Silver fillings found kid-safe
Traditional tooth care contains mercury but doesn't harm children, major studies indicate
By Jonathan Bor
Originally published April 19, 2006
Wading into a dispute that is unlikely to die, two scientific teams have concluded that silver dental fillings containing mercury do not harm the memory, attention, coordination or kidney function of children who receive them.
Scientists who in each case randomly assigned about 500 children to receive traditional fillings with mercury or white "composite" fillings found that those receiving the old-style material excreted slightly more mercury in their urine -- showing that they had greater exposure to the potentially toxic metal.
But scientists found no differences between the two groups on a variety of tests.
"We can eliminate the hypothesis that there are large effects on the central nervous system and the renal systems from amounts that were used in these children," said Dr. David C. Bellinger, a neurologist with Children's Hospital of Boston and lead author of one of the studies.
The studies, appearing in today's Journal of the American Medical Association, "should be reassuring for parents, children and dental professionals," said Sonja McKinlay, an epidemiologist with the New England Research Institute and principal investigator of the Boston-based study.
But long-standing opponents of so-called silver amalgam fillings said the studies were unethical and not designed to detect problems that could take decades to emerge.
"To take a vulnerable subset of people and intentionally insult them with a known neurotoxin -- I don't think it's ethical to do that study," said Dr. David Kennedy, past president of the International Academy of Oral Medicine and Toxicology, a 500-member group that opposes amalgam fillings.
The group has filed complaints with officials at Harvard University and the University of Washington in Seattle, which oversaw the studies. Scientists who conducted the research said they did nothing unethical because they offered treatments that meet accepted standards of care.
Composite fillings, made of an epoxy resin and silica particles, have come into widespread use because they are white and blend into a person's smile. Fillings containing mercury have been used for at least 150 years, and scientists long assumed that a patient's only exposure occurred when the dentist packed a cavity with the material.
In the 1970s, however, scientists using more sensitive laboratory equipment discovered that the exposure continues, with people emitting minute amounts of mercury vapor each time they chew. Patients inhale some of the vapor into their lungs, and the metal enters the bloodstream.
Studies over the years have reached different conclusions about the possible health effects, with some finding a link to neurodegenerative diseases such as Alzheimer's and multiple sclerosis, and others finding no harm at all. Some have shown that dentists who handle the material in the course of their work suffer cognitive declines.
Mercury is one of the most toxic metals studied, and exposure can cause dementia, kidney failure, swelling and other health problems, experts say.
In recent years, controversy has swirled around the use of a mercury preservative in childhood vaccines, with some parents alleging that the vaccines triggered their children's autism. A recent review by the prestigious Institute of Medicine found no such link.
The studies appearing today are the first large, randomized safety trials of amalgam and composite fillings ever done. Considered the "gold standard" in medical research, such trials compare research subjects who are similar in every way except for the treatments being studied.
In the New England study, researchers enrolled 534 children ages 6 to 10 who had untreated decay in their rear permanent teeth and no previous amalgam fillings. The scientists, who designed their study to detect an IQ drop of at least 3 points, found no differences during five years of follow-up.
The scientists also looked for changes in memory, learning and motor skills -- finding none.
In the other study, scientists led by Dr. Tim DeRouen of the University of Washington in Seattle recruited 507 children ages 8 to 10 in Lisbon, Portugal, and tested them over the course of seven years. The scientists said they chose the region because children there have lots of untreated tooth decay and tend not to move out of the area, making their cases easy to track.
The scientists found no differences in memory, attention and physical coordination, as well as the ability of nerves in the legs to conduct signals.
In an editorial also appearing in JAMA, Dr. Herbert L. Needleman of the University of Pittsburgh wrote that the studies were limited in scope, because they were not designed to detect subtle changes that could occur over many years. He said some children might be genetically predisposed to react badly to small exposures to mercury.
Dr. Michael Baylin, a Pikesville dentist, said the studies won't change his belief that small amounts of mercury leaching into a patient's bloodstream over a lifetime can be injurious. He noted that dentists are urged to handle and dispose of the substance carefully so they don't harm themselves or the public.
"You can't throw it down the toilet, you can't pour it down the drain and you have to be very careful in the way you handle it," said Baylin, who stopped using amalgam 30 years ago. "I don't think I'd want to have mercury put in anybody's mouth I cared about."
But J. Anthony von Fraunhofer, director of biomaterials research at the University of Maryland Dental School, said he is convinced that the amount of mercury vapor released as a person chews is too small to hurt anyone. By his calculations, it would take 350 years for enough mercury from a single filling to reach concentrations capable of doing harm.
"In other words, we're talking about an unbelievably long time scale," he said. "Even then, you're not too sure you'd reach anything like a level of concern."