Two long-awaited, government-funded studies found no evidence that dental fillings containing mercury can cause IQ-lowering brain damage or other neurological problems in children.
Children with such fillings were no more likely than other youngsters to suffer such problems, the researchers said.
Some experts found the findings powerfully reassuring. But the studies are unlikely to end the fierce debate over the long-term effects of what are known as amalgam fillings, and some advocates bitterly accused the researchers of conducting unethical experiments on children.
Amalgam fillings, also called silver fillings, are made of mercury and other metals and have been used by dentists for more than a century. But their use has dropped in recent years as more and more doctors switch to resin composite fillings, which are considered more appealing because they are white.
Some advocacy groups and dentists have long contended that the mercury in fillings can leach into the body and cause harmful neurological effects, including autism.
The latest studies were published in Wednesday’s Journal of the American Medical Association.
“We didn’t see any indications of harm to these kids,” said Dr. Timothy DeRouen, a University of Washington 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 any neurological effects. “And we tested them repeatedly over seven years.”
The other study, led by Dr. Sonja McKinlay of the New England Research Institutes, looked at the effect on intelligence, memory and other mental functions, and kidney function. It involved 534 children in New England, ages 6 to 10.
McKinlay said she is confident that such fillings are safe for children in this age group, in large part because the youngsters were given far more amalgam than the average American child gets.
“If there was no sign of any health problems from this study in these kids with all this amalgam in their mouths ... you know it is going to be safe for kids in the same age group in the rest of the country because they are getting much less exposure,” she said.
McKinlay also said that while the study revealed children with the mercury fillings had higher mercury levels in their urine, there was no evidence they had a higher incidence of kidney damage.
Neither study examined autism. Dr. David Bellinger, an author of the New England study, said that autism is so rare that it wouldn’t be expected to be found among the number of children studied. Also, any children with autism would have been eliminated from the study, as would other children with prior neurological disorders.
The National Institute of Dental and Craniofacial Research funded the studies.
“From a scientific point of view, it gives us the confidence that these findings are not equivocal and the similarity suggests that the results are real,” said Dushanka Kleinman, the institute’s deputy director.
An American Dental Association official said the studies offer convincing confirmation of what previous studies have said. “This will give patients the reassurance they are making a safe and good choice,” said Dr. Frederick Eichmiller, director of the ADA’s Paffenbarger Research Center.
The authors acknowledged the limitations of the studies. For example, in the study of the New England children, the authors said the “possibility of very small adverse effects of amalgam on IQ score cannot be completely ruled out.”
Not the final word, some say
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.”
He said, for example, it is not clear whether either study could measure subtle effects on IQ.
Jim Adams, a chemistry professor at Arizona State University and president of the Phoenix chapter of the Autism Society of America, said more research is needed, particularly on the effects that mercury fillings in pregnant women have on their fetuses.
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.
Brown blasted both studies as unethical, saying that children or their guardians were never told of the potential risks of the mercury fillings.
Authors of both studies disputed that contention, saying they disclosed what they were doing and why. And, said DeRouen, “We weren’t doing anything experimental. We were giving standard dental treatment.” DeRouen said a review board at the University of Washington found the allegations to be unfounded.
Pat El-Hinnawy, a spokeswoman for the federal Office for Human Research Protections, said DeRouen’s study is under investigation.
An anti-amalgam group called the International Academy of Oral Medicine and Toxicology also announced it was filing ethics complaints with Harvard, the University of Washington and other institutions that took part in what it characterized “outrageous” experimentation on children.