1. Rabbits and chinchilla have similar developments of teeth length. Compared with lower incisors the upper incisors show a higher growth, whereas the incisors of rats are characterized by a higher growth in the lower than the upper jaw. 2. The attrition of upper incisors mainly depends on growth of the antagonist in the lower jaw. Feeding hay or carrots exclusively high (rabbits, chinchillas) or highest (rats) rates respectively of attrition are observed. It shows that hardness of feedstuffs has not the importance as be supposed. 3. Minimum increases of teeth length, that are the lowest differences between growth and attrition, were observed on upper incisors of rabbits and chinchillas fed with hay or carrots and on lower incisors when fed concentrates (complete pelleted feed or mixed feed with native components). 4. Compared to animals with usual development of teeth length, the reason of disturbances of teeth health in form of ''elephant teeth'' is fewer an overgrowth than a decreased attrition (because faulty conformations of teeth reduce the attrition on each other). Offering hay or carrots in clinic manifestations have only a small effect.
