COVID-19: unmasking the facial protection paradigms

Need for robust facial protection in dental practice

The practice of dentistry is rather unique in that the patient cannot be masked during any dental procedure, and the dentist is in extremely close proximity to the oral operative site, which renders both the operator and the assistant highly vulnerable to airborne infection.¹ Even though the rubber dam insertion might provide some degree of protection against aerosolizing oral fluids, many obligatory emergency procedures, such as surgical removal of teeth and drainage of intra-oral abscesses, preclude the use of such a barrier. Moreover, many dental procedures require the use of a handpiece with irrigant coolants, which generate significant virus-infested aerosols that may remain suspended in the air for prolonged periods. Due to these reasons, a high level of facial protection is required in dentistry, such as surgical masks and filtering-facepiece respirators (FFRs), in addition to eye protection, head caps, disposable gowns, shoe covers, and meticulous disinfection of all surfaces between patients, particularly if aerosol generating procedures (AGPs) are performed.

Differences between surgical masks and respirators

We use surgical masks for two main purposes: to keep ourselves safe from aerosols and droplets generated by others, and to keep others safe by keeping our own expellents within the mask confines. To understand the requirements of RPE in dental practice during the COVID-19 pandemic, it is necessary to discuss the two most common types of disposable respiratory-protection gears, namely surgical masks, and the filtering-facepiece respirators (FFRs) (Figures 1 and 2; Table 1).

Surgical masks are loosely fitting masks that are used in the routine patient-care setting when the procedures do not generate a significant degree of aerosols. Medical-grade surgical masks are certified by the ASTM International (previously known as American Society for Testing and Materials) in the US.^2,3 Surgical masks are adequate for keeping droplets ‘in’, but since they are not tightly fitted around the face, they do not protect against leakage from the sides of the masks. They are also effective in protecting the surgical field from droplets generated by the surgical team.

On the other hand, FFRs, such as Filtering Facepieces (FFPs) in Europe, and N95s in the US, are tightly fitted around the face of the wearer and require fit testing (see below) to ensure their efficacy. Respirator masks are designed to filter over 95% of virus-sized pollutant particles in the air, and according to the seal between the FFPs and the skin of the wearer, FFPs are classified on a scale of 1 to 3. For example, FFP3, the currently recommended mode by the UK regulatory bodies (see below), has a total inward leakage (TIL) of 2% or less. While FFPs are regulated by the EN standard in Europe, N95s are regulated by both the National Institute for Occupational Safety and Health (NIOSH) and the Food and Drug Administration (FDA) in the US.⁴ These respirators are effective in keeping droplets in while preventing leakage of aerosols into the masks, however, due to their high filtering capacity, prolonged wearing may make the wearer uncomfortable and out of breath.

So, which type of device for nose and mouth coverage should we choose for protection against airborne infections during routine dentistry in the face of the current pandemic? Although some studies support the use of FFR over surgical masks,⁵ others show either no difference between the two, or ambiguous results.^6-8 Another confounder is that most of the efficacy studies of FFRs are historical, and have been performed in the context of influenza infection. At the time of writing, there is still a dearth of evidence on which type of mask prevents or mitigates the transmission of SARS-CoV-2. However, due to the high-risk nature of our profession that necessitates the use of aerosol generating procedures (AGPs), it behoves us to use a filtering device that has minimum leakage and provides optimal protection. Ideally, therefore, FFRs are the preferred option over surgical masks for dental practice to protect ourselves, our staff, and our patients until, at least, the pandemic abates.

N95 masks and fit tests

Although the most common FFRs are much more efficient and effective in filtering airborne viruses, they have a major drawback relative to the surgical mask and the face shield in that a fit test is required to ensure that they form a tight seal around the wearer's face. According to the British Dental Association (BDA), a fit test is a legal requirement for anyone who wears a close-fitting mask. An N95 mask which is not fit tested may be totally ineffective and may give the user a false sense of security and protection. The law in the UK requires employers to ensure that all RPE at work is adequate and suitable for the wearer, task and environment.⁹

What is a fit test?

A fit test is conducted to verify that a FFR is both comfortable and correctly fits the user. Fit tests are classified as either qualitative or quantitative. A qualitative fit test is a pass/fail test that relies on the individual's sensory detection of a test agent, such as taste, smell, or involuntary cough due to a reaction to irritant smoke. A quantitative fit test, on the other hand, uses an instrument to measure the effectiveness of the respirator numerically.

The benefits of a fit test include better protection for the employee, and verification that the employee is wearing a correctly-fitting model and size of the respirator. In addition to fit testing when initially selecting a respirator, fit testing must usually be repeated annually, and whenever an employee changes his/her physical condition that could affect the respirator fit (eg facial scarring, dental changes, cosmetic surgery, or an obvious change in body weight). A fit test should always be conducted by a competent person.

