A number of studies have attempted to link dental amalgam to adverse health effects, but literature reviews by national and international public health agencies and organizations continue to concur that amalgam is a safe and affordable restorative material. A 2015 review by the Scientific Committees of the European Commission on the safety of dental amalgam concluded that, while “reduction in the use of mercury in human activity would be beneficial…no increased risks on adverse systemic effects have been documented in the general population as a whole and it is considered that the current use of dental amalgam does not pose any risk of systemic disease.”21 A 2017 systematic review of the potential effect on autoimmunity from various forms of mercury found “no evidence to implicate a role for Hg0 [elemental mercury] exposure from dental amalgams in the development or perpetuation of autoimmune disease, apart from some suggestion of individual sensitivity.”22
Allergic reactions related to dental amalgam are experienced in less than 1% of the treated population, and usually consist of contact dermatitis, oral lichenoid lesions, gingivitis, and stomatitis; removal of the amalgam normally relieves these symptoms.2, 11, 23 Amalgam is associated with burning mouth syndrome less frequently than other dental materials.23, 24 Allergy to mercury is as common as allergies to any metal, although in vitro tests have demonstrated higher cytotoxicity levels in copper and zinc than mercury.11
Mercury appears in elemental, inorganic, and organic forms; the organic form is the primary health concern, as this form is the type commonly found in fish, as methyl mercury (MeHg).2, 25, 26 Elemental, or metallic, mercury (Hg0) is liquid at room temperature and is the form used in dental amalgam, as well as in thermometers and batteries. Up to 80% of mercury vapor can be absorbed by the lungs and released into the circulatory system after which it accumulates in tissues.2, 27, 28 The renal system, the central nervous system, and the developing fetus are particularly vulnerable to mercury toxicity.2, 27, 28 Elemental mercury is poorly absorbed by the digestive system, but trace levels of mercury vapor may be released by amalgam restorations, particularly during chewing, although studies consistently show that mercury leakage from amalgam restorations is within safe limits established by the EPA and other public health organizations.29, 30 Further, scientific studies do not support the association between dental amalgams and effects on the renal and central nervous systems despite their vulnerability to mercury toxicity.2, 27, 28
Although the World Health Organization has estimated that 2 µg/kg body weight per day as the tolerable intake of total mercury per day,30 the U.S. EPA uses a more stringent estimate of 0.1 µg/kg/day.29 The EPA estimate translates to approximately 5.8 µg/day for a 130-pound person. In terms of levels of inhaled mercury vapor, U.S. EPA and the Agency for Toxic Substances and Disease Registry have established 0.2 µg/m3 as the minimal risk level (MRL).31-33
Amalgam restorations release mercury vapor equivalent to approximately 0.2 to 0.4 µg/day for each amalgam-filled tooth surface.34, 35 These values are below the EPA established reference dose of 0.1 µg/kg/day25 (approximately 5.8 µg/day for a 130-pound person).
Overall, the data demonstrate that over time, mercury exposure in the U.S. has been on the decline and that exposure levels in the general population have been below levels of regulatory concern.
The Canadian regulatory authorities published a health technology assessment (HTA) evaluating safety and effectiveness of dental amalgam in 2018.36 It compared amalgam and composite resins in permanent teeth in children and adults. It concluded that both materials were clinically safe. Cost effectiveness analysis found amalgam to be the less costly option. It was suggested that the decision about which material to use should be made jointly with the patient and noted that development of cost-effective and safe amalgam substitutes remains an important goal of the research community.36
Occupational Exposure and Mercury Hygiene
A 2015 study37 looked at occupational exposure of mercury among a convenience sample of dentists and found their levels to be similar to that of the U.S. general population. A 2016 study38 found increased inorganic and total blood mercury concentrations in the U.S. population with dental fillings (not specifically amalgam) during the 2003-2004 NHANES study. Whereas an increase in inorganic, total, and MeHg blood concentrations was observed during the 2010-2012 NHANES,38 the same study38 found a decrease in mercury blood levels for the period 2011-2012 (up to 0.99 µg/L total Hg) as compared to 2003-2004 (up to an average of 1.17 µg/L total Hg); and a 2017 study on NHANES data found a decrease in total and inorganic blood mercury levels in the U.S. population between 2005 and 2012.39 These reported values are well below the EPA reference dose of MeHg equivalent of 5.8 µg/L.29
As part of its mercury hygiene guidance,15 the World Dental Federation (FDI) recommends the use of precapsulated mercury/alloy as the preferred technique to avoid bulk mercury spills and to eliminate the mercury dispenser as a source of mercury vapor. To avoid potential occupational exposure to mercury, FDI recommends 1) avoiding direct skin contact with mercury or freshly mixed amalgam and 2) avoiding exposure to potential sources of mercury vapor (e.g., during placement and condensation of amalgam, during polishing or removal of amalgam, or from malfunctioning or leaky equipment).15 FDI recommends use of high-volume evacuation systems fitted with traps or filters when polishing or removing amalgam as well as following best practices for amalgam waste (please see the ADA Oral Health Topic, “Amalgam Separators and Best Waste Management” for more information about amalgam waste). Phillips’ dental materials textbook also recommends the use of suction and water spray when amalgam is being ground.2 Use of a dental dam when placing or removing amalgam may have some utility in reducing mercury exposure, but the data on this are limited and any effect seen may be small in magnitude and of transient duration.16-18
FDI recommends cleaning amalgam contaminants from instruments before heat sterilization and avoiding heating mercury or amalgam or any equipment used with amalgam.15 Additionally, FDI recommends installation of impervious, easy-to-clean surfaces in the dental operatory, including continuous seamless-sheet flooring extending up the walls and working in well-ventilated areas, with fresh air exchanges and outside exhaust.15