Computer simulation of the SARS-CoV-2 contamination risk in a large dental clinic.

COVID-19, caused by the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) virus, has been rapidly spreading worldwide since December 2019, causing a public health crisis. Recent studies showed SARS-CoV-2's ability to infect humans via airborne routes. These motivated the study of aerosol and airborne droplet transmission in a variety of settings. This study performs a large-scale numerical simulation of a real-world dentistry clinic that contains aerosol-generating procedures. The simulation tracks the dispersion of evaporating droplets emitted during ultrasonic dental scaling procedures. The simulation considers 25 patient treatment cubicles in an open plan dentistry clinic. The droplets are modeled as having a volatile (evaporating) and nonvolatile fraction composed of virions, saliva, and impurities from the irrigant water supply. The simulated clinic's boundary and flow conditions are validated against experimental measurements of the real clinic. The results evaluate the behavior of large droplets and aerosols. We investigate droplet residence time and travel distance for different droplet diameters, surface contamination due to droplet settling and deposition, airborne aerosol mass concentration, and the quantity of droplets that escape through ventilation. The simulation results raise concerns due to the aerosols' long residence times (averaging up to 7.31 min) and travel distances (averaging up to 24.45 m) that exceed social distancing guidelines. Finally, the results show that contamination extends beyond the immediate patient treatment areas, requiring additional surface disinfection in the clinic. The results presented in this research may be used to establish safer dental clinic operating procedures, especially if paired with future supplementary material concerning the aerosol viral load generated by ultrasonic scaling and the viral load thresholds required to infect humans.

Aerosol formation due to a dental procedure: insights leading to the transmission of diseases to the environment.

As a result of the outbreak and diffusion of SARS-CoV-2, there has been a directive to advance medical working conditions. In dentistry, airborne particles are produced through aerosolization facilitated by dental instruments. To develop methods for reducing the risks of infection in a confined environment, understanding the nature and dynamics of these droplets is imperative and timely. This study provides the first evidence of aerosol droplet formation from an ultrasonic scalar under simulated oral conditions. State-of-the-art optical flow tracking velocimetry and shadowgraphy measurements are employed to quantitatively measure the flow velocity, trajectories and size distribution of droplets produced during a dental scaling process. The droplet sizes are found to vary from 5 µm to 300 µm; these correspond to droplet nuclei that could carry viruses. The droplet velocities also vary between 1.3 m s-1 and 2.6 m s-1. These observations confirm the critical role of aerosols in the transmission of disease during dental procedures, and provide invaluable knowledge for developing protocols and procedures to ensure the safety of both dentists and patients.