Zapping cavities!

Get ready for a new weapon to fight cavities: a laser toothbrush!

Why brush your teeth at all? A film of bacteria called plaque builds up along your gums. Brushing scrapes the bacteria loose, preventing them from decaying teeth and inflaming gums.

Toothpaste helps too. An antibacterial agent in many toothpastes kills germs on contact. But bacteria reproduce quickly and mutate into forms immune to such agents. Scientists must constantly invent new ways to keep bacteria in check, says David Phillips, a chemist at Imperial College in London, England.

Here's where the high-tech toothbrush comes in. Phillips and his colleagues inserted a tiny laser, a square millimeter in size, into the head of a toothbrush beneath the bristles. Then they added a light-sensitive dye to ordinary toothpaste.

When people brush their teeth with the special toothpaste, bacteria absorb the light-sensitive dye. The laser hits the dye, causing it to release chemicals that combine with oxygen. The chemical reaction breaks down the bacterias' membranes, killing the microscopic critters that escaped the toothbrush bristles!

The toothpaste dye is colorless, tasteless, and harmless to humans. And the laser is safe--only 5 milliwatts in strength. Users will be able to turn it on and off with a switch on the brush.

Researchers expect the toothbrush and toothpaste to be in stores within two years. The laser toothbrush will cost about $70, the same as an electric toothbrush.