The potential to generate aerosols and splatter during dental procedures is an important health concern. The oral cavity harbours a wide range of bacteria, viruses and fungi which could be expelled through aerosol-generating procedures (AGPs). Although dental staff are at higher risk of respiratory infection there is little empirical evidence to support this. However, mitigation of potential risk would seem to be a sensible precaution.
The aim of this Cochrane rapid review was to assess the effectiveness of methods used during dental treatment procedures to minimize aerosol production and reduce or neutralize contamination in aerosols.
Searches were conducted in the Cochrane Oral Health’s Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL) Medline, Embase, the WHO COVID-19 Global literature on coronavirus disease, ClinicalTrials.gov) and the Cochrane COVID-19 Study Register with no restrictions on the language or date of publication.
Randomized controlled trials (RCTs) and controlled clinical trials (CCTs) on aerosol-generating procedures (AGPs) performed by dental healthcare providers evaluating methods of reducing contaminated aerosols in dental clinics. Studies of preprocedural mouthrinses were excluded. Primary outcomes were incidence of infection in dental staff or patients, and reduction in level and volume of contaminated aerosols. Cost, accessibility and feasibility were secondary outcomes. Two reviewers independently selected studies. One review extracted data with verification by other authors a limited data set related to the main outcomes was extracted. Effect size was measured using differences (MDs) and 95% confidence intervals (CIs) and random effects meta-analysis.
- 16 studies (11 RCTs, 4 CCTs) involving 425 patients were included.
- 8 studies were at high risk of bias and 8 at unclear risk.
- No studies measured infection
- All studies measured bacterial contamination using a surrogate outcome of colony-forming units (CFU)
- The evidence should be viewed with caution as it is of low certainty because of heterogeneity, risk of bias, small sample sizes and wide confidence intervals. It is also unclear as to what is a minimally important difference of CFUs.
High-volume evacuator (HVE)
- 3 split-mouth RCTs, 122 patients showed that HVE use may reduce bacterial contamination in aerosols less than one foot from a patient’s mouth, MD= −47.41 (95%CI; −92.76 to −2.06), but not at longer distances, MD = −1.00, (−2.56 to 0.56) [1 RCT, 80 participants].
- One split-mouth RCT (6 patients) found that HVE may not be more effective than conventional dental suction (saliva ejector or low- volume evacuator) at 40 cm MD= −2.30 (95%CI; −5.32 to 0.72) or 150 cm, MD= −2.20 (95%CI; −14.01 to 9.61).
Dental isolation combination system
- One RCT (50 patients) found that there may be no difference in CFU between a combination system (Isolite) and a saliva ejector (low- volume evacuator) during AGPs (MD −0.31, 95% CI −0.82 to 0.20) or after AGPs (MD −0.35, −0.99 to 0.29). However, an ‘n of 1’ design study showed that the combination system may reduce CFU compared with rubber dam plus HVE (MD −125.20, 95% CI −174.02 to −76.38) or HVE (MD −109.30, 95% CI −153.01 to −65.59).
- One split-mouth RCT (10 participants) receiving dental treatment, found that there may be a reduction in CFU with rubber dam at one-metre (MD −16.20, 95% CI −19.36 to −13.04) and two-metre distance (MD −11.70, 95% CI −15.82 to −7.58). One RCT of 47 dental students found use of rubber dam may make no difference in CFU at the forehead (MD 0.98, 95% CI −0.73 to 2.70) and occipital region of the operator (MD 0.77, 95% CI −0.46 to 2.00).
- One split-mouth RCT (21 patients) found that rubber dam plus HVE may reduce CFU more than cotton roll plus HVE on the patient’s chest (MD −251.00, 95% CI −267.95 to −234.05) and dental unit light (MD −12.70, 95% CI −12.85 to −12.55).
Air cleaning systems
- One split-mouth CCT (two patients) used a local stand-alone air cleaning system (ACS), which may reduce aerosol contamination during cavity preparation (MD −66.70 CFU, 95% CI −120.15 to −13.25 per cubic metre) or ultrasonic scaling (MD −32.40, 95% CI – 51.55 to −13.25).
