. Unfortunately, there is no ideal surface disinfectant. The spectrum of activity, stability and the contact time required to kill microbes all differ between products. Some disinfectants can act as a detergent, whereas others are inhibited by bioburden. Furthermore, not all disinfectants will be suitable on all surfaces as they might damage them or potentially make bioburden harder to remove. Disinfectants are categorised in the USA as low, medium or high level based on their spectrum of activity. Disinfectants for dental needs are largely low level. Table 12.2 gives examples of the commonly encountered disinfectants used in dental care. All disinfectants should be risk assessed, and safety data sheets kept on file. Appropriate storage and handling including the use of PPE is important when handling these chemicals. In the UK, a COSHH assessment will be required for all disinfectants used.

12.5 Choosing Disinfectants When buying a disinfectant for hard surfaces, check if it meets a recognised standard (e.g. ISO International, EN European standards, EPA registered in the USA), and check the claimed range of activity. It needs to be able to kill bacteria, fungi and at least enveloped viruses (e.g. HIV, hepatitis B). It is essential to take note of how long the disinfectant must be in contact with the surface to be effective, as many dental practices have a high turnover of patients with little time between appointments. The contact times for some disinfectants may be as long as 10 min which is unlikely to be achievable in a busy practice. Surface disinfectants aimed at the dental sector tend to be classified as alcohol or non-alcohol by manufacturers. Dental chair manufacturers will normally recommend a product type that is compatible with the upholstery. Concerns have been raised about the use of alcohol on stainless steel surfaces, as it can fix proteins in blood to the stainless steel making them harder to remove. This is of greater concern with surgical instruments where there is a risk of prion transmission than the surfaces in the treatment area. It is advised to use a liberal amount of disinfectant that will wet all the surface to be disinfected. The concentration of disinfectant will be reduced if the wipe is not wet enough, possibly making it ineffective. Pre-soaked wipes are good because they are packaged at the correct concentration. Furthermore, different disinfectants evaporate at different rates, and if they dry out before the minimum contact time, target microbes may escape the disinfection process. Ineffective wiping of surfaces will have the potential to spread contamination rather than eliminate it.

Fungicidal √

√

Slow acting

√

√

Chlorine compounds

Iodophors

√

√

√ at high concentrations

Hydrogen peroxide √ and peroxygen compounds

√

√

Phenolics

Quaternary ammonium compounds

Alcohol

Bacteriocidal (vegetative bacteria) √

Table 12.2  Disinfectants commonly used in dentistry

√

√

√

√

√

Virucidal (enveloped viruses) √

Limited activity

√

√

√

√

– Fast acting – Cheap – Not flammable – Fast acting √ – Not flammable – Fast acting √ – Lower environmental impact Some activity – Can be combined with cleaning chemicals X – Good compatibility with cleaning chemicals – Some are detergents

√

Virucidal (non-enveloped viruses) Tuberculoidal Advantages Slow acting – Fast acting √ – No staining or residue

– High water hardness reduces their efficacy – Hampered by bioburden

– Safety issues

– Corrosive with aluminium, brass, copper and zinc

Disadvantages – Damages some surfaces – Flammable – Hampered by bioburden – Damages metal – Hampered by bioburden – Can stain surfaces

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12.8 Suction Lines

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12.6 Spray or Wipe? Disinfectants are commonly available as liquid sprays and premoistened wipes. Not only must a disinfectant be effective, it should be safe to use. Concerns have been raised about the occupational risks associated with the use of disinfectants especially as sprays. Multiple studies have identified increased occupational asthma and respiratory problems in healthcare workers who frequently use disinfectants. For this reason, premoistened wipes are recommended as they will reduce how much disinfectant is inhaled. If sprays are used, they should be directed into disposable paper towels which can be suitably soaked and then used to wipe surfaces. The CDC advocate the ‘wipe-discard-wipe’ technique; a suitable combined detergent and disinfectant soaked wipe is used first to clean the surface, it is thrown away, and then a second soaked wipe is used to disinfect the surface. This is a more demanding technique both in cost and time, and compliance could be problematic. Appropriate PPE should be worn, including suitable gloves and eye/face protection, as well as ensuring adequate ventilation, when undertaking any decontamination.

