russell, hugo & ayliffe's (principles and practice of disinfection, preservation and...

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Special Issues in Dentistry

Jonathan L.S. CaplinSchool of Environment and Technology, University of Brighton, Brighton, UK

21.2

Introduction

The final two decades of the 20th century saw significant advances in our knowledge of infection control, leading to a reduction in risk and an improvement in the health and safety of both healthcare personnel and patients. The emergence of the human immunodeficiency virus (HIV) and transmissible spongiform encephalopathies (TSEs), and the resurgence of the hepatitis B virus (HBV) and hepatitis C virus (HCV), were drivers for the development of improved infection control and hygiene prac-tices, with each challenge ushering in new technologies and pro-tocols to limit the spread of infection in the dental and other healthcare settings.

The practice of infection control underwent major changes in the 1980s following reports of clusters of patients in the USA who were thought to have acquired HBV during treatment by an HBV-infected dentist [1]. A position paper on infection control in dentistry commented that “Dental practitioners are virtually the only health care providers who routinely place an ungloved hand into a body cavity” [2]. The concurrent epidemic of acquired immune deficiency syndrome (AIDS) caused by HIV prompted the US Centers for Disease Control and Prevention (CDC) to introduce the concept of “universal precautions”, aimed primarily at preventing the transmission of bloodborne viruses in all areas of healthcare including dentistry [3]. The CDC also published its first guidelines for control of infections in dentistry in 1986 [4].

During the 1990s, particularly within the UK, there was con-siderable concern after the emergence of variant Creutzfeld–Jacob disease (vCJD), a novel human form of TSE, and its possible association with bovine spongiform encephalitis (BSE). Although the theoretical transmission of iatrogenic Creutzfeld–Jacob dis-ease (CJD) by surgical and dental procedures had been postulated in 1978 [5], the risk of transmission of prion proteins during dental treatment was not clear, and the heat resistance of prions and their ability to adhere to medical and dental instruments was a source of unease.

The challenges from these serious transmissible diseases led to an increase in the scientific and clinical understanding of infec-tion prevention and control, and resulted in the development of a broad range of guidelines, technical memoranda and official documents. These were based on prevailing theory and scientific data, with the express aim of reducing and minimizing cross-infection in the healthcare and dental setting. In the USA, the CDC published revised guidelines in 1993 for preventing the transmission of bloodborne viruses [6], which was updated 10 years later, when the CDC emphasized “standard precautions” [7].These were addenda to the earlier universal precautions, and included more anatomical sites and body fluids, and incorporated body substance isolation controls.

In the UK, updated guidance on implementing infection control procedures within dental practices was introduced in 2003 by the British Dental Association together with the Depart-ment of Health [8]. This was followed by the UK Department of

Russell, Hugo & Ayliffe’s: Principles and Practice of Disinfection, Preservation and Sterilization, Fifth Edition. Edited by Adam P. Fraise, Jean-Yves Maillard,

and Syed A. Sattar.

© 2013 Blackwell Publishing Ltd. Published 2013 by Blackwell Publishing Ltd.

Introduction, 537Cross-infection, 538Contamination of the working

environment, 542

Compliance with infection control measures, 544

Recent developments in dental hygiene, 544References, 545

Other Health Sectors21

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organisms from patients’ blood splatter from rotary instruments and respiratory and oral secretions.• The spread of microorganisms from contaminated dental unit water lines.

The main cross-contamination and cross-infection routes in the dental setting are illustrated in Figure 21.2.1.

Bloodborne virusesDuring dental procedures, DCPs may be exposed to a wide variety of microorganisms from the blood, saliva and oral cavity of patients, and many of these microorganisms have the potential to be transmitted in the occupational setting via percutaneous and mucocutaneous routes [13]. The most common and serious bloodborne viruses (BBVs) of relevance to DCPs are HBV, HCV and HIV. Needlestick and sharps injuries are the most common means of transmitting these BBVs, and occur with regularity.

The UK Advisory Group on AIDS calculated that the risk of infection with a BBV following a deep penetrating wound with a hollowbore needle or an instrument contaminated with blood is 1 in 3 for HBV [14], 1 in 30 for HCV, and 1 in 300 for HIV [15]. The risks of BBV infection via mucocutaneous exposures are much lower, estimated at 1 in 1000 for HIV [15]. According to CDC estimates as many as 20 different pathogens have the poten-tial to be transmitted to healthcare worker via a needlestick injury, and that approximately 390,000 needlestick and sharps-related injuries occur per annum to healthcare staff [16]. A study by Panlilio et al. of injuries to healthcare workers in the hospital setting recorded during 1997–1998 in the USA, suggests that the figure may be much higher [17]. According to the US National Institute of Occupational Safety and Health, if hospital and non-hospital healthcare workers are included in the data, then esti-mates of between 600,000 to 800,000 needlestick injuries per annum in the USA are more likely [18].

