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Now that the FDA has revised its position on mercury in amalgam fillings, acknowledging that it may have neurotoxic effects on the nervous systems of developing children and fetuses, it is considering revising its rules about dental amalgam. As familiar as we are with these fillings, it may come as a shock to learn that amalgam fillings are 40 to 50 percent mercury by weight and release mercury vapor when we chew. Mercury can have neurotoxic effects, which is especially an issue for the developing brains of small children and fetuses.

How concerned should we be? A five-year study in New England published in JAMA (April 19, 2006 ) followed 534 children aged six to ten with cavities, half of whom received amalgam fillings and half of whom received resin composite fillings. The researchers found no differences in IQ between those with mercury fillings and those without. A seven-year study of 507 children (ages eight to ten) in Lisbon, Portugal found no difference in memory, attention or other measurements of nerve function and responses.

An accompanying JAMA commentary cautioned against overly optimistic interpretations of these results, noting that the five- and seven-year periods may miss later developments and that distinctions that were too fine for the study to make may have large-scale effects given the number of children receiving amalgam fillings. Genetic differences may also result in higher risk for some groups. These are currently the only randomized clinical trials of amalgam fillings.

Despite the mercury content, the FDA recommends against having fillings removed. Doing so may increase your exposure. As for any new fillings for yourself or your children, discuss all options with your dentist and voice your concerns. Note that recent evidence indicates that resin composite fillings may have hormonal effects.

Lastly, the FDA is has reopened the comment period for the proposed rule on classifying amalgam fillings and has asked for comments "supported by empirical data and scientific evidence."