For close to 150 years, dental fillings that contain mercury and other metals have been used to fill cavities. And for the most part, these fillings, known as amalgam, have maintained a good safety record.
But mercury is a known neurotoxin, and little medical research has been done investigating whether the trace amounts of mercury that fillings slowly release could produce any sort of negative cognitive effects, especially when used in children's mouths.
However, several new studies published in this week's issue of the Journal of the American Medical Association offer some reassurance that amalgam fillings are safe.
In one study, 534 New England area children were given either amalgam or mercury-free fillings after a cavity was detected. After five years, there was no statistically significant difference between the two groups when it came to measuring IQ, memory or visual-motor abilities. One notable difference: Children in the amalgam group showed higher levels of mercury in their urine.
Another study of 507 children in Lisbon, Portugal, detected a similar pattern, and found no notable differences in measurements of intelligence. "Both studies support the continued use of dental amalgam as an important treatment option," reads a statement from the American Dental Association.
Overall, amalgam fillings are used less frequently than they were 20 or so years ago, mostly because of their unsightly, metallic appearance. Instead, composite fillings have become increasingly common, since they look more like natural teeth, said dentist Rod Mackert, a professor of dentistry at the Medical College of Georgia and an ADA spokesman on the issue.
Still, an estimated 70 million amalgam fillings are done each year in the United States, so the new studies that look at any dangers are important, Mackert said.
"These were very positive [results]," he said.
However, just two studies on the matter does not mean that amalgam fillings are "risk-free," said University of Pittsburgh School of Medicine dentist Herbert Needleman, in an editorial accompanying the studies.
Longer studies that follow more children may show important differences in cognitive abilities, Needleman said.
"The question of more subtle effects remains open," he said.