Advice on the best way to brush teeth for adults and children is confusing and inconsistent, according to University College London researchers.
There is also a lack of agreement on how often to brush and for how long, they said, because of an absence of good research.
The researchers looked at advice given by dental associations, toothbrush companies and in dental textbooks.
But experts say there is no evidence that one method is better than another.
The UCL researchers, Dr John Wainwright and Prof Aubrey Sheiham, analysed 66 different sources of advice from around the world for their study, published in the British Dental Journal.
The most commonly-recommended toothbrushing method involved a horizontal brush movement with some circular motions.
But six different tooth-brushing techniques were recommended by dentists and dental associations in the study, with no one method being favoured.
Some involved angling the brush at 45 degrees, others involved vertical brush movements while using the brush to 'scrub' the teeth was also recommended.
Most of the advice suggested brushing teeth twice a day, but one source said it should be three times daily.
When it came to how long to brush teeth for, 26 sources advised brushing for two minutes, 12 for two to three minutes and two sources recommended three minutes of brushing.
The UCL study said: "There appears to be no consensus among professional bodies on the best method of toothbrushing for the general population or for people of different ages or with particular dental conditions."
The study added that the wide diversity in recommendations, for something that is done twice a day, "should be of serious concern to the dental profession".
It said there was an urgent need for more research into the comparative effectiveness of brushing methods.
Dr Nigel Carter, from the British Dental Health Foundation, said there was little evidence for recommending one brushing technique over another.
"Dentists generally feel it is better to take a person's existing habits and modify them if necessary," he explained.
"Even children have a preferred way of brushing their teeth, and dentists should point out the areas that are not being cleaned well, rather than teaching them a whole new technique."
Guidance from the Department of Health says that no one brushing technique has been shown to be better than any other.
More important is a systematic and rigorous approach to brushing teeth which cleans all tooth surfaces, it says.
Disclosing tablets containing dye can help to indicate areas that are being missed, the guidance adds.
Prof Damien Walmsley, scientific adviser at the British Dental Association, says children up to the age of seven should be supervised while brushing their teeth.
But he warns that there is little point brushing teeth straight after eating sugary foods to prevent tooth decay.
Bacteria from food starts producing acid after a few minutes, which softens the enamel on the teeth, so brushing during this time could damage the enamel.
"Leave it for an hour or so," Prof Walmsley advises.
Advice on the NHS Choices website says to brush teeth with fluoride toothpaste twice a day for at least two minutes to help keep teeth and mouth healthy.