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Saying that 3D printing has changed this industry is an understatement. Dental laboratories are using 3D printing to cover a range of applications including models, trays, surgical guides, denture bases and teeth, indirect bonding trays, gingiva masks, partial frameworks, and crown and bridge. This technology has changed manufacturing in many ways, but it also presents challenges in regard to safety. Employers must remember that the Occupational Safety and Health Administration (OSHA) requires them to provide a workplace free of hazards.1 By assessing the hazards involved in the 3D printing process, an employer can assure its workers that the employer is minimizing and/or eliminating those hazards. This article will address the considerations employers should take to protect workers from the chemical hazards created by the use of 3D printing processes.
The primary product used in the 3D printing process for dental applications is resin. To begin the process of assessing the hazards that could be associated with operating 3D printing, an employer should read the manufacturer's operating instructions and maintenance instructions for the printer itself and also look at the Safety Data Sheet (SDS) for the materials that will be used in this process. Employers must provide access to SDSs to their workers2-including SDSs for the resin and any cleaning solutions, such as isopropyl alcohol.
Resin SDSs
The employer and employees should read all 16 sections of the SDSs;2 however, this section will cover some of the most important sections for resins.
Section 1 (Identification) provides an emergency contact should you have an issue that requires immediate response. The SDSs reviewed by this author contain varied information in this section, ranging from one phone number outside the US to multiple numbers for different languages. In some cases, the caller may be contacting the manufacturer directly, a poison control center, or a third-party vendor such as Infotrac or Chemtrec.
Section 2 (Hazards Identification)provides:
• Hazard Statements
• Precautionary Statements
• Classification of the product
• A Signal Word ("Warning" or "Danger") is also provided if applicable, and the appropriate Pictograms. For the products reviewed by this author, the Signal Word was "Warning" on some and "Danger" on others. OSHA's Hazard Communication Standard 1910.1200 defines a Signal Word as a word used to indicate the relative level of severity of hazard and alert the reader to a potential hazard on the label. "Danger" is used for the more severe hazards, while "Warning" is used for the less severe.
• Pictograms, if applicable (there are nine). An employer should post an explanation of the pictograms in the workplace to ensure workers understand their meaning as they also appear on product labels. This author's review of SDSs on some resin materials showed the pictograms for "Health" (may cause or suspected of causing serious health effects) and "Exclamation Mark" (may cause less serious health effects or damage the ozone layer).
Section 4 (First Aid) includes having an eyewash facility available in the event that a worker has eye contact with the material.
Section 6 (Accidental Release Measures) should be reviewed to ensure that the appropriate spill response items are on hand to clean up a spill. This section usually also indicates that this material should not be discharged into the drains/surface waters/ground waters.
Section 7 (Handling and Storage) for the SDSs reviewed by this author indicate a storage temperature and that the material should be stored away from heat and open flames. Also, some indicate to avoid sunlight and to keep in the dark.
Section 8 (Exposure Controls/Personal Protection) shows the occupational exposure limits. This section indicates the Time Weighted Average (TWA) for the parts of a mixture that have been established by a governing authority. In the SDSs reviewed by this author, only one showed a TWA-for titanium dioxide that is a part of that particular mixture. The TWA reflects the maximum average exposure a worker can be subjected to without experiencing significant adverse health effects over the standardized 8-hour work period. It is expressed in units of parts per million (ppm) or mg/m3.
• The Personal Protective Equipment (PPE) that an employer should require will vary depending on the engineering controls and administrative controls that have been put in place. In the hierarchy of controls, PPE is the last resort after an employer has implemented other controls. For the most part, the SDSs reviewed by this author show the types of gloves that will protect the worker when handling the material, so an employer should read this section to ensure that the appropriate types of gloves are provided to the workers. An interesting detail on the SDSs reviewed is concerning working clothes that have come into contact with these materials. For the most part, they state to keep working clothes separate from clothes to be worn in other parts of the facility and home. This clothing should be removed immediately if contaminated and kept away from food and drinks. Handwashing is also stressed as an important control.
• For the most part, the SDSs indicate to avoid contact with the eyes, so eye protection is important.
• Proper ventilation is also indicated throughout sections of the SDSs; however, use of respirators is mainly indicated when vapors are excessive.
Section 11 (Toxicological Information) describes the health effects of exposure to the product. For the most part, the SDSs reviewed stated that there are no health effects under normal use; however, an employer should read this section and relay to workers all possible health effects. One that appeared in some SDSs related to reproductive effects. This section also will indicate if the material is carcinogenic.
Section 13 (Disposal Considerations) usually indicates to dispose in accordance with all national and local regulations. Some indicate to avoid discharge into drains or surface water and even to not go into a landfill. Disposal limitations also apply to the empty container and recommend recycling the containers rather than disposal.
