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Some dental laboratory employees might wonder: Why do I have to wear all this personal protective equipment (PPE)? It is, therefore, important for them to understand the steps that their employer has taken to assess the hazards and implement controls prior to requiring PPE. By using the hierarchy of controls, an employer can determine the best ways to reduce or eliminate hazards through a series of assessments.
The first step is to follow the guidance of the Occupational Safety and Health Administration (OSHA) to assess and identify hazards.1 Hazards in a dental laboratory can include chemical hazards, physical hazards, biological hazards, and ergonomic hazards. Once hazards are identified, the employer must evaluate which controls can be used to eliminate or minimize the hazards in accordance with OSHA requirements. This is where the hierarchy of controls comes into play. The National Institute for Occupational Safety and Health (NIOSH) provides excellent guidance for an employer to understand these steps.2
The Hierarchy of Controls
The hierarchy of controls provides five levels of actions to reduce or remove hazards and prevent work-related injuries or illnesses. They are:
Elimination: Physically removing the hazard by changing the work process to stop using the hazardous material, equipment, etc. This is the preferred solution to protect employees because it fully eliminates the hazard.
Substitution: Replacing the hazard through the use of a safer alternative. In this step it is important to assess whether the substituted item presents any other risks since the purpose of this step is to eliminate a risk and not create a new one. NIOSH states in their information on the hierarchy of controls that elimination and substitution "can be the most difficult actions to adopt into an existing process" and are "best used at the design or development stage of a work process, place, or tool."2 That said, they can be the simplest and most cost-effective option.
Engineering controls: Isolating people from the hazard by preventing employees from coming into direct contact with the hazard. This control can involve modifying equipment, reconfiguring the work area, using protective barriers between the worker and the hazard, and installing proper ventilation for the protection of employees.3
Administrative controls: Changing the way people work in order to reduce the duration, frequency, or intensity of exposure to hazards. Some examples of these controls include training, job rotation, rest breaks, and limiting access to hazardous areas.
PPE: Protecting workers with PPE, which can include gloves, masks or respirators, eye protection, noise protection, and gowns/lab coats. The employer is required to ensure that all PPE is worn correctly and consistently, and that it is maintained, stored, and replaced as necessary. OSHA's Standard 29 CFR 1910.132 provides general requirements for PPE, so employers must consult that Standard when developing a PPE Assessment Program.4
After the hazards are identified, the employer must evaluate how to control the hazard so employees can perform their jobs safely. The following are some examples of hazards that may be identified in a dental laboratory work environment and how the hierarchy of controls can be applied to eliminate or minimize employee exposure to these hazards.
Chemical Hazards
Many hazardous chemicals are used in a dental laboratory and can pose a wide range of health hazards including irritation, sensitization, and carcinogenicity. Examples of these chemical hazards include isopropyl alcohol, metal powder, silica, solvents, and chromium. Naturally, an employer must review the safety data sheet and any other information available from the chemical manufacturer to understand the hazards of exposure to each chemical that is used.
In workflows using resin 3D printing technology, 99.9% isopropyl alcohol is used to wash resin models. This chemical has a flash point of around 54°F, making it highly flammable. The employer must, therefore, find a way to protect workers from skin contact and fumes. Per the hierarchy of controls, the first steps are to eliminate or substitute a less hazardous chemical. When that is not possible, engineering controls may then be the most effective. There are systems and equipment on the market now that appear to limit employees' contact with resin and alcohol, however, parts of the workflow that involve alcohol and filling equipment may still require the use of PPE. The employer must ensure that the PPE provided is effective with these chemicals. For instance, when considering the type of glove, a chemical-resistant glove such as a neoprene or nitrile is preferrable. It is also important to provide the correct size of glove for each employee because a glove that is too large may present other hazards.
