Around two-thirds of gum disease patients ignore advice about how long to brush their teeth, a study suggests.
Regular brushing can combat gum disease
A team at University of Newcastle upon Tyne found only one in three patients followed advice to the letter.
However, the study, published in the British Dental Journal, showed many people thought their brushing habits were better than they actually were.
Gum disease can lead to tooth loss, but proper brushing can help to stabilise or even reverse the problem.
For the study, patients were given advice on a regime - which in particular said they should brush their teeth twice a day for two minutes each time.
Each of the 17 study participants used an electronic 'data logger' powered toothbrush that recorded brushing time.
The brush had a light on the handle that flashed when two minutes had elapsed.
Brush twice a day, for two minutes, with fluoride toothpaste
Avoid sugary food, particularly between meals
Clean between teeth, using floss or a mini toothbrush
Chew sugar-free gum, particularly those containing the sweetener xylitol, after meals
They were also asked to fill in diaries detailing their brushing habits.
The data from the logger toothbrushes showed approximately one-third of people followed the advice whereas the diaries suggested that more than half of patients thought they had been compliant.
Lead researcher, Dr Giles McCracken said: "Research has shown that brushing for two minutes is the optimum time for most people to remove the plaque from your teeth.
"If you brush for less time, you aren't removing enough, and if you brush for longer the benefits may not be much greater.
"The fact that many participants in our experiment said they had followed the dentist's advice when our records proved they had not, has implications for the profession, especially in our increasingly litigious society.
"Patients must understand their health is mainly their responsibility, and if they are not going to comply with the advice of health providers like dentists who have their best interests at heart, they must accept the consequences."
The Newcastle researchers are carrying out further research into how advice is given in the dental chair - and whether this can be specially adapted for each individual receiving treatment.
Professor Peter Heasman, who also worked on the study, said: "I think that many dentists and dental hygienists are fully aware that their patients do not always follow their professional advice.
"Nevertheless, we were surprised to find so many of our patients who were unable to follow instructions accurately, even in the short term."