Evaluating dental aerosol and splatter in an open plan clinic environment: implications for the COVID-19 pandemic

Abstract

Aim: To identify splatter and aerosol distribution resulting from aerosol generating procedures (AGPs) in the open plan clinical environment. A secondary aim is to explore the detailed time course of aerosol settling after an AGP. Methodology: Dental procedures were undertaken on a dental mannequin. Fluorescein dye was placed into the irrigation system of the high-speed air turbine handpiece for the first experimental design, and in the second, fluorescein dye was entered into the mannequin's mouth via artificial salivary ducts. Filter papers were placed at set distances around the open plan clinical environment to collect aerosol and splatter under various mitigating conditions including ventilation and aspiration flow rate. An 8-metre diameter rig was set up to investigate the effect of fallow time. Filter papers were analysed using imaging software and spectrofluorometric analysis. Results: The distribution of fluorescein contamination varied widely across the open plan clinic depending on the experimental conditions. Unmitigated (i.e. no suction) procedures have the potential to deposit contamination at large distances. Medium volume dental suction (159 L/min air) reduced contamination in the AGP bay by 53%, and in adjacent and distant bays/walkways by 81-83%. Low volume suction (40 L/min air) gave similar reductions. Cross-ventilation reduced contamination in adjacent and distant bays/walkways by 80-89%. In the most realistic model (dye in mouth with medium volume suction) the samples in distant bays (≥5 m head-to-head chair distance) either gave zero readings or very low readings (< 0.0016% of the fluorescein introduced to the system during the procedure). Almost all (99.99%) of the splatter detected was retained within the AGP bay/walkway. Time course experiments showed that after 10 minutes, very little additional contaminated aerosol settled. Conclusions: The cross-infection risk from conducting AGPs in an open plan clinic environment appears small, particularly when bays are ≥ 5 m apart. There is a major dilution effect from the instrument water spray and a substantial protective effect from using dental suction. The majority of aerosol settles in the first 10 minutes, indicating that environmental cleaning may be appropriate after this time

SARS-CoV-2: characterisation and mitigation of risks associated with aerosol generating procedures in dental practices

“…In a dental surgery of the size used in this study (35 m 3 ), and in the context of SARS-CoV-2, it provides further evidence to support a reduction in fallow time below the current recommend period of ten minutes, 24 in agreement with other recent studies. 25 The use of a phantom head is a clear limitation of this study; the absence of saliva and other biological materials within the oral cavity may conceivably have influenced the particle size distribution of the aerosols. The standard procedures used in this study used aqueous coolant (Supplementary Table 3) which, under normal circumstances, would have led to a large (25-82-fold) dilution in patient-generated saliva.…”

Dental mitigation strategies to reduce aerosolization of SARS-CoV-2

“…To improve the accuracy of the phantom head unit over previous published models, [9, 15, 32] we added an anatomical tongue model and a high-level physiological salivary flow of 1.5 mL min -1 , spread across three positions. Whilst an improvement on models reported in the literature, it is not without its limitations.…”

“…Various methodologies for determining aerosolization in dental environments have been implemented, including the use air particle measurement, [9, 10] biological air sampling, [11, 12] culture of settle plates [6, 13, 14] and fluorescent markers. [9, 15, 16] Each of these methods offers insight into bioaerosol production, but each has its limitations. For instance, settle plates cannot account for the smallest particles that will not settle out of the air, air particle data cannot distinguish “clean” particles from the dental water unit line and those of biological origin, and the use of fluorescent dyes cannot offer information on viability of any potential biological component.…”

Evaluating splatter and settled aerosol during orthodontic debonding: implications for the COVID-19 pandemic

“…The procedure lasted for ten minutes and filter papers were left for ten minutes after the end of the procedure before collection to allow settling of any splatter/settled aerosol; this ten-minute settling time has been reported previously. 41,42,43 The experiment was repeated on three separate occasions. A positive control condition -high-speed air-turbine crown preparation of the upper right central incisor with water coolant -was carried out under the same conditions as the orthodontic debonding procedure, including assistantheld dental suction.…”