Question:
How effective are free-standing clean air systems in dental practice?
Bottom-line:
As with many of the rapid reviews and studies available regarding Covid-19 there is no direct evidence of the benefits of free-standing clean air systems in dental practice. Indirect evidence suggests a small but non-significant benefit that might easily by outweighed by their functionality in a working environment.
Discussion
From the available peer reviewed literature there are two types of air cleaning systems, both mostly a Class 13 high efficiency particulate air (HEPA) filter which can remove 99.95% of particulates. The first are free standing directional units that are large high-volume suction units placed about 1 m from the dental team (Hallier et al., 2010; Yamada et al., 2011). Both units reduced bacterial counts by about 30%. It should be noted that in the Hallier and co-workers paper there was no statistical differences in bacterial counts created prior to the clean air system being activated between, history and examination, ultrasonic scaling with high volume suction (HVS), and tooth extraction. Cavity preparation was an outlier, the authors did not mention the use of HVS during this procedure unlike the scaling, as the bacterial count dropped by approximately 80% it suggests the use of normal HVS might be the significant factor here.
Table 1. Summary Estimate for systematic reviews
| Systematic review | Study type | Effect size | 95%Confidence interval |
| McDonald et al 2002 | RCTs (4) | WMD = -0.76 | -2.17 to 0.65 |
| Eckmanns et al 2006 | RCTs (6) | RR = 0.86 | 0.65 to1.14 |
| Eckmanns et al 2006 | Non-RCTs (4) | RR = 0.87 | 0.60 to 1.25 |
RR – relative risk WMD – weighted mean difference
The second type of clean air system acts as a general air filter. There are two systematic reviews available, Eckmanns looked at mortality in highly immunosuppressed patients, and McDonald looked at asthma symptoms (Eckmanns et al., 2006; McDonald et al., 2002). The overall summary estimate for both reviews weakly favoured the use of HEPA filters, but the results were not statistically significant using a random effects model (See Table 1).
There is no direct evidence regarding UVC in air filters being able to kill Covid-19 (Narla et al., 2020; Shirbandi et al., 2020).
Disclaimer: The article has not been peer-reviewed; it should not replace individual clinical judgement, and the sources cited should be checked. The views expressed in this commentary represent the views of the author and not necessarily those of the host institution. The views are not a substitute for professional advice.
References
ECKMANNS, T., RÜDEN, H. & GASTMEIER, P. 2006. The influence of high-efficiency particulate air filtration on mortality and fungal infection among highly immunosuppressed patients: a systematic review. The Journal of infectious diseases, 193, 1408-1418.
HALLIER, C., WILLIAMS, D. W., POTTS, A. J. C. & LEWIS, M. A. O. 2010. A pilot study of bioaerosol reduction using an air cleaning system during dental procedures. British Dental Journal, 209.
MCDONALD, E., COOK, D., NEWMAN, T., GRIFFITH, L., COX, G. & GUYATT, G. 2002. Effect of air filtration systems on asthma: a systematic review of randomized trials. Chest, 122, 1535-42.
NARLA, S., LYONS, A. B., KOHLI, I., TORRES, A. E., PARKS‐MILLER, A., OZOG, D. M., HAMZAVI, I. H. & LIM, H. W. 2020. The Importance of the Minimum Dosage Necessary for UVC Decontamination of N95 Respirators during the COVID‐19 Pandemic. Photodermatology, Photoimmunology & Photomedicine.
SHIRBANDI, K., BARGHANDAN, S., MOBINFAR, O. & RAHIM, F. 2020. Inactivation of Coronavirus with Ultraviolet Irradiation: What? How? Why?
YAMADA, H., ISHIHAMA, K., YASUDA, K., HASUMI-NAKAYAMA, Y., SHIMOJI, S. & FURUSAWA, K. 2011. Aerial dispersal of blood-contaminated aerosols during dental procedures. Quintessence international (Berlin, Germany : 1985), 42, 399-405.
Picture Credits
