Little risk from dental aerosol procedures: 10 minutes gap is enough between two procedures

Dentists all over the world are concerned about the risks and the safety of dental aerosol procedures. We present the summary of all recent publications on this topic.

Let's start with a recent publication titled Evaluating dental aerosol and splatter in an open plan clinic environment: implications for the COVID-19 pandemic (OSF Preprints, 10 Sept 2020) 

Since there has been very little evidence to support the practice of environmental cleaning in open-plan or closed clinical environments between two patients, this identified the splatter and aerosol distribution resulting from dental aerosol-generating procedures (AGPs) in the open-plan clinic environment. A secondary aim of this study was to explore the detailed time course of aerosol settling after an AGP.

Here we present the author conclusions and our interpretations of the same.

[1] The cross-infection risk from conducting Aerosol Generating Procedures in an open plan clinic environment appears to be small, mainly when bays are 5 m apart in a setting with 3.45 ACH (Air Changes/ Hour).

Interpretation/ Implications: Open plan clinics (open bay set up) is a type of clinic that has multiple dental chairs installed in the room. Plenty of clinics have such arrangements. This finding shows that dental clinics with single operatories and separate operatories are the safest. If your clinic has multiple chairs and the distance between them is much greater than 5 meters, the chance of cross-contamination appears to be small with an ACH setting of 3.45 more than 5 meters. If your clinic has less than 5 meters of distance between two chairs, use only one chair at a time.

[2] With 1.5 m high lateral bay partition with open fronts, at least 99.99% of splatter following an AGP is contained within the bay.

Interpretation/ Implications: Minimal splatter was detected outside of the AGP producing bay. As you move farther, the distant contamination from aerosol was at very low levels. The farther you go from the dental chair that produces aerosol/ splatter, the lesser the splatter and aerosol contamination.

Most contamination is limited to the first 1.5 m from the procedure as shown by previous studies. So if a 1.5 m high bay partition with a patient positioned 73 cm above the floor (operator heights 1.67 m – 1.87 m), it might be adequate to prevent distant splatter contamination. Previous reports had recommended 2 m high partitions.

[3] There is a significant dilution effect from the water spray of dental instruments.

Interpretation/ Implications: Dental-generated aerosol is predominantly due to water or air spray, which would substantially dilute any potential viral presence, whereas in medical aerosol procedures, water irrigation is not used and manipulation of the airway occurs.

[4] Dental suction has a substantial positive effect.

Interpretation/ Implications: Again, the distance matters.  The effect of suction is more potent on more distant contamination.

[5] Comparison of different suction flow rates indicates that even low volume suction (40 L/min air, with a wide-bore aspirating tip) confers a substantial benefit.

Interpretation/ Implications: Use of a high- volume (high vac HVE) suction would be even better.

[6] Time-course experiments show that the majority of dental aerosol settles in the first 10 minutes post-procedure.

Interpretation/ Implications: This means environmental cleaning may be appropriate within this period.
Understand ‘fallow time’:  how much time one has to allow for the droplets to fall & settle before re-entering and disinfecting the surgical room. The earlier numbers given for this fallow time have been as large as 60 minutes or even 2 hours 27 minutes. This area always lacked evidence. This study seems to have shown that the fallow time is far shorter - about 10 minutes.

Reference: Evaluating dental aerosol and splatter in an open plan clinic environment: implications for the COVID-19 pandemic. Click here: OSF Preprints (10 Sep 2020)

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Dental Aerosol Generating Procedures:
Evidence is weak (Grade 4) - BMJ Editorial (20 Aug 2020)
The term “Aerosol- Generating Procedures” became popular after the 2003 SARS epidemic, when small retrospective studies found an association between transmission to healthcare workers and the use of procedures such as endotracheal intubation & non-invasive ventilation. This weak (grade D) evidence has been misused to infer a causal link between procedural aerosols and infection even though aerosols were not measured during these SARS epidemic studies.

Reference: Airborne transmission of covid-19. Click here to read The BMJ Editorial

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Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: a systematic review (2003)

[1] Despite the comprehensive nature of the search, the limitations of the included studies serve to emphasize the lack of high-quality studies which have examined the risk of transmission of microbes responsible for acute respiratory infections to HCWs caring for patients undergoing aerosol-generating procedures.

[2] The findings of this study serve to highlight the lack of precision in the definition of aerosol-generating procedures.

[3] The results of this report should not be generalized to all acute respiratory infections because the evidence available is strictly limited to SARS.

[4] A significant research gap exists in the epidemiology of the risk of transmission of acute respiratory infections from patients undergoing aerosol-generating procedures to HCWs, and clinical studies should be carefully planned to address specific questions around the risks of transmission in these settings.

Click here to read this systematic review (2003)
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Dental procedure aerosols and COVID-19: The Lancet Infectious Diseases (10 Aug 2020)

This communication (letter to the editor) highlighted two main issues:

A. Do aerosols—specifically, dental aerosols—contain potentially infectious virus?

[1] Testing to date has focused on Polymerase Chain Reaction (PCR), and even when positive, viral culture is required to confirm the potential for infection, as shown in investigations of other body sites.

[2] Estimates of risk from aerosols and surface contamination must be based on the recovery of viable virions, not only on PCR testing.

B. Should we compare dental aerosols with medical aerosols?

[1] A dental-generated aerosol is due to water or air spray, which would substantially dilute any potential viral presence, whereas in anaesthesia and upper-airway procedures, water irrigation is not used and manipulation of the airway occurs.

[2] Dental management includes routine use of high-volume evacuation, which reduces aerosol at source, and potential viral load could be further reduced if a dental rubber dam is in place isolating the dentition.

Click here to read the article

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Latest recommendations by the Centres of Disease Control & Prevention (CDC) on aerosol-generating procedures used in dental clinics

In the CDC guidelines, aerosol procedures are NOT contraindicated. The latest report (updated on 28 Aug 2020) recommends the following things if aerosol-generating procedures are necessary for dental care:

A.  To minimize droplet spatter and aerosols,

[1] use four-handed dentistry
[2] high evacuation suction
[3] dental dams

B. CDC also states that Preprocedural Mouth Rinses (PPMRs) with an antimicrobial product (chlorhexidine gluconate, essential oils, povidone-iodine or cetylpyridinium chloride) may reduce the level of oral microorganisms in aerosols and spatter generated during dental procedures.

C. In areas with moderate to substantial community transmission, during patient encounters with patients not suspected of SARS-CoV-2 infection, CDC recommends that dental healthcare personnel (DHCP):

[1] Wear eye protection in addition to their facemask to ensure the eyes, nose, and mouth are all protected from exposure to respiratory secretions during patient care encounters, including those where splashes and sprays are not anticipated.

[2] Use an N95 respirator or a respirator that offers an equivalent or higher level of protection during aerosol-generating procedures.

Click here to read the CDC report updated on 28 Aug 2020