Metal 3D printers are also often used in dental laboratories, and the metal powder used with this equipment presents a hazard that requires protection to the employees who operate and maintain the equipment. These protections include PPE such as tight-fitting and closed protective work clothing (eg, disposable work coveralls), chemical-resistant protective gloves, half-mask or full-mask respirator, and tight-fitting safety goggles. These types of respirators require compliance with OSHA's Respiratory Protection Standard 29 CFR 1910.134.5 In addition, an employer should always review and follow the manufacturer's operating instructions as well as the safety data sheets.
Another chemical hazard encountered in the dental laboratory is silica,6 which may be present in porcelain, investment, stone, pumice, and polishing wheels. Beginning at the top of the hierarchy of controls with elimination could mean outsourcing the tasks that involve silica-containing materials. In terms of substitution, 3D printing is reducing exposure to stone, however, as discussed above, that substitution has its own hazards. Engineering controls are the most commonly used controls to protect workers from silica exposure and include the installation of dust collection systems and the containment of grinding procedures. However, the employer must also consider the employee who is maintaining the suction system and has to empty the filters. This employee's protection is typically PPE. Furthermore, administrative controls should be used to perform air sampling where employees are exposed to these materials. Air sampling often provides the only indication that engineering and other controls are effectively protecting the workers. OSHA's Respirable Silica Standard 29 1910.1053 also requires medical questionnaires to ensure a worker is medically able to wear a respirator along with fit testing.7
Solvents such as disinfectants also require the use of appropriate PPE. Eyes, skin, and inhalation are the main entry routes during the process of disinfecting incoming work. In these situations, nitrile gloves are usually preferrable over latex because they are chemical-resistant. Moreover, latex allergies are not uncommon, so it is best to avoid using latex when possible.
Chromium is another potential chemical hazard and can be present in the wires used for laser welding as well as in the alloys used to make partial frameworks. When heated, chromium releases hexavalent chromium (Cr(VI)), which is known to cause cancer and targets the respiratory system, kidneys, liver, skin, and eyes.8 An employer may elect to eliminate this hazard by outsourcing the production of this part of the dental device. If this process is not eliminated, engineering controls are critical to maintaining worker protection. Proper containment of the process, including suction, is one way engineering controls can prevent an employee from breathing Cr(VI). In the case of open process systems where corrosives are used, PPE must also be required. In addition, air sampling is an important administrative control to ensure that the exposure levels for employees involved in these processes are under OSHA's permissible exposure levels (PEL). As with all hazardous chemicals, safety data sheets should be referenced when choosing PPE.
Physical Hazards
Physical hazards are the most common type of workplace hazard. The employer should assess slip, trip, and fall hazards; electrical hazards such as frayed cords; exposure to moving parts in equipment; and the physical consequences of chemical hazards such as flammability, corrosion, and explosibility. Some physical hazards may not be visible such as noise, mold, vibrations, radiation, and poor air quality.
In a dental laboratory, commonly encountered physical hazards include the use of extension cords, lack of proper management of computer wiring, electrostatic discharge, flammables, corrosives, combustibles, noise, radiation, flying debris from grinding, and poor air quality.
Elimination would be the ideal solution for extension cords. OSHA allows their use only on a temporary basis. Substitution may also be possible for some physical hazards, but engineering controls, administrative controls, and PPE are the most common controls needed to protect workers from physical hazards in a dental laboratory setting.
Engineering controls for physical hazards could include:
• Physical barriers such as guards or shields between the employee and the moving parts of lathes and handpieces to prevent contact with flying debris.
• Electrostatic discharge (ESD) protective mats on floors to reduce electrostatic charge, eg, in the presence of metal printers.
• Dust collection to reduce exposure to dust created during various processes along with air quality monitoring to ensure levels are below OSHA's permissible exposure levels. If they are not, then PPE is required.
Administrative controls can also minimize hazards, so training workers on proper handling and storage of flammables, corrosives, and combustibles is important. Also, providing written procedures on these tasks will assist in reminding employees of these controls. Testing for noise levels is also an administrative control that should be used to determine if hearing protection needs to be required.
