The ABCs of Face Shields

In early 2020, the emergence of SARS-CoV-2 led to a pandemic that continues to pose a public health threat throughout the United States and around the world.¹ The US Centers for Disease Control and Prevention (CDC) and the American Dental Hygienists’ Association recommend that oral health professionals “wear a surgical mask, eye protection (goggles or a face shield that covers the front and sides of the face), a gown or protective clothing, and gloves during procedures likely to generate splashing or spattering of blood or other body fluids.”^2,3

COVID-19 has emphasized the importance of protecting the eyes, nose, mouth, and face from bodily fluids. Face shields are classified as personal protective equipment (PPE)⁴ but were not routinely worn in most dental settings prior to the pandemic. The Occupational Safety and Health Administration requires “the PPE selected must be appropriate for the task.”⁵ The Bloodborne Pathogens standard (29 CFR 1910.1030) states: “When splashes, sprays, splatters, or droplets of blood or other potentially infectious materials pose a hazard to the eyes, nose, or mouth, then masks in conjunction with eye protection (such as goggles or glasses with solid side shields) or chin-length face shields must be worn.”⁵ 

Prior to the pandemic, the American National Standards Institute (ANSI) and the International Safety Equipment Association (ISEA) did not have universal standards for design, testing, manufacturing, or performance of face and eye protection, including face shields from biological hazards.⁴ The pandemic highlighted the need to develop standards for eye and face protection for ­high- risk occupations. As such, the ANSI/​ISEA Z87.62-2021 provides a set of requirements regarding the safety and effectiveness of face shields.⁶

Face shields provide a barrier and some protection from direct splashes and splatters; however, they do not protect the wearer from small airborne particles.^1,3,4 A medical/​surgical face mask and eye protection must be worn in addition to a face shield during aerosol-producing dental procedures.^4,5,7 

Evidence-Based Findings

The COVID-19 pandemic spurred an interest in research on aerosols, fluid dynamics, and the effectiveness of PPE. Thus, recent studies have greatly improved the understanding of how airborne particles behave during a variety of circumstances. Oral health professionals need to become familiar with this body of knowledge so they can choose the most effective face shield for their circumstances. 

In a simulation of a patient coughing, Lindsley et al⁸ found the face shields tested were able to decrease exposure of large particles by 96% immediately following a cough. When small aerosolized particles were produced, however, the face shield demonstrated a 68% effectiveness. Large droplets settled more quickly than small particles because small aerosols are suspended in the air for longer time periods, and the distance aerosolized particles travel reduces the level of protection provided by face shields. The researchers determined face shields may serve as an adjunct to reduce exposure to respiratory infections. 

Salimnia et al⁹ compared and contrasted the levels of protection provided by face masks and face shields by simulating talking and exhaling via an aerosol-generating system. They determined a face shield alone did not provide protection during the simulated bacterial transmission. Surgical masks alone provided “good” protection. Interestingly, this study did not find the combination of a mask and face shield offered a significantly higher level of protection than the surgical mask alone. The authors did note, however, a mask and shield provided the best protection. 

Ronan et al¹⁰ investigated face shields as a substitute for surgical masks using a simulator and an airbrush diffuser to simulate a cough. As expected, researchers found higher levels of contamination to the cheek and neck regions closer to the periphery of the shield. Face shields designed with extended coverage below the chin (height = 29.5 cm) and covering the entire side of the face (width = 40.0 cm) may improve the efficacy of blocking particles. 

Samaranayake et al¹ conducted a systematic review that included 21 studies evaluating the effectiveness of face masks, respirators, and protective eyewear. Only one of the studies took place in a dental setting during aerosol-generating procedures.¹¹ Aerosol contamination was measured on blood agar plates placed around the headrest of two patients. The clinician’s masks, gowns, and head caps were also tested for microbes. Their findings concluded face shields were inferior to masks in preventing penetration of aerosols due to openings around the shields. Twelve of the reviewed studies used a simulated model and/​or laboratory-controlled settings. Simulated models and lab simulations do not necessarily replicate the environment or circumstances of actual dental procedures in clinic settings.

