People who brush their teeth too hard and for too long could be causing permanent damage, experts have warned.
People should spend two minutes cleaning their teeth, say experts
A study by researchers at Newcastle University say there is little evidence to show that longer and harder brushing makes teeth cleaner.
In fact, they found that it increases the risks of permanently damaging the protective layer on teeth and harming gums.
They suggest that people should brush their teeth for two minutes and apply pressure equivalent to the weight of an orange at 150 grams.
Those recommendations are based on a study of 12 people over four weeks.
During this time, these people tested 16 different ways of brushing their teeth, varying on the length of time and pressure applied.
They brushed their teeth for between 30 seconds and three minutes and applied pressure equivalent to between 75 grams and 300 grams.
They used oscillating electric toothbrushes, which were wired up to a computer that took time and pressure measurements.
You could actually be harming your gums and possibly your teeth
Professor Peter Heasman, Newcastle University
Researchers recorded the levels of plaque before and after brushing and found that plaque removal steadily improved as brushing times and pressure were increased.
However, their results showed that when people brushed for longer than two minutes, at a pressure higher than 150 grams, they were not removing any additional plaque.
Although the people involved in the study used electric toothbrushes, the researchers said similar results would have been expected if they had used ordinary toothbrushes.
Peter Heasman, professor of periodontology at Newcastle University's School of Dental Sciences who led the study, said the findings showed people should not brush their teeth too hard or for too long.
"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.
"Despite this, anecdotal evidence within the dental profession suggests that the majority of the population still believe that the longer and the harder you brush, the better for your teeth it is.
"The way in which you brush your teeth is just as important, and this goes hand in glove with the time you spend brushing and the pressure you apply to them."
Professor Heasman said that people who are unsure if they are brushing their teeth correctly should seek advice from a dentist.
"It is virtually impossible for the average user to gauge how much pressure they are applying during their brushing regime.
"For example, the force you apply to your toothbrush could be quite light but the pressure will be much greater because you are applying that force to a very small area.
"If you are unsure how to go about brushing your teeth, the best thing to do is to make an appointment with your dentist or dental hygienist who will be able to train you in the correct techniques and will show you approximately how much pressure you should be applying."
The study is published in the Journal of Clinical Periodontology.