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'Coating' on teeth could stop plaque: The American Association for the Advancement of Science in Boston

A biological coating that stops bacteria getting a hold on teeth could help make plaque a thing of the past, scientists said yesterday.

Two microbiologists from a dental centre in Boston have been studying the habits of an organism they believe is found only in adult human mouths.

'These organisms, of all the places to inhabit on the planet, have selected the surfaces of human teeth as their main habitat,' Ronald Gibbons told the meeting.

Scientists have never spotted the bacterium, Actinomyces viscosus in the mouths of babies, have only found it in children if their first teeth have appeared, and say it vanishes if someone has all their teeth taken out. They believe the bacterium may be passed on to children by their mothers.

It is harmful because it builds up to form a dental plaque associated with gum disease and root decay. Dr Gibbons found that a class of proteins in human saliva are shaped so that one end of their structure sticks fast to the enamel coating of a tooth, while the other end attracts the bacteria. The bacteria are not attracted to the proteins while they float in the fluids in the mouth, but as soon as the protein sticks to a tooth, it changes shape, exposing a part of itself which the bacteria easily recognises. Dr Gibbons has found that if he cuts off the part of the protein the bacteria can spot, they have no way of gripping the protein, or the tooth.

He uses an enzyme to cut the protein at the right place, ensuring it is still able to perform useful functions in the mouth, but leaving the harmful bacteria nothing to hold on to. 'I can imagine a time when you could visit your dental hygienist, they would scrape off any film built up on your teeth and replace it with a coating of this new version of the protein.'

He said it might also be possible to include the protein in toothpaste.

Saliva is rich in calcium and phosphate, without which teeth would dissolve. The saliva's special proteins help prevent the calcium and phosphate from crystallising out.

Dr Gibbons said his replacement approach was particularly attractive because the modified protein would still perform this vital role. 'The coating would not greatly upset the natural ecology of the mouth, any more than brushing your teeth,' he said.

He explained that unlike using an antibiotic, the engineered protein would not kill off the bacteria, just make it impossible for them to stick to teeth. The scientists have tested their new tooth coating in the laboratory, but have yet to try it on people. Trials should go ahead in the next few months.

Dr Gibbons has patented the coating, and two pharmaceutical companies have already shown an interest in it.