Ultrastructure of lingual enamel epithelium in rabbit permanent incisors

The recent observation that the lingual surface of the permanent rabbit incisor, in contrast to the rodent incisor, is covered with enamel near the initially formed tip, initiated a histologic study of the enamel epithelium in this region. Tooth buds from fetal New Zealand white rabbits aged 27 and 30 days in utero were processed for transmission electron microscopy. Examination of longitudinal and cross-sections revealed a transition of secretory ameloblasts to postsecretory ameloblasts on the facial aspect of the enamel organ. Incisally, the facial ameloblast layer was continuous with postsecretory ameloblasts on the lingual aspect. More apically on the lingual surface, a gradual transition between postsecretory and reduced ameloblasts occurred. This study shows that by day 27 in utero, the ameloblasts on the lingual aspect of the tooth are in the postsecretory and degenerative stages and that, by day 30, the enamel epithelium lingually has been replaced by cementum on the prismatic enamel and by connective tissue.