Characteristics of droplets emission immediately around mouth during dental treatments

Control measures aiming for removing droplets generated during dental treatments have been attracted increasing attention after COVID-19 pandemic, but the emission characteristics of droplets around the source (namely, the mouth) have still not been fully understood. The present study investigated experimentally the emission characteristics of droplets around mouth during typical dental treatments. A manikin being treated by portable dental instruments simulated the dental treatments, while the laser light scattering technique and particle image velocimetry (PIV) technique were employed to perform the measurements. The peak mass fraction of droplets occurs around the droplet size from 20 mu m to 100 mu m, while the mass fraction of droplets with the diameter less than 200 mu m accounts for over 80 %. By fitting with the Rosin-Rammler equation, the mean size of droplets (d) are 54.96 and 98.93, and the size distribution parameter (n) are 1.35 and 1.58, respectively, for the process of air-powder-polishing and ultrasonic scaling. The dominant emission direction of droplets is towards the dummy' head and chest. The emitted droplets formed approximately a cone shape, and its angle varied from 25 degrees to 83 degrees for different conditions. The maximum velocity of droplets at the location near the dummy's mouth exceeds 1.0 m/s for most conditions. The injecting flow rate and treated tooth position are the major factors influencing the emission direction, angle, and velocity. It is expected that the results can further increase our understanding of emission characteristics of droplets and provide accurate initial conditions for CFD simulations.