At first glance you might think that the picture on the right side is an old tooth brush, but it is actually the one on the left that is 3 months old!
This is a good visual to demonstrate why it is important to make sure you change your toothbrush or electric toothbrush head every 3 months. It is actually the mechanical action of the brush bristles that remove all of the plaque from your teeth. The only benefit of toothpaste is to provide fluoride and minerals to strengthen enamel, and of course to give us that minty fresh breath!
Another reason to make sure you change your brush regularly is the bacteria build up over time on the bristles, shown in the picture below:
Image credit: American Dental Association