Millions of people have them in their mouths, yet their widespread use in treating cavities is one of the more contentious issues in dentistry. So-called silver amalgam fillings contain about 50 percent mercury, with the remaining material made from a powder of silver, tin, zinc, and copper. Some experts are concerned that the release of microscopic amounts of mercury vapor—a consequence of chewing food, grinding teeth, and exposing the fillings to hot substances—might cause neurological problems or kidney damage, particularly in sensitive populations, such as children and pregnant women. Others, including the American Dental Association, say the safety data are reassuring. The Food and Drug Administration is taking a closer look.
"We know that mercury can have toxic effects on the nervous system, but it has not yet been determined that dental amalgams have adverse health effects because of their mercury content," says Mary Long, an FDA spokesperson. "But we are examining the evidence and performing a risk-based evaluation to see if more special controls on safety and effectiveness are justified." The agency is considering whether to change the classification and labeling of the product, which would allow tighter safety regulations and possible warnings to patients about any health risks. The FDA is expected to issue a ruling next summer.
The American Dental Association supports the agency's review but says that, based on the available evidence, limitations on the use of amalgam fillings or warning labels directed to certain types of patients are not warranted. "We've looked at silver amalgams harder than any other filling material, and there's just no evidence that it harms any of the sensitive groups," says J. Rodway Mackert, a spokesperson for the ADA and a professor of dental materials at the Medical College of Georgia's School of Dentistry.
There were no statistically significant differences in neuropsychological and neurobehavioral effects among children whose dental caries were treated with mercury amalgam fillings and those treated with a composite dental restorative material, according to two studies in the April issue of JAMA.
Dental (silver) amalgam is a widely used restorative material containing 40 - 50 percent elemental mercury that emits small amounts of mercury vapor, according to background information in the articles. Because mercury is an acknowledged neurotoxin, there are widespread concerns about the health effects of exposure to this metal. But no randomized trials have been previously published that address the concern that inhalation of mercury vapor released by amalgam dental restorations causes adverse health effects. It is estimated that more than 70 million dental amalgam restorations are placed annually in the U.S.
David C. Bellinger, Ph.D., M.Sc., of Children's Hospital Boston, and colleagues compared the neuropsychological and renal (kidney) function of children whose dental caries (cavities) were restored using amalgam or mercury-free materials. Between September 1997 and March 2005, the researchers studied 534 New England children, aged six to ten, who were randomly assigned to receive either amalgam or resin composite materials. The children had an average of 15 tooth surfaces restored during a five-year follow-up.
