WASHINGTON – Silver dental fillings contain mercury, and the government for the first time is warning that they may pose a safety concern for pregnant women and young children.

The Food and Drug Administration posted the precaution on its Web site earlier this month to settle a lawsuit – making the move a victory for anti-mercury activists.

The warning is not aimed at the general population, only at two groups already urged to limit mercury from another source – seafood – because too much can harm a developing brain.

The fillings, formally known as dental amalgams, “contain mercury, which may have neurotoxic effects on the nervous systems of developing children and fetuses,” reads the FDA Web posting.

That doesn’t mean it truly harms, and the FDA advises against removing existing fillings.

The agency still is studying whether the small amount of mercury vapor released by chewing and brushing is enough to cause neurological disorders or other problems in youngsters. There have been only a handful of rigorous studies comparing children given either amalgam fillings or tooth-colored resin composite fillings that are mercury-free – and those studies haven’t detected any brain problems.

Nor has that research settled the long-simmering scientific controversy. Two years ago, the FDA’s own independent scientific advisers said that while amalgam fillings were safe for most people, more research was needed about potential effects on fetuses and children under 6.

And this spring, the FDA put dentists on notice that it is considering additional controls, including whether to require warnings that would advise consumers of the mercury in amalgams before they have a cavity filled or perhaps even restrict use in small children and certain other patients. It is accepting public comments until July 28.

Expect a final ruling by July 28, 2009, a date set by that legal settlement.

“It’s a watershed moment,” said Michael Bender of the Mercury Policy Project, who with other advocacy groups had sued the FDA in hopes of forcing restrictions on amalgams.

“This court settlement signals the death knell for mercury fillings,” added Charles Brown, an attorney for Consumers for Dental Choice.

Not so fast, say dentists who point to medically crucial reasons to use amalgams – and worry that people who can’t afford more expensive alternatives might avoid dental care.

“We don’t want these choices taken away based on junk science. We don’t want them taken away based on misguided fears,” said Dr. Edmond Hewlett, a dental professor at the University of California, Los Angeles, and an American Dental Association adviser.