Nearly half of Australia is ignoring advice from dentists and are holding on to their toothbrushes a lot longer than they should.

The Australian Dental Association recommended people switch out their crusty toothbrushes at least every three months and there are a few good reasons to do so.

A report commissioned by Colgate suggests on average only 40 per cent of Australians are holding on beyond 90 days.

Younger people are holding on to their toothbrushes the longest, with 7 per cent of people aged 25 to 34 years and 45 per cent of those aged 18 to 24 years keeping their toothbrush for more than three months.

Tasmania is apparently the most diligent state, with 76 per cent heading to the dental aisle every quarter and the ACT is the most lax, with only 46 per cent doing so.

Why you need to change your toothbrush

“Using an old toothbrush is like trying to clean your floors with a worn-out broom,” said Dr Mikaela Chinotti, an ADA oral health promoter.

“You just won’t get the same level of cleanliness, and in the case of oral hygiene, this can lead to a buildup of plaque, which can cause tooth decay and other oral health issues.”

Your mouth is filled with bacteria, so by doing the right thing and cleaning your teeth will lead to bacteria building up on your tooth brush.

It’s not just the bacteria, but when the bristles get frayed, it diminishes their cleaning effectiveness.

If your toothbrush looks like this, it’s time for a new one.

How to know it’s time to change your toothbrush

If you can’t remember the last time you bought a toothbrush, then take that as your sign to get a new one.

However, the three months is just a rough guide and there are other tell-tale signs it is time for a new one you should look out for.

• Check the bristles: If the bristles are frayed and are no longer standing up straight, put the toothbrush in the bin, it’s time for a new one
• Do you teeth feel clean? The main purpose of brushing your teeth is to clean them, so if you’re teeth feel fuzzy or just not sparkling clean, get a new toothbrush
• It smells: If it smells, then it’s harbouring all that bacteria and it is time for another.

Healthline also suggests getting a new toothbrush if you or someone you live with has been sick recently, or if someone accidentally uses yours.