12.7 Zoning Zoning the surgery into dirty and clean zones facilitates a methodical and efficient approach to surface cleaning. Signs or a colour-coded system can be placed on the wall in the surgery that makes it clear where these zones are. Whilst treating patients the team members’ gloved hands should only touch the surfaces within the dirty zone. These surfaces will need to be cleaned at both the start and end of the day and between each patient. Clean zones should be cleaned at the end of each session or where there is visible soiling. Modern dental equipment and cabinetry tends to have rounded edges and minimal grooves, to facilitate cleaning. Hands-free, foot-operated and voice-activated controls of the dental chair help interrupt cross infection. It is conceivable that future developments might include antimicrobial hard surfaces, but further research is required. The use of disposable plastic barriers is prudent where surfaces are irregular and difficult to clean. Barriers are essential for sensitive equipment including light-curing units and imaging sensors that cannot be steam sterilised. There does need to be a modicum of common sense with barriers too, as they have the potential to generate a lot of plastic waste that will impact on efforts to address sustainability.

12.8 Suction Lines The dental suction lines and spittoon (if present) require attention when decontaminating the dental surgery. Many dental chairs are equipped with both a high volume suction line and a second lower volume line used with saliva ejectors. The aspirator tips for both lines should be single use, including those used for surgical

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Fig. 12.1  A suction line cleaning system should be used daily

suction. Metal surgical aspirating tips are unlikely to be effectively cleaned due to their narrow lumens. Aspirating tips are hollow and therefore should not be reprocessed in a non-vacuum autoclave. It can be confusing when procuring equipment as reusable aspirating tips are readily available, so there is an assumption they are fine to be used; they are outdated and have been superseded by single-use tips. Care should be taken when using saliva ejectors as there is a risk of drawback into the patient’s mouth from the suction tube if the patient closes their lips around it like a straw. The use of high volume suction is essential for many dental procedures to keep the mouth free of both liquid and debris. It also assists infection control by helping remove aerosols when undertaking clinical care. The passage of the fluids along the tubing of the aspirating lines will lead to biofilm formation, as well as the accumulation of blood and saliva and other debris removed from the mouth. This can narrow the lumens of the tubing and decrease the efficacy of the suction generated, at worst leading to back flow into the patient’s mouth. Subsequently it is important to routinely clean and disinfect the suction lines at least daily (Fig. 12.1). Non-foaming disinfectants and cleaners formulated for this purpose should be used.

12.9 Routine Environmental Cleaning Routine cleaning is facilitated by having an uncluttered environment with surfaces that are in good condition. Cracks, rips and tears in surfaces will allow contaminants to evade cleaning measures. Impervious flooring, ideally with coved surfaces, should only be used in clinical areas, and the use of carpet elsewhere should be

12.10 Portable Electronic Devices as Fomites

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Toilets

Clinical areas

Kitchen

General

Fig. 12.2  Colour coding is used to designate area specific mop use

minimised as it is harder to clean. Clinical areas should never be carpeted or have cloth-covered furniture, as these can’t be properly cleaned. Floors and non-clinical areas can be cleaned with regular household products, where the relevant safety precautions are assessed and implemented. Dust and dirt harbour microorganisms; to reduce the risk of accumulating potential pathogens, daily cleaning is essential. A combination of vacuuming and mopping floors with household detergent simply achieves this. Mops designated only for use in clinical areas are advised, and by using a colour coding system, cleaning staff can be clear which mops and buckets are for specific areas (Fig. 12.2). Disposable mop heads are preferable; otherwise they stay wet and allow microbes to grow, and buckets should be dried after use for the same reason. Where mops are not thrown away after use, they should be stored head up so the water can drain off, rather than being left in a wet bucket between use. Mop buckets should be left to dry upside down. Whilst we understandably need to cater to our younger patients while they wait for their appointments, soft toys should not be provided to play with as they aren’t easily cleaned and have been identified as a potential vector for the spread of infections, e.g. MRSA. Toys that can easily be cleaned are of course acceptable. Regular cleaning of waiting room toys should be part of the cleaning schedule.

12.10 Portable Electronic Devices as Fomites The ubiquity of the mobile phone which is carried with us all day has been identified as a potential infection control risk. Attention should be given to keeping phones out of the clinical treatment area and wiping touchscreens with a suitable disinfectant.

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Fig. 12.3  An example of a protective tablet case that can be disinfected between patients. (Courtesy of FutureNova)

This extends to tablets which are increasingly becoming integrated with practice record keeping and educational software. Disposable plastic shields and readily cleaned cases are now available for tablets used in healthcare and are recommended where a tablet is being used in a clinical area (Fig. 12.3). Computer keyboards and other peripherals should be covered or wipeable; some models may even be cleaned using a thermal washer disinfector. Software is available that allows for voice-­ controlled hands-free charting too.

