Mercury in the Dental Office Workplace Exposure

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Mercury in the Dental Office
Workplace Exposure
Exposure to mercury and mercury vapor has been recognized as a potential health hazard to dental personnel for many years. Because mercury is a liquid at room temperature, it is able to form alloys with other metals without the need for heating the components. It is also easily vaporized at room temperature. Exposure can occur either through direct skin contact with mercury or mercury-containing compounds or through the inhalation of mercury vapor. Inhalation of mercury vapor is the primary route of exposure. Approximately 80% of inhaled mercury is absorbed through the lungs. The vapor pressure of mercury increases rapidly with increases in temperature.
Sources of mercury contamination in the dental environment include expression of excess mercury from amalgam, leakage from dispensers, improper storage of scrap amalgam, leakage from amalgam capsules during trituration, mercury vaporization from contaminated instruments placed in sterilizers, grinding of amalgam during removal of restorations, and amalgam condensation with ultrasonic condensers. Mercury spills and the subsequent accumulation of mercury in carpeting or cracks in the flooring material seem to be the major source of mercury contamination in the dental office.
Cleanup of mercury on seamless vinyl or linoleum floors is relatively easy to accomplish, but complete decontamination of carpets is almost impossible, except for removal of the carpet. Studies, however, have found little or no difference in ambient air concentrations of mercury vapor between offices with carpeting and those with hard floor coverings. Each kind of flooring poses unique problems with regard to spilled mercury. Mercury spilled on hard surfaces tends to be dispersed more widely and divided into smaller droplets, whereas mercury spilled on carpets is confined to a smaller area.
Much attention has been focused on mercury vapor leakage from disposable and reusable amalgam capsules. Both types of capsules are possible sources of mercury vapor during trituration, with neither having a proven superiority. However, researchers have concluded that disposable capsules are preferable because their usage greatly reduces the risk of accidental mercury spills.
Other items of dental office equipment that are subject to contamination can act as indirect sources of mercury. These include amalgamators, sterilizers, cabinets and countertops, cuspidors, drains, filters in heating and cooling systems, waste containers, capsule storage areas, and drapes.
The current standards, as established by the American Conference of Governmental Industrial Hygienists are:

Threshold Limit Value (TLV) (Allowable exposure level to mercury vapor, 8 hours per day, 40 hours per week)= 0.025 milligrams/cubic meter (25 micrograms/cubic meter).

Note: This was changed from 0.05 mg/m3 in 1994.
Normal mercury level in urine= 0 to 20 micrograms/liter (one microgram equals one-millionth of a gram).
Allowable maximum limit in urine= 150 micrograms/liter.
Health Risks
The adverse effects and symptoms of mercury poisoning are:

  1. Tremor observed in fine voluntary muscle movements, such as handwriting, eventually progressing to convulsions.

  2. Loss of appetite.

  3. Nausea and diarrhea.

  4. Sensitivity to mercury — in extremely rare cases, individuals may develop a mercury sensitivity, or allergic reaction. Patients and dental office personnel may be affected, and symptoms may vary from a local dermatitis near recently placed amalgam restorations to a generalized erythema over the entire body.

  5. Depression, fatigue, increased irritability, moodiness.

  6. Insomnia.

  7. Swollen glands and tongue.

  8. Ulceration of oral mucosa.

  9. Dark pigmentation of marginal gingiva and loosening of teeth.

  10. Nephritis.

  11. Pneumonitis.

  12. Birth defects in offspring.

It has been reported that the effects of mercury poisoning are generally not neurologically measurable until the urinary mercury level reaches 500 micrograms per liter.

