Absence of enamel matrix on root-analogue surfaces of rabbit permanent incisors.

Permanent incisors from fetal New Zealand white rabbits aged 27-29 in utero from offspring of New Zealand white rabbits until the 4th d after parturition were processed for scanning electron microscopy. Macroscopic examination and measurements on standardized scanning electron micrographs revealed that the lingual surface of unerupted teeth was covered with developing enamel extending about 2.1 mm from the incisal end as evidenced by the presence of typical Tomes' pits. Such structures were not observed more apically where the lingual tooth surface appeared to be covered by cementum. The permanent incisors erupted into the oral cavity at birth and attrition was initiated within a few hours after parturition, leading to an inverse correlation between attritional loss of tooth substance and extension of lingual enamel. The findings indicate that the enamel-covered, linguoincisal part of the rabbit permanent incisors is not a root-analogue surface. The results are discussed in the light of recent studies on rabbits and rodents.