12.11 Body Fluid Spills Although a household detergent is suitable for regular environmental cleaning, in the event of a body fluid spill, including vomit, urine, blood or faeces, a separate protocol and equipment is needed. Spillage kits are readily available to assist with cleaning up after such an event (Fig.  12.4). It is also worth noting that it is not uncommon for patients to try and help after an incident and inadvertently make things worse; for example, after their child has been sick in the waiting room, parents may start trying to mop things up with tissues or paper towels and end up spreading the vomitus around more. Not only must we help with the crisis to hand that has led to the spill but also be in control of the situation to stop the potential spread of infective material. This is done by not only having the correct spill kit to hand but staff who are trained to use it. A practice policy on dealing with spills formalises this approach. A detergent wipe followed by a disinfectant wipe should suffice for small spots of blood, avoiding alcohol disinfectants where the contaminated surface is stainless steel. A spill kit should contain PPE, a scoop, an adsorbent powder and a disinfectant. PPE should include gloves, mask, eye protection and a disposable apron. Some spill kits will contain an adsorbent powder made from zeolites, a type of mineral that soaks up moisture like that used for cat litter, but it doesn’t disinfect. A kit that uses troclosene sodium [also known as sodium dichloroisocyanurate (NaDCC)] granules is preferable as it will both soak up and disinfect the surface. However, this

12.11 Body Fluid Spills

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Fig. 12.4  Spillage kits allow for a quick response to an incident because not only are all the things needed in one place but also the instructions on what to do are included

Table 12.3  Management of spills based on their size and type Size of spill Spot

Management 1. Wipe off with a disposable alcohol wipe or non-alcohol disinfectant wipe if the surface is stainless steel 2. Clean with water and a detergent 3. Dry with disposable paper towel Minor (10 cm 1. Disposable paper towels are placed over the spill to contain it diameter) 2. Gently flood the paper towels with 1% hypochlorite solution, and leave for at least 2 min 3. Dispose of the paper towels in the clinical waste stream 4. Steps 3–5 for minor spills Urine 1. Due to the risk of chlorine gas release, a gelling agent (available in commercial urine spill kits) or paper towels should be used to soak up the area first. These are then disposed of 2. Clean the area using a detergent

must be used with caution as not all surfaces will tolerate it and furthermore it releases chlorine gas, so ensure there is adequate ventilation. Hypochlorite solution diluted to 1% is the preferred choice of disinfectant for cleaning up after a spill due to its broad range of activity. It will however damage some surfaces and should itself be cleaned away after use, using water. It cannot be used on fabrics, hence why fabric chairs and carpets should be eliminated from dental practices. PPE must be worn when managing a spill. Extra care is needed if there is broken glass involved. All waste generated in cleaning up a spill goes in the clinical hazardous waste stream. The size of the spill will guide how it is managed, as detailed in Table 12.3.

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12.12 Laboratory Work Impressions and other stages of prosthodontic work will be contaminated in saliva and sometimes blood. It is essential that any contamination is removed from these items before they make their way to the dental laboratory, to not only protect the recipients who handle them but also those who transport and deliver them. Accuracy is critical in prosthodontic dentistry, and it is important that impressions are not distorted by the decontamination process. Prior to disinfection, lab work should be rinsed under running water to clean it. While this may remove about 40% of contamination, it still needs to be disinfected. It is advised that all lab work is fully soaked in a disinfectant intended for the purpose where the manufacturer not only confirms its spectrum of activity but gives assurance which impression materials it is compatible with (Fig. 12.5). The manufacturer’s recommended immersion time should be followed, which tends to be about 10 min. The lab work is then rinsed and if necessary dried prior to packaging it. Sprays to disinfect lab work are not recommended as they may not fully cover all surfaces, especially undercuts on impressions. At least one manufacturer has developed a crown and bridge impression material that can be sterilised in an autoclave and remain accurate; whether this is a novelty or an indicator of a future trend remains to be seen. It has been noted that shade guides used in prosthodontic Fig. 12.5 Impressions must be disinfected before they are sent to the laboratory

Further Reading

115

dentistry might change colour with time due to repeated disinfection and the chemicals used; one suggestion is to keep an unused shade guide as a reference that the working one can be periodically checked against.

Further Reading Doll M, Stevens M, Bearman G. Environmental cleaning and disinfection of patient areas. Int J Infect Dis. 2018;67:52–7. Kramer A, Schwebke I, Kampf G. How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infect Dis. 2006;16(6):130. Quinn MM, Henneberger PK, et al. Cleaning and disinfecting environmental surfaces in health care: toward an integrated framework for infection and occupational illness prevention. Am J Infect Control. 2015;43(5):424–34. Rutala WA, Weber DJ.  Selection of the ideal disinfectant. Infect Control Hosp Epidemiol. 2014;35(7):855–65.

