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

Precise control of digital dental unit to reduce aerosol and splatter production: new challenges for future epidemics

BACKGROUND

During dental procedures, critical parameters, such as cooling condition, speed of the rotary dental turbine (handpiece), and distance and angle from pollution sources, were evaluated for transmission risk of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), simulated by spiking in a plasmid encoding a modified viral spike protein, HexaPro (S6P), in droplets and aerosols.

METHODS

To simulate routine operation in dental clinics, dental procedures were conducted on a dental manikin within a digital dental unit, incorporating different dental handpiece speeds and cooling conditions. The tooth model was immersed in Coomassie brilliant blue dye and was pre-coated with 100 μL water spiked-in with S6P-encoding plasmid. Furthermore, the manikin was surrounded by filter papers and Petri dishes positioned at different distances and angles. Subsequently, the filter papers and Petri dishes were collected to evaluate the aerosol splash points and the viral load of S6P-encoding plasmid in aerosols and splatters generated during the dental procedure.

RESULTS

Aerosol splashing generated a localized pollution area extended up to 60 cm, with heightened contamination risks concentrated within a 30 cm radius. Significant differences in aerosol splash points and viral load by different turbine handpiece speeds under any cooling condition (P < 0.05) were detected. The highest level of aerosol splash points and viral load were observed when the handpiece speed was set at 40,000 rpm. Conversely, the lowest level of aerosol splash point and viral load were found at a handpiece speed of 10,000 rpm. Moreover, the aerosol splash points with higher viral load were more prominent in the positions of the operator and assistant compared to other positions. Additionally, the position of the operator exhibited the highest viral load among all positions.

CONCLUSIONS

To minimize the spread of aerosol and virus in clinics, dentists are supposed to adopt the minimal viable speed of a dental handpiece with limited cooling water during dental procedures. In addition, comprehensive personal protective equipment is necessary for both dental providers and dental assistants.

Quantifying strategies to minimize aerosol dispersion in dental clinics

Many dental procedures are aerosol-generating and pose a risk for the spread of airborne diseases, including COVID-19. Several aerosol mitigation strategies are available to reduce aerosol dispersion in dental clinics, such as increasing room ventilation and using extra-oral suction devices and high-efficiency particulate air (HEPA) filtration units. However, many questions remain unanswered, including what the optimal device flow rate is and how long after a patient exits the room it is safe to start treatment of the next patient. This study used computational fluid dynamics (CFD) to quantify the effectiveness of room ventilation, an HEPA filtration unit, and two extra-oral suction devices to reduce aerosols in a dental clinic. Aerosol concentration was quantified as the particulate matter under 10 µm (PM10) using the particle size distribution generated during dental drilling. The simulations considered a 15 min procedure followed by a 30 min resting period. The efficiency of aerosol mitigation strategies was quantified by the scrubbing time, defined as the amount of time required to remove 95% of the aerosol released during the dental procedure. When no aerosol mitigation strategy was applied, PM10 reached 30 µg/m3 after 15 min of dental drilling, and then declined gradually to 0.2 µg/m3 at the end of the resting period. The scrubbing time decreased from 20 to 5 min when the room ventilation increased from 6.3 to 18 air changes per hour (ACH), and decreased from 10 to 1 min when the flow rate of the HEPA filtration unit increased from 8 to 20 ACH. The CFD simulations also predicted that the extra-oral suction devices would capture 100% of the particles emanating from the patient's mouth for device flow rates above 400 L/min. In summary, this study demonstrates that aerosol mitigation strategies can effectively reduce aerosol concentrations in dental clinics, which is expected to reduce the risk of spreading COVID-19 and other airborne diseases.