NEW YORK - A NEW study adds to evidence that mercury-containing dental fillings do not harm children's brain development, as some have feared.

Silver fillings, called amalgams, have been used to treat cavities for more than a century. The fillings are made from a combination of metals, including mercury, and research has shown that small amounts of mercury vapour are released from the fillings over time.

Because mercury poisoning is known to damage the central nervous system and kidneys, consumer groups and some experts have concerns about the potential health effects of low-level mercury exposure from amalgam fillings.In the new study, researchers in Portugal and the US followed 507 children who had received either amalgam or resin-based fillings when they were between 8 and 12 years old.

Over seven years, the two groups showed no differences in their rates of neurological symptoms, such as tremors, vision or hearing deficits, or coordination problems.

Dr Martin Lauterbach, a neurologist at the University of Lisbon in Portugal, led the study. The findings are published in the Journal of the American Dental Association.

The results add to evidence from two recent studies - including one of this same group of children - that found no evidence that amalgam fillings harmed children's intellectual or behavioural development.

Still, mercury-containing fillings remain controversial. An advisory panel to the US government recently said that while existing evidence suggests the fillings are generally safe, more study is needed into certain unanswered questions - such as how amalgam fillings in pregnant women might affect fetal development.

Some consumer groups, dentists and lawmakers believe that amalgam fillings should be banned. The American Dental Association (ADA) maintains, however, that the weight of the scientific evidence indicates that the fillings are safe, and should continue to be an option for patients.

According to the ADA, strong, durable amalgam fillings may be the best choice in certain situations, such as when treating the molars - the large teeth in the back of the mouth that bear much of the work of chewing.

As newer filling materials have become available, however, fewer people in the US and Western Europe have been receiving mercury-containing fillings. In recent years in the US, less than one-third of new fillings have been the amalgam variety.