- Another CCT (50 patients) found that laminar flow in the dental clinic combined with a HEPA filter may reduce contamination approximately 76 cm from the floor (MD −483.56 CFU, 95% CI −550.02 to −417.10 per cubic feet per minute per patient) and 20 cm to 30 cm from the patient’s mouth (MD −319.14 CFU, 95% CI – 385.60 to −252.68).
Disinfectants ‒ antimicrobial coolants
- Two RCTs evaluated use of antimicrobial coolants during ultrasonic scaling. Compared with distilled water, coolant containing chlorhexidine (CHX), cinnamon extract coolant or povidone iodine may reduce CFU:
- CHX (MD −124.00, 95% CI −135.78 to −112.22; 20 patients),
- povidone iodine (MD −656.45, 95% CI −672.74 to −640.16; 40 patients),
- cinnamon (MD −644.55, 95% CI −668.70 to −620.40; 40 patients).
- CHX coolant may reduce CFU more than povidone iodine (MD −59.30, 95% CI −64.16 to −54.44; 20 participants), but not more than cinnamon extract (MD −11.90, 95% CI −35.88 to 12.08; 40 patients).
The authors concluded: –
We found no studies that evaluated disease transmission via aerosols in a dental setting; and no evidence about viral contamination in aerosols.
All of the included studies measured bacterial contamination using colony-forming units. There appeared to be some benefit from the interventions evaluated but the available evidence is very low certainty, so we are unable to draw reliable conclusions.
We did not find any studies on methods such as ventilation, ionization, ozonisation, UV light and fogging.
Studies are needed that measure contamination in aerosols, size distribution of aerosols and infection transmission risk for respiratory diseases such as COVID-19 in dental patients and staff.
The pandemic resulting from the emergence of the novel SAS-CoV-2 virus at the end of 2019 was the catalyst for this Cochrane rapid review. This is because of the potential risk of transmission to dental staff and patients resulting from AGPs in the dental setting. Interestingly a recent American survey (Estrich et al, 2020) and an Italian observational study (Nardone et al, 2020) would suggest that, with simple precautions, the risks are low in line with other studies on respiratory diseases in the profession.
While the review identified a number of studies these used a surrogate outcome measure (CFUs) and relate to bacterial contamination rather than viruses. None of the included studies were at low risk of bias and had a small number of patients and had wide confidence intervals so the quality of the available evidence is of very low certainty.
A pre-publication version of this review was made available to the SDCEP working group to facilitate their rapid review of AGPs in dentistry. As part of that review SDCEP went through a considered judgement process modelled on the GRADE evidence-to-decision frameworkwhich takes into consideration the context, risks benefits and harms. In this way they were able to produce agreed positions on the use of various AGP mitigation approaches which add value to this Cochrane review.
There is a clear need for addition well conducted and reported studies on dental aerosols and transmission risk for respiratory disease. The review authors note that that they identified two current ongoing studies and more are likely to emerge because of the focus of activity around COVID-19. This could potentially affect the findings whihc are corrrect as of September 2020.
Kumbargere Nagraj S, Eachempati P, Paisi M, Nasser M, Sivaramakrishnan G, Verbeek JH. Interventions to reduce contaminated aerosols produced during dental procedures for preventing infectious diseases. Cochrane Database of Systematic Reviews 2020, Issue 10. Art. No.: CD013686. DOI: 10.1002/14651858.CD013686.pub2.
Cameron G. Estrich, Matthew Mikkelsen, Rachel Morrissey, Maria L. Geisinger, Effie Ioannidou, Marko Vujicic, Marcelo W.B. Araujo, Estimating COVID-19 prevalence and infection control practices among US dentists, The Journal of the American Dental Association, Available online 15 October 2020
Nardone M, Cordone A, Petti S. Occupational COVID-19 risk to dental staff working in a public dental unit in the outbreak epicenter. Oral Dis. 2020 Sep 3. doi: 10.1111/odi.13632. Epub ahead of print. PMID: 32881190.
Dental Elf – 30th April 2020