The other eight studies in the systematic review tested mask and respirator contamination but did not include the effectiveness of face shields. Samaranayake et al¹ concluded that a combination of eye protection and face shields in addition to masks and/​or respirators provided the best protection against aerosol-generated bacteria transmission. Most of the studies were conducted using manikins in an upright face-to-face or side-facing position rather than in a supine position. A supine position may significantly change the direction of air flow from a patient during dental procedures and, therefore, must be considered when selecting a face shield. 

Design and Structure

ANSI/​ISEA administers the standards for design, performance, and manufacturing in accordance with Z87.1-2021 for the vast majority of commercial eye and face protection presently used in the US.¹² There is no standard or regulation of face shields in dentistry; the majority are purchased and distributed through dental supply companies.² 

A face shield has three basic components: frame, visor, and suspension system.⁴ When choosing a frame, also referred to as headgear, several factors should be considered including durability, weight, and adjustability.⁴ To support comfort, a lightweight durable plastic is usually best. Frames can be adjustable or nonadjustable to accommodate personal eyewear, loupes, and/​or a head light, and fully or partially encircle the circumference of the head (Figure 1). Some allow for detachable visors for easy replacement. The CDC recommends that face shields should be easily wipeable with a disinfecting wipe, or washable with soap and water.² Frames can now be custom made to fit an individual’s head with a three-dimensional (3D) scan and then 3D printed.¹³ 

Visors, or windows are generally attached to the frame and can be removable or fixed. Made from a variety of materials including polycarbonate, cellulose acetate, polyvinyl chloride, and polyethylene terephthalate glycol, visors come in several widths, lengths, and strengths.¹⁴ Most medical and dental visors are made from acetate, as it provides the best clarity and tends to be the most scratch resistant when cleaned multiple times daily. The longevity of the visor can be extended by treating it with anti-glare, anti-fogging ultraviolet light and scratch-resistant coatings.

A suspension system is the mechanical interaction of springs and shock absorbers that interlock a device. A suspension system can fully or partially encompass the head or neck. An elastic band, ratchet adjusting plastic headband, Velcro, or pin-lock systems are some of the circumferential suspension systems on the market.⁴ Eyeglass attachments or a neck brace may be included in partially circumferential suspension systems. Foam or Styrofoam (Figure 2) is placed on the interior forehead area for comfort and absorption on many systems.

Selection and Proper Use 

Choosing a face shield and using it properly depend on the indication of use and the anticipated risks of a procedure. Currently, the CDC does not have a recommendation or requirement for face shields in the dental office, only protective eye wear of which a face shield qualifies.² Aerosols, splashes, and sprays can flow around the shield, therefore a face shield should never function as the primary source of respiratory protection and should always be used in combination with a protective face mask.² While thickness is not a major consideration, length, design, and aerodynamics of the shield are. The shield should extend to the ear, below the chin, and cover the forehead to ensure maximum protection from infectious particles (Figure 2 through Figure 5).^2,4

When choosing a face shield, the type of airflow created should be considered. Viola et al¹⁵ conducted a study on the airflow generated by a cough during extubation of a patient in a supine position with the clinician in the 12 o’clock position. Their findings concluded that when the clinician positioned his or her hands for the procedure directly in the particle airflow, the hand interference dispersed airflow upward toward the chin of the clinician. As such, a face shield would have to cover under the clinician’s chin to minimize the risk of exposure to the direct cough. Therefore, the directionality of the airflow must be a design consideration when choosing a face shield (Figure 6).

Suspension of air-generated particles is another important consideration when choosing a face shield. A systematic review by Innes et al¹⁶ found particles that remained in the air for 2 hours to 6 hours depending on the specific aerosol-generating procedure. Therefore, a commercial heavy-duty face shield, like the one tested by Viola et al,¹⁵ with protection and coverage below the chin, over the head, and extending past the ears improved protection (Figure 4).   

Roberage⁴ noted advantages and disadvantages of face shields in relation to other PPE. Some of the advantages noted were:

• Covered a larger portion of the face
• Ability to wear with other eye and face PPE
• Provided protection from touching and potentially contaminating a mask and facial structures
• Ability to easily disinfect
• Relatively inexpensive

Disadvantages included fogging and glare that can interfere with visual clarity. 