Dental Unit Waterlines

13

Water is used widely in dentistry, either as a coolant, irrigant or both, for many of the treatments provided to patients. The source of this water is either from the mains supply or is purified such as that produced by distillation or is produced by deionisation equipment or reverse osmosis equipment. Purified water may either be generated in the practice or may be bought in from commercial suppliers. When buying in water for use on patients, it is important that it is suitable for medical use and is not intended for other uses such as from the motor trade and intended for use in car batteries as it does not come with the assurance that it is fit for human consumption. It is not essential that any water used in dental units is sterile for providing routine dental care but the user should at least ensure that it is of potable quality as defined by local water regulations. Water that is intended for use in dental units must not be stored for long periods of time in large quantities as bacteria can multiply in stagnant water. Even sterile water will rapidly become contaminated once the storage container has been opened and exposed to the environment. The water supply to the dental unit may be either directly from the mains supply or may be fed from a reservoir that is independent of the mains water supply. The reservoir is usually fitted directly to the dental unit, but in some cases there may be a cold water storage tank that supplies cold water to the whole practice. This arrangement is not recommended to supply the dental unit as there is a risk of stagnation of the water. In some countries the local Water Regulations outlaw a direct connection from the mains supply to such things as medical equipment. This type of regulation is intended to reduce the risk of back siphonage from the water contained in the equipment back into the mains water supply in the event of a drop in water pressure in the mains water. In some countries it is permitted to manage this risk by inserting a non-return valve into the plumbing between the equipment and the mains water feed. In some countries the only method that is allowed for connection to the mains water supply is via an air gap where there is no direct connection but where the plumbing to the equipment is separated from the mains supply by a specified distance. It is essential therefore that the local Water Regulations are consulted

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5_13

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13  Dental Unit Waterlines

Fig. 13.1  Dental unit independent bottle reservoir system

before connecting to a mains water supply. It would be expected that reputable manufacturers of dental equipment will be familiar with local Water Regulations and be able to advise accordingly. Although it should be noted that it is ultimately the responsibility of the user to ensure that the equipment is compliant, the principle of caveat emptor applies (Fig. 13.1). Where the local Water Regulations make direct connection to the mains water supply difficult, the best option is to install dental equipment with an independent water supply. This will either be built into the equipment during manufacture or can be fitted to existing equipment. This will not only comply with Water Regulations but will also give the user direct access to the dental unit water supply to provide a choice of water quality and allow the introduction of chemical agents to manage potential problems. The main problem that is known to occur with dental unit water is the presence of bacterial contamination. The source of this contamination does not usually arise from the source water directly, unless it has been contaminated during storage, but arises from within the dental unit itself. The contamination exists in the form of a biofilm that proliferates on the walls of the plastic tubing that carries water through the dental unit. The biofilm originates from environmental bacteria that will be present in very small numbers in water flowing through the tubing. The source of these bacteria is either from the source water put into the system, from the air or the operators hands when water is put into the reservoir or from retraction through the dental handpiece. Some of these bacteria then attach themselves to the inner walls of the tubing and begin to multiply. They are able to remain attached to the walls of the tubing because of the laminar nature of the water flow through the tubing, with

13  Dental Unit Waterlines

119

the slowest flow adjacent to the tubing; thus they remain largely undisturbed. Biofilm begins to form on the tubing within hours of water being introduced into the system and begins to mature within about 72 h of forming. As the bacteria multiply, some of them secrete an extracellular matrix that further binds them to the walls of the tubing and eventually the biofilm becomes dense and impenetrable. It is also highly organised once it has matured and channels develop within the matrix that allows nutrients to be carried deep into the matrix allowing further development within the biofilm. The density of the matrix that is formed then makes the biofilm very resistant to many forms of treatment that might be used to attempt to treat the biofilm. As the biofilm develops, small fragments are shed from the surface and enter the water flowing through the unit and are then expelled through the terminal equipment fitted to the outlet such as a dental handpiece, air/water syringe or an ultrasonic/air scaler. The bacteria that are suspended in the water flowing through the tubing are said to be in the planktonic phase. These planktonic bacteria will contaminate the patient’s oral tissues or may be aerosolised and inhaled by either the patient or surgery staff exposed to the aerosol (Fig. 13.2). Many of the bacteria making up the biofilm are environmental commensals and considered to be non-pathogenic to most people. Some, however, may be potentially pathogenic and have the ability to cause disease in susceptible individuals. Although it is thought to be relatively rare, there is a real risk of serious infections arising from the DUWS.  An example of this is Legionella sp. which has been implicated in the death of both patients and dentists. The death of a patient in Italy from legionella pneumonia shortly after receiving dental treatment in a dental practice where the same strain of Legionella was isolated from dental unit water has been reported. There has also been the report of the death of a dentist in the

