In life, the diastem between the incisors and molars is filled by the cheeks and tong, effectively creating separate incising and grinding chambers. There is a sphincter muscle to facilitate this action. The lagomorphs , the rabbits and hares, have a very small second incisor immediately behind the main one on each side. The Aye Aye , unlike humans and the majority of living primates have two upper and two lower incisors in each quadrant of the jaw. A curious adaptation in the Aye Aye of Madagascar is the acquisition of continuously growing rodent-like incisors.
Sheep have no upper anterior teeth at all.
The ruminants, such as cows, crop and swallow. Later they regurgitate the contents of the caecum to chew their cud. A large volume of saliva buffers and protects the teeth. The most extreme adaptation is the Monodon , the narwhale. It is a rare example of a unilateral tooth.