Study tracks risk of mercury fillings

The first clinical trials to study the safety of mercury amalgam dental fillings showed no mental or physical impairments in children carrying the fillings for as long as seven years, according to two studies published today in the Journal of the American Medical Association.

“If I were a parent or a dentist looking at these trials, I would have to conclude that we should stick with amalgam,” said epidemiologist Sonja M. McKinlay of the New England Research Institutes, who led one of the trials.

Critics, however, charged that the studies were not designed to detect problems that might manifest themselves in adulthood, as has been observed with some other metals such as lead.

“The question of subtle effects remains open,” wrote Dr. Herbert Needleman of the University of Pittsburgh School of Medicine in an editorial in the same journal.

Mercury amalgam fillings are the most commonly used filling because they are cheaper, easier to use and more durable. Resin composites are typically used for cosmetic reasons in front teeth, but are not as durable as amalgam and their long-term health effects are unknown.

Gold fillings, which do not contain mercury, are also used, but they are much more expensive and more difficult to install.

Mercury is toxic in sizable doses – such as those ingested when eating substantial quantities of mercury-contaminated fish, for example – and critics have charged that it must therefore produce damaging effects at lower doses as well.

A series of epidemiological studies over the years, however, have shown no link between dental fillings and neurological or other problems.

Two decades ago, the development of new, more sensitive instruments revealed that minute traces of mercury vapor escape from the fillings, sparking renewed concern about the potential health effects. The current studies were begun in 1996 to address those concerns.

McKinlay and her colleagues studied 534 children at dental clinics in New England who previously had no fillings. Half were assigned to receive mercury amalgam fillings and the other half, white composite resin fillings like those typically used for cosmetic purposes on front teeth.

Epidemiologist Timothy A. DeRouen of the University of Washington and his colleagues studied a group of 507 children in Portugal using a similar protocol.

The researchers found no changes in IQ, memory, attention, visual functioning or nerve signaling over the course of the study.