A LASER wand could replace the dentist's drill if clinical trials beginning next year are successful. The key is photodynamic therapy (PDT), in which light activates a killer molecule that wipes out bacteria in decaying teeth.

In tests on extracted teeth, Mike Wilson and his team at the Eastman Dental Institute in London have shown that PDT sterilises the infected tooth tissue. Once teeth in people's mouths are clear of infection, their bone tissue should be able to regenerate itself.

The team also hopes PDT could help combat other infections, particularly the hospital "superbugs" that are resistant to antibiotics. The team has already tested PDT against MRSA, a virulent superbug. "We wiped out over 99.9 per cent of the colony in samples where human tissue was present," Wilson told the BA meeting.

To treat cavities, dentists drill the parts of the tooth infected with decay-causing bacteria, leaving only healthy tissue. "Most dentists are overcautious and drill away a large part of the tooth," says Wilson.

PDT uses a photosensitiser molecule which binds only to the bacteria. When the photosensitiser is bathed in laser light, it releases oxygen radicals that kill the bacteria by punching holes in them.

Wilson says he has disinfected extracted teeth using a photosensitiser called toluidine blue. He will begin clinical trials in people with cavities next year.

The researchers don't think bacteria will become resistant to PDT. "So far, we haven't found any one site the photosensitiser is binding to," explains Mark Wainwright of the University of Central Lancashire, who is also working on PDT. "It just seems to adhere generally around the cell walls." He says the bacteria would have to change several aspects of their structure to become resistant.

From New Scientist magazine, 16 September 2000.