Fig. 13.2  Scanning EM view of bacteria in biofilm on dental unit waterline wall

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13  Dental Unit Waterlines

USA from legionella infection where the same strain of legionella was isolated from the dental unit water supply (DUWS). In some countries, the UK, for example, when cases of Legionella infection are identified, the patient’s recent dental treatment history is investigated. There have also been studies reported where a number of patients, some of which were known to be immunocompromised, were colonised by antibiotic-­resistant Pseudomonas sp. that was shown to originate from DUWS. Several national and international collaborative studies have shown that the problem of DUWS contamination is widespread and that the quality of the water obtained from the dental unit would not meet recognised drinking water standards. Some studies have shown that it is not uncommon to find total bacterial counts in DUWS in the order of half a million bacteria per ml of water. Drinking water standards will allow up to about 100–500 bacteria per ml of water, and therefore it is clear that in some cases, the water used in some dental practices could not be considered to be potable. Not only is there a risk of exposure to large numbers of vegetative bacteria, but there is a risk of exposure to the products of bacterial breakdown such as endotoxin. It has been speculated that the regular exposure of dental healthcare staff to bacterial endotoxin found in DUWS can lead to the development of late-onset asthma, the incidence of which is greater in dentists than the general public. This supports the proposal that dental surgery staff may be at greater risk of adverse incidents from environmental risks than are their patients who will be less exposed. This can be further supported by studies that have shown that dental surgery staff have far higher levels of legionella antibodies than do a random sample of the general public which is strongly suggestive of occupational exposure. Having identified the risks posed by contamination of DUWS then there follows that there is an obligation to ensure that these risks are managed. There are over 100 products available on the world market that it is claimed will manage the risk of contaminated DUWS.  Not all of the claims made by the manufacturers of these products have been independently validated, and therefore before choosing a treatment product or system, it is advised that independent clinical trial evidence is sought from peer-reviewed journals. Most of the systems and products available to treat DUWS are based on chemical treatments that require access to the waterlines via an independent water reservoir or a dosing device. There are basically two types of treatment modalities available; one simply reduces the number of planktonic bacteria found in the water that flows through the unit, the other strips the biofilm from the surface of the tubing and then has a chemical agent added to the water supply that prevents the reformation of new biofilm. Simply adding a chemical agent to reduce the number of planktonic bacteria in the water does not address the problem of endotoxin that may be secreted into the water from the biofilm. Also, it will not treat any bacteria that may be contained within portions of biofilm that may be shed from time to time from the layer of biofilm on the surface of the tubing. These clumps of biofilm may also cause problems by blocking fine passages in equipment, e.g. dental handpieces (Fig. 13.3).

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Fig. 13.3 Biofilm removed from a single dental unit following aggressive chemical treatment

The complete system for treating DUWS includes a chemical that strips biofilm from the tubing. Most of the systems available utilise an aggressive chemical treatment that attacks and breaks down the biofilm, which is then flushed away by running large amounts of water through the system after terminal connectors are removed from the tubing. This treatment and flushing are known as purging and will also dilute and flush away the aggressive chemical used. The reservoir is then filled with a freshly made-up maintenance solution which, while not toxic to humans, prevents the biofilm from re-establishing. This solution is used constantly in the reservoir following purging and will then maintain the DUWS free of biofilm. It is not recommended that the maintenance solution is made up in bulk quantities and then stored for long periods of time as it may become contaminated with some types of bacteria. Opportunistic pathogens including Pseudomonas sp. can survive and proliferate in dilute disinfectant solutions. It is good practice to monitor the water quality produced by the DUWS, and therefore a system of regular microbial testing should be devised. Regular samples of water should be collected aseptically from each outlet through which water is run, for example, from the dental handpiece, the air/water syringe and if fitted an ultrasonic or air scaler. These samples can be sent to a suitable laboratory for independent testing. Alternatively, they can tested in-house using a dip inoculum system

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Fig. 13.4  Incubated dip inoculum devices estimating the number of colony forming units (cfu) in water samples

which uses agar on a plastic strip that is dipped into the water sample and then left for a period of time to allow bacterial colonies to develop. Once the colonies have developed, the approximate bacterial count can be estimated by comparing with a chart provided by the manufacturer. The number of colonies that develop will represent an estimation of the number of bacteria in the original water sample. It should be noted that whilst this is not a highly accurate means of providing a total viable count of bacteria present, it will provide a good guide as to the efficacy of the treatment of the DUWS. If at any time a high bacterial count is indicated, then it may be necessary to purge the system again and then retest the system (Fig. 13.4).

