Particle Size Analysis in Aerosol-Generating Dental Procedures Using Laser Diffraction Technique

Abstract

The global outbreak of coronavirus disease 2019 (COVID-19) has raised concerns about the risk of airborne infection during dental treatment. Aerosol-generating dental procedures (AGDP) produce droplets and aerosols, but the details of the risks of COVID-19 transmission in AGDP are not well-understood. By discriminating between droplets and aerosols, we devised a method to measure particle size using laser diffraction analysis and evaluated aerosols generated from dental devices for providing a basis for proper infection control procedures. The droplets and aerosols generated from dental devices were characterized by multimodal properties and a wide range of droplet sizes, with the majority of droplets larger than 50 μm. AGDP emitted few aerosols smaller than 5 μm, which are of concern for pulmonary infections due to airborne transmission. In addition, the use of extraoral suction was found to prevent the spread of aerosols from high-speed dental engines. This study suggests that the risk of aerosol infections is considerably limited in regular dental practice and that current standard precautions, such as mainly focusing on protection against droplet and contact infections, are sufficient. While several cases of airborne transmission of COVID-19 in general clinics and emergency hospitals have been reported, cluster outbreaks in dental clinics have not yet been reported, which may indicate that AGDP does not pose a significant threat in contributing to the spread of SARS-CoV-2.

Keywords: COVID-19; aerosol generating dental procedure; airborne transmission; dental public health; infection control; laser diffraction analysis; particle size analysis; transmission based precautions.

Figure 1

(A) Through-cylinder system; layout and schematic of the cylinder and laser detection device for aerosol measurement. The acrylic cylinder (20 cm in diameter and 90 cm in length) is set at an angle of 15 degrees. Aerosols from devices were transported by airflow (0.8 m/sec) to the laser position and particle size data was taken at a real-time speed (1 Hz) for 25 seconds. (B) The relationship between the position of the aerosol source and the aerosol measurement device. Dental devices were fixed to the column stand (upper). As an example of use, the extraoral suction is placed at the 9 o'clock position to the left of the dental instrument with the direction of aerosol ejection at the 12 o'clock position (lower). The system was covered during measurement to prevent excess airflow from the exterior by a vinyl sheet and the safety cabinet.

Figure 2

Distribution patterns of droplet size emitted from the devices and validation of the removal effect of the cylinder on large droplets. In each data set, data from direct spraying (left), and through-cylinder (right) are shown separately. Droplet size distribution (DSD) histogram graph emitted from ultrasonic scaler (A), 3-way syringe (B), nebulizer (C), humidifier (D). The curve in the graphs represent the droplet cumulative volume frequency and the percentage of a particular size of the droplet. Each experiment was performed independently at least four times, and the results of one representative experiment are shown.

Figure 3

Distribution pattern of droplet size emitted from the dental engine at various speeds and validation of the effect of extraoral suction. Data from the through-cylinder is shown. Droplet size distribution (DSD) histogram graph emitted from the dental engine at the speed of 200,000 rpm (A), 100,000 rpm (B), 5,000 rpm (C). Distribution pattern of droplet size emitted from the dental engine with extraoral suction by low set with 180 degrees, strong set with 180 degrees, and strong set with 90 degrees (D–F, respectively). The curves in the graphs represent the droplet cumulative volume frequency and the percentage of a particular size of the droplet. Each experiment was performed independently at least four times, and the results of one representative experiment are shown.