Response to Letters to the Editor, “ Sources of SARS CoV-2 and Other Microorganisms in Dental Aerosols”

We thank Ortega et al., Smith et al., and Ng et al. for their letters to the editor regarding our article. Before we address their comments, we wish to emphasize that our goal was to identify the sources of microorganisms originating from aerosol-generating dental procedures (AGPs), not during other aerosol-generating activities that occur in the dental setting.

We recognize that symptomatic and presymptomatic patients have high salivary viral loads and have demonstrated that in our recent publication (Chaudhary et al. 2021), but as practicing clinicians, we have not encountered symptomatic patients seeking care in outpatient dental clinics. Therefore, our subjects were recruited from the outpatient population seeking dental care and not from a coronavirus disease 2019 (COVID-19) ward. Based on the American Dental Association (ADA) guidance at the time (ADA 2020), we followed up all patients with 48-h phone calls, and none reported symptoms in that window, suggesting that none of our subjects were presymptomatic during the study. Therefore, the point by Smith et al. that the data cannot be extrapolated to presymptomatic patients is well taken, and we look forward to studies that investigate this group as potential sources of COVID-19 transmission.

Saliva from dental personnel was not tested for 2 reasons: 1) without accurate contact tracing data and viral genome sequencing, positive salivary tests in dental personnel cannot be attributable to transmission from the patient, and 2) dental personnel involved in direct patient care wore N95 masks and face shields during the visit based on the ADA guidance, which has been shown to result in undetectable viral loads (Ionescu et al. 2021). Transmission from patient to personnel was not the objective or scope of our study, and we look forward to studies that test this hypothesis.

Aerosol settling times following AGPs vary widely; while general modeling studies (e.g., Gao et al. 2021) and dental simulation studies (e.g., Nulty et al. 2020) examined aerosol condensates over a 2-h window, the National Physical Laboratory reported that during actual patient treatment using high-volume evacuation, all aerosol events, regardless of their source, diminished to background levels within 10 min on average and within 20 min at most (Tompkins 2020). Our samples were collected 30 min following each procedure, and the AGPs ranged from 60 to 90 min. Therefore, the settling times ranged from 90 to 120 min.

We agree with Ng et al. that undetectable viral levels in the aerosol were most likely due to low salivary loads, coupled with dilution of the saliva by the irrigant and at-source aerosol mitigation with a high-volume suction device. This is exactly the point that we are trying to make, so we are not certain why the authors believe this finding to be irrelevant.

The guidance from Centers for Disease Control and Prevention (CDC) and ADA during the pandemic was (and still is) to use high-volume suction devices during AGPs. This represented a significant departure from the then-prevalent practice of using saliva ejectors, and our main objective was to emphasize that our findings were based on AGPs generated following continuous use of high-volume intraoral evacuators and that these results could not be generalized to saliva ejectors. In parallel, we conducted a randomized, triple-blinded study comparing saline (control), 1% hydrogen peroxide, 0.12% chlorhexidine, or 0.5% povidone-iodine (Chaudhary et al. 2021) and reported reductions in salivary viral loads in patients with COVID-19 by 61% to 89% at 15 min and by 70% to 97% at 45 min, with no statistically significant differences between mouthwashes. The CDC/ADA guidelines to use mouthwashes on all patients preclude conducting a rinse/no-rinse comparison, and the findings of our parallel study informed our decision to use hydrogen peroxide as the mouthwash of choice at a time when resources were extremely scarce and being sequestered for use in COVID-19 wards.