If you use a manual toothbrush, you will be familiar with the statement that you should change your toothbrush every three months. It may be something you see displayed at a dental surgery when you go for an appointment, among other places. But is it true?

Some might think this is just a ruse to get people to spend more money buying toothbrushes. Cynical people might think dentists have shares in toothbrush manufacturers and thus a vested interest. But, it is true. You really should change it that often.

The main reasons were explained in a video by American dental hygienist Teeth Talk Girl. She explained that not only is it “extremely necessary” to change it every three months (and this will also apply to the head of an electric toothbrush), but it may be that it needs to be changed even sooner.

Firstly, toothbrush usage soon flattens the bristles, which means they are no longer actually brushing the teeth as they are not hitting them at the right angle. This is a prime example of where flatter bristles might require an early change.

A second reason is the accumulation of germs, which can lead to tooth decay. Efforts to cleanse these with boiling water or disinfectant have limited effects.

She also said if you get ill, the infectious agent may get on your toothbrush when you next clean your teeth, so it should be promptly replaced to avoid re-infection.

The Healthline website offers similar advice, with extra advice on the last point about illness; that throat infections such as Strep A are a particularly strong reason to change.

It also adds another particularly yucky reason: If someone accidentally uses the wrong toothbrush it should definitely be chucked out. Even if it’s someone you often kiss, you don’t want to be sharing germs like that.

So, yes, you should indeed change your toothbrush regularly. And if you still think your dentist has a vested interest in that, maybe it is worth considering that better toothbrush usage means they will get to give you fewer fillings!