Further Reading Pankhurst CL, Coulter W, Philpott-Howard JN, Surman-Lee S, Warburton F, Challacombe S. Evaluation of the potential risk of occupational asthma in dentists exposed to contaminated dental unit waterlines. Prim Dent Care. 2005;12(2):53–9. Walker JT, Bradshaw DJ, Finney M, Fulford MR, Frandsen E, ØStergaard E, Ten Cate JM, Moorer WR, Schel AJ, Mavridou A, Kamma JJ, Mandilara G, Stösser L, Kneist S, Araujo R, Contreras N, Goroncy-Bermes P, O’Mullane D, Burke F, Forde A, O’Sullivan M, Marsh PD.  Microbiological evaluation of dental unit water systems in general dental practice in Europe. Eur J Oral Sci. 2004;112(5):412–8.

Glossary

Adaptive immunity  A specific immune response to a single antigen Aerosol  A fine suspension of liquids or solids in the air. This may include microorganisms and be a method for spreading diseases AIDS  Acquired immunodeficiency syndrome; the stage of HIV infection where the immune system is so badly depleted that opportunistic infections and cancers can manifest. Indicated by less than 200 CD4 cells per cubic mm of blood Antigen  Molecules recognised by the immune system as not being part of the host (non-self) Antibodies  Proteins that bind to specific antigens and signal other immune cells to destroy what it has bound to Arnold device  A now defunct machine that was used to sterilise instruments using steam under atmospheric pressure Asepsis  The exclusion of pathogenic microorganisms from the patient treatment area BBV  Blood-borne virus, e.g. HIV Beijing declaration  A strategy developed after the 2009 World Workshop on Oral Health and Disease to manage HIV positive members of the dental team B cells  A type of white blood cell that produces antibodies Bioburden  Microorganisms and body matter that contaminate instruments making them dirty Biofilm  A film of bacteria contained within a dense extracellular matrix BSE  Bovine spongiform encephalitis; a prion-mediated disease in cows. Also known as mad cow’s disease CDC  Centers for Disease Control and Prevention; a public body in the USA whose aim is to protect against health and safety threats CFU  Colony forming units. Units used when performing viable bacterial counts; it indicates the minimum number of viable bacteria present but does not take into account individual bacteria where they are clumped together Check valve  A plumbing fitting that only allows water to travel in a pipe one way Cirrhosis  Severe damage to the liver with scarring following prolonged inflammation Commensal  Non-pathogenic microorganisms that live as a parasite without causing disease © Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5

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Glossary

Detergent  Substance that reduces the surface tension between two substances to facilitate cleaning Disinfection  A process that removes most, but not all, potentially harmful microorganisms DUWS  Dental unit water system. Describes the tubing and associated equipment containing water in the dental unit Endotoxin  A poisonous substance that forms part of the microorganism (usually the cell wall) that is released after death of the cell Exotoxin  A poisonous substance that is produced by a microorganism that is secreted into the environment Exposure prone procedure  Where the gloved hands of a clinician are not fully visible at all times during an operative procedure whilst using sharp instruments or alongside sharp body tissues Fomite  Inanimate surfaces with the potential to harbour microorganisms Herd immunity  The protective effect of stopping the transmission of an infection within a population when sufficient people are immune HBV  Hepatitis B virus HCV  Hepatitis C virus HIV  Human immunodeficiency virus HTM 01-05 Health Technical Memorandum 01-05; an English guidance document on patient safety when decontaminating reusable instruments in primary care dental practices Immunised  Made immune to a specific infection Infection control  The prevention of nosocomial infections Innate immunity  A non-specific and immediate immune response to the presence of non-self molecules LDU  Local decontamination unit; may be colloquially called a “steri” or “decon” room Macrophage  A type of white cell that plays multiple important roles in the immune response including presenting antigens and destroying invading organisms Miasma  Before the germ theory of disease it was thought that infections were spread by foul smelling air; miasma Minamata Convention  An international treaty to protect human health and the environment from the effects of mercury MMR vaccine  A combined vaccine against measles, mumps and rubella Morbidity  State of being diseased or unhealthy Mortality  Death caused by a disease or condition Nosocomial infection  Infections following healthcare Pandemic  A new disease that spreads worldwide Pathogen  A microorganism capable of causing disease in a susceptible host PEP  Post-exposure prophylaxis Planktonic  Microorganisms in suspension in water Potable  Water that is safe to drink or use for food preparation PPE  Personal protective equipment

