Inside Dental Assisting
Guidelines to minimize exposure to mercury and mercury vapor.
Dental amalgam has been used for over 150 years to fill the voids caused by tooth decay in millions of people. Amalgam restorations are strong, less likely to break than some other materials, and are the least expensive type of restorative material. However, dental amalgam contains mercury, and some concerns have been raised about its safety. Amalgam is approximately 50% elemental mercury by weight, and is mixed with a powdered alloy composed of silver, tin, copper, and zinc.1,2 During placement of amalgam restorations, mastication, and brushing, small amounts of mercury vapor can be released.3,4 As the Internet provides a range of information concerning dental amalgams, determining the difference between fact and opinion is not an easy task.
Mercury is unique in that it is the only metal that is a liquid at room temperature. The mercury in dental amalgam is used to bind the alloy into a durable and solid filling material. For many years, bulk elemental mercury—sometimes referred to as liquid or raw mercury—was dispensed in the office by the dentist or assistant prior to being mixed with an alloy to form dental amalgam. Since 1984, the American Dental Association (ADA) has recommended that dental offices use only precapsulated amalgam.
Exposure to Mercury or Mercury Vapor
Dental amalgam releases low levels of mercury vapor that could be inhaled. Based on the best available scientific evidence, the Food and Drug Administration (FDA) considers dental amalgam restorations safe for adults and children 6 years of age and older. There is still a limited amount of clinical information regarding any potential effects of amalgam restorations on children under 6, pregnant women, and breastfed infants. However, the estimated amount of mercury in breast milk attributable to amalgam restorations is low enough to fall below the general levels for oral intake considered to be safe by the Environmental Protection Agency (EPA). After reviewing the existing data, the FDA concluded breastfed infants are not at risk for adverse health events due to the mother’s exposure to mercury vapor from dental amalgam restorations.1
A small number of people are allergic to mercury or one of the other components of dental amalgam. Amalgam restorations may cause localized reactions in this population, ranging from oral lesions to symptoms similar to a skin allergy. People who have reactions to dental amalgam usually have a family history of metal allergies.3
Under certain circumstances, dental personnel may be exposed to mercury or sources of mercury vapor. Potential sources of exposure include malfunctioning bulk mercury dispensers and amalgamators, leaking or used capsules, vaporization from contaminated instruments, and open storage of amalgam scrap, in addition to during trituration, placement and condensation of amalgam, and polishing or removal of restorations. To protect personnel from possible exposure, dental offices should use only precapsulated amalgam in an amalgamator that has a completely enclosed arm. If possible, capsules should be recapped after use and stored in a closed container to be recycled. It is recommended that care be used when handling amalgam; skin contact with mercury or freshly mixed amalgam should be avoided. High-volume evacuation fitted with traps or filters should be used when finishing and removing amalgam.6
Minimizing Impact of Amalgam Waste
Managing amalgam waste requires knowledge of and commitment to best practices. For an overview of methods, the ADA’s Best Management Practices for Amalgam Waste provides guidelines beneficial to all dental personnel.
For example, dental offices that continue to place amalgam restorations can minimize the generation of amalgam waste by being cautious when mixing amalgam capsules. If a one-spill capsule is enough to fill a preparation, a double-spill capsule should not be mixed. When cleaning up after procedures, the excess amalgam in the amalgam well should never be removed with high-speed suction. It is recommended that all contact and noncontact scrap amalgam, capsule waste, and extracted teeth with amalgam restorations be collected and stored in a appropriately labeled, tightly closed container for that sole purpose. All scrap amalgam should be recycled through an amalgam recycler.7
To minimize the amount of amalgam waste generated, amalgam capsules should be stocked in a variety of sizes. While handling amalgam waste, which may be mixed with saliva or other potentially infectious material, personal protective equipment such as utility gloves, masks, and protective eyewear should be used.
Generally, amalgam waste should be stored in a covered plastic container labeled “Amalgam for Recycling.” However, requirements for collecting, storing, and transporting amalgam waste vary from one community to the next, and different recyclers may have their own requirements for containers and what may be placed in them. It is important to consider only recyclers who comply with the American Dental Association-American National Standards Institute (ADA-ANSI) standard, which is meant to encourage recycling.5
Proper management of dental waste amalgam includes maintenance of filters and chairside traps. Because of the difficulty in effectively removing all amalgam particles from reusable traps without spilling particles, disposable traps are recommended. Although finer filters require more frequent cleaning and changing, size-100 mesh traps are more effective in catching smaller particles than size-40 mesh traps. To ensure that the finer trap does not affect the functioning of the vacuum system, manufacturers’ guidelines should be followed regarding cleaning or changing the traps. Safety glasses, gloves, and masks should be worn when maintaining all filters and traps.