In the USA, exposure to HIV, HBV or HCV by percutaneous injury has been shown to have an average risk of infection of 0.3%, 6–30% and 1.8%, respectively [16, 19]. A report by the UK Health Protection Agency (HPA) in 2008 [20] based on national surveillance data of exposures to BBVs occurring in England, Wales and Northern Ireland from 2000 to 2007, documented 914 percutaneous exposure incidents between 2006 and 2007, of which 68% were caused by hollowbore needles. Physicians and dentists reported the highest number of occupational exposures, and the highest proportion of percutaneous injuries (48%) involved patients with HCV. Although there may be some ques-tions regarding the accuracy of the transmission data, percutane-ous injuries are an occupational hazard for healthcare workers, and the numbers of reported needlestick incidents make this a pressing problem for those involved in injury control and prevention.

Hepatitis B and C virusesViral hepatitis occurs endemically worldwide and has become a major public health problem, with an estimated 350–400 million persons with chronic HBV infections alone [21]. There are six

Health’s issue of the revised Health Technical Memorandum (HTM) 01-05 Decontamination in Primary Care Dental Practices [9]. It requires that practices work at or above the “essential quality requirements” described in the guidance, and that all practices should have a detailed plan on how to achieve the aim of “best practice”.

The introduction, and professional acceptance, of practical, unambiguous, evidence-based guidelines had a positive impact on dental cross-infection and contamination issues, and to date there have been no reports of cross-infection-related illness in UK dental practices [10]. In the USA, there have not been any reported cases of HIV transmission from dental care professionals (DCPs) to patients since 1992, no cases of HCV transmission, and the last transmission of HBV from a DCP to patients was reported in 1987 [1].

More recently, the 2009 H1N1 influenza pandemic again focused attention on the prevention of transmission in dental and other healthcare settings. Both the US Occupational Safety and Health Administration (OSHA) and the UK Department of Health issued specific guidance and recommendations based on scientific rationale and previous experience [11, 12].

A full exposition of all the potential cross-infection and con-tamination risks in dentistry, and the measures to mitigate them, is beyond the scope of this chapter and can be found in other publications [7, 9]. Instead, this chapter will examine three of the most pressing issues in current dental hygiene where poten-tial hazards to the health and safety of both dental staff and patients are seen. The concerns addressed here are cross-infection, particularly of bloodborne viruses and prion proteins; contamination and decontamination of dental instruments and the working environment; and compliance with infection control measures.

Cross-infection

Cross-infection – the person-to-person spread of infectious microorganisms – is a serious issue for all health professionals but the potential for cross-infection in dentry is particularly high due to a number of factors. These include the performance of invasive procedures resulting in exposure to blood and other potentially infective materials, the use of complex and intricate instruments requiring cleaning and decontamination, the incorrect use of decontamination and sterilization facilities/procedures, high patient turnover, and the location of many dental surgeries in converted residential and commercial premises.

The main cross-infection routes in dental surgeries include the follwoing:• Inadequate decontamination and sterilization of surgical instruments and equipment.• Percutaneous injuries from “sharps” and the transmission of bloodborne viruses.• The spread of microorganisms from hands and from aerosols contaminated with respiratory pathogens and other micro-

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Chapter 21.2 Special Issues in Dentistry

dental setting from patient to DCP, from DCP to patient, or from patient to patient. There have been no reported cases of HBV transmission from DCP to patient in the USA since 1987 [1]. Factors contributing to the fall in HBV cross-infection rates include a greater use of gloves during dental examination and treatment, more care when handling sharp instruments, and an increased uptake of HBV vaccination [22]. Nevertheless, despite the introduction and use of universal precautions, patient-to-patient HBV transmission still occurs [34]. A problem that may affect surveillance and reporting rates for HBV is that approxi-mately 50% of HBV infections are asymptomatic or subclinical [35], which makes it difficult to link sporadic cases to a specific DCP or dental surgery.

To minimize the risk of HBV infection, DCPs are advised to have immunization against HBV [6], and over 80% of US dentists and over 90% of UK DCPs reported HBV vaccination by 1992 [36, 37]. All healthcare workers, including DCPs and those who may perform procedures likely to result in exposure to HBV, have an ethical and legal duty to protect the health of their patients. DCPs should be aware of their immune status and if they believe that they have been infected they have a responsibility to seek medical advice and undergo appropriate testing. If found to be infected, the DCP may have limitations placed on the procedures that they can carry out. In the UK, not taking proper advice or not acting accordingly, would be regarded as a case of serious professional misconduct and could lead to disciplinary and pos-sible legal action [38, 39].

types of hepatitis virus (A–F) and HBV and HCV infections are an important infectious occupational hazard in the dental profes-sion. HBV is generally transmitted in the dental setting via per-cutaneous injury with contaminated needles and syringes, and mucous membrane exposures to infected blood [22].

