Do FFP3(N99) masks provide more protection in the dental surgery?
I came across this very relevant rapid review about the use of masks in dentistry. The brilliant UK based Dental Elf published it. I thought that it might be helpful if I outlined their review in this short blog post.
I have only changed their text into my blog style. Their message and content remain the same.
Firstly, the authors point out the following:
“The article has not been peer-reviewed; it should not replace individual clinical judgement, and the sources cited should be checked.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”.
As a result, you should treat the findings with a degree of caution. However, they do provide us with some guidance.
What did they ask?
They asked the following simple question.
“How much additional protection does a Class 3 filtering facepiece (FFP) mask offer over an FFP2 mask or a standard fluid-resistant surgical facemask (Type IIR) when worn during aerosol-generating procedures (AGPs) in dentistry”?
As there are differences in the nomenclature of masks between countries. I would like to clarify this.
The N95 mask is equivalent to the FFP2 mask
The N99 is equivalent to the FFP3 mask.
What did they do?
They did a rapid review of the available evidence. Details of their search strategy are in the original paper.
They included observational studies comparing the effect on aerosol and bioaerosol contamination from the use of high-volume aspiration with and without rubber dam. There was no language or date restriction. They searched Ovid (Medline), Scopus (Elsevier) and the Cochrane databases (See Original article).
What did they find?
They found seven studies that fulfilled the inclusion criteria. Three studies related to high volume suction (Harrel et al., 1996; Jacks, 2002; Devker et al., 2012), and four related to the use of rubber dam (Cochran et al., 1989; Samaranayake et al., 1989; Dahlke et al., 2012; Al-Amad et al., 2017). The studies were all moderate to low quality. There was insufficient data for meta-analysis.
High volume suction
Harrel and co-workers (Harrel et al., 1996) looked at the use of high volume suction. They did an in vitro study and used an ultrasonic scaler for 1 minute to generate a dye-containing aerosol. They repeated the experiment ten times. They found that the high-volume evacuator attachment produced a 93% reduction in surface contamination .
Jacks performed a similar in-vitro study resulting in a 90.8% reduction in surface contamination (Jacks, 2002).
There was only one in-vivo study. Devker and co-workers (Devker et al., 2012), cleaned half the mouths of 30 dentate subjects using an ultrasonic scaler as a control and the other half using high volume suction. They recorded bacterial cultures using culture plates that they placed on the operator and patient. They found that when they used the suction, there was an 81% reduction in bacterial culture forming units.
Rubber dam placement
In one study by Cochran (Cochran et al., 1989), They collected microbial data during the preparation and placement of amalgam and composite resin restorations with and without the rubber dam. The use of the rubber dam resulted in a 90% to 98% reduction in microorganisms.
Similarly, Samaranayake (Samaranayake et al., 1989) did an in-vivo study with ten child patients in each arm. The control group had conservative dentistry with high volume suction only. The experimental group had high volume suction with rubber dam isolation. They found that the mean reduction in culture forming units at 1 meter was 87.9% ±10.3 with the rubber dam .
Dahlke conducted an in-vitro study using dye, rubber dam and high-volume suction while preparing the surface of a typodont tooth with a dental handpiece. They repeated the experiment 24 times. They concluded that using a rubber dam resulted in a 33% reduction in surface contamination.
The final study involved 52 senior dental students performing restorative dental treatment with and without a rubber dam (Al-Amad et al., 2017). This produced strange outlier results with an increased level of contamination, which may highlight technique sensitivity.
We put the three components into clinical workflow.
There are three components:
- High-volume suction reduces bioaerosols by about 81% to 90%
- Rubber dam reduces bioaerosols by a further 30% to 90%
- Fluid resistant surgical facemask filter 62% airborne particles
- FFP2 masks filter 94% airborne particles
- FFP3 masks filter 99% of airborne particles
Putting these components together in a clinical environment, a well-trained dental team using high-volume suction, and rubber dam could reduce the bioaerosol by about 99%.
If we take the efficacy of the masks as stated in government guidance and apply it to this reduction, we get an overall decrease in AGPs of 99.62% for the surgical mask, 99.94% for FFP2 masks and 99.99 for FFP3 respectively, with a risk difference (RD) of 0.37% between the surgical mask and FFP3 and a relative risk of 0.996 (See Table 1). With the lower suction efficiency of 81% without the use of rubber dam, this difference would change to 7.03% RD and RR of 0.929.
There was insufficient data to produce confidence intervals.
