TUESDAY, April 18, 2006 (HealthDay News) -- Two new studies that found amalgam fillings to be safe are sure to revive the debate over whether or not "silver" fillings can harm other parts of the body.
While the latest research did report higher levels of mercury in children's urine after they received amalgam fillings, there were no statistically significant ill effects on the children's kidney function or their neurological capacities.
"We saw no observable differences in neuropsychological or kidney outcomes. I think the findings should be fairly reassuring," said the lead author of one of the studies, David Bellinger, a professor of neurology and environmental health at Harvard Medical School and a senior research associate at Children's Hospital in Boston.
However, he added, "We can't reject the hypothesis that there is a sensitive subgroup that may confer a little more vulnerability [to mercury in fillings]."
Amalgam fillings are actually composed of more mercury than silver -- they're about 50 percent mercury. Dental experts contend that when mercury is bound to the other metals it's encapsulated and doesn't pose a health risk. Consumer groups, however, contend that mercury, a known neurotoxin, does leak out in the form of mercury vapor and then gets into the bloodstream.
Results of the latest studies appear in the April 19 issue of the Journal of the American Medical Association.
Bellinger's study included 534 children between the ages of 6 and 10 at the start of the study. The children were from either the Boston area or from Maine. None of the children had amalgam fillings before the study.
On average, the children needed 15 tooth surfaces restored. That doesn't mean an average of 15 cavities -- one tooth can have multiple surfaces that need restoration.
The youngsters were randomized into two treatment groups. Half received amalgam fillings, and the other half received resin composite fillings.
The researchers then followed the children for five years, and periodically tested their IQs and their kidney function.
After five years, they found no statistically significant differences in the two groups. There was, however, a slight decrease in IQ score in the amalgam group.
The second study was done on 507 children from Lisbon, Portugal, between the ages of 8 and 10. As in the first study, the children were randomized to receive either amalgam fillings or resin fillings. In the amalgam group, an average of 18.7 tooth surfaces were restored and an average of 21.3 surfaces were restored in the resin composite group.
The study lasted seven years and the researchers periodically measured memory, attention and concentration, motor skills and nerve conduction velocities.
These researchers also found no statistically significant differences between the two groups.
"These are two well-done studies designed by scientists that have no particular axe to grind," said Dr. Rod Mackert, a professor of dental materials at the Medical College of Georgia and a spokesman for the American Dental Association. "They have carefully looked at this issue and shown there is no effect on the target organs of concern in children. We can be confident that amalgam doesn't cause adverse health effects."
Not everyone agrees that these studies are the final word on amalgam's safety, however.
In an editorial in the same issue of the journal, Dr. Herbert Needleman, from the University of Pittsburgh School of Medicine, pointed out that since it's well known that mercury is toxic at doses much higher than those in fillings, it's not unreasonable to suspect that in lower doses it could still have some adverse effects. He said that dentists and dental assistants have motor function and cognitive deficits that correlate with the number of fillings they've put in, and that some studies have suggested that mercury may be a risk factor for multiple sclerosis and Alzheimer's.
"Although the studies by Bellinger et al and by DeRouen et al provide important new data on the health effects of mercury containing dental amalgam in children, there are, as the authors clearly delineate, limits to the inferences that can be drawn from these data," he wrote.
Needleman said the length of the studies may have been too short to pick up more subtle neurological deficits.
Charlie Brown, national counsel for Consumers for Dental Choice, a group that favors banning mercury-containing fillings altogether, said the studies have significant limitations, and don't prove that amalgam fillings are safe. For example, he pointed out that the study done on the children in Lisbon didn't control for mercury in the children's diet. Since they're close to the ocean, it's likely that fish -- which often contain mercury -- were a large part of their diet.
Brown also expressed concern that the researchers on the Portuguese studies already had their minds made up that amalgam was safe before they began the study. He said the lead researcher had already testified for the American Dental Association on the safety of amalgam fillings. "This was a handpicked group. They were already advocates for mercury fillings," he said.
Brown said the use of amalgam fillings is all about convenience and money, and said that "modern dentists don't use mercury fillings."
Mackert, however, said that studies have shown that amalgam tends to last longer and is more durable than resin composite fillings.
The U.S. Food and Drug Administration recently announced that they will hold hearings to assess the safety and potential neurotoxicity of dental amalgam. Those hearings are scheduled for September 2006.
To learn more about amalgam fillings, visit the U.S. Centers for Disease Control and Prevention.