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Literature favours air purifiers as COVID-19 transmission risk mitigant


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Air purifying systems have been shown to reduce particle count and fallow time after aerosol generating procedures in dental settings. (Image: Don Pablo/Shutterstock)
Jeremy Booth, Dental Tribune International

By Jeremy Booth, Dental Tribune International

Thu. 12. August 2021


LEIPZIG, Germany: The pandemic has been a trying time for dentists, particularly for owner-dentists who must make decisions that may influence the safety of their treatment team. Recent studies have found that the rate of SARS-CoV-2 transmission in dental settings has been lower than what was expected when the pandemic was declared, and the literature has shown that air purifiers could play a role in keeping transmission rates down.

Scientists urged the World Health Organization in August last year to recognise that SARS-CoV-2 could be spread through microdroplets that are small enough to remain airborne for extended periods. By this time, many dental clinic owners had already reviewed and upgraded their supplemental ventilation systems, and many more were considering it. The use of air purifiers to reduce the risk of transmission in dental settings has since been validated by various scientific studies; however, uncertainty remains.

An April 2021 review by the Scottish Dental Clinical Effectiveness Programme (SDCEP) examined recent literature concerning the mitigation of aerosol-generating procedures (AGPs) in dentistry. Many of the research papers were experimental in nature and not all were peer-reviewed, owing to the abundance of scientific research that is currently being conducted and the urgency of publishing it. The SDCEP review found that air cleaners were not recommended to reduce the risk of SARS-CoV-2 transmission, owing to a lack of “higher certainty evidence” on their efficacy as a mitigating tool.

One of the studies that the SDCEP review analysed had been published by UK researchers in November 2020 in the British Dental Journal. The researchers measured and compared particle count during AGPs that were conducted with and without the use of high-volume extraction.

They wrote: “Without the use of an external high-volume extraction device during aerosol generating procedures, there is a significant increase of PM2.5- and PM10-sized particle count from the use of micromotor high-speed, air turbine high-speed, slow-speed and ultrasonic handpieces.”

The study, titled “A clinical study measuring dental aerosols with and without a high-volume extraction device”, can be accessed here.

Extra-oral scavenging found to reduce particle count

The SDCEP review also cited a study by researchers from the UK which was published on the preprint server medRxiV in January. The study examined the calculation of fallow time after AGPs in care facilities that were mechanically ventilated and non-mechanically ventilated, and whether extra-oral scavenging (EOS) could reduce aerosol production and fallow time. They found that AGPs carried out in mechanically ventilated treatment rooms produced a low particle count, which returned to baseline within a period of 10 minutes after AGPs. EOS was found to have a greater effect in non-mechanically ventilated environments, and to reduce the spike in particle counts in mechanically ventilated rooms.

The authors wrote: “AGPs 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.”

The study, titled “Fallow time determination in dentistry using aerosol measurement”, can be accessed here.

In May, researchers in Germany studied small particle concentration caused by AGPs during dental student training under high-flow suction both with and without the use of a mobile EOS device. Lower particle count was detected after high-speed tooth preparation when an EOS device was used. The researchers found that high-flow suction was effective in reducing the small particle count, which was further reduced through the use of an EOS device.

“The additional use of an EOS device should be carefully considered when performing treatments, such as high-speed tooth preparation, that generate particularly small particles when more people are present and all other protective options have been exhausted,” the authors wrote.

The study, titled “The efficacy of an extraoral scavenging device on reducing aerosol particles ≤ 5 µm during dental aerosol-generating procedures: An exploratory pilot study in a university setting”, was published in BDJ Open in May 2021 and can be accessed here.

High-volume aspiration found to be viable mitigation strategy

A study by researchers in Leeds in the UK aimed to evaluate risk mitigation strategies during AGPs by measuring viral air concentrations during crown preparation and root canal access procedures. The procedures were carried out using an air turbine or high-speed contra-angle handpiece (HSCAH) with the mitigation strategies rubber dam or high-speed aspiration or with no mitigation strategy.

The researchers wrote: “Compared to an air turbine, the HSCAH reduced settled bioaerosols by 99.72%, 100.00%, and 100.00% for no mitigation, aspiration, and rubber dam, respectively. Bacteriophage concentrations in the air were reduced by 99.98%, 100.00%, and 100.00% with the same mitigations. Use of the HSCAH with high-volume aspiration resulted in no detectable bacteriophage, both on non-splatter settle plates and in air samples taken 6 to 10 minutes post-procedure.”

The researchers concluded that the use of HSCAH together with high-volume aspiration or a rubber dam meant that a prolonged fallow period could be avoided. “Equipping our dental surgeries with these tools will be crucial to protecting the health, safety, and future of dental teams and services,” they wrote.

The study, titled “Dental mitigation strategies to reduce aerosolization of SARS-CoV-2”, was published in the Journal of Dental Research in August and can be accessed here.

The results of a number of studies suggest that air purifiers do help to reduce the risk of SARS-CoV-2 transmission in dental settings; however, as the SDCEP review found, the subject requires further study, meaning that owner-dentists may have to personally appraise the literature before a general consensus can be reached.

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