Dangers of Mercury Fillings

Mercury-based dental amalgam fillings were first used as a dental restorative in France in 1826.  Mercury dental amalgams are an almost ideal substance for restorative work, with easy installation, low creep, minimal dimensional change, and high compressive strength. Typically, amalgam fillings will outlast other restorative materials.  It is estimated that the average American adult has seven mercury amalgam dental fillings.

In recent years dental amalgam has been seen as a source of human exposure to potentially toxic mercury. In addition, its disposal can also be a source of environmental mercury pollution. As a result the use of mercury-containing dental amalgams has become controversial and has been banned in several European countries. In North America, the traditional view is that the advantages of mercury-containing amalgam outweigh any possible health risks and is still widely used.

While the absolute danger has not been established, it is known that the mercury can enter the human system from evaporation of mercury from the surface of the filling and subsequent inhalation, leaching of mercury into saliva, and the migration of mercury through the tooth dentinal tubules from where it could enter the blood supply to the pulp.

The study at the University of Saskatchewan in Canada looked how mercury in the amalgam changed over time. Mercury can exist in several different forms, each with a different level of toxicity. 

Using a special X-ray technique, the scientists analyzed the surface of freshly prepared metal fillings and compared these with the surface of aged fillings (about 20 years old) from a dental clinic. Fresh fillings contained metallic mercury, which can be toxic. Aged fillings, however, typically contain a form of mercury, called beta-mercuric sulfide or metacinnabar, which is unlikely to be toxic in the body. However, the scientists found that the surfaces of metal fillings seem to lose up to 95 percent of their initial mercury content over time.

The original mercury goes through significant chemical reactions over time, implying that there is a release of mercury. And though the final state of mercury found in older dental fillings may be less toxic, the question remains just how much of the more toxic original mercury was separated from the original amalgam and entered the body.

In summary, the researchers lead by George Graham concluded that “the use of electron yield Hg LIII XAS reveals the formation of β-HgS on the surface of an aged dental amalgam restorative, a chemical form that is biounavailable and unlikely to pose a toxic hazard. Of greater concern, perhaps, is the nature of the surface mercury that has been lost from the amalgam, estimated here to be up to 95% of that of a fresh filling. Possibly this missing mercury is in the form of β-HgS abraded from the surface of the filling, or alternatively, it predominantly corresponds to mercury lost prior to formation of β-HgS by the established mechanisms discussed above. Whatever the cause, human exposure to mercury lost from fillings is still of concern.”