Mercury vapor is absorbed rapidly by the lungs. Within approximately ten minutes of absorption, about 30 percent of the mercury in the lungs is transferred to the blood. Inhalation of large amounts can damage the lower parts of the bronchial tree and lung tissue.
Mercury can accumulate in the kidneys, liver, brain, and heart. The highest concentrations are in the kidneys and liver. The central nervous system is particularly sensitive to mercury, since mercury passes easily through cell membranes and has a special affinity for nerve tissue. Over years of exposure, the accumulation of mercury in the central nervous system can affect the motor control centers of the brain. The effect of the mercury is to block the metabolism of the neurons, thus producing necrosis and irreversible damage.
The Amalgam Controversy
Recently, considerable interest has been focused on the possible effects of mercury vapor released from the surfaces of dental amalgam restorations. New technologies that permit detection of very low levels of mercury in the air and body tissues have raised questions as to whether the minute levels of mercury released from amalgam surfaces pose a health risk for patients with amalgam restorations.
Studies have demonstrated that patients are exposed to mercury vapor when amalgams are placed as a restoration, when existing amalgams are removed, and during chewing. Some studies suggest that blood levels of mercury are elevated in patients during these situations and that the levels are correlated with the number of amalgams and the occluding surface areas. Other studies have shown no difference in blood levels in patients with or without amalgam restorations.
It has also been alleged that the use of dental amalgam is associated with multiple sclerosis and leukemia. The National Multiple Sclerosis Society has found no evidence to support this allegation, and these reports have been strongly challenged by the scientific community.
Rare allergic reactions to mercury in dental amalgam restorations can occur in patients within a few hours to several days after placement of the amalgam restorations. Symptoms may be limited to areas in contact with amalgam, or they may be generalized; such symptoms may include eczema, urticaria, and wheals on the face, or dryness and soreness of throat and mouth, fever, hives, and swelling of lips, tongue, and mucosa. Most of these symptoms are self-limiting in about two weeks and can be treated with an antihistamine. For patients who do not respond to antihistamine therapy, removal of amalgam restorations is recommended.
An evidence-based analysis of the Amalgam controversy can be found at: (click on “Full text” in the right column for the full article)
The ADA Statements on Dental Amalgam can be found at:
On July 28, 2009, the FDA released its Final Regulation on Dental Amalgam, classifying amalgam and its components as a class II medical device. By classifying a device into Class II, the FDA can impose special controls (in addition to general controls such as good manufacturing practices that apply to all medical devices regardless of risk) to provide reasonable assurance of the safety and effectiveness of the device. The FDA’s website on dental amalgam can be found at:
Patch Tests for Sensitivity to Mercury or Nickel
There are individuals who are hypersensitive or who have allergic reactions to mercury or nickel. The use of amalgam or nickel-containing alloys is not recommended for these patients. It is the opinion of the ADA Council on Scientific Affairs that patch tests for mercury or nickel should not be used indiscriminately for all patients. These tests may induce sensitivity in individuals who were not sensitive to amalgam restorations and/or nickel-containing prostheses. Furthermore, the validity of the patch test results and the suggested interpretation of the monitored patient reactions have not been well documented.
A detailed medical history of the patient and consideration of the benefit-to-risk ratio should play a major role in deciding when to order patch tests. When a patch test is indicted, the informed consent of the patient should be obtained. Patch tests should then be performed by a professional trained in the administration and interpretation of these tests. Referral to a physician who specializes in this testing, such as an allergist or a dermatologist, is strongly recommended.
Mercury Hygiene Guidelines
The ADA classifies amalgam scrap in the following manner:

  • Non-contact amalgam (scrap) is excess mix leftover at the end of a dental procedure. Many recyclers will buy this clean scrap.

  • Contact amalgam is amalgam that has been in contact with the patient. Examples are extracted teeth with amalgam restorations, carving scrap collected at chair side, and amalgam captured by chair side traps, filters, or screens.

  • Chair side traps capture amalgam waste during amalgam placement or removal procedures (traps from dental units dedicated strictly to hygiene may be placed in the regular garbage).

  • Vacuum pump filters or traps contain amalgam sludge and water. Some recyclers will accept whole filters, while others will require special handling of this material.

  • Amalgam sludge is the mixture of liquid and solid material collected within vacuum pump filters or other amalgam capture devices.

  • Empty amalgam capsules are the individually dosed containers left over after mixing precapsulated dental amalgam.

The use of disposable precapsulated alloys eliminates many potential sources of mercury vapor and minimizes the possibility of accidental spillage. Offices using precapsulated alloys have been shown to have lower mercury vapor levels. In 1994 the American Dental Association passed a resolution recommending that dentists eliminate the use of bulk dental mercury and bulk amalgam alloy, and that they use only precapsulated amalgam alloy in their dental practices.

The following items should be considered when establishing an effective mercury control program:

  1. Use only precapsulated alloy so there are no bottles of mercury to store. If, for some reason, elemental mercury must be stored, store it in unbreakable, tightly sealed containers on stable surfaces.

  2. Perform all operations involving mercury over an area that has an impervious and suitable lipped surface so as to confine and facilitate recovery of spilled mercury or amalgam. Whenever possible, perform these operations over a tray.

  3. Clean up any spilled mercury immediately.

  4. Use a no-touch technique for handling amalgam. If contact is made with mercury, the area affected should be washed with soap and water to reduce the time that the microscopic particles cling to the skin.

  5. Use tightly closed disposable capsules during amalgamation. Loss of mercury during trituration can be detected by wrapping adhesive tape around test capsules prior to the mechanical mixing. If the capsules are tight and no mercury is thrown out, the adhesive tape will be clean after trituration.

  6. Place non-contact, scrap amalgam in wide-mouthed, airtight container that is marked “Non-contact Amalgam Waste for Recycling.” Make sure the container lid is well sealed.

