Scientists have found a cure for sensitive teeth. Sufferers could soon be fitted with a tiny glass bead infused with fluoride, which proved 100% successful at stopping pain in a small trial group at Leeds University.

Stuck to an upper tooth, the bead slowly releases low levels of fluoride to form a protective cap over exposed nerves.

"The volunteers were so happy with the beads that when the trial ended they refused to give them back," said Gayatri Kotru, a research assistant at the Leeds Dental Institute, where the bead was developed.

The device was being tested for the prevention of tooth decay when a volunteer said that the over-sensitivity of her teeth had disappeared. A trial of 15 patients in 2002 showed similar results.

The researchers are now embarking on a larger experiment with 100 patients, expected to last six months.

"Desensitising toothpastes have only a temporary effect," said Dr Kotru. "Our bead is replaced easily and painlessly every two years."

The problem affects about 9 million people in the UK and is steadily rising as people keep their own teeth for longer. Years of grinding and decay remove the protective enamel outer layer, exposing the nerve-rich dentine below.

The flattened beads, about 3mm across, are stuck to the outside of an upper molar with dental cement. The infused fluoride slowly leaches into saliva, triggering a chemical reaction that seals tiny fluid-filled nerve channels called tubules.

"You won't be getting them off the shelf," said Dr Kotru. "Only the dentist can put it on for you; it's not something you can just stick on yourself."

If the new trial goes well, Dr Kotru said, the beads could be available within two years.