Quantitative evaluation of dental bio-aerosols using particle count values. Part 1: the effect of High Volume Aspiration and natural ventilation.

Abstract

AimRoutine dental treatments are frequently associated with aerosol generating procedures (AGP). Recently dental AGP have attracted significant attention as a possible vector for the transmission of SARS-CoV-2 and attempts have been made to establish when a surgery may be safely decontaminated following a dental AGP — the ‘fallow time’. There is a paucity of research in the dental literature regarding the near real time generation and dispersion of dental aerosol following a dental AGP. Study aims are to: (1) monitor dental aerosol generation and dispersal through semi-continuous particle count values (PCV), and (2) use this information to delineate a range of suitable fallow times.MethodFollowing baseline measurements, five identical dental AGP were conducted on a dental manikin for each of three groups: (SEO) saliva ejector only, (HVA) high volume aspiration, (WO) high volume aspiration with windows open. For each procedure PCV were recorded every 2.2 minutes with a Light Scattering Airborne Particle Counter (LSAPC) for 3.3 hours. Eleven dependent variables were analysed, including baseline PCV, total PCV, peak PCV, time taken to return to one sample standard deviation of baseline PCV, and a time series extending from 15 minutes to 3 hours after cessation of AGP. Due to heterogeneity, the data was analysed with Krushkall-Wallis test and Dunn-Bonferroni post hoc.ResultsBetween group mean baseline PCV were not statistically significant. Compared with SEO, WO had a statistically significant impact on peak PCV (p=.009) and HVA had a statistically significant impact on total PCV (p=.006). With the exception at 2 and 3 hours, PCV throughout the time series were statistically significantly lower for WO and HVA in comparison with SEO. WO PCV were influenced by outdoor aerosol levels.Four of the five SEO procedures failed to return to baseline PCV within 3.3 hours. Following AGP, the mean time for the HVA procedures to return to baseline PCV was 17.12 minutes, 95% CI [4.96 to 29.28]. The effect of HVA on the time taken to return to baseline PCV was very large (Glass’s Δ= -4.943, CLES=1.00).ConclusionThere is a significant benefit in opening windows during AGP. The effect of HVA on reducing fallow time is very large. Under the conditions of this study, PCV suggest that it might be safe to consider a fallow time of 29.28 minutes.

Using Computational Fluid Dynamics to Evaluate the Role of Air Purification in Reducing Fallow Time in Dentistry

“…Another pressing reason to model this open window scenario is the paucity of studies undertaken on this, despite the volume of guidance which recommends it. One study recently undertaken by Haigh, Vasant and O'Hooley [31] attempted to display the effects of an open window on particle removal in another mannequin study; however, they were unable to definitively quantify the effect this had, although they did conclude that it reduced airborne particle volume. Their study also did not include particles below 0.3 micrometres, which is a disadvantage given that this is the size of particle into which viruses fall.…”