Conclusion

Face shields vary in design, function, and effectiveness. they can serve as an effective barrier and may be indicated for procedures that create large particles and droplets but are less effective at offering protection from small airborne aerosols. Face shields serve as an adjunct and should not be used as a substitute for effective respiratory and eye protection. Achieving the highest levels of protection against COVID-19 and other respiratory diseases necessitates wearing goggles, face mask or respirator, and/​or a face shield that provides protection from the transmission of potentially infectious particles to the facial area. Additional well-designed controlled studies that mimic real-life dental procedures are needed to determine the most effective PPE to ensure oral health professionals are protected from the transmission of disease. 

References

1. Samaranayake LP, Fakhuruddin KS, Ngo HC, Chang JWW, Panduwawala C. The effectiveness of respiratory protective equipment (RPE) in dentistry and other health care settings: a systematic review. Acta Odontol Scand. 2020;78:626–639.
2. United States Centers for Disease Control and Prevention. Guidance for Dental Settings. Available at: cdc.g/​v/​coronavirus/​2019-ncov/​hcp/​dental-settings.html. Accessed December 21, 2021.
3. American Dental Hygienists’ Association. ADHA Interim Guidance on Returning to Work. Available at: adha.org/​resources-docs/​AD_​A_​TaskForceReport.pdf. Accessed December 21, 2021.
4. Roberage RJ. Face shields for infection control: a reviewJ J Occup Environ Hyg. 2016;13: 235–242. 
5. Occupational Safety and Health Association. Personal Protective Equipment (PPE) Reduces Exposure to Bloodborne Pathogens. Available at: osha.gov/​sites/​default/​files/​publications/​bbfact03.pdf. Accessed December 21, 2021.
6. International Safety Equipment Association. ANSI/​ISEA Z87.62-2021. Available at: safetyequipment.org/​product/​ansi-isea-z87-62-2021/​. Accessed December 21, 2021.
7. Kohn WG, Collins AS, Cleveland JL, et al. Guidelines for infection control in dental health-care settings—2003. MMWR Recomm Rep. 2003;52(RR-17):1–66.
8. Lindsley WG, Noti JD, Blachere FM, Szalajda JV, Beezhold DH. Efficacy of face shields against cough aerosol droplets from a cough simulator. J Occup Environ Hyg. 2014;11:509–518.
9. Salimnia H, Meyer MP, Mitchell R, et al. A laboratory model demonstrating the protective effects of surgical masks, face shields, and a combination of both in a speaking simulation. Am J Infect Control. 2021;49:409–415. 
10. Ronen A, Rotter H, Elisha S, et al. Investigation of the protection efficacy of face shields against aerosol cough droplets. J Occup Environ Hyg. 2021;18:72–83. 
11. Bentley CD, Burkhart NW, Crawford JJ. Evaluating spatter and aerosol contamination during dental procedures. J Am Dent Assoc. 1994;125:579–584.
12. American Safety Equipment Association. ANSI/​ASEA Z87.1-2020 Standard. Available at: https:/​/​safetyequipment.org/​isea-standards/​ansiisea-z87-accredited-standards-committee/​ansiisea-z87-1-2020standard/​ Accessed December 21, 2021.
13. Zhang PC, Ahmed Y, Hussein IM, et al. Optimization of community-led 3D printing for the production of protective face shields. BMC. 2020;6:2–8. 
14. Grainger. Face Shield Protection. Available at: grainger.com/​know-how/​safety/​ppe-in-the-workplace/​eye-face-protection/​kh-face-shield-protection-373-qt. Accessed December 21, 2021.
15. Viola IM, Peterson B, Pisetta G, et al. Face coverings, aerosols dispersion and mitigation of virus transmission risk. IEEE Open Journal of Engineering in Medicine and Biology. January 30, 2021.
16. Innes N, Johnson IG, Al-Yaseen, et al. A systematic review of droplet and aerosol generation in dentistry. J Dent. 2021;105(103556):1–13. 

From Dimensions of Dental Hygiene. January 2022;20(1):14-17.