Over time bristles of the toothbrush become frayed and distorted making it less effective at cleaning your teeth. The Bite Dental team give advice on when you should throw away your toothbrushSo if your bristles start to bend in different directions, it is time to chuck it out! Plus over time it traps particles of food, toothpaste and plaque causing bacteria to grow on your toothbrush. Your toothbrush should be replaced every three to four months.