PPE: The Last Line of Defense: A Review of Hierarchy of Controls and Precaution Levels in the Dental Setting

The goal of any infection control program in the dental setting is to prevent disease transmission, eliminate cross-contamination, and minimize exposure to infectious diseases. To mitigate these risks, it is important to identify potential hazards before treatment to ensure the health and safety of dental healthcare personnel (DHCP). The Centers for Disease Control and Prevention (CDC) recommends using a hierarchy of controls. The hierarchy of controls provides a framework to systematically identify workplace hazards while providing guidance on how to control and remove the hazards from the workplace.¹ The hierarchy of controls categorizes and prioritizes intervention strategies to control occupational exposure to infections while offering layers of protection for DHCP. The hierarchy is designed so that feasible and effective control measures can be implemented in order of preference. The control measures are ranked beginning with the most reliable and effective and ending with those that rely on correct and consistent use and consequently are least effective (Figure 1).² The hierarchy of controls from most effective to least effective consists of elimination, substitution, engineering controls, administrative controls, workplace controls, and personal protective equipment (PPE).³

Elimination is the first and most effective level of control because it removes the risk completely; it involves physically removing the hazard.³ Hazards can be eliminated by re-designing work processes. Although elimination is the most effective control measure, it is also the most difficult to implement due in part to the upfront costs of making changes to daily operations.³ After the focus shifts to long-term savings, elimination becomes a viable option.³

Substitution is similar to elimination in that the goal is to remove the risk; however, with substitution, the hazard is replaced. Although the procedures for elimination and substitution are inherently similar, elimination examines action whereas substitution assesses products and chemicals.⁴ Substitution, like elimination, is often met with resistance because safer alternatives can be more expensive than their hazardous counterparts.⁴ Before implementing elimination or substitution measures, it is prudent for DHCP to invest time in researching the best alternatives.⁴

When elimination and substitution control measures are not practical, the next best approach is the implementation of engineering controls. Engineering controls are achieved by mechanical means and involve isolating the individual from the hazard or placing a barrier between the individual and the hazard.⁵ Commonly, there is a physical change to the work environment when engineering controls are implemented.⁶ Engineering controls that prevent hazards from reaching DHCP include the use of sharps containers, instrument cassettes, or ventilation systems that remove contaminants from the air before they can be inhaled.⁷ Current CDC guidelines recommend placing a patient with suspected or confirmed illnesses such as SARS-CoV-2 infection in a single-person room with the door kept closed whenever possible.⁸ When SARS-CoV-2 community transmission levels are high, the CDC recommends limiting patient volume in the office.

Administrative controls involve policy changes and help to ensure efficient processes and procedures.⁶ These measures change the way people work or act.⁴ Examples of administrative controls include personal hygiene, isolation, limiting the size of gatherings, social distancing, warning labels, and training.^4,7A recent study published in the International Journal of Oral Science recommends 1% hydrogen peroxide or 0.2% povidone iodine for a preprocedural mouthrinse.⁹ There are advantages and disadvantages to implementing administrative control measures. Administrative controls can be instituted more readily and used until more effective control measures can be implemented. Yet administrative control measures rely heavily on compliance to be effective, and it is rare to achieve perfect compliance.⁴

Workplace controls and PPE are the least effective control measures. Workplace controls are daily procedures that result in safer behaviors; they include measures such as handwashing and one-handed needle capping. According to the Occupational Safety and Health Administration (OSHA), PPE should be considered the last line of defense against worker injury and illness because it is the least effective.¹⁰However, it is usually the main focus of infection control protocols because, similar to administrative controls, PPE can be easily implemented when available.⁴ PPE includes gloves, face shields, goggles, fluid-resistant gowns, and surgical caps. It should be noted that simply donning PPE is not sufficient. DHCP must be trained on several aspects of PPE, including when to use it, how to don and doff, when to replace it, and how to store and dispose of it.¹⁰

When using the hierarchy of controls, eliminating the hazard is the ultimate goal. When elimination is not possible or feasible, lower levels of control measures can be applied. The higher levels of control are more effective and protective, whereas lower-level controls have a greater risk of illness or injury. Following the hierarchy of controls usually helps to implement safe infection control systems that reduce the risk of illness or injury for DHCP.³