Biological Hazards
Biological hazards involve employee exposure to bodily fluids, which can expose them to pathogens. In 1992, OSHA published the Bloodborne Pathogen Standard 29 CFR 1910.1030 and in that standard defines bloodborne pathogens as pathogenic microorganisms that are present in human blood and can cause disease in humans.9 These pathogens include, but are not limited to, hepatitis B virus (HBV) and human immunodeficiency virus (HIV).
In a dental laboratory, biological hazards can be present during receiving; in the model department, denture repair department, and implant department; and during shade verifications and chairside services.
Most dental laboratories are still receiving analogue impressions from a dental office. In order to protect employees who are unpacking and disinfecting these items, the dental laboratory must offer the HBV vaccine and provide PPE if other controls do not eliminate these biohazards. With recent developments in digital dentistry, analogue impressions are increasingly being eliminated through the use of digital scans. So, perhaps one day this will no longer be a hazard in the dental lab. However, under the current industry workflows, PPE is still the required control and should include gloves, masks, eye protection, and gowns to be worn over street clothes.
Similarly, the main concern for the model department is when clinically poured models are received from the dental client. The laboratory may not know if the dentist or staff disinfected the impression before pouring the model, and, therefore, must treat it as a potential biological hazard. 3D printing models is one way that stone models are being eliminated, thus eliminating this hazard. In addition, engineering controls such as a wet model trimmer helps to minimize dust when grinding on models, and PPE should be required when grinding or die trimming.
Although dentures arriving at the denture repair department have been disinfected before arrival, the technician repairing the denture may uncover areas that disinfectant did not reach while grinding on the denture. Engineering controls should thus be used to create barriers between the worker and the rotary equipment. Furthermore, administrative controls should also be used for cleaning and disinfecting the pressure pot as well as tools used on the repair. Another example of an administrative control would be placing the denture repair in its own water source before placing it into the pressure pot to eliminate cross-contamination of the pressure pot between repairs.
In addition, items received by the implant department from the dental client are also disinfected upon receipt, but it is not unusual for the implant technician to see blood. In that case, the item should be returned to receiving for additional disinfection. PPE is the best control for the implant technician, and administrative controls should be implemented to clean and disinfect work areas where there may be cross-contamination.
Although most biological hazards are encountered through dental materials and devices received from the dental clinic, there are two possible circumstances in which a dental technician may be exposed to biological hazards associated with direct interaction with a patient. These circumstances include shade verification appointments that take place in the dental laboratory either with or without a dentist present and chairside services that the dental technician might provide in the dental clinic. Elimination of these services could be considered, however, both services have been shown to be valuable to the dental clients where allowed. In the case of shade verification visits, regulations regarding whether these visits can take place in the dental laboratory and if a dentist must be present varies by state, so laboratory owners should familiarize themselves with the specific guidelines within the state that they operate. The NADL provides shade verification guidelines available for download as well as a list of the 13 states that allow in-laboratory shade verification.10 During the early days of the COVID-19 pandemic, many laboratories implemented administrative controls to screen patients entering the dental lab before their appointments. However, these administrative controls seem to have relaxed recently even though COVID-19 remains a hazard. Dental laboratories might consider continuing to implement patient screenings in addition to PPE controls. That said, PPE is still considered the best control for direct patient contact, and even in the case of chairside services in the dental office, the employer of the technician is still the party responsible for providing that PPE.
Ergonomic Hazards
In addition to mitigating any chemical, physical, or biological hazards, an employer also must ensure that employees are interfacing with their work areas in ways that will prevent musculoskeletal disorders (MSDs). Employers should assess potentially risky tasks such as lifting heavy items, bending, reaching overhead, pushing and pulling heavy loads, working in awkward body postures, and performing the same or similar tasks repetitively. Exposure to these known risk factors for MSDs increases a worker's risk of injury, however, work-related MSDs can be prevented.