A successful fit test only qualifies an employee to use the specific brand/make/model and size of respirator that he or she wore during that test. Respirator sizing is not standardized across models or brands. For example, a medium in one model may not offer the same fit as a different manufacturer's medium model.

Face shields

While different types of mask can keep the vulnerable mucosa of the respiratory tract relatively safe from the insult of airborne pathogens, the extreme amount of spatter and projectile of bodily fluids generated by dental procedures warrant additional protection of the eyes and face. It is well-known that the average person unconsciously touches the face frequently, and that respiratory viruses have the ability to remain active on surfaces, such as the skin of the hands and face. In our context, direct contact is one of the major modes of SARS-CoV-2 spread, and face shields (Figure 3) mitigate such spread of infection from hands and skin to the mucosa of the eyes, nose and mouth.

Face shields consist of a clear material that acts as a barrier for the face and they are effective against direct spatter and spray of saliva, blood, and irrigation fluids during dental procedures. They are to be used as an adjunct to surgical masks or FFRs, since most face shields are not sealed around the side of the face and are ineffective in protecting against leakage of aerosol from the wide open margins.

The major advantages of face shields are that they are inexpensive, easily fabricated, and reusable after disinfection. Even though evidence is not available regarding the effectiveness of face shields against the SARS-CoV-2 virus, authorities such as the US Centers for Disease Control (CDC) and the American Dental Association recommend the use of face shields in addition to surgical masks and FFRs for routine dentistry.^10-12

Powered air-purifying respirators (PAPRs)

Another type of respirator, which is less well-known among HCWs, is the powered air-purifying respirator (PAPR), which uses a battery-powered blower to force air through a filter, cartridge, or canister into the breathing zone of the wearer, contained by either a loose-fitting hood or helmet, or a tight-fitting facepiece (Figure 4). PAPRs afford less breathing resistance than non-powered respirators and may therefore be more comfortable, and particularly suitable for those working long hours with physical exertion in high-risk areas, and hence they are not particularly common in dental practice. Moreover, most components of a PAPR can be disinfected and reused. However, some of the drawbacks of PAPR include its high cost compared to other facemasks, and special training required for their proper use and disinfection. In addition, the visual field of the wearer might be affected since the downward vertical field of view is limited when wearing a PAPR. Another drawback of PAPR is, due to its design, the simultaneous use of dental loupes or microscopes might not be possible.

Currently, the CDC recognizes that PAPRs provide increased protection and decrease likelihood of infection transmission when compared to other reusable FFRs.¹³ However, clear guidelines regarding the use of PAPRs in dental settings are not yet available, and due to its large size, restriction of field of view and the inability to use some dental equipment simultaneously, the use of PAPRs in dental practice is not currently widespread. Nonetheless, PAPRs are a serious alternative that must be considered in jurisdictions where the COVID-19 prevalence is relatively high.

Current UK and US recommendations

The current recommendations in the UK is to use FFP3 for all AGPs in the dental office. ADA has also considered the issue of asymptomatic patients unknowingly treated by the dental profession during the COVID-19 pandemic, as up to 40% of them could present without symptoms.¹¹ Due to the risk of SARS-CoV-2 transmission from the latter group who may attend the clinic, ADA recommends the judicious use of FFRs, such as N95 respirators or equivalent, along with eye protection such as goggles or face shields, in routine dentistry.

Face masks and skin health

Prolonged use of face masks by HCWs can cause various types of skin damage, such as irritation, allergic reactions or pressure sores. When adhesives are used in respirators, the superficial layer of the skin can be removed by the adhesive, causing skin erosion, bullae formation and tearing of skin; this condition is termed medical adhesive-related skin injury (MARSI).¹⁴ Some simple measures can be taken to mitigate such damage, such as keeping the skin moisturized with skin creams, and changing the face mask periodically to prevent prolonged adhesion to the skin. Also, various commercial products are available (eg 3M Cavilon^TM No Sting Barrier Film) to ameliorate such facial infections.

Conclusions

COVID-19 pandemic is evolutionary, dynamic and unceasing. The consensus is that we have to co-exist with SARS-CoV-2 for the foreseeable future. This new ‘normal’ dictates that dentistry has to ‘adapt and adopt’ in order to deliver care to the needy, whilst we ourselves, as care deliverers, take appropriate precautions to obviate cross infection. As the unique nature of dental practice places dental professionals at a very high risk category for contracting infection, the current recommendations support using a high level of facial protection, such as FFP3 or N95 respirators, along with face shields, disposable gowns, head caps and shoe covers, particularly when AGPs are to be performed. While PAPR offers additional protection, their practicality and appositeness are issues that need judicious evaluation, particularly in locales where the disease is raging. Although skin damage is possible with prolonged wearing of face masks, there are simple solutions that can mitigate this issue. Above all, the COVID-19 is a moving target, and the foregoing commentary and recommendations need to be reviewed periodically in light of its evolutionary progress worldwide.