May 04, 2020

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“The article has not been peer-reviewed; it should not replace individual clinical judgement, and the sources cited should be checked.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.

How much extra protection does an FFP3 mask offer in the dental surgery?

Mark-Steven Howe

Dental Elf

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:

  1. High-volume suction reduces bioaerosols by about 81% to 90%
  2. Rubber dam reduces bioaerosols by a further 30% to 90%
  3. Fluid resistant surgical facemask filter 62% airborne particles
  4. FFP2 masks filter 94% airborne particles
  5. 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
Surgical mask 62 92.78 99.62 6.84 0.931
FFP2 94 98.86 99.94 1.08 0.989
FFP3 99 99.81 99.99 0.18 0.998
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.

BOS guidance

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, CaliforniamedRxiv.

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.

GOV.UK. 2020. COVID-19 ( personal protective equipment (PPE) [Online]. Available: [Accessed 29th April 2020].

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.

HARREL, S. K. & MOLINARI, J. 2004. Aerosols and splatter in dentistry: a brief review of the literature and infection control implications. The Journal of the American Dental Association, 135, 429-437.

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.

LI, R., LEUNG, K., SUN, F. & SAMARANAYAKE, L. 2004. Severe acute respiratory syndrome (SARS) and the GDP. Part II: Implications for GDPsBritish dental journal, 197, 130-134.

LONG, Y., HU, T., LIU, L., CHEN, R., GUO, Q., YANG, L., CHENG, Y., HUANG, J. & DU, L. 2020. Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta-analysisJ Evid Based Med.

OBERG, T. & BROSSEAU, L. M. 2008. Surgical mask filter and fit performanceAm J Infect Control, 36, 276-82.

PARK, M., THWAITES, R. S. & OPENSHAW, P. J. 2020. COVID‐19: Lessons from SARS and MERS. European Journal of Immunology, 50, 308.

RAJGOR, D. D., LEE, M. H., ARCHULETA, S., BAGDASARIAN, N. & QUEK, S. C. 2020. The many estimates of the COVID-19 case fatality rateThe Lancet Infectious Diseases.

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.

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Have your say!

  1. I saw this and thought it was particularly encouraging. However rubber dam is not routinely used in ortho, and I think its use is limited, so I wonder what you think about the applicability to orthodontic procedures? I assume the highest risks would be use of 3-in-1 for bonding procedures, air abrasion, and IPR with a high speed bur, but I’m also concerned about removing large amounts of composite with a slow speed at debond.

  2. I’ve stopped my practice on March 13th when here in Bulgaria a state of emergency was issued. I think that the main problem would be, the risk of contaminated aerosol to get into contact with the next patient. Busy Orthodontic practices are like cinemas, to much people enter the office. The aerosol can flies around for hours and sticks to walls, ceiling. It is wiser to cover the source than to cover ourselves with PPE from different kinds.
    It is really important for me that more contagious aerosol drops where found in the rooms where staff were changing PPE than in patients rooms.
    Stay safe!
    P.S. I may have a working decision of the problem. Will be glad to discuss it by email.

    1. Neeltje van Doremalen, Ph.D, Dylan H. Morris, M.Phil.,Myndi G. Holbrook, B.Sc, Amandine Gamble, Ph.D. at all. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med 2020; 382:1564-1567
    2. Chen N, Zhou M, Dong X, Qu J, Gong F, Han Y, et al. (15 February 2020). “Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study”. The Lancet. 395 (10223): 507–513. doi:10.1016/S0140-6736(20)30211-7. PMC 7135076. PMID 32007143. Archived from the original on 31 January 2020. Retrieved 9 March 2020.

    Currently me and few other friends with specific knowledge and abilities are trying to make this negative chamber concept popular, because we strongly believe in it’s effectiveness.
    The same concept is used here. We have, almost ready for production, single-use wrapping around the shield, which will seal it for ultimate protection, but allowing air to get in from the room for breathing. Aspiration system of the unit, put into the chamber creates the negative pressure to evacuate aerosol and air flows into it through gaps in the sleeves where the hands of the dentist are( in the side panels). Thus contamination out of the chamber can not happen. Of course there are components of the exhausted air such as microorganisms that would be unacceptable to release into the surrounding outdoor environment (indeed, the original purpose of the negative-pressure room), the air outlet must, at a minimum, be located such that it will not expose people or other occupied spaces. The air after the aspiration system must first be filtered or disinfected by ultraviolet irradiation or chemical means before being released to the surrounding outdoor environment. Every office should think about where the aspiration pump outlet is to ensure it does not throw contaminated air in the vicinity. Now we are developing such device. As there are a lot in office vacuum devices with filters available, I am still not convinced that we need to buy another suction device if we already have HVE build in our dental units.

  3. The differences in the masks are not accurately described here. I highly recommend reading this article posted on the CDC site that explains the filtration process in masks, how they are rated and verified.

    “Collection efficiency of surgical mask filters can range from less than 10% to nearly 90% for different manufacturers’ masks when measured using the test parameters for NIOSH certification”…Surgical masks aren’t tested for inward particulate filtration. Level 2/3 have the same particulate filtration efficiency rating, but the PFE is only for outward filtration from clinician towards patient and not for inward filtration from patient to clinician.

    I have not seen any high-quality research that adequately quantifies our risks as orthodontists in contracting COVID-19 from patients after an aerosol generating procedure common in the orthodontic office.

    This was the best explanation I could find for explaining what we know about contagions in aerosols and droplets.

  4. Thank you for posting this, Dr. O’Brien. I wonder what the risk difference would be if we assume the good HVE value of 93% without rubber dam use.

  5. You need to read the paper in context that we generate dental aerosols, not medical aerosols- they are very different. Medical aerosols are airborne body fluids. Dental aerosols are water contaminated by saliva. Hence, the risk is significantly less. Also it is not 100% certain as to transmission by aerosol. The risk to dentists is VERY small indeed

    we know 90+% of dental aerosol is reduced by high speed suction alone, so we are looking at a very small risk. IMHO the BOS guidance is excessive and out of proportion to risk

    we need to see this in proportion

  6. Here’s another paper to bin the idea the N95 mask is better
    JAMA . 2019 Sep 3;322(9):824-833. doi: 10.1001/jama.2019.11645.
    N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial

    Conclusion: “Among outpatient health care personnel, N95 respirators vs medical masks as worn by participants in this trial resulted in no significant difference in the incidence of laboratory-confirmed influenza”

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