Proper handling and use of mercury in the oral health care setting is referred to as mercury hygiene. Designated as a hazardous substance by the National Occupational Health and Safety Commission, mercury is considered a health risk in the workplace and must be handled according to specific guidelines.
Permissible exposure limits in the United States are0.1 and 0.05 mg/cubic meters. Dental offices, which use liquid mercury on a regular basis in amalgam restorations, are required to follow appropriate measures to manage and reduce the risk of mercury spills and vapor release.
Pure mercury in the dental workplace is found in predosed amalgam capsules that include separate compartments for alloy powder and mercury. Amalgam has been used to fill teeth for thousands of years and has been available in its present formulation since the late nineteenth century. Amalgam contains 50% metallic mercury, 35% silver, 9% tin, 6% copper, and a trace of zinc. United States dentists place more than 100 million amalgam fillings each year. Dental mercury, supplied in the form of an odorless, silvery liquid with a metallic luster, is considered harmful at concentrations greater than 3%, and toxic at concentrations greater than 25%.
Amalgam—As applied to dentistry, a filling material composed of mercury, silver, tin, copper, and zinc.
Mercurialism—Chronic poisoning from mercury.
Dental employers are required to conduct a risk assessment for mercury hygiene that includes the following documentation:
- date of the assessment
- the product name for mercury-containing substances
- a statement that the material safety data sheet (MSDS) and other relevant information have been reviewed
- a statement on the significance of the degree of risk
- a list of control measures in place
- a decision on the need for health surveillance
Amalgam that is mixed but unused during restoration care is normally collected and sold for reprocessing. Minor particles, plus amalgam dust formed during the removal of old restorations, is removed by rinsing or by high speed suction. Significantly lower amounts of mercury are found in dental operatory waste water when amalgam separators are used. Use of a rubber dam and high-speed evacuation are also appropriate control measures.
The American Dental Association reports that amalgamators, the mixing machines used to produce amalgam, may become contaminated with mercury and emit minute amounts of mercury vapor. Old amalgamators may need to be classified as hazardous waste for disposal.
Disposable monitoring discs are available that measure any hazard from mercury vapor in dental offices. Discs are assessed by an appropriate agency, and the office is given a report and advice on mercury hygiene.
Following mercury exposure, first aid procedures are as follows:
- Eye contact: Flush under upper and lower lids for 15 minutes, and seek medical attention.
- Skin contact: Wash contaminated clothing thoroughly with soap and water. Seek medical attention.
- Inhalation: Move victim to fresh air, give artificial respiration if necessary. Seek medical attention.
- Ingestion: Give a conscious victim water and induce vomiting. Seek medical attention. For a person who is unconscious or convulsing, do not give anything by mouth or induce vomiting.
Since spilled mercury gives off a toxic, odorless vapor, spills must be cleaned up immediately if predosed capsules break. Persons handling cleanup should wear gloves and collect mercury with a suction pump and aspirator bottle. A regular vacuum cleaner is not appropriate since a vacuum cleaner can spread mercury vapor. No mercury should enter drains. Fine droplets may be covered with calcium polysulphide, powdered sulfur, or a 20% solution of sodium thiosulphate. Droplets are to be put in a closed container.
Inhalation of mercury vapor is toxic, and there is danger of cumulative effects of exposure. Possible complications include difficulty breathing, cough, fever, nausea, vomiting, headache, excessive salivation and metallic taste, cardiac abnormalities, pulmonary irritation and pneumonitis, edema, fibrosis, kidney and brain damage, and death.
Effects of accidental ingestion are burning of the mouth and throat, thirst, nausea, and vomiting. Mercury is not usually absorbed well enough through ingestion to cause acute effects.
Eye contact with mercury in liquid form may cause irritation and redness. Skin contact may result in allergic reactions and irritation. Enough mercury can be absorbed through the skin for toxicity.
The chronic health effects of mercury exposure are termed mercurialism. Mercurialism includes fine tremors and erethism, a syndrome of psychological effects including abnormal shyness, depression, despondency, irritability, or excitability. With severe mercury exposure, hallucinations, loss of memory, and mental deterioration may occur. Other possible chronic health effects are kidney damage, stomatitis, increased tooth mobility, blue pigmentation of the gum tissue, diarrhea, and weight loss. Individuals with pre-existing conditions affecting the respiratory system, kidneys, and nervous system may find their conditions aggravated by mercury exposure.
Proper mercury hygiene results in a safe working environment for dental personnel. With control measures in place, dental amalgam does not appear to represent an environmental problem. Organized dentistry claims that mercury combined into amalgam forms a biologically inactive substance. Its widespread and long-term use have not brought to light any adverse side effects in dental patients.
Health care team roles
An employer is required to identify staff members who may be exposed to mercury, such as dentists and chair-side assistants, then conduct and document appropriate training. Issues to be addressed include any factors that may affect the level of exposure, such as working hours and preventive measures used in the practice. Safe work practices in handling mercury overlap with dental workplace safety in general. They include:
- avoiding contact and inhalation of vapor during handling of mercury
- wearing gloves and protective eyewear
- storing capsules in a cool area in labeled containers and protected from breakage
- never disassembling capsules
- salvaging amalgam waste and residue for recycling
- separating clinical clothing from street wear
Dental employers must re-evaluate mercury risk when work practices are modified with new or improved control measures, when new information becomes available, or every five years.
Roberts, Howard W., D.M.D.; Daniel Leonard, D.D.S.; and John Osborne, D.D.S., M.S.D. "Potential Health and Environmental Issues of Mercury-contaminated Amalgamators." Journal of the American Dental Association (January 2001): 58.
American Dental Association. 211 East Chicago Ave., Chicago, IL 60611. (312) 440-2500. <http://www.ada.org>.
Consumers for Dental Choice. National Institute for Science, Law and Public Policy, 1424 16th St., NW Suite 105, Washington, DC 20036. <http://www.amalgam.org>.
United States Environmental Protection Agency. Office of Emergency and Remedial Response, 1200 Pennsylvania Ave. NW, Washington, DC 20460. <http://www.epa.gov/superfund/tools/merc/index.htm>.
"The Dental Amalgam Issue." DAMS Inc., Consumers for Dental Choice website. <http://www.www.amalgam.org>.
"Mercury—Emergency Spill and Release Facts." EPA Office of Emergency and Remedial Response website March 1997. <http://www.epa.gov/superfund/tools/merc/index.htm>.
"Potential Biological Consequences of Mercury Released from Dental Amalgam." Swedish Medical Research Council, Appendix VIII. <http://www.health.gov/environment/amalgam/appendixVIII.htm>.
Walsh, L. J. "Hazardous Substance Assessment for Mercury in Dentistry." WHSO Dental School website <http://www.www.members.nbci.com/_XMCM/dnlwalsh/mercury.htm>.
Cathy Hester Seckman, R.D.H.