Precaution Levels

Infection control practices are designed to protect DHCP and prevent the spread of infectious diseases among patients.¹¹Various levels of precautions have been developed to provide high levels of protection for healthcare providers and their patients. These precautions are the preemptive steps that must be taken by the healthcare team member to prevent the spread of infection and minimize exposure.¹² In 1985, amid the outbreak of the HIV epidemic, the CDC introduced universal precautions.¹³Universal precautions are a set of infection control techniques to prevent the transmission of bloodborne pathogens through exposure to blood and other bodily fluids known to contain infectious materials.^13,14 Examples of these techniques include hand hygiene, aseptic techniques, donning of PPE, and the use of barriers. Shortly after the introduction of universal precautions, in 1987 the CDC introduced body substance isolation guidelines, which promoted avoidance of all potentially infectious body substances even in the absence of blood.¹³ These guidelines, however, only required healthcare professionals to wash their hands after removing gloves if they were visibly soiled.¹³ In 1996, the CDC combined the major features of universal precautions and body substance isolation to form current standard precautions.¹³ At that time, guidelines were also introduced for transmission-based precautions, which include three subcategories: airborne, droplet, and contact.¹³

Standard Precautions

Standard precautions are minimum infection control practices that apply to the care of all patients, regardless of their disease state. They apply when there is a risk of exposure to the following: blood; body fluids and excretions (except sweat), whether or not they contain visible blood; non-intact skin; and mucous membranes.^13,14 Standard precautions consist of the following practices: hand hygiene before and after patient contact, respiratory hygiene/cough etiquette, aseptic technique/safe injection practices, sharps safety, the use of PPE, routine cleaning and disinfecting of environmental surfaces, reprocessing reusable instruments, and waste management.^11,15 Considering the COVID-19 outbreak, it is prudent for DHCP to understand that standard precautions alone will not protect against transmission of the virus.¹⁶ The spread of COVID-19 in the dental setting can be facilitated by the following: close personal contact, usually within 6 feet, of an infected individual; droplets produced by the respiratory tract when an individual coughs or sneezes; droplets generated from procedures that create aerosols; and contaminated surfaces.¹⁷ In addition to standard precautions, DHCP must implement transmission-based precautions.

Transmission-Based Precautions

Transmission-based precautions are the second tier of current basic infection control principles. They should be used in conjunction with standard precautions when standard precautions are not sufficient to interrupt routes of transmission.^13,15,18,19 Transmission-based precautions are concerned with the following: patient contact (direct and indirect), droplets, and aerosols.¹²They are dependent on the source of the infection, type of infection, and how the infectious organism is transmitted.^12,20

Contact precautions should be used when patients have known or suspected infections or colonization that can be spread through direct or indirect physical contact with items or surfaces in the patient's environment.^12,13 Current guidelines recommend placing patients in a single room if available and limiting movement of patients within the treatment setting.¹⁸Hand hygiene must be performed by DHCP before entering and leaving the treatment room.²¹ DHCP must put on gloves before entering the room and wear appropriate PPE, especially when providing treatment that potentially involves contact with patients and their immediate environment.¹⁸ To minimize cross-contamination, all PPE must be disposed of by DHCP before they leave the treatment room.¹⁸ Last, the patient treatment room must be properly cleaned and disinfected along with any equipment used during patient care that cannot be disposed of.¹⁸

Droplet precautions should be used for patients with known or suspected pathogens that are transmitted by respiratory droplets.¹⁸ Transmission is associated with exposure to pathogenic droplets generated by coughing, sneezing, or talking within 3 to 6 feet of the source.^12,13,18 Droplet precautions incorporate some of the same guidelines that are used for contact precautions. Current guidelines also recommend that DHCP cover their eyes, nose, and mouth before entering the treatment room, placing masks on patients when they are not receiving treatment, and instructing patients to follow cough etiquette.^18,22,23

