Mercury fillings called safe

Mercury fillings called safe2 studies track health of children over years
By Ronald KotulakChicago Tribune science reporterPublished April 19, 2006

Dental fillings containing mercury do not cause any measurable neurological problems in children who have had the fillings for at least seven years, according to two studies reported in Wednesday's issue of the Journal of the American Medical Association.

The studies are the first to compare children receiving mercury amalgam fillings with children who got mercury-free fillings made of composite materials, and were undertaken because of long-standing concerns about the use of mercury in "silver" fillings.

Dental amalgam, which contains 40 percent to 50 percent elemental mercury, has been in use for 150 years because the material is relatively cheap and long lasting. U.S. children currently have an estimated 100 million amalgam fillings.

However, the use of amalgam to fill cavities has sharply declined over the last 15 years, as patients increasingly prefer the look of composites, which better match the natural color of teeth. Seventy percent of fillings in the U.S. are now done with composite materials, generally a combination of plastic and silicate, according to the American Dental Association. Amalgam is still the material of choice for cavities that are difficult to keep free of saliva during filling.

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 Harvard Medical School neurologist David Bellinger, 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."

In an accompanying JAMA editorial, Dr. Herbert Needleman of the University of Pittsburgh School of Medicine, who played a key role in exposing the danger of lead poisoning in children, said further studies are needed to assess any long-term risks from dental mercury, including factors that may make some children more vulnerable.

Bellinger, who also was involved in lead-poisoning research in the 1970s, agreed that further studies of possible long-term adverse effects are warranted because mercury in high doses is known to damage the brain and nervous system.

A number of population studies have failed to find a link between mercury fillings and learning or memory problems.

But because the act of chewing can release a tiny amount of mercury vapor, scientists have been cautious about giving the metal a clean bill of health. Some people have become so concerned about a potential threat from mercury that they have had their amalgam fillings removed and replaced with composites.

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 them 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 the researchers found no significant difference between the two groups in IQ scores, memory, visual-motor function and kidney function. The children were evaluated yearly with a large battery of tests.

Children receiving the amalgam fillings had 50 percent more mercury in their urine than those getting the composites, Bellinger said, though 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 higher 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.

The second study, headed by Dr. Timothy DeRouen of the University of Washington, involved 507 children ages 8 to 10 in Lisbon, Portugal. The children were randomly assigned to receive mercury or composite 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 them 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.

"The fact that two studies done independently in different regions of the world come up with the same conclusion suggests to me that we probably are on the right track," Bellinger said.

The International Academy of Oral Medicine and Toxicology, which is opposed to mercury fillings and water fluoridation, criticized the two studies in a statement as "designed to fail." The group also called the research unethical, saying the child subjects and their guardians were not fully informed of the potential risks of exposure to a toxic substance.

Chicago-area dentists said they rarely receive questions about potential health problems from mercury fillings.

"The studies provide more scientific proof that amalgam fillings don't cause neurological problems," said Dr. Trucia Drummond, a dentist with offices at 30 N. Michigan Ave. in Chicago. "In the last 10 years I've had almost no questions from patients about the safety of amalgam. They usually opt for the more aesthetic composite fillings."

Dr. Keith Suchy, a dentist who practices in Westchester, agreed.

"The trend toward composites is being driven by their ability to match tooth color and not by any concerns about amalgam safety," he said.