People who live in fear of the dentist's drill could be in for a more comfortable future - as new plasma technology arrives.

"Plasma jets" could one day be used to clean out bacteria from tooth cavities, say researchers from Saarland University in Homburg, Germany.

Tests reported in the Journal of Medical Microbiology found the plasma destroyed bacteria in infected teeth.

They say plasma dentistry may be available within three to five years.

Matter can be either solid, liquid, a gas or a fourth type, plasma, which is actually the most common in the universe.

While there are many natural forms of plasma, including the contents of our sun and lightning, modern technology relies heavily on plasma technology - for example in fluorescent lighting and the manufacture of semiconductors.

Artificial plasmas can be created when energy is added to a gas, perhaps using an electrical field or a laser.

The resulting matter can behave differently when it comes into contact with other particles.

While many artificially-created plasmas are extremely hot - for example, the flame on an arc welder - advances in recent years have allowed the creation of much cooler plasmas.

This, in turn, has opened the possibility of using them on the human body, where they could offer a very precise way of targeting tiny areas.

In this case, the properties of the plasma are harmful to bacteria, without affecting the surrounding tissue.

Normally, a dentist's drill is used to clean out bacteria from a cavity, before the filling is inserted.

The German team used a plasma jet to do the same job and found that it was able to do this quickly and efficiently, even where the bacteria were arranged in resistant "biofilms" on the dentine - the main part of the tooth under the enamel.

'Uncomfortable'

Dr Stefan Rupf, who led the study, said the low temperature killed the microbes while preserving the tooth.

He said:"Drilling is a very uncomfortable and sometimes painful experience. Cold plasma, in contrast, is a completely contact-free method that is highly effective.

"Presently, there is huge progress being made in the field of plasma medicine and a clinical treatment for dental cavities can be expected within 3 to 5 years."

Professor Bill Graham, a physicist from Queen's University Belfast, said that plasma medicine had the potential to pick out tiny targets, perhaps even single cells.

He said that "plasma scalpels" were already being used in sports medicine to treat collagen problems, and there was great interest in the technology for use in burns patients.

He said: "Obviously, as with any new treatment, we need to check that it can be used safely, but there is no evidence at the moment that there are any problems."