Study Of Children's Fillings Finds No Mercury Exposure

April 08, 1999

CHAPEL HILL - Mercury exposure from dental amalgam fillings poses no threat to children's health, according to a new study by researchers at the University of North Carolina at Chapel Hill School of Dentistry.

Environmental exposure to mercury was low in the North Carolina children studied, the scientists said, and they could detect no additional exposure to mercury from dental work done to primary teeth, also known as baby teeth.

A report on the findings appears in the current issue of Pediatric Dentistry. Authors are Drs. Diane Dilley, associate professor of pediatric dentistry, and James W. Bawden, Alumni Distinguished professor and former dean of dentistry, both at UNC-CH.

"We compared primary teeth from children who had had fillings with primary teeth from children without fillings," Dilley said. "We did find tiny amounts of mercury in the teeth we examined, but statistical analysis showed no correlation between the number of fillings and the amount of mercury present.

"In other words, the children we studied not only got very little mercury from their environment, they also got none we could detect from the fillings," she said. "They were safe from mercury exposure."

Mercury contained in dental fillings has been a concern to a small percentage of people over the past several decades because mercury can have devastating effects at higher concentrations in the body, she said. Overexposure to environmental mercury through industrial waste water, for example, caused severe nerve damage and mental retardation among children living near Minamata Bay, Japan, in the mid-1950s.

With no scientific evidence to support their claims, however, some people have said mercury fillings caused multiple sclerosis and numerous other maladies, Dilley said.

Comparisons of primary teeth excavated from beneath a 12th-century Norwegian church with primary teeth collected from Norwegian children in 1971 and 1972 showed the latter contained 10 times as much mercury as teeth from the pre-industrial age children. Studies of rats exposed to mercury vapor showed mercury stored in rat molars correlated closely with levels of mercury to which the animals had been exposed intentionally.

For those reasons, the UNC-CH researchers felt that mercury levels in primary teeth could reflect total mercury exposure and be used to determine if mercury from fillings added measurably to total exposure. Using a sophisticated technique known as atomic absorption spectrophotometry, the scientists analyzed mercury concentrations in 27 primary teeth and in urine samples from 21 children and evaluated dietary surveys completed by parents of 26 children.

Only two subjects had detectable mercury concentrations in their urine, and those were low. Levels in six children who ate seafood regularly did not differ significantly from those who ate little or no seafood.

"We had an ideal situation to measure mercury, and we could find no evidence that amalgam fillings contributed any measurable amount of it," Bawden said. "This work is good news for most places in central North Carolina because it means our children aren't being exposed to much environmental mercury. It's also good news on a much larger scale because it indicates that children are not getting significant amounts of mercury from their fillings."

Testing baby teeth or others that have come out for various reasons may now be recognized as the most accurate way of determining long-term mercury exposure, he said. Children living near industrial areas using such harmful metals as lead and mercury might need to be tested periodically for environmental exposures to ensure their safety.

The National Institute of Dental Research and the U.S. Public Health Service's Bureau of Maternal and Child Health supported the study.
Note: Dilley can be reached at 919-966-2739, Bawden at 919-966-1165.

University of North Carolina at Chapel Hill

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