Dentition is the type, number, and arrangement of teeth in an animal. An adult human has 32 teeth. The incisors are used for cutting; the canines for gripping and tearing; and the molars and premolars for crushing and grinding food. A herbivore has relatively unspecialized teeth that grow throughout life to compensate for wear (plant fibers are very tough) and are adapted for grinding. A carnivore has a range of specialized teeth related to killing, gripping, and crushing bones. In carnivores, unspecialized milk teeth are replaced by more specialized adult teeth, which have to last a lifetime.