Silver dental fillings containing mercury may have neurotoxic effects on the nervous systems of developing children and fetuses, the U.S. Food and Drug Administration (FDA) has said on its Web site.

The new warning for pregnant women was issued as a part of the settlement with several consumer advocacy groups. The federal agency plans to issue a more specific rule for fillings that contain mercury by July 2009.

Dental amalgam, which is made up of liquid mercury and a powder containing silver, tin, copper, zinc and other metals, has long been used to fill or restore teeth that have cavities. However, pregnant women should not avoid seeking dental care, but should discuss options with their health practitioner, the agency said.

According to the FDA, the mercury concentration in dental amalgams is generally about 50 percent by weight, while the silver concentration ranges from 20 to 35 percent.

The agency also added that patients with amalgam fillings should not get them removed/replaced as they are durable and cheap and these advantages might outweigh any potential health risk.