More than two-thirds of people who believe they are looking after their teeth by brushing twice a day are still at risk of decay, a survey has found.

A national study by Newcastle University Dental School found that more than two out of three people who say they brush their teeth twice a day have substantial deposits of plaque in their mouths.

This is probably because they are brushing incorrectly.

Lead researcher Dr Jimmy Steele said that many people have never learned to brush their teeth properly.

He urged anyone in doubt to ask their dentist for advice at their next visit.

Dr Steele said: "Maintaining good oral hygiene is perhaps the one thing people should do more than anything else if they want to avoid tooth decay and tooth loss."

The report, on adult dental health, published by the Office for National Statistics, reveals that:

• 73% of the population have large deposits of plaque
• Among those who said they brushed their teeth twice a day, 69% had substantial plaque deposits
• 38% of the population have never been shown how to clean their teeth

Despite the findings of the survey total tooth loss is becoming a rarity.

It is forecast that by 2018, only 5% (one in 20) people will have no teeth, compared with 13% now.

The British Dental Association (BDA) said that most people were good at brushing their teeth, but not very good at brushing the point where the tooth meets the gum - and this is where many problems can occur.

Dentists recommend brushing twice a day using a fluoride toothpaste, placing the brush at the neck of the tooth (where it meets the gum) and scrubbing gently - using very short horizontal movements at a 45% angle to the tooth.

The BDA advises people not to brush too hard, which can damage the teeth and gums.