Airborne precautions should be used for patients with known or suspected pathogens that can be transmitted through the air, such as aerosols or dust particles containing infectious material.^9,10,13 Like droplet precautions, airborne precautions follow guidelines similar to contact precautions. Current recommendations for airborne precautions include placing masks on patients when they are not receiving treatment, placing patients in an airborne infection isolation room (AIIR) or private patient room with a closed door if an AIIR is unavailable, restricting susceptible team members from entering the treatment room, using a fit-tested National Institute for Occupational Safety and Health (NIOSH)-approved N95 or higher-level respirator for team members, and limiting movement of patients.¹⁸ The CDC encourages everyone to remain up to date with all recommended COVID-19 vaccine doses.⁸

Current guidelines also recommend vaccinating susceptible individuals immediately after unprotected contact with vaccine-preventable infections.¹⁸

Each precaution category will require DHCP to don and doff specific PPE and treat the patient according to specific guidelines. Printable signs for contact, droplet, and airborne precautions are available for DHCP to place outside treatment rooms for guidance and can be retrieved from the CDC website (Figure 2 through Figure 4).^21,22,24

Personal Protective Equipment

When performing procedures that result in exposure to pathogenic microorganisms and other potentially infectious material, all DHCP must wear PPE to prevent the risk of disease transmission, minimize exposure to hazards that cause injuries and illnesses, and reduce the risk of occupational exposure.^23,25 PPE must be worn to protect the skin and mucous membranes and respiratory epithelium of DHCP from exposure to pathogenic organisms and infectious materials by contact, droplet, and respiratory transmission. PPE should be designed to fit comfortably and securely to ensure the worker is safely covered and not exposed.²⁵ Under normal conditions of use and for the duration of time it is used, PPE should not permit the passage of blood, fluid, or other potentially infectious material to street clothes (clothes worn from home to the clinical setting), undergarments, skin, or mucous membranes.²³ PPE for DHCP may include gloves, masks, particulate filter respirators, eyewear, face shields, surgical caps, ear plugs, and fluid-resistant gowns.²⁶

Nonsurgical, surgical, or heavy-duty utility gloves should be worn by DHCP, depending on the task, to prevent the hands from becoming contaminated with blood or other infectious fluids and to eliminate cross-contamination in the clinic.²³ DHCP must perform hand hygiene before donning and doffing gloves.

Surgical masks should also be worn by DHCP during all clinical activities that produce splatter and aerosols. The American Society of Testing and Materials is an organization that establishes the criteria for mask performance and use in the healthcare setting. Five standards are used to test the qualities of facemasks: fluid penetration resistance, bacterial filtration efficiency (BFE), sub-micron particulate filtration efficiency (PFE), differential pressure (delta P), and flammability.²⁶ These tests help to cate-gorize masks as low barrier, moderate barrier, and high barrier, or level 1, level 2, and level 3, respectively. Fluid penetration resistance refers to the ability of the mask to minimize the transfer of fluid from the outer to the inner layers. BFE measures the effectiveness of the mask to filter bacteria.²⁶ Sub-micron PFE refers to the ability of a mask to filter aerosols.²⁶ Delta P determines the breathability of a mask, and flammability determines the likelihood of a material demonstrating higher than normal flammability properties.²⁶ Surgical masks should cover the nose and mouth without any gaps and have a filtration efficiency of at least 95%. Masks must be changed if they become contaminated from exhaled air, droplets, spray, or touching from contaminated fingers between patients or during patient treatment.²³

Particulate filter respirators should be worn when airborne precautions are necessary because they are designed to protect the respiratory tract and filter particles out of the air for the user.²⁶ The CDC recommends the use of NIOSH-certified particulate respirators. There are seven classes of filters for NIOSH-approved filtering facepiece respirators available.²⁷ NIOSH approves a minimal level of filtration at 95%. There are conflicting guidelines and recommendations concerning the use of respiratory protective equipment.²⁸A systematic review and meta-analysis conducted by Smith et al in 2016 compared level-3 surgical masks and N95 respirators.²⁸ The meta-analysis review revealed insufficient data to state conclusively that N95 respirators were superior to level-3 surgical masks in protecting against transmission of acute respiratory infections.²⁸ Data analyzed from the systematic review showed that the use of N95 respirators, when compared with level-3 surgical masks, did not associate a lower risk of laboratory-confirmed influenza.²⁸ Current interim guidelines recommend the use of respirators rated N95 or higher for all aerosol-generating procedures in the dental setting.¹⁶ In the absence of an N95 respirator, DHCP should don a level-3 surgical mask with a chin-length face shield.^16,29 Reusable respirators must be properly disinfected according to the manufacturer's instruction for use.¹⁶OSHA requires employers to have a respiratory protection program in place with the use of N95 respirators.³⁰