Ergonomics is a means of fitting the job to the worker in order to help lessen muscle fatigue, increase productivity, and reduce the number and severity of work-related MSDs. The employer must ensure that employees are following the controls that have been put into place.
Elimination and substitution can be considered, but engineering controls are the most desirable, where possible. They can include11:
• Providing seating that can be adjusted to the employee
• Using a device to lift and reposition heavy objects
• Reducing the weight of items to limit force exertion
• Repositioning items to eliminate long or excessive reaching
• Redesigning tools or providing ergonomically-designed tools to enable neutral postures
Administrative controls and work practices can also be used to control ergonomic issues. They can include11:
• Rotating workers and/or tasks to minimize the duration of exertion, repetitive motions, and awkward postures
• Requiring heavy items to be lifted by two people
• Providing "floaters" for periodic breaks between scheduled breaks
• Providing training on the proper use and maintenance of pneumatic and power tools
PPE also helps with ergonomic issues. For instance, padding sharp edges where there is direct contact with hard, sharp, or vibrating surfaces. In a dental laboratory this might be done at a workstation used by an office worker with a computer station, a technical designer who uses a computer, and production technicians at typical dental laboratory workstations.
Conclusion
Employers must assess all hazards in the dental laboratory, implement controls, train employees on the use of the controls, and re-assess the controls regularly to ensure their efficacy. According to OSHA's Recommended Practices for Health and Safety Programs,1 "To be effective, any safety and health program needs the meaningful participation of workers and their representatives. Workers have much to gain from a successful program and the most to lose if the program fails. They also often know the most about potential hazards associated with their jobs. Successful programs tap into this knowledge base."
Although PPE is the last step in the hierarchy of controls,12 it is still a very important step. As discussed throughout this article, employers must provide PPE that is safely designed, fits the employees, and is appropriate for protection from the identified hazard. A PPE program should be implemented that includes employee training and addresses the hazards present as well as the selection, maintenance, and monitoring of PPE.
About the Authors
Mary A. Bartlett
President
Safelink Consulting Inc.
References
1. Recommended practices for health and safety programs. OSHA website. https://www.osha.gov/safety-management/hazard-Identification. Accessed April 30, 2024.
2. NIOSH. Hierarchy of controls. CDC website. https://www.cdc.gov/niosh/topics/hierarchy/default.html. Updated January 17, 2023. Accessed April 30, 2024.
3. NIOSH. Directory of engineering controls. CDC website. https://www.cdc.gov/niosh/engcontrols/. Updated January 14, 2015. Accessed April 30, 2024.
4. CFR 29: 1910.132 - general requirements. OSHA website. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.132. Updated November 18, 2016. Accessed April 30, 2024.
5. CFR 29: 1910.134 - respiratory protection. OSHA website. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.134. Updated September 26, 2019. Accessed April 30, 2024.
6. Silica, crystalline. OSHA website. https://www.osha.gov/silica-crystalline. Accessed April 30, 2024.
7. CFR 29: 1910.1053 - respirable crystalline silica. OSHA website. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1053. Updated May 14, 2019. Accessed April 30, 2024.
8. Hexavalent chromium. OSHA website. https://www.osha.gov/hexavalent-chromium. Accessed April 30, 2024.
9. CFR 29: 1910.1030 - bloodborne pathogens. OSHA website. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1030. Updated May 14, 2019. Accessed April 30, 2024.
10. NADL legislative & legal affairs. NADL website. https://nadl.org/members/legislative/. Accessed May 3, 2024.
11. Ergonomics. OSHA website. https://www.osha.gov/ergonomics/control-hazards. Accessed April 30, 2024.
12. Personal protective equipment. OSHA website. https://www.osha.gov/personal-protective-equipment. Accessed April 30, 2024.