While there is little evidence that saliva and gingival cervical fluid can transmit the virus, the presence of the hepatitis B surface antigen (HBsAg) in saliva and gingival cervical fluid of HBV-positive patients has been recorded [23, 24]. HCV is mainly trans-mitted via blood-to-blood contact, although RNA from HCV has been detected in saliva and in salivary glands of patients with sialadenitis and Sjögren’s syndrome [25, 26]. Higher levels of HCV RNA have been detected in the gingival sulcus than in the saliva of patients with HCV [27], while the presence of HCV RNA in toothbrushes used by hepatitis C patients has also been noted [28]. Despite these finding, no evidence has been produced on the risk of transmission for HBV and HCV after mucocutaneous exposure [20].

During the early 1980s in the light of a worldwide resurgence of HBV, a number of reviews of infection control in dentistry were initiated. In 1986, the CDC published infection control rec-ommendations for dentistry [4] after reports of a number of cases of HBV transmission from DCPs to their patients. Between 1972 and 1999 in the USA, three general dentists transmitted 23 HBV infections to their patients [29–31], and three oral surgeons infected 169 of their patients [31–33]. However, despite the infec-tivity of HBV/HCV, there is a low risk of transmission in the

Figure 21.2.1 Routes of cross-contamination and cross-infection in the dental setting.

DENTAL CAREPROFESSIONAL

PATIENTsaliva, blood, fluids, tissue

INSTRUMENTS

ROOM AIR

EXTERNAL ENVIRONMENT

WATER &DENTAL UNIT WATER LINES

WORK SURFACES

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combination of antiretroviral drugs within 72 h is the preferred option [53]. Advice specific to the UK is the administration of zidovudine, together with lamivudine and nelfinavir, ideally within 1 h, although post-exposure prophylaxis up to 2 weeks is considered useful [54].

There are few data on the rates of percutaneous injuries and cross-infections in resource-limited countries, where the preva-lence of HIV and the risk of infection are high [55–58]. There are variations in the intensity and severity of the HIV epidemic in different parts of the world, and thus its effect on the local health workforce. For example, in Botswana, there are nearly twice the number of women health workers than male health workers, and since HIV/AIDS infection and resultant morbidity and mortality rates among women are higher than those for men, the impact on healthcare provision is notable [59].

HIV transmission from patient to DCP and from DCP to patient within the dental setting remains a rare but significant problem. However, the introduction of standard and universal infection control protocols and procedures for dealing with per-cutaneous injuries have mitigated the impact of transmission.

Transmissible spongiform encephalopathyTSEs are a group of incurable and invariably fatal neurodegenera-tive conditions in humans and animals caused by abnormal prion proteins (PrPSc). Sporadic cases in humans have an unknown etiology and occur at the rate of approximately one per million persons, and are responsible for 85–90% of CJD infections. Familial cases arising from a mutation make up 5–10% of all CJD cases, and occur at the rate of less than one in a million persons. Less than 5% of CJD cases are iatrogenic, resulting from transmis-sion of prions via surgical equipment or following transplants of the cornea and dura mater, or the administration of pituitary growth hormones derived from human cadavers [60].

The first cases of vCJD appeared in the 1990s and the discovery of its relationship with the consumption of beef from cattle affected by BSE (“mad cow disease”) caused serious concerns, particularly in the UK, which had the highest number of BSE and vCJD cases [61]. BSE was initially observed in cattle in the UK in 1986, and there was some epidemiological evidence that the bovine agent had originated from the scrapie agent, which had been present in sheep in the UK for at least 200 years [62]. The suspicion of a linkage between vCJD and BSE [63] was strong enough for the British government to make BSE a notifiable disease in June 1988. It was estimated that up to 50% of the dairy herds in the UK were affected by BSE, and to limit the spread of prions the UK government banned feed supplements containing sheep and cattle offal in 1989, although the ban was not strictly enforced until the early 1990s. In March 1996, the then Secretary of State for Health announced that 10 cases of vCJD in young adults were most likely associated with exposure to BSE before the offal ban [64].

Since the risk of transmission of prion proteins during dental treatment was not clearly understood, the Spongiform Enceph-alopathy Advisory Committee (SEAC) in the UK published a

The implementation of universal precautions and protocols to minimize exposure to HBV during dental treatment, the adop-tion of HBV vaccination programs and the provision of post-exposure prophylaxis for DCP, has had considerable success in the resource-rich USA, northern Europe and Australia, but in Africa, the Middle East, Asia and South America the situation remains static. In many cases, basic treatment facilities and equipment, lack of up-to-date knowledge, non-compliance with barrier pre-cautions and vaccination uptake, together with HBsAg rates in the general population of up to 15% [22], the risk of transmission of the virus in the dental setting is still a major problem in devel-oping countries.

