An experimental approach to analyze aerosol and splatter formations due to a dental procedure

Abstract

Throughout 2020 and beyond, the entire world has observed a continuous increase in the infectious spread of the novel coronavirus (SARS-CoV-2) otherwise known as COVID-19. The high transmission of this airborne virus has raised countless concerns regarding safety measures employed in the working conditions for medical professionals. Specifically, those who perform treatment procedures on patients which intrinsically create mists of fine airborne droplets, i.e., perfect vectors for this and other viruses to spread. The present study focuses on understanding the splatter produced due to a common dentistry technique to remove plaque buildup on teeth. This technique uses a high-speed dentistry instrument, e.g., a Cavitron ultrasonic scaler, to scrape along the surface of a patient's teeth. This detailed understanding of the velocity and the trajectory of the droplets generated by the splatter will aid in the development of hygiene mechanisms to guarantee the safety of those performing these procedures and people in clinics or hospitals. Optical flow tracking velocimetry (OFTV) method was employed to obtain droplet velocity and trajectory in a two-dimensional plane. Multiple data collection planes were taken in different orientations around a model of adult mandibular teeth. This technique provided pseudo-three-dimensional velocity information for the droplets within the splatter developed from this high-speed dental instrument. These results indicated that within the three-dimensional splatter produced there were high velocities (1-2 m/s) observed directly below the intersection point between the front teeth and the scaler. The splatter formed a cone-shape structure that propagated 10-15 mm away from the location of the scaler tip. From the droplet trajectories, it was observed that high velocity isolated droplets propagate away from the bulk of the splatter. It is these droplets which are concerning for health safety to those performing the medical procedures. Using a shadowgraphy technique, we further characterize the individual droplets' size and their individual velocity. We then compare these results to previously published distributions. The obtained data can be used as a first step to further examine flow and transport of droplets in clinics/dental offices.

Fig. 1

The experimental schematics for the three different experimental orientations. a Case 1: The teeth are 0 ° and the point of the CUS is 90 ° from the x-axis, respectively. b, c Case 2 and 3: The teeth are rotated to be 45 ° from the x-axis. The point of the CUS is rotated so that it is 5˚ in reference to the front of the teeth. b The configuration with a P₁ data collection plane and c shows the P₂ data collection plane. d, e Diagrams of the lower mandible teeth with the appropriate teeth numbers (black) and the coordinate system in reference to the scaler tip and the front of the central incisor teeth (red). The tip of the CUS rests firmly against the d front of tooth #24 in Case 1, and e tooth #25 for Cases 2 and 3. f An image of the scaler tip being used with the CUS for this study experiments. The water jet is located within the concave side of the CUS tip

Fig. 2

A top-down view of the Cavitron and the teeth to show the locations of the 1 mm thick laser sheet for the two data collection planes. a The data collection plane, which was parallel to the Cavitron tip, P₁ and b the data collection plane that was perpendicular to the Cavitron tip, P₂. Raw OFTV images obtained from both of the laser plane locations, c P₁ and the d P₂ with the CUS and teeth at 0 °

Fig. 3

The velocity measurements for Case 1: P₁ plane with the teeth model and scaler point at an 0 ° and 90 ° angle, respectively. a The $v$ (y-direction) component of velocity, b the $u$ (x-direction) component of velocity, and c the magnitude of the velocity vector with the laser sheet 3 mm away from the point of the CUS. The velocity magnitude for a P₁ plane positions d 6 mm and e 9 mm away from the tip of the CUS

Fig. 4

Case 1: The far field velocity magnitudes for the P₁ plane at a location a 15 mm and b 20 mm from the tip of the CUS

Fig. 5

a The droplet locations at one instant in time for Case 1, P₁ plane with the scaler at 0˚ angle, with the laser sheet 20 mm from the point of the Cavitron. b The particle trajectories for 20% of droplets identified at the same laser sheet location. The color bars correspond to the velocity magnitude of the detected individual droplets

Fig. 6

a The mass fraction distribution of the measured droplets for the 16.2 ml/min case compared to the 29.5 ml/min at the onset of the CUS. b The velocity measurements at the various droplet diameters detected for both flow rates of 16.2 ml/min and 29.5 ml/min. The error bars correspond to the standard deviation of the measured velocity for the 0.15 μs of data gathered

Fig. 7

The velocity measurements for Case 2: P₁ plane with the teeth model at a 45 ° angle from the x-axis and the scaler 5˚ from the surface of the tooth. The a $v$ component of velocity, b the $u$ component of velocity, and c the magnitude of the velocity measured in a P₁ plane that is 3 mm from the CUS tip. The velocity magnitude in a P₁ plane d 6 mm and e 9 mm away from the CUS tip

Fig. 8

The far field velocity magnitudes for the P₁ plane at a location a 15 mm and b 20 mm from the tip of the CUS. These maps are related to the Case 2

Fig. 9

The velocity measurements for Case 2: P₁ plane with the teeth model at a 45˚ angle from the x-axis and the scaler 5˚ from the surface of the tooth. The a $v$ component of velocity, b $w$ component of velocity, and c the magnitude of the velocity vector with the laser sheet 3 mm away from the front of the teeth. The same average values for d-f the laser sheet 6 mm away from the front of the teeth and for g-i the laser sheet 9 mm away from the teeth’s surface

Fig. 10

Case 1: setup $v$ (left column) and $u$ (right column) components of velocity at a P₁ plane (a, b) 6 mm and (c, d) 9 mm away from the tip of the CUS

Fig. 11

Case 1: setup $v$ (left column) and $u$ (right column) components of velocity at a P₁ plane (a, b) 15 mm and (c, d) 20 mm away from the tip of the CUS

Fig. 12

Case 2: setup $v$ (left column) and $u$ (right column) components of velocity at a P₁ plane (a, b) 6 mm and (c, d) 9 mm away from the tip of the CUS

Fig. 13

Case 2: setup $v$ (left column) and $u$ (right column) components of velocity at a P₁ plane (a, b) 15 mm and (c, d) 20 mm away from the tip of the CUS