Before changing the chairside trap, the vacuum system should be flushed with a disinfecting solution. Suction lines should be flushed at the end of the day, and the trap should be changed in the morning when the particles in the trap are dry. If traps are changed at the end of the day, the particles should be allowed to dry after flushing the lines before removing the trap. Avoid line cleaners that contain bleach or chlorine, which may dissolve mercury from the amalgam particles and increase the release of mercury into the dental wastewater.7
Those using replaceable amalgam traps must take care to properly remove and dispose of both amalgam and non-amalgam fragments while cleaning the trap for reuse. After opening the unit to expose the amalgam trap, non-amalgam fragments such as cement should first be removed with a cotton forceps and discarded in the garbage. Next the visible amalgam can be removed by tapping the contents into a properly labeled container; the container should then be tightly closed. The trap can be reused as long as it is visibly clean; however, once clearly contaminated, the trap should be stored in a properly labeled container and recycled.
Disposable amalgam traps should be removed and placed in a properly labeled container. They should not be washed under running water or placed either in the trash or medical waste sharps container.
The vacuum pump filter should be replaced regularly, in keeping with the equipment manufacturer’s recommendations and should then be disposed of properly—not in trash or in medical waste sharps container. During this process, the filter should be removed and held over a tray or other container to catch spills. After decanting as much liquid as possible without losing visible amalgam, the amalgam-free liquid can be rinsed down the drain. After placing the lid on the filter, it should be placed inside the box in which it was originally shipped. When the filter box is full, the used filters must be recycled properly; the amalgam recycler should be contacted to be sure it accepts these filters.7
Amalgam separators are designed to remove amalgam waste particles that were missed by chairside traps and filters. Amalgam particles in dental wastewater can range from smaller than 0.45 micrometers to larger than 3 millimeters. Amalgam separators can use several separation techniques to remove the various-sized particles from dental waste discharge: sedimentation, filtration, centrifugation, or ion exchange. Sedimentation units reduce the speed of wastewater and allow the amalgam particles to settle out. Filtration units remove not only coarser particles, but some finer ones also. Centrifuge units draw the amalgam particles out of the wastewater using centrifugal force. Combination units use any two or more techniques to remove even the most minute amalgam particles and dissolved particles of mercury.8,9
Maintenance of amalgam separators varies by unit—some need to be decanted daily, while others require the entire unit to be recycled or replaced every 3 to 18 months. A loss of suction power or an unusually noisy vacuum pump is a warning sign that requires attention. There may also be clogs in the line, which can occur over time. Bleach or other chlorine-containing solutions should never be used to clean suction lines, as they can remobilize bound mercury and compromise the efficacy of the amalgam separator, allowing the mercury to enter the waste stream.5
Other Mercury Sources
There are other sources of mercury in dental offices: Blood pressure units, thermometers, thermostats, fluorescent light bulbs, and electric equipment with switches may contain mercury and should be recycled when replaced. In the event these items break, use a mercury spill kit to clean up visible elemental mercury. Nitrile gloves should be worn because mercury can penetrate latex. Mercury spill kits can be purchased from amalgam recyclers, dental product suppliers, or any company that specializes in OSHA-compliant supplies. All material used to clean up the spill, along with any broken glass, should be placed in a sealed plastic bag or container labeled “Mercury Waste.” All contaminated materials should be disposed of by a hazardous waste hauler. These items should not be placed in a sharps container, medical waste pail, or in the trash.7
Collected waste, as well as gloves and coverings, should be placed in a container for recycling and should be sealed. A reputable firm licensed to handle amalgam waste should be contacted to remove the waste. Be sure to give the waste hauler a complete listing of all materials collected, and request a receipt that states potentially hazardous waste was handled according to federal or state mandates. Hazardous waste haulers must provide a waste manifest to document receipt and shipment.
Dental amalgam is still considered to be an important and safe restorative material used in dental offices around the world. However, it is essential to understand the various protocols needed when dealing with this material and its scrap, taking appropriate measures in the maintenance of dental equipment, and protecting the environment.
1. U.S. Food and Drug Administration: Medical Devices, About Dental Amalgam Fillings. www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DentalProducts/DentalAmalgam/ucm171094.htm. Updated August 8, 2009. Accessed July 12, 2011.
2. American Dental Association: Statement on Dental Amalgam. www.ada.org/1741.aspx. Updated August 25, 2009. Accessed August 10, 2011.
3. American Dental Association: Oral Health Topics. www.ada.org/3094.aspx. Accessed July 21, 2011.
4. Agency for Toxic Substances and Disease Registry. Public Health Statement Mercury CAS#: 7439-97-6. www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=24. Accessed July 10, 2011.
5. American Dental Association: Best Management Practices for Amalgam Waste. http://www.ada.org/sections/publicResources/pdfs/topics_amalgamwaste.pdf. Accessed July 3, 2011.
6. ADA Council on Scientific Affairs. Dental mercury hygiene recommendations. I 2003;134(11):1498-1499.
7. New York State Department of Environmental Conservation: Managing Dental Mercury. http://www.dec.ny.gov/chemical/8513.html. Accessed August 11, 2011.
8. McManus KR, Fan PL. Purchasing, installing and operating dental amalgam separators. J Am Dent Assoc. 2003;134(8):1054-1056.
9. Sarrett DC. Dental Amalgam Separators. ADA Professional Products Review.2007;2(4):1-5.
About the Author
Karen L. Comisi, RDA
“Dental Care with a Difference”®, PC
Ithaca, New York