Glossary

125

Prion  A proteinaceous infectious particle; the smallest infectious matter we know of Pyrogens  Heat stable substances in the cell wall of certain bacteria that cause a febrile reaction (raised temperature) when introduced into the blood or tissues RO water  Reverse osmosis water; produced by filtering water with semipermeable membranes to remove minerals and ions Safer sharp  Sharp medical equipment with engineering controls that aim to reduce risk of percutaneous injury to the user Sharps injury  Where the skin is cut by a dirty sharp instrument Seroconversion  The ability to detect a specific antibody in a person’s blood Spaulding classification  A system that identifies how medical equipment should be reprocessed based on what parts of the body it comes in contact with Standard Precautions  The assumption that all bodily fluids, mucous membranes and no intact skin are contaminated and the measures undertaken that reduce the risk of transmission of these associated diseases Sterile  Articles that are free from living organisms Sustainability  Using our resources effectively whilst maintaining them for future generations T cells  A type of white blood cell that is critical in cell-mediated immunity TDS meter  A device that measures total dissolved solids (minerals and ions) in water Thermocouple  A sensor that is used in temperature measuring equipment Toxin  Poisonous substance produced by microorganisms Universal precautions  Management of the assumption all blood and certain body fluids are contaminated Vaccine  An agent that stimulates the immune system to generate antibodies against a specific disease Vaccination  The use of an agent to prevent an infectious disease vCJD  Variant Creutzfeldt-Jakob disease; a prion-mediated neurological disease in humans WHO  World Health Organization Zoning  Demarcating areas within treatment rooms and the local decontamination unit which are considered dirty or clean

Index

A Acquired immune deficiency syndrome (AIDS), 8 Active adaptive immunity, 45 Anaesthetics, 78 Antigens, 43, 44 Aspergillus sp., 15 Automated cleaners, 73, 75 B Bacille Calmette-Guérin (BCG) vaccine, 49 Bacterial cells, 13 Beijing Declaration, 51, 52 Benchtop pressure steam sterilisers (PSS), 79, 80, 82 Biofilm, 118, 119 removal, 121 Blood borne viruses, 52 bacterial infections bordatella pertussis, 19 meningitidis, 18 tuberculosis, 18 ebola virus, 18 hepatitis B, 16 hepatitis C, 16 HIV, 16, 17 influenza, 17 mumps, 17, 18 noravirus, 17 Body fluid spills, 112, 113 Body fluids, 9 Bordetella pertussis, 19 Bovine spongiform encephalitis (BSE), 9 B type vacuum autoclave, 92

C Candida albicans, 15 Centers for Disease Control and Prevention (CDC), 8 Certificate of conformity, 99–101 Chemical monitoring, of sterilisation cycles, 86 Chlorhexidine, 40 Chloroplatinic acid, 38 Clinical dental equipment certificate of conformity, 99–101 numbers of instruments, 97, 98, 101, 103 repairing and disposal, of instruments, 103 single use, 98, 99 Clostridium tetani, 12, 49 Colour coding, 111 Contact dermatitis reactions, 38 Creutzfeldt-Jakob disease (CJD), 9 D Decontamination, in dentistry, 62, 63 Deionisation, 117 Dental disinfection and environmental decontamination body fluid spills, 112, 113 disinfectants, 107 choosing, 107 in dentistry, 108 liquid spray, 109 premoistened wipes, 109 surface, 107 fomites, 105 laboratory work, 114, 115 respiratory and hand hygiene, 105

© Springer Nature Switzerland AG 2020 M. R. Fulford, N. R. Stankiewicz, Infection Control in Primary Dental Care, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-16307-5

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Index

128 Decontamination, in dentistry  (cont.) routine environmental cleaning, 110, 111 suction lines, 109, 110 treatment areas, 106, 107 zoning, 109 Dental instruments, cleaning methods automated cleaners, 73, 75 manual cleaning, 66–68 ultrasonic cleaning, 70–72 Dental unit independent bottle reservoir system, 118 Dental unit waterlines bacterial contamination, 118 drinking water standards, 120 Dental unit waterline wall, 119 Dental unit water supply (DUWS), 120 Detergent wipe, 112 Digital radiography, 24 Diphtheria, 13 Dip inoculum system, 121 Disinfection, 61 E Elastomeric impression materials, 38 Endotoxins, 13, 120 Exotoxins, 13 F Fomites, 12 G Geobacillus stearothermophilus, 87 Gypsum waste, 24 H Hand hygiene, 29 alcohol hand rubs, 32 moisturiser, 32 soap and water, 29, 32 Handpiece markings, 101 Hard-line approach, 51 Heat sterilisation, 78 Helix device, 88 Hepatitis, 6 Hepatitis B, 15 Hepatitis B immunoglobulin, 47–48 Herd immunity, 45, 46

