SCIENTISTS have adapted the “friendly bacteria” idea promoted by the makers of yoghurt to help in the war against dental decay.

They have developed a new bug to beat off the tooth fairy. The genetically modified (GM) bacteria will prevent decay by displacing the germs that cause cavities.

The company making the bug has just won approval to conduct trials on humans, the first step towards introducing it on a more widespread basis. If it works, a dentist could simply rub the bacteria onto patients’ teeth — potentially protecting them from decay for years or even for life.

It would also become the first big therapeutic application of GM organisms — plants and animals whose DNA has been altered, usually by incorporating genes from unrelated species.

“The idea is simply to use good bacteria to fight bad bacteria,” said Jeffrey Hillman, chairman and chief scientific officer at Oragenics, based in Florida.

His team’s approach focuses on streptococcus mutans, one of several hundred bacterial species found in people’s mouths, but the one blamed for most tooth decay. The bug produces an acid that eats away the enamel coating that protects teeth.

However, Oragenics has created a strain of the germ that has been genetically modified to prevent it producing the damaging acid. It is also better adapted to survive in the mouth, so displaces the original decay-causing strain.

Children as young as one could be given the germ as soon as they start growing teeth.

However, it must first pass through years of safety testing. It will be at least 2009 before it could go on the market.

Approval for the trial follows years of research and delays over fears the GM germ could revert to a decay-causing form.

Clinical trials involving GM viruses have already led to at least one death.

This time America’s Food and Drugs Administration has placed tough restrictions on the trials, insisting the tests be conducted on people with dentures.This is because such people can remove their teeth entirely and sterilise them in bleach should there be doubts over safety.

The Oragenics approach reflects a worldwide shift in the perception of dental cavities. In the past these have been treated as surgical problems to be put right by fillings.

Recently, however, researchers have begun to see tooth decay as an infectious disease that might be treated with vaccines.

Dental decay remains a problem in Britain — especially in children. The 2003 Children’s Dental Health Survey found 13% of children under 15 had needed fillings.

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