Protective eyewear with side shields should also be worn for any clinical procedure that generates splatter or aerosols and should be cleaned with soap and water between each patient's appointment.²³ These safety glasses should be fabricated with polycarbonate, fit snuggly around the eyes, and have an antifog feature to assist with clarity for vision.³¹ Current guidelines recommend use of a chin-length face shield.²⁹

Gowns should be worn to prevent fluid or splatter from reaching the skin or street clothes. In healthcare, there are several terms for gowns used interchangeably, including surgical gowns, isolation gowns, surgical isolation gowns, nonsurgical gowns, and procedural gowns.³² The Food and Drug Administration (FDA) recognizes gown standards established by the American National Standards Institute/Association of the Advancement of Medical Instrumentation (ANSI/AAMI).³² The ANSI/AAMI has established four barrier protection levels for gowns and recognizes three types of gowns that should be used in healthcare settings: surgical gowns, surgical isolations gowns, and nonsurgical gowns.³² DHCP should select a gown that carries a label describing the intended use with the desired level of protection based on the four risk levels established by ANSI/AAMI.³² Gowns should be long sleeved, be cuffed at the wrists, cover the knees, cover the neck, and tie in the back to offer the highest protection for DHCP.³² Current guidelines recommend DHCP don a clean isolation gown when entering the patient treatment area and remove it before leaving.¹⁶ After each use, disposable gowns should be discarded and cloth gowns should be laundered.¹⁶If a gown becomes soiled during a procedure, it should be changed.²³

It is essential that DHCP use PPE appropriately, based on risk of exposure (due to the type of activity being performed) and transmission category, whether contact, droplet, or aerosol.³³ DHCP should understand which PPE they need to wear, when they need to wear it, and why. Having this knowledge will offer the greatest level of protection and help to prevent the spread of disease within the office. The donning and doffing sequences for PPE are equally important. There is more than one acceptable method to don and doff PPE (Figure 5). The CDC provides the following on the donning sequence^34,35:

1. Identify and gather the proper PPE.

2. Perform hand hygiene.

3. Put on an isolation gown.

4. Put on a surgical mask or NIOSH-approved N95 or higher filtering facepiece respirator.

5. Put on a face shield or goggles.

6. Perform hand hygiene before putting on gloves.

Basic hand hygiene must be performed before donning and doffing PPE. If redonning, DHCP can use an alcohol-based hand rub. The CDC provides the following on a doffing sequence²⁰:

1. Remove gloves.

2. Remove isolation gown.

3. Perform hand hygiene.

4. Remove face shield or goggles.

5. Remove and discard respirator or surgical mask.

6. Perform hand hygiene after removing the respirator/facemask.

Employers are required to provide PPE when higher levels of control, engineering, work practice, and administrative controls are not feasible or do not provide adequate protection from infectious diseases.¹⁵In addition, employers are required to implement a PPE program that offers ongoing training on potential hazards-the selection, maintenance, and use of PPE.¹⁵

Conclusion

Infection control practices are essential to the delivery of oral healthcare services to prevent the transmission of disease, eliminate cross-contamination, and minimize exposure to occupational hazards and other infectious materials. Due to the COVID-19 pandemic, dentistry is experiencing a paradigm shift in infection control protocols. Although all DHCP should don PPE during clinical procedures, it is prudent for them to understand that PPE is the last line of defense, and it is critical to use the hierarchy of controls to offer the most effective and highest level of protection in the clinical setting when possible. To protect DHCP, several preventive strategies must be employed before the donning of PPE. CDC guidelines regarding infection control practices in the dental setting and PPE requirements are subject to change as researchers continue to understand the dynamics of the SARS-CoV-2 virus and other emerging diseases.

About the Authors

Joy D. Void-Holmes, RDH, BSDH, DHSc, AADH
Dental Hygiene Program Chair
Fortis College
Landover, Maryland
Adjunct Faculty
American Denturist College
Eugene, Oregon
CEO/Founder Dr. Joy RDH Washington, DC

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