High volume evacuation (HVE) suction, 40 HIV virion budding, 14 Host defence mechanism, 15 Host tissues, 15 Humectants, 32 Hypochlorite solution, 113 I Immune system antigens, 43, 44 chickenpox, 50 elements of, 43 emerging and regional risks, 50 hepatitis B vaccines, 47, 48 herd immunity, 45, 46 influenza (seasonal flu), 49 pathogenic organisms, 43 tetanus, 49, 50 tuberculosis (TB), 48 vaccines, 44 Incubated dip inoculum devices, 122 Independent water supply, 118 Infected oral healthcare worker hepatitis B, 52 hepatitis C, 53 HIV, 51 other infections, 53 safer sharps, 56, 57 sharps injuries, 54, 55 Infection control cost barrier, 23 in dentistry infections, transmission of, 12 microbes, transmission of, 12 parasitic microorganisms, 11 environmental impact of, 23, 24, 26 history, 10 in density, 5, 6 germ theory, of disease, 4 hepatitis, 6 HIV/AIDS, 7–9 principle, 3 prions, 9, 10 steam age, 7 patient and staff safety regulation, 21 regulation of, 21, 22, 27 risk management, 23 standards, 22, 23 sustainability, 25 Influenza A and B viruses, 49

Index Instrument cleaning, 65, 66 Instrument package labelling, 100 L Local decontamination unit (LDU), 89, 95 airflow, 94, 95 clean/packaging and sterilisation area, 92, 93 components, 91 dirty/cleaning area, 92 plumbing, 93, 94 potential, 90 reprocess instruments, treatment room, 89 room design and work flow, 89–91 services and surfaces, 93 Lymphoid tissue, 44 M Manual cleaning, 66–69 Measles, mumps and rubella (MMR), 48 Meningococcus, 18 Minamata Convention, 26 Moist body substances, 8 Mycobacterium bovis, 48 Mycobacterium tuberculosis, 12, 18 N Neisseria meningitidis, 18–19 Norovirus, 17 O Open type instrument cassettes, 102 Opportunistic pathogen, 15 P Passive immunisation, 15, 48 Pathogen associated molecular patterns (PAMPs), 44 Pattern recognition receptors (PRRs), 44 Personal protective equipment (PPE) for eyes, 35 eye wash kit, 35 gloves, 36–39 for nose and mouth, 35, 36 pre-treatment, 40 risk management, 34 safety risk, 34 uniform and aprons, 39

129 Planktonic bacteria, 119 Portable electronic devices, as fomites, 111, 112 Post exposure prophylaxis (PEP), 55 Potential airborne pathogens, 40 Pre-soaked wipes, 107 Pseudomonas sp., 121 Purging, 121 R Radiographic waste chemicals, 24 Reverse osmosis (RO), 93 Rheumatic fever, 15 Routine environmental cleaning, 110, 111 S Seasonal influenza, 49 Semmelweis, I., 3 Sickness presenteeism, 53 Single shot water system, 82 Sodium dichloroisocyanurate (NaDCC), 112 Sterile, 61 Sterile gloves, 37 Sterilisation, in dentistry benchtop steam sterilisers, use of, 82, 83 boiling water, 78 dry heat, 78 heat sterilisation, 78 methods, 77 moist heat, 79 PSS, 79, 80 type B pressure steam sterilisers, 81 type N pressure steam sterilisers, 80, 81 type S pressure steam sterilisers, 81 validation, 83, 84, 86–88 water supply, 82 Steriliser data logger, 85 Steriliser integrated printer, 85 S type autoclaves, 92 Suction line cleaning system, 110 Sulphur, 38 T Tetanus, 13 Thermal washer disinfector, 112 Total dissolved solids (TDS), 94 Type B pressure steam sterilisers, 81 Type N pressure steam sterilisers, 80, 81 Type S pressure steam sterilisers, 81

Index

130 U Ultrasonic cleaning, 70–72 V Vaccination Act of 1853, 47 Varicella zoster virus, 50

W Wall mounted apron dispensers, 39 Washer disinfector, 102 Water Regulations, 117 Wipe-discard-wipe technique, 109