Exposure to the heavy metal mercury can wreak havoc on the nervous system. So it's no surprise that the use of mercury in dental fillings has triggered controversy, especially when dentists give them to growing children. Now, two new clinical trials indicate that mercury fillings are no more harmful to a child's brain than non-mercury fillings. But that doesn't prove it's risk-free, warn some scientists.
Dental amalgam consisting of up to 50% mercury has been a popular treatment for cavities for almost 2 centuries. Every year, dentists use it to treat almost 70 million cavities--a little less than half of the total cavities filled. That's because it's less expensive, easier to apply, and lasts longer than composite resin fillings. Some research indicates that vapors from mercury fillings may be linked to diseases such as multiple sclerosis and Alzheimer's disease in adults. But until now, there were no randomized clinical trials of its effects on children.
Two research groups examined whether children with mercury fillings were more likely to develop neurological problems than did those with non-mercury resin fillings. Teams from the University of Washington in Seattle and the New England Research Institute in Watertown, Massachusetts, each treated more than 500 children with existing cavities. Half received amalgam fillings; the other half, resin fillings. Although the children treated with amalgam had notably higher mercury levels in their urine than their counterparts during the 5 and 7 year studies, there was no significant difference in IQ, memory, or attention. "I would think this would put to bed the issue about whether the vast majority of kids are going to experience adverse effects" to mercury amalgam, says Timothy DeRouen, a University of Washington biostatistician and a co-author of one of the two papers in this week's issue of the Journal of the American Medical Association.
"These sorts of trials are well overdue," says Michael Bates, an epidemiologist at the University of California, Berkeley. But he adds that overall, the link between fillings and health problems is still poorly understood and warrants more investigation. Pediatrician Herbert Needleman is even more cautious. The research "cannot be used to say there's no risk," says Needleman, who studies lead exposure in children at the University of Pittsburgh in Pennsylvania. Longer studies with more patients might reveal a subtle difference between the two groups, he says. And, Needleman notes, the researchers acknowledge that they didn't consider children who are genetically predisposed to high mercury sensitivity. "There's going to be a tidal wave of people saying, 'See, dental amalgam is safe,'" he says. "I don't think that's a scientific conclusion."