Effects of mechanical ventilation and portable air cleaner on aerosol removal from dental treatment rooms.

OBJECTIVES: To evaluate the mechanical ventilation rates of dental treatment rooms and assess the effectiveness of aerosol removal by mechanical ventilation and a portable air cleaner (PAC) with a high-efficiency particulate air (HEPA) filter. METHODS: Volumetric airflow were measured to assess air change rate per hour by ventilation (ACHvent). Equivalent ventilation provided by the PAC (ACHpac) was calculated based on its clean air delivery rate. Concentrations of 0.3, 0.5 and 1.0 µm aerosol particles were measured in 10 dental treatment rooms with various ventilation rates at baseline, after 5-min of incense burn, and after 30-min of observation with and without the PAC or ventilation system in operation. Velocities of aerosol removal were assessed by concentration decay constants for the 0.3 µm particles with ventilation alone (Kn) and with ventilation and PAC (Kn+pac), and by times needed to reach 95 % and 100 % removal of accumulated aerosol particles. RESULTS: ACHvent varied from 3 to 45. Kn and Kn+pac were correlated with ACHvent (r = 0.90) and combined ACHtotal (r = 0.81), respectively. Accumulated aerosol particles could not be removed by ventilation alone within 30-min in rooms with ACHvent<15. PAC reduced aerosol accumulation and accelerated aerosol removal, and accumulated aerosols could be completely removed in 4 to 12-min by ventilation combined with PAC. Effectiveness of the PAC was especially prominent in rooms with poor ventilation. Added benefit of PAC in aerosol removal was inversely correlated with ACHvent. CONCLUSIONS: Aerosol accumulation may occur in dental treatment rooms with poor ventilation. Addition of PAC with a HEPA filter significantly reduced aerosol accumulation and accelerated aerosol removal. CLINICAL SIGNIFICANCE: Addition of PAC with a HEPA filter improves aerosol removal in rooms with low ventilation rates.

Risk for dental healthcare professionals during the COVID-19 global pandemic: An evidence-based assessment.

OBJECTIVES: Heightened anxiety among dental healthcare professionals (DHPs) during the COVID-19 pandemic stems from uncertainties about the effectiveness of personal protective equipment (PPE) against dental aerosols and risk levels of asymptomatic patients. Our objective was to assess the risks for DHPs providing dental care during the pandemic based on available scientific evidence. METHODS: We reviewed the best available evidence and estimated the annualized risk (p=das(1-1-p0p1(1-e)yn) for a DHP during the COVID-19 pandemic based on the following basic parameters: p0, the prevalence of asymptomatic patients in the local population; p1, the probability that a DHP gets infected by an asymptomatic patient; e, the effectiveness of the PPE; s, the probability of becoming symptomatic after getting infected from asymptomatic patient; da, the probability of dying from the disease in age group a; n, number of patients seen per day; and y, number of days worked per year. RESULTS: With the assumption that DHPs work fulltime and wear a N95 mask, the annualized probability for a DHP to acquire COVID-19 infection in a dental office, become symptomatic, and die from the infection is estimated at 1:13,000 (0.008 %) in a medium sized city in the US at the peak of the pandemic. The risk estimate is highly age-dependent. Risk to DHPs under the age of 70 is negligible when prevalence of asymptomatic cases is low in the local community. CONCLUSIONS: Risk of COVID-19 transmission in dental office is very low based on available evidence on effectiveness of PPE and prevalence of asymptomatic patients. Face shields and pre-procedure oral rinses may further reduce the risks. CLINICAL SIGNIFICANCE: DHPs should follow guidelines on pre-appointment protocols and on PPE use during dental treatments to keep the risk low.