.
Nothing terrible, but it's best to change it because the bristles get softer and don't do the job. I actually change it every 4 months when I go to the dentist and he gives me a new one.
A black hole will appear in your bathroom and will suck your entire house into it.
3 months of tooth brushing should last a lifetime.
But what sort of toothbrush is it?
I like the best toothbrush which tends to be Oral B.
Yes, my dentist only gives out Oral B soft.
Nothing
"You'll probably be really hungry by then!"
Then you are using it for 4 months. And then 5 and so on and so on. Nothing is going to happen.
The three-month rule is generally because of bacteria. If you're using a nasty toothbrush, you're introducing more bacteria into your mouth. Most toothbrushes can last for years without significant wear and tear, unless you're getting into the high-end sonic ones.
probably nothing since ive done it
You disappoint the people who make and sell toothbrushes. They push the idea that you "need" to change it frequently. As long as you continue brushing at least daily, even with a 4-month-old or even a year-old toothbrush, you are far better off than by not brushing.
Your teeth will fall out.