On its web site, the FDA has dropped much of its reassuring language about dental amalgam. And it's added what amounts to a warning: "Dental amalgams contain mercury, which may have neurotoxic effects on the nervous systems of developing children and fetuses."

And there's more. "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 bioburden, should not avoid seeking dental care, but should discuss options with their health practitioner," the FDA web site now says.

The changes come in response to a lawsuit filed by consumer groups and individuals concerned about mercury exposure. To settle the suit, the FDA agreed to update its web site.

And the federal agency also agreed to rule -- within one year -- on exactly how dental amalgam products should be regulated, and exactly what warnings consumers should receive from their dentists and doctors.

"It's been a long time coming," Nick Brooks, a staffer for Consumers for Dental Choice, one of the groups that brought the lawsuit, tells WebMD.

"This is a good thing. It will be good to have a rule finalized in a year," FDA spokeswoman Peper Long tells WebMD. "In some cases, we know mercury can have effects on the nervous system. It is something we need information on so we can give the public the best information on the risk from a product like this."

The FDA in 2002 proposed to classify the mercury-containing fillings as a Class II device -- meaning a device that isn't absolutely safe and should carry some kind of special controls (a Class I device, like a Band-Aid, needs no warning; a Class III device, like a cardiac defibrillator, requires specific FDA approval).

But the FDA never issued a final ruling. It's proposed "white paper" on the topic was voted down in a 13-7 vote by a 2006 advisory panel made up of experts in dentistry and in neurology.

Neurologist Karl Kieburtz, MD, of the University of Rochester, co-chaired the panel.

"The panel's concern was there are populations that are particularly susceptible to the neurological effects of mercury and might experience these effects at the very low levels of exposure seen with dental amalgam," Kieburtz tells WebMD. "That was the tenor of the committee -- 'Let's consider vulnerable populations' -- so we said fair enough, these vulnerable populations should at least get a warning."

Kieburtz notes that panel members also agreed that there was no cause for alarm and said there was no reason for pregnant women or others to have their dental fillings removed.

"To the best of my knowledge, there is no clinical evidence in humans that dental amalgams have led to harm," Kieburtz says. "Is there a theoretical reason to suspect harm? Yes. There is a rationale for concern, but no evidence there is harm. So there is a theoretical concern and a lack of evidence and that has led to a precautionary rule."

Indeed, clinical studies suggest that dental fillings cause  harm. But because millions and millions of children and pregnant women received the fillings, the  cost of cleaning toxic mercury is a big task.

Amalgam fillings are made from liquid mercury mixed with a powder containing silver, tin, copper, zinc, and other metals. It was once thought that the mercury in fillings was permanently trapped in the amalgam. Not any more.

When people chew, the fillings emit mercury vapor that is absorbed by the body. Even for people with lots of fillings, it's a small amount of mercury.

But since mercury is toxic even at very low levels, there's growing concern that the mercury in fillings could be the straw that breaks the camel's back for people with other mercury exposures. And dental professionals are routinely exposed to the vapors.

Even now, the FDA does not recommend that people have their fillings removed. But the agency does say that people concerned about the possible health effects of dental fillings should talk with their "qualified health care practitioner."