After years of asserting that mercury in fillings was safe, the Food and Drug Administration now says it may be harmful to pregnant women, children, fetuses, and people who are especially sensitive to mercury exposure.

"Dental amalgams contain mercury, which may have neurotoxic effects on the nervous systems of developing children and fetuses," the FDA now says on its Web site.

The agency posted the revised assessment online Tuesday as part of a settlement with consumer advocates. The FDA also committed to issuing special controls on mercury fillings in July 2009.

Those controls could range from giving patients information to adding warnings prohibiting use of the fillings in some people.

While bans are unlikely, the FDA may conclude that the cavity-repair treatment, called dental amalgam, should not be used in certain patients such as pregnant women, FDA spokeswoman Mary Peper Long said.

The FDA does not recommend removal of old mercury fillings. But it advises patients who are worried to talk to their doctors.

"Pregnant women and persons who may have a health condition that makes them more sensitive to mercury exposure, including individuals with existing high levels of mercury . . . , should not avoid seeking dental care," the FDA Web page says, "but should discuss options with their health practitioner."

The American Dental Association said the settlement "in no way changes the federal agency's approach to or position on dental amalgam."

Amalgam is "a safe, affordable and durable material that has been used in the teeth of more than 100 million Americans," the ADA said in a statement.

But consumer groups - and some dentists - who fought for the agreement were exultant.

"We have won our 10-year battle," declared dentist Stephen Markus of Haddon Heights.

Philadelphia Councilwoman Blondell Reynolds Brown, sponsor of a new ordinance requiring city dentists to give patients a brochure about the potential dangers of amalgams, said she was "thrilled."

"The federal government . . . is recognizing . . . that there is value in giving consumers information," she said.

Mercury-based metal blends have been used to repair teeth for more than a century. Resins, porcelain, gold, and other materials used for fillings are more expensive and not as durable.

Mercury, which makes up about half the amalgam by weight, chemically bonds to powdered silver, tin and zinc. While this produces a hard substance, mercury vapor is released when the filling is placed, removed, and even during chewing.

A shift away from amalgam could affect dental supply firms, health insurers, and uninsured dental patients.

The lower cost of amalgam "opens up availability" to patients with financial constraints, said William Jellison, senior vice president of Dentsply, a global dental-products firm based in York.

He said he was not aware of any studies that showed ill effects from mercury fillings.

Until Tuesday, the FDA's Web site said federal agencies "have found no scientific studies that demonstrate dental amalgam harms children or adults."

That statement was removed as part of the settlement.

"Gone, gone, gone are all of FDA's claims that no science exists," e-mailed Charles Brown, attorney for the lead group, Consumers for Dental Choice, in Washington.

Mercury, which accumulates in the body, is toxic to the brain, the nervous system, and other organs. There is debate, however, over what level and type of exposure may be harmful, and whether some people are particularly at risk.

Epidemiological studies and clinical trials have not connected amalgams to health problems, but in animal studies, mercury vapors have damaging effects. Numerous human studies have found that mercury in the blood, brain, and other tissues increases with the number of amalgam fillings.

Mercury has been removed from thermometers and vaccines, controls have been tightened on mercury emissions from coal power plants, and pregnant women have been warned about consuming fish tainted by mercury.

In 2006, an FDA advisory committee rejected an FDA report that declared amalgam fillings safe. Although the panel did not pronounce them unsafe, it said the FDA's conclusions were not reasonable given the current state of knowledge.

Whatever controls the FDA imposes, mercury fillings have been landing in fewer mouths since the 1980s. Surveys estimate that a third to a half of U.S. dentists have stopped using amalgam, following the lead of many European countries.

Markus, the Haddon Heights dentist, made the break 18 years ago. Emerging research influenced his thinking, but so did his own observations.

The American Dental Association insisted mercury was "inert" in fillings, yet it advised special storage precautions – and still the vapors ate "a hole in the top of the storage jar," he said.

Now, Markus has a special separator to remove mercury that would otherwise go into the sewer system. All New Jersey dentists must install separators by late next year.

"I saw the future," he said.

Read the FDA's new thinking on mercury, dental fillings

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Contact staff writer Marie McCullough at 215-854-2720 or mmccullough@phillynews.com.

Staff writer Sandy Bauers contributed to this story.