When you’re sitting in the dentist’s chair waiting to have a cavity filled, you don’t see the package the amalgam filling comes in. But if you did your eye might well be drawn to a couple of “contraindications,” med-speak for “situations in which the dentist should not use this product.” In addition to ho-hum warnings about not using the amalgam, which contains about as much mercury as a thermometer, in patients known to be allergic to amalgam (duh), the manufacturers say it should not be used in children age 6 and under, or in pregnant women.

The reason, of course, is that mercury is a known neurotoxin, especially dangerous to developing brains. For decades anti-mercury activists have pushed the industry to develop substitutes (so-called composites, or resins, are now available), and even to persuade people to have their fillings ripped out, but have made very little headway.

Now they have won a big one. In a legal settlement, the U.S. Food and Drug Administration has changed the information on its Web site about amalgam fillings to say that they “may have neurotoxic effects on the nervous systems of developing children and fetus,” and that pregnant women “should not avoid seeking dental care, but should discuss options with their health practitioner.” Previously, there was no such warning. The FDA also agreed to decide by next year whether mercury fillings need more regulation.