  7. Stock amalgam capsules in a variety of sizes. After mixing amalgam, place the empty capsules in a wide-mouthed, airtight container that is marked “Amalgam Capsule Waste for Recycling.” Capsules that cannot be emptied should likewise be placed in a wide-mouthed, airtight container that is marked “Amalgam Capsule Waste for Recycling.” Make sure the container lid is well sealed. When the container is full, send it to a recycler.

  8. Salvage contact amalgam pieces from restorations after removal. Store and label contact amalgam waste separately from non-contact waste. Recycle the contact amalgam waste according to instructions provided by your recycler.

  9. Recycle amalgam scraps through refiners who are properly licensed by the Environmental Protection Agency. The ADA’s Directory of Dental Waste Recyclers can be found at:

  10. Work in well-ventilated spaces that have rapid fresh air exchanges. If air conditioning is present, replace filters often.

  11. Avoid carpeting dental operatories, as decontamination is not possible. The use of a continuous, seamless sheet of flooring that extends up the walls at least 10 centimeters is recommended. If the operatory is already carpeted, do all mercury transfers in another area. Carpeting and floor cracks serve as collectors for spilled mercury.

  12. Eliminate the use of mercury-containing solutions.

  13. Avoid heating mercury or amalgam. Keep it away from direct sunlight and other heat sources.

  14. Water spray and high-volume evacuation should be used when removing old amalgam restorations or finishing new ones. A fiber-type mask should also be worn when cutting out old amalgams. Evacuation systems should have traps or filters, which should be checked and cleaned or replaced periodically.

  15. Use conventional dental amalgam compacting procedures, manual and mechanical, but avoid the use of ultrasonic amalgam condensers.

  16. Expressing excess mercury from amalgam must be avoided. Disposable pre-capsulated alloys should be used.

  17. Amalgamator arms and capsules should be covered during trituration.

  18. Contaminated instruments should be thoroughly cleaned before sterilization.

  19. Disposable items contaminated with mercury should be discarded in properly sealed containers.

  20. Have periodic mercury vapor level determinations made in operatories.

The ADA’s Best Management Practices for Amalgam Waste (2005) can be found at: and at
The latest ADA Mercury Hygiene Guidelines can be found at: (click on “Full Text” in the right column)
Office Monitoring
Periodic monitoring can be a valuable adjunct for assessing the effectiveness of mercury hygiene procedures in the dental office. The dental office should be monitored for mercury vapor once every two years, or more frequently if contamination is suspected.

In the event of serious contamination, such as a spill, the office should be monitored until a safe threshold is reached. Arrangements for monitoring can usually be accomplished by contacting the local Office of Environmental Health.

Medical Surveillance
Biologic monitoring through periodic urine analysis for mercury is a recommended method for assessing the exposure of dental office personnel. These periodic checkups are excellent as an indirect evaluation of the effectiveness of mercury hygiene in an office.
The maximum allowable mercury level is 0.15 milligrams/liter (150 micrograms/liter) according to OSHA, and the normal level generally is approximately 0.015 milligrams/liter (15 micrograms/liter).
Cleanup of Spilled Mercury
Any spilled mercury should be cleaned up immediately. Effective techniques for cleanup of any spilled mercury include using a wash-bottle trap connected to a low-volume aspirator of the dental unit for removing visible droplets of mercury. The trap bottle connection should keep the mercury in the bottle and not let it be sucked into the dental unit. Other devices for recovering mercury include handheld pumps, aspirator bulbs, or plastic syringes. Sponges are generally not effective for mercury cleanup. Adhesive tape, tin foil, or a fresh mix of dental amalgam can remove droplets of mercury if undisturbed. Reagents that combine with mercury may facilitate cleanup. Commercially available spill cleanup kits that contain a combination of these devices and materials have proved useful. A household vacuum cleaner should not be used on spilled mercury or on contaminated floors.

  1. The adverse effects of mercury poisoning have been investigated by many researchers and are well documented. The dental profession should be sufficiently informed on both diagnosing and preventing systemic toxicity.

  2. Occupational exposure to mercury is a potential hazard for dental personnel, but is completely preventable with the implementation of proper mercury hygiene practices.

  3. There is no evidence in the scientific literature that the minute amounts of mercury vapor that may be released from amalgam restorations pose a health threat. Allergic reactions to mercury and other constituents of amalgam have been documented, but are exceedingly rare.

  4. Dental amalgam, which has been used extensively for more than 100 years, has an exemplary record of safety and benefit to the dental patient.

  5. Although it is practically impossible to totally eliminate mercury contamination in the dental workplace, adherence to the aforementioned guidelines should minimize health risks associated with exposure to mercury. Prevention of exposure is most readily accomplished by reducing the chance that mercury will be released into the environment.

A literature review and synopsis of mercury hygiene issues by the Air Force Dental Evaluation and Consultation Service can be found at:

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