What's in Your Teeth Doesn't Affect Your Brain

During the past decade or so, increasingly sensitive technology has shown that some of the mercury in silver dental fillings is vaporized with chewing. And links have been found between urine, blood, and tissue levels of mercury and the number of silver fillings people have.

Nonetheless, studies that have attempted to answer the question of whether mercury in silver fillings is harming people's health have come up with contradictory results. None of the studies, however, was a randomized clinical trial.

Now the results of two such trials have been published in the April 19 JAMA. Neither found neurocognitive damage from silver fillings containing mercury.

Sonja McKinlay, Ph.D., president of the New England Research Institutes, and her colleagues recruited approximately 500 children for their study. The children were aged 6 to 10, had never had fillings before, and had decay in at least two posterior teeth that needed to be removal and filled.

The children were randomized to receive, as replacement material, either silver fillings or white fillings (a resin composite material that was developed as an alternative to silver fillings and does not contain mercury). Children in both groups were matched for age, gender, race, I.Q., and other possibly confounding variables. If they needed fillings during the next five years, they received the same kind they had initially received.

Both at the start of the study and at the five-year follow-up, subjects were measured for urine levels of mercury and tested for I.Q., learning, memory, and visual-motor performance.

After five years, the silver-filling group had significantly higher levels of mercury in their urine than did the white-filling group, the investigators found—that is, 0.9 ug/g versus 0.6 ug/g creatinine-adjusted levels. Nonetheless, the 0.9 ug/g was comparable to average levels reported for American adults and within the range generally considered safe. Furthermore, the silver-filling group, like the white-filling one, experienced increases in I.Q., learning, memory, and visual-motor scores from the start of the study. Moreover, there were no statistically significant differences in five-year scores between the two groups. In fact, children in the silver-filling group who had received the most silver fillings scored slightly higher on I.Q. at five years than did children who had received fewer silver fillings.