Ultrasonic scaling in COVID-era dentistry: A quantitative assessment of aerosol spread during simulated and clinical ultrasonic scaling procedures

Objective: Healthcare agencies recommend limited use of aerosol-generating procedures to mitigate disease (COVID-19) transmission. However, total dispersion patterns of aerosols, particularly respirable droplets, via dental ultrasonic units is unclear. The purpose of this study was to characterize and map total spatter, droplet and aerosol dispersion during ultrasonic scaling in simulated and clinical contexts.

Methods: Ultrasonic scaling was performed on dental simulation units using methylene blue dye-stained water. All resultant stain profiles were photoanalysed to calculate droplet size and travel distance/direction. Airborne particle concentrations were also documented 0-1.2 m (0-4ft.) and 1.2-2.4 m (4-8ft.) from patients during in vivo ultrasonic scaling with a saliva ejector.

Results: Stain profiles showed droplets between 25 and 50µm in diameter were most common, with smaller droplets closer to the mouth. In-vivo particle concentrations were uniformly low. The smallest (<1 µm, PM1) and largest (>10 µm, PM10+) particles were most common, especially within 1.2 m (4ft.) of the patient. Respirable particles (PM2.5) were uncommon.

Conclusions: Tests showed the highest concentration of small droplets in zones nearest the patient. While uncommon, particles were detected up to 2.4 m (8ft.) away. Furthermore, observed particle sizes were consistent with those that can carry infectious agents. Efforts to mitigate the spread of inhalable aerosols should emphasize proximate regions nearest the procedure, including personal protective equipment and the use of evacuation devices.