The Food and Drug Administration reviewed 34 recent research studies and found "no significant new information" that would change its determination that mercury-based fillings don't harm patients, except in rare cases where they have allergic reactions.
The FDA released a draft of its review ahead of a two-day meeting next week to discuss the safety of mercury used in dentistry.
Consumer groups opposed to its use disputed the FDA's conclusions. The groups plan to petition the agency for an immediate ban on use of the cavity-filler in pregnant women.
"The science is over. There is no safe level of exposure," said Charles Brown, a lawyer for one of the groups, Consumers for Dental Choice. "The only thing standing between this and a ban is politics. They are still pretending it is a scientific question, but it isn't."
Amalgam fillings, also called silver fillings, by weight are about 50 percent mercury, joined with silver, copper and tin. Dentists have used amalgam to fill cavities since the 1800s. Today, tens of millions of Americans receive mercury fillings each year. Amalgam use has begun to decline, however, with many doctors switching to resin composite fillings, considered more appealing since they blend better with the natural coloring of teeth.
With amalgam fillings, mercury vapor is released through tooth-brushing and chewing. In general, significant levels of mercury exposure can permanently damage the brain and kidneys. Fetuses and children are especially sensitive to its harmful effects.
Scientists have found that mercury levels in the blood, urine and body tissues rise the more mercury fillings a person has. However, even among people with numerous fillings, exposure levels are well below those known to be harmful, the report said.
"If substantial scientific evidence showed that dental amalgam posed a threat to the health of dental patients, we would advise dentists to stop using it. But the best and latest available scientific evidence indicates that dental amalgam is safe," Dr. Ronald Zentz, senior director of the American Dental Association's council on scientific affairs, said in prepared remarks to be delivered Wednesday to the joint meeting of FDA experts on dental products and neurology.
Among those expected to address the joint panel is Rep. Diane Watson, D-Calif., who has introduced legislation that would effectively ban the use of mercury in dental fillings by 2008. Watson will press the FDA for a ban and call on the agency to study the environmental impact of dental mercury, spokesman Bert Hammond said.
Also on the legislative front, Sen. Mike Enzi, R-Wyo., and other Senate colleagues have asked President Bush's nominee to head the FDA about the safety of mercury fillings. An Enzi spokesman said the lawmaker has yet to receive Dr. Andrew von Eschenbach's answers to those questions.
Meanwhile, representatives of the National Multiple Sclerosis Society and Alzheimer's Association are expected to testify that there is no known scientific evidence to connect mercury fillings and the two diseases that are the focus of their respective groups. And Swedish and Canadian experts are to discuss how their countries regulate amalgam fillings.
The meeting likely won't be the last word in the drawn-out fight over mercury fillings. As early as the 1840s, dentists were squabbling over whether gold or mercury-silver fillings were better — a feud that led to the disbanding of the first national dental society in the United States, according to a March article in the Journal of the California Dental Association.