Human immunodeficiency virusAIDS has been around for nearly 30 years now, and concerns regarding the transmission of HIV are well documented. There are some data indicating seroconversion of healthcare workers following occupational exposure to HIV [13, 40], but overall the transmission risk is thought to be low. Six cases of HIV transmis-sion from an HIV-positive dentist to his patients in Florida were recorded in the early 1990s [41], and in 1991 another Florida dentist with AIDS was investigated as a potential source of infec-tion. Retrospective epidemiological analysis and molecular virol-ogy indicated that there was no evidence of HIV transmission from the dentist to any of his patients [42]. There have been no further reports of transmission of HIV from infected DCPs to patients in the USA since the CDC began its surveillance program [43]. To control the risk of transmission, the CDC published further infection control guidelines in 1993 [6] which were updated and revised in 2003 in light of the development of new technologies and issues arising during the preceding decade [7].

Scully and Greenspan [44] reviewed the rate of HIV transmis-sion in the dental care settings in the UK, USA and France to November 1, 2005. They found that there has been probable transmission from an HIV-infected healthcare worker to a patient in only three reported cases – a Florida dentist [45], a French orthopedic surgeon [46] and a French nurse [47]; the route of transmission was confirmed only for the orthopedic surgeon. By 2007, there had been five cases of HIV seroconversion following needlestick injury in healthcare workers reported in the UK, and the last documented case was in 1999 [20]. Data from Klein [48] suggests that the rate of occupational exposure to HIV among DCPs has fallen in the decade prior to 2003, although it has been noted that healthcare workers tend to underreport percutaneous injuries [49, 50].

Occupational exposure to HIV should be treated as a medical emergency to ensure that the appropriate HIV Limulus amoebo-cyte is implemented without delay [51]. The current CDC re -commendation for HIV exposures [52] is the administration of a mixture of two nucleoside reverse-transcriptase inhibitors (NRTIs) or one NRTI and one nucleotide reverse-transcriptase inhibitors (NtRTI) immediately following exposure; for example zidovudine (ZVT) and lamivudine (3TC) or emtricitabibe (FTC), and tenofovir (TDF) and 3TC or FTC. Within Europe, a triple

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Other potential pathogensPotentially pathogenic bacteria and viruses can be found in the oral cavity and saliva of most patients. Dental procedures, espe-cially the use of high-speed instruments, produce aerosols and splatter which can spread the oral microorganisms from the patient to the local environment, contaminating the workspace, instruments and the DCP.

A number of studies have investigated the bacterial contamina-tion of aerosols, work surfaces, instruments and dental impres-sions. The first reports of the production of aerosols and splatter contaminated with microorganisms during dental procedures was in the late 1960s and early 1970s [83, 84]. A wide range of bacteria and viruses have been isolated from aerosols, dental unit water lines (DUWLs) and impression materials. including patho-gens such as Pseudomonas aeruginosa, Burkholderia cepacia, Legionella pneumophila, Mycobacterium tuberculosis, Staphylococ-cus aureus, cytomegalovirus, herpes simplex virus 1 and 2, oral and respiratory streptococci, and waterborne environmental con-taminants [85–92]. Microorganisms can colonize water lines and dental equipment, resulting in the formation of biofilms, often refractory to conventional decontamination protocols [93]. These biofilms, may in turn, produce aerosols [94]. Indirect data in the form of seroprevalance studies showed that dentists have higher antibody titers to respiratory syncytial virus, influenza viruses and cytomegalovirus than the general public, and the titers in dentists rise over time following graduation – most likely a con-sequence of increasing exposure to saliva and oral microorgan-isms from their patients [92].

The contamination of DUWLs in dental surgeries by endotox-ins is further indirect evidence of bacterial contamination [95]. Waterlines can frequently become contaminated with Gram-negative bacteria, which contain endotoxins – heat-stable chemi-cals derived from the lipopolysaccharide from their cell walls. Endotoxins are responsible for septic shock syndrome [96], and a number of other clinically significant conditions such as hepa-totoxity [97], disseminated intravascular coagulation [98] and respiratory distress [99]. A recent study of dental unit water and dental aerosols by Huntington et al. [100] using the Limulus amoebocyte lysate assay, found a significant correlation between bacterial load and endotoxin concentration. The study also showed that endotoxin-contaminated water is aerosolized during dental procedures, adding to the exposure risk for both DCPs and patients.

