The Debate: What Are Aerosol-Generating Procedures in Dentistry? A Rapid Review

Types of Studies

A rapid review of the literature was performed with the aim of identifying and collating guidance documents that detail what dental procedures should be considered an AGDP. The review focused on dental procedures and exposures that are likely to occur within the dental setting. Exposures in the medical setting are outside the scope of this review. The further matter of PPE was not assessed directly.

Search Methods for Identification of Studies

Data Collection and Analysis

Main Findings

The COVID-19 pandemic has refocused international attention on the transmission of pathogens in aerosols. This review has looked at a wide range of international dental guidance documents and position statements. We found that, frequently, the evidence on AGDPs and AGEs within dentistry was interpreted in different ways, with this reflecting a general lack of consensus and ambiguity across the documents. Occasionally, these differences were subtle, but often they were pronounced. For example, there is a clear lack of agreement about which dental procedures and/or exposures should be considered aerosol generating and also a lack of consistency as to how these procedures are categorized. This is often reflected in whether the document separates procedures into AGDP/non-AGDP (17/26 of the guidance documents) or whether they are categorized by COVID-19 transmission risk (4/26). Guidance documents that were published by government bodies, typically at an earlier stage of the pandemic (April/May), tended to specify only whether or not procedures were deemed an AGDP, whereas professional bodies, who typically published guidance later (June), tended to be more descriptive by also categorizing the risk of COVID-19 transmission attributable to each procedure. Those bodies using the transmission risk approach did not use consistent categories to describe that risk. As well as official guidance documents, our literature search also returned published nonguidance journal articles. These articles followed a similar pattern to the guidance documents, in that there was wide variation in the inclusion of procedures and, when named, a lack of consensus as to which procedures did or did not constitute an AGDP (Alharbi et al. 2002; Li et al. 2004; Zemouri et al. 2017; Ather et al. 2020; Bizzoca et al. 2020; Careddu et al. 2020; Jamal et al. 2020; Long et al. 2020; Martins-Filho et al. 2020; Meng et al. 2020; Passarelli et al. 2020; Peditto et al. 2020; Peng et al. 2020; Pethani et al. 2020; Ren et al. 2020; Săndulescu 2020; Shi et al. 2020; Suri et al. 2020; Turkistani 2020).

Twenty-one of 26 guidance documents agree that procedures that do not involve the use of rotatory instruments or induce the gag reflex can be considered non–aerosol generating. However, 11 of 26 do not state exactly which procedures do not constitute an AGDP. Those documents that do provide some clarification present their information in different ways; some make allowances for whether a patient has tested COVID positive or negative (British Society for Restorative Dentistry 2020), while others advise the use of adjuncts to mitigate risk, and others do neither. Guidance from the UK Faculty of General Dental Practitioners (FGDP) (Faculty of General Dental Practitioners 2020), the British Society of Periodontology (BSP) (British Society of Periodontology and Implant Dentistry 2020), and the British Society of Restorative Dentistry (BSRD) (British Society for Restorative Dentistry 2020) appear to be the first documents to clearly separate procedures by risk of COVID-19 transmission, specifying low, moderate, and high risk. However, there are still inconsistencies across these documents, such as the classification of procedures that induce a gag reflex. One notable area of contrasting advice surrounds the use of the slow speed handpiece. Several British guidance bodies, as well as the Australian government guidance document, state that a slow speed handpiece, used in a dry field with high-volume evacuation, represents a low to moderate COVID-19 transmission risk (9/26). However, 4 of 26 guidance documents have so far regarded the use of the slow speed handpiece as an AGDP at high risk of COVID-19 transmission, including some European countries and Canada (Alharbi et al. 2002; Li et al. 2004; Jamal et al. 2020).

Evolving Evidence

The WHO’s stance in March 2020 was that aerosol transmission of COVID-19 was not a concern, with the virus primarily transmitted through respiratory droplets and contact routes (World Health Organization 2020b). At that time, no strong evidence existed about how long saliva droplets stay in the air (physical decay), whether the droplets remain infectious (biological decay), or if they can be acquired by another person (Xu et al. 2020). In March 2020, Liu et al. published an article in which they assessed 35 aerosol samples taken from 2 Wuhan hospitals and concluded that levels of SARS-CoV-2 in aerosol were low or undetectable (Liu et al. 2020). However, research recently published in June 2020 has demonstrated that SARS-CoV-2 can remain in aerosol and infectious for considerably longer than most respiratory infectious diseases, including both SARS and Middle East respiratory syndrome (Fears et al. 2020). Interestingly, recent research has pointed to dental unit water lines, rather than saliva, as the main source of the microbiota present in dental aerosols. Studies have looked at the microbiota present in dental aerosols, which has been shown to be remarkably homogeneous across patients and highly similar to those identified in dental unit water lines. The same is true for the bioload identifiable in dental aerosols from a range of AGDPs. The small degree of variability in pathogen and bioload is likely to be due to factors such as the number of carious teeth and the presence of periodontal disease (Kumar and Subramanian 2020).

