Fallow time determination in dentistry using aerosol measurement

Abstract

AimTo calculate fallow time (FT) required following dental aerosol generating procedures (AGPs) in both a dental hospital (mechanically ventilated) and primary care (non-mechanically ventilated). Secondary outcomes were to identify spread and persistence of aerosol in open clinics compared to closed surgeries (mechanically ventilated environment), and identify if extra-oral scavenging (EOS) reduces production of aerosol and FT.MethodsIn vitro simulation of fast handpiece (FHP) cavity preparations using a manikin was conducted in a mechanically and non-mechanically ventilated environment using Optical Particle Sizer™ and NanoScan™ at baseline, during the procedure and fallow period.ResultsAGPs carried out in the non-mechanically, non-ventilated environment failed to achieve baseline particle levels after one hour. In contrast, when windows were opened after AGP, there was an immediate reduction in all particle sizes.In mechanically ventilated environments the baseline levels of particles were very low and particle count returned to baseline within 10 minutes following AGP. There was no detectable difference between particles in mechanically ventilated open bays and closed surgeries.The effect of the EOS was greater in non-mechanically ventilated environment on reducing the particle count; additionally, it also reduced the spikes in particle counts in mechanically ventilated environments.ConclusionHigh-efficiency particulate air filtered mechanical ventilation along with mitigating factors (high-volume suction) resulted in reduction of FT (10 minutes). Non-ventilated rooms failed to reach baseline level even after one hour of FT. There was no difference in particle counts in open bay or closed surgeries in mechanically ventilated settings. The use of an EOS device can reduce the particulate spikes during procedures in both mechanical and non-mechanical environments.This study confirms that AGPs are not recommended in dental surgeries where no ventilation is possible. No difference was demonstrated in FT required in open bays and closed surgeries in mechanically ventilated settings.Clinical significanceAGPs should not be carried out in surgeries where ventilation is not possible. Mechanical ventilation for AGPs should be gold standard; where not available or practical then the use of natural ventilation with EOS helps reduce FT. AGPs can be carried out in open bay environment with a minimum of 6 air changes per hour of mechanical ventilation. Four-handed dentistry with high-volume suction and saliva ejector are essential mitigating factors during AGPs.

Dental Mitigation Strategies to Reduce Aerosolization of SARS-CoV-2

“…We determined a wide variation in the time for particles of all sizes to return to pre-AGP levels, although larger particles required less time with the HSCAH. Shahdad et al (2021) reported similar variability and suggested that fallow time estimates were longer for procedures where the handpiece was used in 5-min bursts, comparable to our protocol. A recent study indicated that <0.1% of aerosolized fluorescein dye was detectable after 30 min of fallow time ( Allison et al 2021 ).…”

“…It uses artificial teeth, which lack the anatomical intricacies of human teeth. However, previous particle analyses revealed little difference between plastic and real teeth ( Shahdad et al 2021 ). Our model does not imitate the effects of a patient breathing or other patient behaviors, such as talking or coughing, that would likely contribute to bioaerosol production.…”

“…To improve the accuracy of the phantom head over previously published models ( Allison et al 2021 ; Holliday et al 2021 ; Shahdad et al 2021 ), we added an anatomical tongue model and a high-level physiological salivary flow of 1.5 mL min −1 , spread across 3 positions. While an improvement, our model has limitations.…”

“…The requirement for, and length of, a period of fallow time is unclear, with estimates ranging from 2 to 180 min ( Robertson et al 2020 ; Ehtezazi et al 2021 ; Shahdad et al 2021 ). However, this is often based on particle data alone.…”