Most Canadians having dental amalgam in their mouth are exposed to mercury at levels surpassing the reference exposure level (REL)

Mercury amalgam restorative material generally contains 50% mercury in a complex mixture of copper, tin, silver, and zinc. Mercury is a strong toxin and has been demonstrated to have damaging effects on the kidney, central nervous system, and cardiovascular system. Realizing the dangers of mercury amalgam, Norway, Denmark, and Sweden have enacted legislation that has banned mercury amalgam in their countries.

Dental amalgam fillings are a major source of mercury exposure in Canada, compared to food (including fish), indoor and outdoor air, drinking water and soil. The primary route of exposure to mercury from amalgam is via inhalation of elemental mercury vapor emanating from in-place amalgam fillings. It has been well documented that this mixture continually emits mercury vapor, which is dramatically increased by chewing, eating, brushing, and drinking hot liquids.

Despite such well studied mercury exposure by dental amalgam, US FDA considers dental amalgam fillings safe for adults and children ages 6 and above. The agency states that "the amount of mercury measured in the bodies of people with dental amalgam fillings is well below levels associated with adverse health effects".

After years of negotiations, 19 January 2013, Governments agreed to the text of a global legally binding instrument on mercury and gave birth to the “Minamata Convention on Mercury”. This  mercury treaty is meant to lift health threats to the lives of millions of people worldwide by a global legally-binding treaty to prevent mercury emissions & releases to the environment. Interestingly the use of mercury in medical applications was widely excluded from the ban.

This new study is the first North American population-based survey to specifically quantify the dental amalgam load. It is based on the Canadian Health Measures Survey (CHMS) conducted between 2007 and 2009, by Health Canada and Statistics Canada, using a statistically representative population survey of 5,604 Canadians aged 6 years to 79 years. Unique to this survey was the collection of data for survey participants of the number of tooth surfaces that were specifically restored with dental amalgam. Besides the data on the number of dental amalgam restorations, the CHMS further included urine analysis for mercury concentration (UHg), providing a direct measure of the incremental increase in UHg per amalgam-filled tooth surface. The focus of this study was to determine the exposure to Hg from dental amalgam among participants of the CHMS, and then to extrapolate those results to the Canadian population older than 6 years of age. Subsequently from the total exposed population, the author calculated the number of Canadians expected to exceed the dose associated with the Canadian chronic reference exposure level (REL) for elemental mercury, as well as the number of amalgam-filled tooth surfaces that should not, on average, result in exceeding the dose associated with that Canadian REL.

The results of this study show that about 64% of all Canadians aged 6 years and older cary one or more amalgam-restored tooth surfaces. Altogether the Canadians have about 191 million amalgam surfaces, representing about 76.4 million amalgam-restored teeth.  The total mass of Hg carried in those teeth is approximately 38 metric tons. Of Canadians with dental amalgam restorations, 80.4% experience a daily dose of Hg that exceeds the Canadian REL-associated dose. The number of amalgam surfaces that will not result in exceeding the REL-associated dose varied from two amalgam surfaces (children, both sexes) to seven surfaces (adult males).

The author notes that "it is apparent from the decline in amalgam placement, and increase in use of alternate materials, that viable alternative (non-Hg) restorative materials exist and reliance on dental amalgam for the restoration of carious teeth is no longer necessary or essential". Anyhow, the UNEP Mercury treaty has not banned the further use of dental amalgan, but allows to phase down amalgam use over a time period appropriate to domestic needs, an approach advocated by the World Health Organisation (WHO).