There are particular problems in dentistry with three emerging or re-emerging pathogenic bacteria, namely methicillin-resistant S. aureus (MRSA), M. tuberculosis (TB) and vancomycin-resistant Enterococcus (VRE). Worldwide rates of tuberculosis and multidrug-resistant TB are rising, particularly in Africa, Asia and South America, and it is estimated that 30% of the world’s popu-lation is infected with M. tuberculosis [101]. Spread via direct contact and airborne respiratory droplets, there is considerable potential for transmission in dentistry. DCPs should take ade-quate precautions including minimizing aerosol production during dental procedures, the use of barrier techniques and the

position statement in 2007 regarding vCJD and dentistry [65]. The statement highlighted the difficulty in removing adherent prion proteins from contaminated dental instruments, the heat resistance of prions, and the potential infectivity of dental pulp and other tissues. In light of earlier research [66–68], SEAC con-cluded that the risk of transmission of vCJD through dental procedures was higher than previously thought, and recom-mended that endodontic reamers and files be single-use, dispos-able items only [65]. While SEAC was correct to invoke the precautionary principle, reviews of the understanding of the transmission of prion proteins via dental practice generally sug-gested that the risks were low and not supported by epidemio-logical evidence [69–71]. Examination of dental pulp from sporadic CJD (sCJD) patients did not reveal any evidence of PrPSc [72], and no significant levels of PrPSc were detected in oral-related vCJD tissues [73].

The first published study to investigate possible links between vCJD and dental surgery [74] found no compelling evidence of an increased risk, although the authors noted limitations in the data, and the possibility that some of the 130 cases examined were attributable to dental procedures. A recent assessment of the risk of sCJD transmission during endodontic treatment [75] found that if current official decontamination procedures were carried out on endodontic instruments, the risk of secondary infection would be effectively null, whereas if decontamination procedures were not used or were ineffective, the risk of being infected during treatment was 3.4–13 per million procedures. The authors estimated that the risk of infection was comparable to other high-risk medical procedures such as death during general anesthesia or after liver biopsy, but stressed the impor-tance of the use of single-use instruments or adequate prion decontamination and inactivation. Despite the demonstration of the transmission of PrPSc to the pulpal tissue of experimental hamsters [76], evidence suggests that dental pulp, gingival tissue and blood, and saliva have very low risk of potential infectivity [60, 61, 73]. It has been noted that effective decontamination of endodontic instruments remains problematic and can leave sig-nificant levels of debris, leading to the theoretical possibility of disease transmission [67, 68, 77].

The theoretical risk of transmission of prion disease during dental procedures caused a re-evaluation of the decontamination procedures for dental instruments, and ushered in further guide-lines from government and professional organizations [78–80]. However, a lack of clinical and epidemiological evidence, and the paucity of experimental studies on vCJD, meant that the guide-lines were prepared on the assumption that there was a definite risk of transmission from dental instruments [81].

In the UK, updated guidance was introduced in 2007 on the premise that, as long as high standards of infection control are maintained and that instruments used on patients in the “at-risk” category are decontaminated correctly, there is no requirement to quarantine or dispose of them, nor to take a medical history prior to treatment. In other words, to treat at-risk patients in the same manner as any other patients [82].

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airborne contamination, as did the use of a rubber dental dam to prevent splashing. High-volume evacuators (HVEs) have been shown to reduce airborne contamination by more than 90%, and high-efficiency particulate air filters or ultraviolet light irradia-tion of the ventilation system are also effective but expensive options. The CDC recommends the use of rubber dams and HVEs to reduce splatter [1]. Attention to the risk from aerosols was again focused during the 2009 H1N1 influenza pandemic [11, 12, 111].

Dental unit water linesDUWLs supply water for high-speed dental handpieces, air–water syringes and ultrasonic scalers and are an indispensable part of dental equipment. The fact that DUWLs frequently contain bio-films that continually shed organisms was first reported by Blake in 1963 [112].

Bacterial species such as S. aureus, Mycobacterium avium and Legionella species including L. pneumophila, as well as fungi and protozoa, have been isolated from DUWLs [113]. A more recent study of the numbers and composition of bacteria in DUWLs showed that bacterial concentrations can reach excessive values, and that the predominant species were of oral cavity flora, opportunistic pathogens and environmental aquatic microbiota. Ralstonia pickettii was detected in all the units examined, and Sphingomonas paucimobilis and Brevundimonas vesicularis were commonly found [114].