Cleaning Solutions
The use of 3D printing has also introduced some cleaning solutions that were not commonly used in dental laboratories. Cleaning solutions are used with 3D printing to wash away the liquid layer of resin that remains on the surface of the 3D printed object. Isopropyl alcohol (IPA) seems to be the most common alcohol used, with a chemical formula of C3H8O. It varies in strength from 70% to 99%.
As with the resin discussed above, an employer must obtain an SDS on this chemical and make it available to its workers. After reviewing the SDS for IPA,3 the author noted that the Signal Word is "Danger" and the pictograms are the Exclamation Point and Flame. This chemical has a Flash Point of 18.3°C/64°F; therefore, it should be protected from physical damage and stored in a cool, dry, well-ventilated location away from any area where fire hazards may be acute. Non-sparking type tools and equipment should be used around this chemical. Even empty containers can be hazardous because they could contain product residues such as vapors or liquid.
Other precautionary notes for IPA include that it can be irritating to the eyes and vapors may cause drowsiness and dizziness. It can also cause mild skin irritation. The PPE indicated for protection to workers includes wearing of impervious protective clothing to prevent skin contact, gloves as specified in the SDS such as neoprene and nitrile, and chemical safety goggles and/or a full face shield where splashing is possible.
Storage of IPA is regulated by OSHA in 1910.106.4 If you can smell it, the chemical is in the air and the vapors must be controlled. OSHA indicates that "the quantity of liquid that may be located outside of an inside storage room or storage cabinet in a building or in any one fire area of a building shall not exceed 25 gallons of Category 1 flammable liquids in containers." This container needs to be air-tight. A quantity of more than 25 gallons must be stored in a flammables cabinet. The maximum storage inside a flammables cabinet is 60 gallons; however, there could be more than one flammables cabinet in the room. The containers inside the flammables cabinet should hold no more than 5 gallons each, and the smaller the container the better. The seals on the containers are important because the flammables cabinet is vented and the containers inside the cabinet need to keep the vapors inside the smaller containers. For ventilation, the air exchange in the room should be six times per hour. If IPA is stored outside of the main building but in the other storage, these same requirements must be met.
Some dental laboratories are purchasing distilling equipment so they can reuse the IPA. It is highly recommended that a commercial distiller be purchased rather than using a "homemade" version because the distillation process itself can pose significant risks due to the vapors. The user should follow all of the manufacturer's instructions for installation and use. It would be wise to consult with the local fire marshal to ensure that the installation and use meet local fire codes.
There are also OSHA requirements for distillers. Section 1910.106(3)(v)(a) requires ventilation in an area where distillation is being performed to be ventilated at a rate of not less than 1 cubic foot per minute per square foot of solid floor area.
Most dental laboratories dispose of used IPA. As indicated above, an employer should consult the SDS and, specifically, Section 13. Two controls that an employer should consider when disposing of IPA are:
1. Research your local regulations for hazardous waste disposal. This can involve hiring an independent waste disposal service. For smaller amounts, check with your local waste disposal service to see if they have any suggestions for removal.
2. Inform your waste disposal service that your bottle contains IPA along with material in the object that is being washed with the IPA, as there usually are residues. The hazard waste company may ask for the SDSs for the resin.
Exercise Caution
In summary, unfortunately, there is no answer to the question of the extent of the hazardous nature of resin. The author's research found no OSHA or National Institute for Occupational Safety & Health (NIOSH) published exposure limits. The particulates of resin are nano particles, and OSHA does not have a standard for nano particle levels, so there is no Permissible Exposure Limit. This means that if air sampling or individual monitoring were performed, there is no comparison measurement for over-exposure. It is known that if the particles get into the lungs, they lodge in the lungs.5 Even though OSHA does not have a standard for this product, they could cite an employer under the General Duty Clause6 if the employer has not taken steps to protect workers.
Employers should include the following protections in their consideration for engineering controls, administrative controls, and PPE:
• Training workers on this hazard with currently available information. The Hazard Communication Standard7 requires them to train on hazards of chemicals, so they could be cited on that standard 1910.1200 if they are not protecting their workers.
• Enclosing the 3D printer inside a cabinet that is ventilated to the outside. Air being ventilated to outside should pass through a system as well.
• Ensuring that air being taken out of the 3D printer is not recirculated into the work area.
• Installing independent ventilation systems. The ventilation of the machine itself is mainly for the protection of the 3D printer, so independent ventilation systems could be installed for the protection of the workers.
• Retaining work clothes, including laboratory coats, in the 3D printing rooms so they are not worn into other parts of the laboratory.
• Not allowing workers who do not work in that area to enter the work area or gather around those areas. Particulates can hang in the air.
• Requiring a supplied-air respirator.
• Requesting for NIOSH to come into the laboratory if a worker is complaining about their concerns for their health.
About the Author
Mary A. Bartlett
President
SafeLink Consulting
Cumming, GA