A new toothpaste made from crab's shell could reduce trips to the dentist by fighting infection in the mouth.

The paste, which could be on sale in a year's time, contains tiny polymer particles each enclosing a speck of bacteria-killing agent.

Because they are sticky, the particles lodge in areas of the teeth and gums vulnerable to infection and are not washed away by saliva.

As they react with water, each particle breaks down over time to release its load of triclosan - a widely used antimicrobial chemical.

Dr John Smart, who developed the toothpaste with Phd student Sandra Kockisch at the University of Portsmouth, said: "The idea was to find some way to keep the therapeutic agent in the oral cavity for longer.

"Gels and mouthwashes don't stay in the mouth for very long. But everyone uses toothpaste. We have incorporated these particles into a glycerol base, which is the basic material of toothpaste."

The team looked at four different polymers from which to produce the sticky particles. The best performer was chitosan - derived from chitin, the main component of crab and beetle shells.

In laboratory tests, the particles stuck to tissue washed by mouth saliva for a couple of hours. But the researchers hope to get them to stick for as long as 24 hours, to build up optimum protection.

One of the biggest challenges was getting triclosan into the particles, because the drug is not water soluble. Another was to ensure that the particles were the right size. Too large, and they would feel gritty; too small, and they would not contain enough of the drug.

So far only a basic toothpaste containing a cleaning agent but no fluoride or flavouring has been produced. However the team hopes a finished product will be ready for the market in about a year.

-- Anonymous, September 23, 2002