Since the water used during routine dental procedures can develop bacterial contamination above levels considered accept-able for safe drinking water, regular monitoring for microbes in the DUWL water is recommended, as is the application of a dis-infecting procedure. Flushing water lines will not remove biofilms but will reduce the concentration of bacteria in the water phase [115], and the CDC recommends that additional measures such as chemical agents are required [1, 7]. A review of several studies investigating the use of line cleaners/disinfectants to flush water lines and remove particulate waste, biofilms and planktonic microbes, concluded that only 13 out of 28 such procedures reduced the total viable count and biofilm levels by more than 94% [116]. It has been suggested that flushing the water lines after each use is the only way to guarantee that residual microbial contamination can be removed [117]. Water lines made from polytetrafluoroethylene (PTFE) appear to be more resistant to biofilm formation than tubes made from polyethylene (PE), and may be inhibitory to P. aeruginosa, and water lines of larger-bore diameter (4 mm rather than 1.6 mm) exhibited a reduction in bacterial counts [118].

The relationship between respiratory disease and exposure to airborne and aerosolized bacteria in dental personnel is ambigu-ous, with insufficient data to confirm any linkage between them. It has been reported that DCPs have higher levels of Legionella antibodies than the general population [119] and other studies have confirmed the resistance of Legionella species to flushing DUWLs [115]. Two studies have shown a relationship between occupational exposure to contaminated DUWLs and asthma in

wearing of face-masks, and, where possible, the installation of high-efficiency ventilation systems [102].

MRSA has become a major problem in hospitals and a regular source of healthcare- as well as community-acquired infections. A 2005 study in the USA found that 4.6% of patients attending community healthcare facilities were infected or colonized with MRSA [103]. MRSA is no more pathogenic than other strains of S. aureus, but is resistant to most commonly used antibiotics. MRSA colonizes the nose, axillae, perineum and damaged skin, and is common in hospitalized patients and increasingly in the community setting. Although no special precautions are required for the dental treatment of patients with MRSA, DCPs colonized with MRSA should not be involved in invasive dental proce-dures, and specific treatment to eradicate colonization is avail-able [8].

VREs are multidrug-resistant strains of the gut bacterium Enterococcus. Like MRSA, they are no more pathogenic than sen-sitive strains of enterococci, but their resistance to vancomycin and other antimicrobials makes their eradication problematic. Enterococci have been isolated from necrotic root canals, and secondary endodontic root infections are frequently caused by Enterococcus faecalis [104]. E. faecalis and vancomycin-resistant E. faecium have also been implicated as a cause of bacteremia and endocarditis following dental surgery, although no link between endocarditis and dental treatment was observed in a case–control study of 273 patients [105]. Nevertheless, their resistance to most available antibiotics, and their potential for contaminating surgi-cal instruments and for colonizing DCPs and the working envi-ronment [106], make them potentially problematic in the dental setting.

Contamination of the working environment

Aerosols and splatterHigh-speed rotating drills, ultrasonic scalers, rotary polishers, DUWLs and compressed air used in dental cleaning and restora-tive work produce aerosols and splatter contaminated with saliva, blood and microorganisms from the patient’s oral cavity [94, 107, 108]. Splatter droplets are particles larger than 50 µm in diameter that are airborne briefly before settling [107], whereas aerosols are invisible particles with diameters of less than 10 µm that can float on air currents [109].

Recent studies indicate that the area contaminated by aerosols and splatter droplets is much larger than originally thought. Mile-jczak [110] detected bacterial deposits up to 2.6 m from the dental chair, and a study by Rautemaa et al. isolated bacteria up to 1.5 m from the patient’s mouth, and found that the use of rotary and ultrasonic instruments resulted in increased bacterial numbers and a greater area of contamination than during periodontal and orthodontic treatment [89].

A review by Harrel and Molinari [107] of the literature on reducing aerosol contamination concluded that the use of a 0.1% chlorhexidine mouthwash prior to a dental procedure reduced

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immersed in ultrasonicators prior to sterilization although small cleaning machines specifically designed for this purpose are avail-able. The British Dental Association (BDA) recommends the use of appropriate cleaning machines but allows careful manual clean-ing (as detailed by the BDA) if no machine is available [8]. An earlier recommendation from the Medical Devices Agency was to sterilize dental instruments with lumens, cavities or recesses in a vacuum autoclave [133]. It has been noted that dental depart-ments within district general hospitals use sterile services depart-ments to decontaminate their instruments, but in many cases busy workloads result in manual cleaning and the use of non-vacuum sterilizers [134]. To ascertain how handpieces are decontaminated in general dental practice, Smith et al. carried out an observational survey of 179 dental practices in Scotland between 2003 and 2004. They found that in nearly all surgeries the handpieces were cleaned prior to autoclaving in bench-top steam sterilizers, usually by manual wiping using disinfectant-impregnated cloths, although a minority of surgeries had dedicated handpieces for surgery [135].

