It's all well and good to brush your teeth twice a day, but you could be causing more damage than good if you're brushing incorrectly.

Freshbrush, a New Zealand toothbrush company, released a study in time for World Oral Health Day on March 20 and found that of the 1000 New Zealanders surveyed, more than half were brushing their teeth with the wrong bristles and were too harsh on their teeth, said the Daily Mail.

Dentists recommend using a soft bristled toothbrush but 54 per cent of people were found to be using medium or hard-bristled toothbrushes.

It is also recommended that you brush your teeth and gums gently, as brushing too hard and vigorously can wear away tooth enamel and harm your gums.

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Despite this, 64 per cent of people said they were brushing their teeth "somewhere between gentle and vigorously" and 21 per cent said they were brushing too hard.

The majority of people, 77 per cent, brush twice daily, which is a good sign.

Experts say you should replace your toothbrush every three months. And if you've been suffering with a cold or flu it's a good idea to replace your toothbrush.

It's also a good idea to keep your toothbrush away from anyone else's and clean it regularly, according to British dentist Dr Rhona Eskander.

"The mouth harbours literally hundreds of different types of micro-organisms, some of which can be transferred to a toothbrush during use," she said.

"Rinsing a toothbrush under running water from the tap does not remove all these germs."

Within just two days, toothbrushes can become heavily infected with disease-causing bacteria, viruses and fungi.

Sharing a toothbrush is not only unhygienic, it's also "gross" according to the Freshbrush study, with 50 per cent of people said they were grossed out by the idea of sharing their partner's toothbrush.