Behind the mask

The objective is to choose a mask that filters the most pathogens. So many choices for masks, though, make it harder to choose the best mask for our own individual needs.

Sep 1st, 2004
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by Elizabeth Hughes, RDH, BS, MS, and Charles John Palenik, MS, PhD, MBA

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We cannot protect ourselves from microorganisms everywhere we go and still function in modern society. However, we can protect ourselves while in our work environment. One of the most efficacious means available to reduce our exposure is to choose a mask that filters the most pathogens. But with so many choices, how do we choose the best mask for our own individual needs?

In December 2003, the Centers for Disease Control and Prevention issued new infection-control recommendations for dentistry (www.cdc.gov/mmwr/preview/ mmwrhtml/rr5217a1.htm). These recommendations updated those made in 1993.

The guidelines consolidate recommendations for preventing and controlling infectious diseases and managing personnel health and safety concerns related to infection control within dental settings. The guidelines introduce a number of new or significantly revised infection-control and prevention issues. One of these issues is the selection and proper wearing of masks. The CDC recommends that a surgical mask and eye protection with solid side shields or a face shield be worn to protect mucous membranes of the eyes, nose, and mouth during dental procedures likely to generate splashing or spattering of blood or other body fluids.

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Wearing masks that cover both the mouth and the nose during surgical procedures has been a routine procedure for almost 90 years. Today, masks are also commonly worn during nonsurgical medical procedures, which is especially valid when airborne-spread diseases are present within a population.

Protecting the practitioner

Originally, masks were developed to reduce the chances of postoperative infections in patients that are caused by microorganisms in the respiratory tracts of the surgical team. Although there is some controversy as to the effectiveness of masks to reduce postsurgical infections, they are considered standard during surgery or when respiratory microorganisms are a concern.

In recent years, facemasks have also been viewed as an important means to protect health-care workers (HCW) from potential respiratory disease agents. The primary source of such pathogens is the patient. Sprays, splashes, and some aerosols of body fluids and other potentially infectious materials can be involved. Speaking, coughing, and sneezing also release organisms into the immediate environment. The masks usually worn in dental practices are less protective against the inhalation of aerosolized particles of oral fluids. This is due to mask design and fabrication and to the movement patterns in and out of the mask. Even under the best of circumstances leakage can occur during inhalation and while exhaling. Protection against airborne infection requires the use of a respirator (N-95 respirator, for example). Such masks are designed to push all inhaled air through the filter, rather than around the edges. Respirators are more uncomfortable to wear, especially for extended periods, such as in dental practice. They are not usually needed to practice dentistry.

Surgical masks are primarily worn to protect the practitioner. The level of protection afforded the patient is not easily measured and may be minimal.

The most effective method of protection employs engineering and work-practice controls. Control examples include processes that assure routine emission of acceptable dental unit water, use of rubber dams and high-volume evacuation, and the application of preprocedural mouth rinses.

If occupational risk remains after institution of engineering and work-practice controls, personal protective equipment (PPE) should also be used. The employer is required to provide PPE at no cost to the employee. Masks are considered "appropriate" PPE only if they do not permit blood and other potentially infectious materials to pass through to or reach skin or the mucous membranes of the nose and mouth. Protection can only be expected under normal conditions of use and for the duration of time for which a mask was designed. Various performance expectations require different types of masks.

Under OSHA standards, the employer must ensure that employees use appropriate PPE correctly. PPE — in this case, masks — is required to be readily accessible in the correct sizes and proper types for the hazards present.

About masks

The Food and Drug Administration is responsible for regulating medical devices. Surgical masks are examples of regulated FDA medical devices. (See Table 1 for the characteristics used to describe surgical masks.) Surgical masks are primarily tested in laboratory situations, not in actual clinical use on HCW.

Surgical masks are disposable and composed of multiple layers of synthetic (microfiber) filter materials designed to collect and retain microscopic particles. The minimum goal is to filter out at least 95 percent of small particles that directly contact the mask. This level of function is thought to be protective.

In 1995, the National Institute for Occupational Safety and Health (NIOSH) began to certify three classes of filters — N, R, and P series (resistant to the penetration of oily substances) — each with three levels of filter efficiency (95 percent, 99 percent and 99.9 percent). NIOSH, a part of the CDC in the Department of Human Health and Safety, is the federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness.

Masks come in a variety of shapes and sizes. Some masks are preformed domes, while others are more pliable. Masks are secured to the user by elastic bands, ear loops, or some type of tie. Most masks are form-fitted over the bridge of the nose and cheeks to reduce fogging by warm expelled air.

