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.
A large 2006 study found no statistically significant differences in IQ, motor function, or memory in children who had numerous mercury-containing amalgams. It did find that kids with amalgams had significantly higher mercury levels in their urine, but researchers observed no problems in kidney function that could have resulted from mercury poisoning. Another study, published in February in the Journal of the American Dental Association, supports the 2006 findings. Its Portuguese authors found no significant differences in brain function between a group of children whose cavities had been treated with amalgams and a group treated with composite resin material.
But some experts are not convinced amalgams are safe. One of the groups leading the charge against the use of amalgams is the International Academy of Oral Medicine and Toxicology, which funded one of the original studies, published in 1991, on mercury and dental amalgams. The group's past president, David Kennedy, a retired dentist in San Diego, is convinced that studies showing exposure to mercury in children and adults, as well as in the fetuses of mothers with amalgam fillings, should be enough to convince the FDA to ban the material. At the very least, says Kennedy, the FDA should require dentists to obtain an informed consent from patients who choose amalgam fillings.
The ADA, on the other hand, last month advised the FDA against adding warning labels or requiring informed consent, arguing that doing so may cause some patients who are already apprehensive about the dentist to avoid dental care altogether. The ADA contends that while microscopic amounts of mercury may be excreted into the body from fillings, no study has linked the presence of those amounts with adverse health outcomes.
The resin alternative. The primary alternative to silver amalgams is composite resin, a tooth-colored material that bonds tightly to the tooth inside the cavity. These fillings are becoming more popular because of their cosmetic appeal and because the strength of the material has improved considerably in the past few years. Dentists do not have to remove as much of the tooth when using resin fillings as they do when using amalgams. But, according to one study, composites may have to be replaced as much as 50 percent more often than silver fillings.