CHICAGO — Dental fillings containing mercury do not cause measurable neurological problems in children who have had the fillings for at least seven years, according to two studies, including one by University of Washington researchers.

The studies, published today in the Journal of the American Medical Association, are the first to compare children receiving mercury amalgam fillings with children who got mercury-free fillings made of composite materials. The reports, however, are unlikely to end a fierce debate over the issue.

"We didn't see any indications of harm to these kids," said Dr. Timothy DeRouen, a UW professor of biostatistics and dental public-health sciences, who led a study of 507 children, ages 8 to 10, in Portugal to determine if mercury fillings had neurological effects. "And we tested them repeatedly over seven years."

He added, "This is the only objective evidence we have at this point. ... Everything else is anecdotal."

Mercury amalgam is a silver-colored powder of silver, copper, zinc and other metals held together by mercury. It has been used to fill cavities for more than 150 years because the material is relatively cheap and long-lasting. U.S. children now have an estimated 100 million amalgam fillings.

However, the use of amalgam has declined sharply over the past 15 years, in part because patients increasingly prefer the look of composites, which better match the natural color of teeth. Seventy percent of fillings in the United States are now done with composite materials, generally a combination of plastic and silicate, according to the American Dental Association.

Although the findings from the two studies may allow parents to breathe easier about mercury fillings, they still leave open the question of subtle neurological problems that may occur over decades.

"The studies indicate that on average we probably don't have much to worry about from amalgam used in the quantities that it is used for dental purposes," said Dr. David Bellinger, a neurologist at Harvard Medical School and lead author of The New England Children's Amalgam Trial.

"The studies do leave open the question that there could be some small percentage of children who are particularly sensitive [to mercury] and we wouldn't have been able to detect them in our study," he said.

A number of population studies have failed to find a link between mercury fillings and learning or memory problems. But, because chewing can release a tiny amount of mercury vapor from fillings, scientists have been cautious about giving the metal a clean bill of health.

Bellinger's trial, funded by the National Institutes of Health, was designed to assess the risks directly. It involved 534 children from the Boston area and Farmington, Maine, who were 6 to 10 years old and who never had a cavity filled, despite needing dental care. Half of the children were randomly assigned to receive mercury amalgam fillings and the other half a mercury-free composite. The average child received 10 fillings.

After five years, researchers found no significant difference between the two groups in IQ scores, memory, visual-motor function and kidney function. The children were evaluated yearly.

Children receiving the amalgam fillings had 50 percent more mercury in their urine than those getting the composites, Bellinger said, although the levels were still relatively low.

Children with amalgam fillings averaged 0.9 micrograms of mercury in their urine, compared with 0.6 in children with composite fillings. (A microgram is one-millionth of a gram.) Levels of mercury in urine greater than 50 micrograms have been associated with neurological, kidney and immunological impairment.

Other common sources of mercury exposure include contamination in some foods, such as fish, and air pollution.

In the second study, headed by DeRouen, the children were randomly assigned to receive mercury or composite fillings. Over the study period, children in the amalgam group had an average of 18.7 fillings and children in the composite group had an average of 21.3 fillings.

After seven years, the researchers found no significant differences in neurological function between the two groups.

The only difference was that the children with the composite fillings were 50 percent more likely to need their fillings replaced.

"These findings, combined with the trend of higher treatment need later among those receiving composite, suggest that amalgam should remain a viable dental restorative option for children," DeRouen said.

Dr. J. Robert Kelly of the University of Connecticut, speaking for the American Dental Association, said: "This adds to a growing body of opinion that dental amalgam is a safe and effective material. I am absolutely convinced that it is not a health issue."

Others cautioned against reading too much into either study.

"It is predictable that some outside interests will expand the modest conclusions of these studies to assert that use of mercury amalgam in dentistry is risk-free," Dr. Herbert Needleman, a professor of psychiatry at the University of Pittsburgh, wrote in an accompanying editorial. "This conclusion would be unfortunate and unscientific."

Charlie Brown, counsel for Consumers for Dental Choice, an advocacy group pushing to end the use of mercury in dental fillings, said both studies ignore research that indicates mercury causes a host of physical and mental problems.

He also blasted both studies as unethical, saying children or their guardians never were told of the potential risks of mercury fillings.

Authors of both studies disputed that contention, saying they disclosed what they were doing and why. And, DeRouen said, "We weren't doing anything experimental. We were giving standard dental treatment."

DeRouen said a UW review board found the allegation to be unfounded.

Material from the Los Angeles Times and The Associated Press is included in this report.

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