Within the UK, specific guidance for decontamination in primary-care dental practices was contained in HTM 01-05 [9]. This was based on previously issued guidance, including HSG (93)40, which was introduced to manage the transmission of HBV infections [136]. It introduced benchmarks and compliance targets, and requires that practices work at or above the “essential quality requirements” described in the guidance, and that all practices should have a detailed plan on how to achieve the aim of “best practice”. The essential quality requirements are: (i) for all instruments to be sterilized in a bench-top autoclave and stored under aseptic conditions; (ii) that single-use instruments should be mandatory for endodontics; and (iii) that bagged instruments should be given a use-by date. The main require-ments for best practice are: (i) the use of an approved automatic washer disinfector for the decontamination and disinfection of dental instruments; (ii) the provision of a room or area separate from the dental treatment area for decontamination operations; and (iii) a specifically-designed separate facility for the storage of reprocessed dental instruments.

Clinical wasteWaste produced in dental practices falls into the categories of clinical and non-clinical waste, which must be segregated. Clinical waste includes waste contaminated with blood, saliva or other body fluids, and is potentially hazardous to persons coming into contact with it, and must be placed in pre-labeled, UN-type approved, puncture-proof containers. Clinical waste includes needles and scalpel blades (sharps), and partially-discharged and fully-discharged local anesthetic cartridges [8].

Extracted teeth can be disposed of in sharps containers for eventual incineration, but teeth containing mercury amalgam are incineration hazards and should be treated as dental amalgam waste. In the UK, HTM 07-01 Safe Management of Healthcare Waste [137] advises dentists to dispose of dental amalgam waste in amalgam separators prior to disposal by an authorized waste disposal company.

DCPs, although a statistically significant association was found only in the UK study [120] and not in the US study [121].

Impressions, prosthetics and dental instrumentsThe contamination of impressions with saliva and blood, together with oral bacteria and respiratory pathogens, has been docu-mented for some time. There are studies suggesting that DCPs and dental laboratory technicians are at risk of infection from cross-contaminated elastomeric dental impressions made in the dental clinic [122], although a review considered the risk of cross-infection to be relatively low [123]. The American Dental Associa-tion produced three guidance documents for the disinfection of impressions [124–126], while the Medicines and Healthcare Products Regulatory Agency of the UK Department of Health produced the MAC Manual [127]. This provides advice on all aspects of decontamination, including of dental instruments and impressions, based on guidance from the European Union’s Medical Devices Directive.

The extent and impact of the problem is still under debate. A review by Kugel et al. [128] of 400 US dental laboratories found that only 44% of the them knew when incoming impressions had been disinfected, and as a precaution 94% of the labs routinely disinfected all impressions they received, illustrating a lack of communication between DCP and dental laboratory personnel. Junevicius et al. [91] studied the artificial contamination of algi-nate and silicon impressions with Serratia rubidaea and found that silicon impressions had lower contamination rates than algi-nate impressions. They also noted that rinsing the impression under running tapwater was an ineffective means of reducing contamination and that disinfection was required. However, an investigation of bacterial numbers on 107 impression samples revealed that contamination was often at a low level, and the authors questioned whether disinfection was necessary if ade-quate hygiene and handling protocols were adhered to [129]. One particular source of cross-infection in the dental laboratory is the bacterial contamination of the pumice slurry used on polishing wheels to apply final polishing of implants, dentures and pros-thetics [130]. Freshly prepared pumice slurry containing disin-fectant was free from contamination; after 3 days’ use colony counts approached 109/g [131].

Prosthetic devices, matrix bands, burs, polishing cups and endodontic files are often contaminated with a patient’s blood, body fluids and tissue, and are difficult to clean properly. Endo-dontic files used to prepare root canals are likely to become con-taminated with blood, tissue and bone fragments, which can remain attached even after cleaning and autoclaving [67], and it is recommended by US and UK authorities that they be single-use items only [7, 9].

Dental handpieces pose problems due to their complex design, with lumens and recesses inherent in their design which make effective cleaning difficult. Despite not having direct contact with the oral tissues and fluids, the internal workings can become contaminated via splatter, and potentially spray back into the oral cavity [132]. Because of their design, handpieces cannot be

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Training in infection controlThe introduction in the UK of HTM 01-05 [9] and the equivalent guidance in the USA of RR17 [7] have propelled the dental pro-fession into a period of rapid change with respect to practice of infection control and an understanding of the scientific evidence behind the guidance. All DCPs should have up-to-date knowledge of what appropriate infection control measures will prevent cross-contamination and infection transmission, why such meas-ures are needed, and how to incorporate best practice standards with the new guidelines. Infection control policies for practices should be regularly reviewed and updated where applicable, and to ensure compliance it is essential that regular monitoring of the procedures is carried out.

