How do rodents keep their front teeth from getting too long?

Rodents such as mice, rats, beavers and squirrels have incisors that never stop growing. These teeth are kept at the right length by regular chewing on food and other materials. The front surface is harder than the back, which helps create a sharp, self-sharpening edge as the teeth wear down. Without this constant wear, the teeth would become dangerously overgrown.