BRUSHING too hard and for too long with an electric toothbrush could cause permanent damage, a new study has found.

Researchers at Newcastle University have issued a warning to the millions of people using electric brushes.

While electric toothbrushes can help people improve their dental hygiene, over-zealous use can wear away enamel or gum tissue.

Professor Peter Heasman, of Newcastle University's School of Dental Sciences, said: "Although we found that you have to brush your teeth reasonably long and hard to get rid of the harmful plaque which causes dental diseases, our research shows that once you go beyond a certain point you aren't being any more effective. You could actually be harming your gums and possibly your teeth."

The research, published in the Journal of Clinical Periodontology, found that brushing for two minutes and exerting about 150 grams (about the weight of an orange) of pressure seemed to be the best approach.

Twelve volunteers took part in a study which examined 16 combinations of brushing times, ranging from 30 seconds to three minutes, and different levels of pressure.

Researchers found that plaque removal steadily improved as brushing times and pressures were increased.

However, they found that those brushing longer than two minutes, at a pressure higher than 150 grams, were not removing any additional plaque and were at risk of damaging teeth and gums.

Prof Heasman had this advice for anyone using an electric toothbrush: "You should rest the head against the tooth and let the brush do the work. It should be firm but don't press too hard."