TORONTO — No evidence of lower IQ in kids after mercury amalgam fillings: studies

Two highly anticipated studies have found no evidence that "silver fillings" cause neurological problems in children because of their mercury content.

The studies -- one conducted in the United States and the other in Portugal -- both concluded that children whose cavities were filled with mercury amalgam showed no detectable lowering of IQ or impairment of memory, co-ordination, concentration, nerve conduction or kidney function over time.

Researchers followed the children for five to seven years to regularly assess whether there were measurable indications of brain or kidney damage. Previous studies in adults had suggested that these organs might be particularly sensitive to the toxic metal.

"What we found over the course of the study is the amalgam fillings had no adverse effects on the IQ of these children as well as on a range of other neuropsychological measures and kidney function," said Dr. Sonja McKinlay, a scientist at the New England Research Institute in Watertown, Mass., who headed the U.S. study.

"We took great pains to design our study in a way that our tests would be sensitive enough to detect as little as a three-point drop in IQ," McKinlay said in a release.

"Given the rigorous nature of the study designs and that both clinical trials confirmed the other's results, I think these findings should be reassuring for parents, children and dental professionals."

Dr. Jack Cottrell, president of the Canadian Dental Association, said results from the studies reinforce the organization's long-held position that mercury amalgam fillings are safe.

"Dental amalgam has been a much studied restorative material and one that has been subjected to a lot of questions," Cottrell said Tuesday from his dental office in Port Perry, Ont. "But really the bottom line, and what we've been telling patients and the public, is it's a substance that's safe, we've been using it for 150 years, it is durable, and it is a cost-effective way of filling teeth."

But the U.S.-based International Academy of Oral Medicine and Toxicology denounced the studies, calling their designs flawed and their use of vulnerable young children to study the safety of mercury fillings "appalling."

The organization said numerous studies have linked mercury to a vast array of neurophysiological conditions, from autism to Alzheimer's disease.

Researchers for both studies, which each randomly assigned 500 children needing dental work to have either mercury amalgam or composite fillings, found that participants who received silver fillings had slightly elevated levels of mercury in their urine. But they said those mercury levels remained low.

The studies, both publicly funded, are published in Wednesday's issue of the Journal of the American Medical Association. They are the first randomized clinical trials to evaluate the safety of mercury fillings in children.

"What's particularly impressive is the strength of the evidence," said Dr. Lawrence Tabak, director of the National Institute of Dental and Craniofacial Research, which partly funded the U.S. trial. "The studies evaluated mercury exposure in two large, geographically distinct groups of children and reached similar conclusions about the safety of amalgam.''