The US government's Food and Drug Administration (FDA) has issued a health warning that mercury fillings given to millions of Britons every year can be dangerous.

More than half of an amalgam filling is made up of a highly toxic metal, mercury, which is more poisonous than lead and causes many ailments including fatigue, depression heart conditions and Alzheimer's disease. Research suggests that this could be linked to high blood pressure, infertility, and disorders of the central nervous system as well.

The British Department of Health had earlier issued a statement that mercury fillings posed no danger. But now it says that 'Dental amalgams contain mercury, which may have neurotoxic effects on the nervous systems of developing children and foetuses.'  It also added that when amalgam fillings are "placed in teeth or removed they release mercury vapour", and that the same thing happens when chewing.

The FDA is now reviewing its rules and may end up restricting or banning the use of the metal.

Norway and Denmark have already banned mercury from fillings while Finland and Japan have severe restrictions.

However, as against these findings, a study of Portuguese and U.S. children evidences that mercury is safe. The study found no difference in the rates of neurological symptoms between those children with amalgam and those with mercury-free fillings.

A spokesman said: 'These fillings are a safe, durable and affordable cavity choice for dental patients that do not pose a health risk.'

More and more dentists are setting up mercury-free practices, and more patients are demanding fillings made of resin and glass.

But the BDA now says that the alternatives "have improved over time. Trends towards greater use of these materials imply that there is to be a sustained reduction in the use of dental amalgam."