Using masks

Bacterial filtration efficiency (BFE) and Particulate filtration efficiency (PFE) values are important. BFE measures the filtering of bacteria that range in size from one to five microns (micrometers. µm). Microns are one thousandth of a millimeter, or 10-6 meters. PFE measures much smaller (0.1 to 1.0 micron) particulate (nonviable) matter. When considering a surgical mask, BFE and PFE values (percent retained) and the size of the particle upon which the values are based are important. To have the proper mask for a given application, several different types and sizes of masks must be available.

Even with high filtering efficiency, some inhaled and/or exhaled air can pass unfiltered around the edges of the mask. The greater the edge leakage of a mask, the lower the actual, in-use BFE and PFE values will be. The bottom line is that a mask is only as good as it fits. To accommodate the fit of several sizes and shapes of faces, more than one type and size of surgical facemask should be present in the dental practice.

Breathability, or Delta P, measures the pressure drop across a facemask. The higher the Delta P values, the more difficult the mask is to breathe through. People with breathing difficulties should use masks with lower Delta P values.

Fluid resistance measures a facemask's ability to minimize fluids traveling through the material. The greater the fluid resistance of a mask, the lower the potential exposure to blood and body fluids caused by splashes, spray, and spatter. Surgical masks are available with fluid-resistant outer layers and tissue inner layers or fluid-resistant outer and inner layers. Selection as to fluid resistance is influenced by the procedures being conducted and personal preference.

A surgical-type mask — with >95 percent bacterial filtration efficiency — should be used for the vast majority of dental procedures. Such masks are sufficiently protective against aerosols and large-droplet spatter.

Masks are to be changed after every 20 minutes of heavy exposure to fluids or after an hour of normal use. As they become wetter, masks become less effective. Surgical masks are considered to be single-use, disposable items and should be discarded after each patient treatment. Remove masks by touching only the ties, bands, or loops.

Regulations and recommendations

OSHA requires that masks in combination with eye-protection devices — such as goggles or spectacles with solid shields, or full-length face shields — be worn whenever splashes, spray, spatter, or droplets of blood or other potentially infectious materials may be generated and when eye, nose, or mouth contamination can be reasonably anticipated.

The new CDC Infection-Control Guidelines also address the issue of masks. The CDC recommends that a surgical mask and eye protection with solid side shields or a face shield be worn to protect the mucous membranes of the eyes, nose, and mouth during dental procedures likely to generate splashing or spattering of blood or other body fluids.

Adverse reactions

Wearing surgical masks is not without risk. Masks can irritate facial skin by friction/rubbing. Facemask material coloring (dyes) and printing can also cause irritation or even hypersensitivity. Those with sensitive skin may be better served through the use of masks with white outer layers and white, nonprinted inner layers.

Materials used to fabricate surgical masks can also cause hypersensitivities. Latex substances, including adhesives containing latex, may be present. The metal strip or bar used to better fit a mask to a user's face can be problematic. In a limited number of cases, metals can be released and cause difficulties.

Tuberculosis

When airborne infection-control precautions are necessary (for example, for tuberculosis patients), a NIOSH-certified particulate-filter respirator (for example, N95, N99, or N99.97) should be used. N95 refers to the ability of a filter to retain one-micron particles in an unloaded state with a filter efficiency of >95 percent (with a 5 percent leakage). The flow rate assumed is ≤50 liters/minute, which is thought to be the maximum airflow rate produced by a health-care worker during breathing. Current research indicates that the nuclei of infectious droplets measure between one and five microns. When properly tested and fitted correctly, N95 respirators should be adequate for the situation.

The majority of the surgical masks used in dentistry are not NIOSH certified respirators. Wearing such masks may not adequately protect the wearer fromexposure to TB, especially if the fit is not proper. Such masksdo not meet OSHA requirements for respiratory protection against known cases of TB. However, there are some surgical masks (surgical N95 respirators) that do meet the requirement and are certified as being respirators by NIOSH.

Fortunately, N95 respirators are not often required. Detailed information regarding airborne-transmission precautions and respirator programs, including fit-test procedures, are available at www.cdc.gov/ niosh/99-143.html.

The Organization for Safety and Asepsis Procedures recently published "From Policy to Practice: OSAP's Guide to the Guidelines." This workbook is designed to help dental practices better understand the recommendations and identify effective, efficient methods for implementation.

More information can be obtained at www.osap.org or by calling (800) 298-6727.

Elizabeth Hughes, RDH, MS, is a full-time faculty member of Indiana University School of Dentistry in the Periodontics and Allied Dental Programs. Charles John Palenik, MS, PhD, MBA, is an assistant director of Infection Control Research and Services at the Indiana University School of Dentistry. Dr. Palenik has authored numerous articles, book chapters, and monographs, and is the co-author of the popular Infection Control and Management of Hazardous Materials for the Dental Team. He serves on the Executive Board of OSAP, dentistry's resource for infection control and safety. Questions about this article or any infection-control issue may be directed to office@osap.org.

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