Within the UK, qualified dental surgeons receive undergradu-ate and postgraduate training in infection control but dental nurses and hygienists were not required to undergo specific train-ing until 2008. As noted by John et al. [145] in a study of 254 dental nurses in England in 2001, only 40% had formal qualifica-tions. Within the UK, the General Dental Council mandated com-pulsory registration as from July 31, 2008. Dentists, dental nurses and dental technicians must hold a qualification approved by the General Dental Council in order to be eligible to apply for regis-tration and to undertake continuing professional development (CPD) [146]. There are a number of CPD courses run by dental organizations, health authorities and private providers available for dentists, dental nurses and technicians.

Therefore, to maintain standards and achieve “essential quality requirements” and “best practice”, all new staff should be trained in infection control procedures before working in the practice [8]. The training should include information on how infections are spread, how to prevent and control the spread of infections, the monitoring of procedures and the periodic review of the control of infection policy for the practice, the appropriate use of post-exposure prophylaxis, and how to manage accidents or personal injury within the practice.

Recent developments in dental hygiene

Ozonated liquidsDespite being considered a dangerous and toxic gas, ozone in the form of ozonated liquids has been used as an alternative for infec-tion control and wound care for many years, particularly in Russia and Cuba [147]. Recent research has shown that ozonated fluids exhibit marked antimicrobial and anti-inflammatory properties [148], have high compatibility with mammalian cells [149] and have a role in the management of periodontal disease [150]. The use of ozonated water, gels and oils has been demonstrated to reduce the level of oral microbiota including unattached bacteria and microbes in plaque and periodontal pockets, and to minimize oral soft tissue infection following dental surgery and accidental trauma [151, 152]. They are also highly effective against MRSA [153] and bacterial spores [154], and have been found to be an effective sanitizer for DUWLs [155].

The final disposal of clinical waste is also subject to a number of provisions and regulations, including the completion of a hazardous/special waste consignment note containing details of the type of waste, the waste disposal company and when the waste was disposed of, and a certificate of safe destruction provided by the waste carrier.

Compliance with infection control measures

The achievements in infection control in dentistry over the past 30 years, both in theory and in application, have been impressive, and the acceptance of different practices, procedures and proto-cols by DCPs have significantly reduced occupational infection risks in dentistry [138].

Nevertheless, despite the recommendations being based on sci-entific and clinical evidence, there are reports of non-compliance by DCPs [139]. Millership et al. [140] documented three reported cases of failure of decontamination of dental instruments in the UK; breaches included not autoclaving dental handpieces, the use of cold disinfectant solutions, dental mirrors contaminated with dried blood, and the reuse of surgical blades, suture needles and gloves. A 2005 study of 856 dental hygienists in the USA [141] found that compliance with infection control guidelines had improved compared with a previous study, but dental hygienists had misconceptions about infectious disease transmission. An occupational study of 179 dental surgeries in the UK by Smith et al. [142] noted that although a majority (70%) of surgeries had control of infection management policies, only half of these had been documented, and audits of decontamination and infection control procedures were apparent in only 11% of surgeries. In most cases, infection control training was by demonstration or observed practice, leading the authors to highlight the poor train-ing and lack of documentation in some UK dental surgeries.

If non-compliance is occurring in resource-rich developed countries, then it can be assumed that the incidence of non-compliance would be high in resource-poor developing countries due to issues of cost or availability. For example, 146 Nigerian dentists were monitored by questionnaire [143] which revealed wide ranges of compliance in the use of gloves, face-masks, pro-tective eyewear, sterilization methods and HBV vaccination uptake. The unavailability of equipment due to lack of funding was the main reason for non-compliance. A paper detailing over 100 general dental practices surveyed in north Jordan [144], reported low compliance with a number of infection control rec-ommendations; only one-third of dentists were vaccinated against HBV, only 18% disinfected impressions before sending them to the dental laboratory, only 32% used dedicated containers for the disposal of sharps, and only 63% sterilized items using an auto-clave. The authors comment that only approximately 14% of general dentists surveyed were considered to be compliant with recommended infection control measures, and that there was a lack of formal and obligatory infection control courses and guide-lines in Jordan.

545


Dental caries and periodontal disease are frequently localized infections, and successful treatment includes the eradication of bacteria within the lesions. PDT has been employed as a disinfec-tion strategy by the topical application of TBO and irradiation of the coated lesion with LED light via a thin optical light guide [173–175].

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Photodynamic therapyInitially reported in 1900 as a means of killing microbes [161], photodynamic therapy (PDT) has been mainly employed as an alternative treatment for tumours, using porphyrin photosensi-tisers and laser light [162]. The photoactive dye is taken up by the target cells and following irradiation with light of a specific wave-length, cell death occurs as a result of the production of active singlet-oxygen radicals [163]. The bactericidal effect of PDT against a range of gram-positive and gram-negative bacterial species, including antibiotic-resistant strains, planktonic cultures, biofilms and in vivo, has revealed its potential as an effective antimicrobial therapy and hygiene strategy in dentistry and der-matology [164, 165].

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