Table 1. Differences in face mask effectiveness in dental AGP
|Mask Type||Filtration (%)||HVS* only (%)||HVS+ RD (%)||RDiff (%)||RR|
|HVS- High volume suction RD – Rubber Dam RDiff – Risk difference RR – Relative risk|
When we use high volume suction, and a rubber dam during dental AGP procedures, there may be no significant additional benefit in wearing an FFP3/FFP2 or surgical mask.
However, there is a much more significant difference if we reduce the quality of the HVS and do not use a rubber dam. It may be that the moderate benefit of FFP2 and FFP3 masks is lost over time due to functional factors such as movement of the mask or cross-contamination from extended wear compared to changing masks between patients (Greenhalgh et al., 2020).
Where the supply of FFP3 masks might limit the delivery of primary dental care, we will need to consider if the additional benefit is outweighed by the harms of delaying or restricting care to asymptomatic and healthy patients.
Finally, these results are hypothetical and due to the lack of specific studies of virus penetration of facemasks in dentistry are based on surrogate and composite outcomes. There is an urgent need for specific studies to address mask performance in the dental surgery environment.
The Bottom-line answer is:
“From the evidence that we found there would appear to be small additional protection (0.4%) offered by and FFP3/FFP2 masks compared to a surgical facemask during aerosol-generating procedures if we use a combination of high volume suction and rubber dam”.
In the absence of rubber dam, this difference increases to 7%.
I have also included the references that they used, as we hope that you may find them useful. I would like to thank the author for letting me circulate this on my blog.
Since I published this post the British Orthodontic Society have released new guidance on AGPs. It is relevant to this blog post and interfaces nicely. BOS guidance on AGPs.
AL-AMAD, S. H., AWAD, M. A., EDHER, F. M., SHAHRAMIAN, K. & OMRAN, T. A. 2017. The effect of rubber dam on atmospheric bacterial aerosols during restorative dentistry. Journal of infection and public health, 10, 195-200.
BENDAVID, E., MULANEY, B., SOOD, N., SHAH, S., LING, E., BROMLEY-DULFANO, R., LAI, C., WEISSBERG, Z., SAAVEDRA, R. & TEDROW, J. 2020.COVID-19 Antibody Seroprevalence in Santa Clara County, California. medRxiv.
COCHRAN, M. A., MILLER, C. H. & SHELDRAKE, M. A. 1989. The efficacy of the rubber dam as a barrier to the spread of microorganisms during dental treatment. The Journal of the American Dental Association, 119, 141-144.
DAHLKE, W. O., COTTAM, M. R., HERRING, M. C., LEAVITT, J. M., DITMYER, M. M. & WALKER, R. S. 2012. Evaluation of the spatter-reduction effectiveness of two dry-field isolation techniques. J Am Dent Assoc, 143, 1199-204.
DEVKER, N. R., MOHITEY, J., VIBHUTE, A., CHOUHAN, V. S., CHAVAN, P., MALAGI, S. & JOSEPH, R. 2012. A study to evaluate and compare the efficacy of preprocedural mouthrinsing and high volume evacuator attachment alone and in combination in reducing the amount of viable aerosols produced during ultrasonic scaling procedure. The journal of contemporary dental practice, 13,681-9.
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GREENHALGH, T., CHAN, X. H., KHUNTI, K., DURAND-MOREAU, Q., STRAUBE, S., DEVANE, D., TOOMEY, E., IRELAND, E. S. & IRELAND, C. 2020. What is the efficacy of standard face masks compared to respirator masks in preventing COVID-type respiratory illnesses in primary care staff?[Internet]. Oxford, UK: Oxford COVID-19 Evidence Service.
HARREL, S. K., BARNES, J. B. & RIVERA-HIDALGO, F. 1996. Reduction of aerosols produced by ultrasonic scalers. Journal of periodontology, 67, 28-32.
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JACKS, M. E. 2002. A laboratory comparison of evacuation devices on aerosol reduction. Journal of dental hygiene: JDH, 76, 202-206.
KOHN, W. G., COLLINS, A. S., CLEVELAND, J. L., HARTE, J. A., EKLUND, K. J. & MALVITZ, D. M. 2003. Guidelines for infection control in dental health-care settings-2003.
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SAMARANAYAKE, L., REID, J. & EVANS, D. 1989. The efficacy of rubber dam isolation in reducing atmospheric bacterial contamination. ASDC journal of dentistry for children, 56, 442-444.
Emeritus Professor of Orthodontics, University of Manchester, UK.