ATHENS, Ga., Sept. 28 (UPI) -- The amount of mercury in dental amalgam -- the mixture of metals used most often for fillings -- is small, but the more fillings a person has the higher risk they will feel the effects of exposure to the metal.
People with eight or more fillings may be exposed to unhealthy levels of mercury, at least partially due to the way it changes in the body, researchers at the University of Georgia report in a study published in the journal Ecotoxicity and Environmental Safety.
Dental amalgam is a mixture of metals -- about half mercury, with silver, tin and copper making up the rest -- that has been used for more than 150 years because it is cheap and durable.
Mercury has long been known to be bad for health, causing brain, heart, kidney, lung and immune system damage with exposure at high levels, but at lower levels is considered relatively safe depending on its use.
"It's important for doctors and patients to be informed in their selections," Lei Yin, a researcher in the department of environmental health science at the University of Georgia and lead author of the study, said in a press release. "We now have an excellent starting point to evaluate the potential risk of dental material on human health."
For the study, researchers analyzed the levels of several types of mercury in the bodies of 14,703 dental patients, grouping by the number of fillings they had received over the course of their lifetimes as either zero, one to eight or more than eight.
The researchers found people with more than eight fillings had about 150 percent more mercury in their blood than those with no fillings. The average American has three fillings, and about 25 percent of Americans have 11 or more fillings, the researchers report.
"Tooth decay is one of the most prevalent chronic diseases," Yin said. "I think a majority of people have experienced dental fillings, but the kind of materials the dentist uses isn't something that's really discussed."