All rodents have one pair of upper and lower chisel-shaped 'incisor' teeth that are covered with hard enamel on the front and a softer substance like bone on the back. As the rodent gnaws, the backs of the chisel-shaped teeth wear away faster to maintain a sharp edge. The incisors grow all of the time or continuously. If the rodent does not keep gnawing, the front incisors will grow right out of its mouth and prevent it from eating. The incisors might cause death by growing inwards into the jaw or skull.
Rodents have no pointed teeth called canine teeth.
There is a gap between the front incisors and the molars. Rodents can curl back their lips out of the way of the sharp front teeth into the gap between the front teeth. This leaves the front teeth bare. It makes it easier for the rodent to gnaw hard food or wood without injuring its mouth. It also helps keep unwanted wood, nut shells and soil from being eaten along with the food.