In light of the changing evidence, WHO recently changed its stance on aerosol transmission of COVID-19 and announced a planned update to its guidance on modes of transmission. With evidence emerging and changing at such a pace, it is, perhaps, unsurprising that there is not a wider consensus on both what constitutes an AGDP/AGE and how these events may correlate to COVID-19 transmission risk.

Current Knowledge

When we assimilate this current knowledge and its impact on dental staff and patient safety, it becomes clear that the picture is neither simple nor well defined. Our review has shown that despite determined, worldwide efforts to clarify the aerosol-producing nature of dental procedures and exposures, an obvious answer is not readily available, not least because of the novelty of the SARS-CoV-2 virus and the continually emerging research on it.

Critical gaps in our knowledge still exist, such as what constitutes an AGDP, the true presence and formation of the bioload associated with a range of AGDPs, and the risk of transmission of COVID-19 for each dental procedure. In light of this, perhaps a more realistic and adaptable approach to categorizing procedures/exposures in dentistry is to expand upon the “AGE” model—that is, to recognize that in the complex environment of the dental practice, the risk of COVID-19 transmission of procedures/exposures is best assessed as a continuum, rather than in a binary manner. For simplicity, a low/moderate/high-risk model is proposed, which is flexible enough to take account of the type of AGDP, the environment, and any predisposing risk factors for both the patient and the dental team. Importantly, the model should be inherently flexible, such that a particular procedure can be readily upgraded or downgraded with regard to its COVID-19 transmission risk, depending on such factors as a patient’s medical history, as well as the publishing of newly emerging evidence.

Recommendations

Currently, there is much uncertainty within the literature as to which dental procedures should be considered aerosol generating. There is also a lack of evidence as to how effectively the SARS-CoV-2 virus transmits through aerosol, although this continues to change rapidly. Further research is required to clarify the risk of each dental procedure/exposure, enabling dentists to plan a working environment that is as safe as possible for staff and patients.

The current knowledge base and emerging evidence would suggest that categorizing dental procedures solely as aerosol generating or not aerosol generating is overly simplistic. In line with the FGDP (Faculty of General Dental Practitioners 2020), BSP (British Society of Periodontology and Implant Dentistry 2020), and BSRD (British Society for Restorative Dentistry 2020) approach, procedures and exposures can be best thought of as being on a spectrum of risk, which is affected not just by the procedure itself. Risk stratification should take a holistic approach with consideration given to the type of dental procedure, the use of water from dental water lines (Kumar and Subramanian 2020), the use of risk mitigating factors such as HVE and rubber dam, the working environment (ventilation), the duration of exposure, the proximity of the clinician to the aerosol, the manipulation of high viral-load tissue such as the oropharynx (Lindsley et al. 2010), and the medical and social history of the staff and patient.

An example of how such a model might work in practice may look like this: the use of the high-speed handpiece might be considered at high risk of COVID-19 transmission. As a short procedure, with the use of HVE (Long et al. 2020), rubber dam (Bizzoca et al. 2020), and excellent ventilation (Office of the Chief Dental Officer 2020), it may be possible to downgrade this risk to moderate. If that procedure was undertaken on a healthy, young patient by a healthy, young dentist (Centers for Disease Control and Prevention 2020) who was wearing full PPE, including an FFP3 mask (Estrich et al. 2020), there may be scope to downgrade the risk further still. However, if evidence emerged that manipulation of certain oral tissues (Lindsley et al. 2010) or a certain salivary bioload (Kumar and Subramanian 2020) was at particularly high risk of COVID-19 transmission, there would be scope within the model to again upgrade the procedure.

Conclusion

Despite there being plentiful national and international guidance available, there remains ambiguity as to what constitutes an aerosol-generating dental procedure. It is recommended that future published guidance should stratify the COVID-19 transmission risk (low/moderate/high) of each procedure/exposure in a standardized international approach that can be readily updated and that allows flexibility for patient and environmental factors. When giving advice on the level of PPE or fallow time required between dental procedures, any relevant modifying factors should, where possible, be stated.