Characterization and mitigation of aerosols and spatters from ultrasonic scalers.

BACKGROUND: Dental procedures often produce aerosols and spatter, which have the potential to transmit pathogens such as severe acute respiratory syndrome coronavirus 2. The existing literature is limited. METHODS: Aerosols and spatter were generated from an ultrasonic scaling procedure on a dental manikin and characterized via 2 optical imaging methods: digital inline holography and laser sheet imaging. Capture efficiencies of various aerosol mitigation devices were evaluated and compared. RESULTS: The ultrasonic scaling procedure generated a wide size range of aerosols (up to a few hundred µm) and occasional large spatter, which emit at low velocity (mostly < 3 m/s). Use of a saliva ejector and high-volume evacuator (HVE) resulted in overall reductions of 63% and 88%, respectively, whereas an extraoral local extractor (ELE) resulted in a reduction of 96% at the nominal design flow setting. CONCLUSIONS: The study results showed that the use of ELE or HVE significantly reduced aerosol and spatter emission. The use of HVE generally requires an additional person to assist a dental hygienist, whereas an ELE can be operated hands free when a dental hygienist is performing ultrasonic scaling and other operations. PRACTICAL IMPLICATIONS: An ELE aids in the reduction of aerosols and spatters during ultrasonic scaling procedures, potentially reducing transmission of oral or respiratory pathogens like severe acute respiratory syndrome coronavirus 2. Position and airflow of the device are important to effective aerosol mitigation.

Quantitative analysis of droplet deposition produced by an electrostatic sprayer on a classroom table by using fluorescent tracer.

Due to the ongoing COVID-19 pandemic situation, measures to mitigate the risk of transmission of the SARS-CoV-2 virus in an indoor setting are urgently needed. Among the various types of disinfectant methods, electrostatic spraying is often applied to decontamination in public places. For quantitatively characterizing electrostatic spraying, we developed the novel evaluation method by using a fluorescent tracer. By applying this method, we performed three different experiment cases (static test on a table, static test on a cylinder, and dynamic test on a table) to figure out its unique characteristics (Coulombic fission and wraparound effect) and measure its performance in various aspects. To be specific, bimodal distribution with peak sizes of ~10 and ~100 µm was found due to Coulombic fission. Otherwise, a unimodal distribution with a peak size of ~100 µm occurred for the uncharged droplets. As a result, the effective contact area increased by 40-80 % due to small progeny droplets. The wraparound effect was examined on two different cylinders: copper (Cu) and polyvinyl chloride (PVC) pipe. When the target surface was not charged (Cu 0 kV and PVC 0 kV), the average normalized concentrations on the backside of the cylinder (θ = 180°) increased by around 67 % for charged droplets. Meanwhile, when the target surface was highly charged (PVC -19 kV), the average normalized concentrations at θ = 180° were increased more than two times for charged droplets.

Evaluation of decontamination methods for commercial and alternative respirator and mask materials - view from filtration aspect.

This study aims to evaluate the filtration performance of three commercially available (3M 8210 respirator, Halyard 48207 surgical mask, and 3M 1820 procedure mask) and two alternative face mask and respirator materials (Halyard H600 sterilization wrap and Cummins EX101) after selected decontamination treatments, including isopropanol (IPA) treatments (soaking or spraying), ultraviolet germicidal irradiation (UVGI), and heat treatments (dry heat at 77 °C or steam heat). Both IPA soaking and spraying removed most electrostatic charges on all four electret materials (three commercial and one alternative), causing significant deterioration of filtration efficiency to unacceptable level. The other non-electret alternative material sustained its N95-grade performance after both IPA soaking and spraying treatments, demonstrating the possible application of IPA disinfection for non-electret alternative respirator/mask materials. UVGI preserved the filtration of all three commercially available respirator/mask materials after up to 10 treatments, suggesting it can be a possible decontamination method for hospital and clinic use without compromising respirator/mask performance. The considerations of the practical implementation of this method was discussed. Between the two heat treatment methods tested, dry heat showed better compatibility with electret material by sustaining both filtration efficiency and fit (tested on commercial respirator only), although adding moisture was reported in favor of virus inactivation. Heat treatment is easily accessible method for general publics to implement at home, while it is recommended to maintain the moisture level below saturation. Comparing to size-integrated method, the size-resolved fractional efficiency measurement technique, although more time consuming, proved to be a better method for evaluating respirator/mask filtration performance after decontaminations by providing more sensitive detection of performance degradation and the capability of distinguishing charge loss to other mechanisms causing efficiency deterioration. Detailed descriptions are provided in methodology part to emphasize the cares needed for an appropriate efficiency evaluation. The limited results in this study on worn masks made of alternative sterilization wrap indicated possible performance degradation of electret material caused by normal human wearing activities, suggesting the need of assessing respirator/mask decontamination strategy by testing practically worn-and-decontaminated/reused samples instead of unworn only-decontaminated counterparts.