Assessment of respirable aerosol concentrations using local ventilation controls in an open multi-chair dental clinic

Dental procedures require patients to be unmasked throughout most of a dental visit, with some procedures generating both inhalable and respirable aerosols. Understanding aerosol generation and transport were important to developing protocols to protect both the patient and workers in dental environments early in the COVID pandemic. This study investigated the need, suitability, and effectiveness of using local exhaust ventilation units during patient procedures and examined the impact of patient density in a large, multi-chair dental clinic at an academic institution. Phase One measured respirable aerosol concentrations at the dental assistant's breathing zone and in neighboring unoccupied patient operatories. Results were compared during four dental procedures with three local ventilation (LV) options, with a single faculty performing procedures on a simulated patient. Phase Two deployed LV in all active patient operatories during procedures on actual patients and examined the impact of clinic patient occupancy on respirable aerosol concentrations throughout the clinic. During Phase One, respirable aerosol concentrations in nearby operatories were significantly higher during ultrasonic scaling (mean = 3.8 and SD = 0.3 µg/m³) and lower during rubber cup polishing (mean = 0.8 and SD = 0.5 mg/m³) (p < 0.001). While the same trend was identified for the dental assistant, differences were not significant. There was no difference in respirable aerosol concentrations by LV type when measured at the dental assist (p = 0.51, task means 3 to 32. 5 µg/m³) or neighboring rooms (p = 0.93, task means 0.6 to 4.0 µg/m³), indicating no improved control for any device tested. For Phase Two, the clinic deployed the extraoral suction (EOS) system in each patient operatory. The background-adjusted aerosol concentrations were significantly reduced (F < 0.001) when the operatories were occupied at 50% compared to 25%, likely attributed to increased air filtration of the room with double the EOS systems in use. While this study provides only a single case investigation, findings confirming respirable aerosol concentrations by procedure and across days provided insights into patient scheduling, local exhaust ventilation selection, and operation, which could be useful to other open multi-chair dental clinics.