Old "silver" dental fillings, also called amalgams, may not be as toxic as many people feared. A new study that examined the surface chemistry of silver-colored, mercury-based dental fillings suggests that the surface forms of mercury may be less toxic than previously thought. The study appears online in American Chemical Society journal Chemical Research in Toxicology.
In the study, Graham George of the University of Saskatchewan and colleagues note that mercury-based fillings have been used by dentists to repair teeth for more than a century. In recent decades their use has become controversial because of concerns about exposure to potentially toxic mercury. However, mercury can exist in several different chemical forms, each with a different toxicity. Prior to this report, little was known about how the chemical forms of mercury in dental amalgam might change over time.
"The dental amalgam on the surface of an old tooth filling may have lost as much as 95 per cent of its mercury but what’s left is in a form that is unlikely to be toxic in the body," study leader Graham George said in a statement.
The scientists analyzed the surface of new metal fillings using a special X-ray method and compared them with the surface of fillings about 20 years old. New fillings contained metallic mercury, which can be toxic. Aged fillings, however, contained a form of mercury, called beta-mercuric sulfide or metacinnabar, which is unlikely to be toxic in the body.
The surfaces of metal fillings appeared to lose up to 95 percent of their mercury over time. The loss could be due to factors including evaporation, dental hygiene products (those containing peroxide, for example), and foods that contain sulfur, including onion, garlic and coffee.
Even though the scientists warned that mercury from old fillings may not be as harmful as thought, exposure to mercury from lost fillings is still a concern, as well as mercury from other sources, including fish.
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