Cellular proliferation in the tooth germ of the rat incisor

Abstract

Mitotic activity has been studied in parasagittal sections of incisor tooth germs from thirty-five rats ranging from birth to 76 days of age. General sites of mitosis in the tooth germ have been visualized, and quantitative analyses have been made regarding the axial distribution of mitotic figures and mitotic indices in the internal enamel epithelium and pre-odontoblast layer. Comparisons have been made between young and old rats and between maxillary and mandibular incisors. The overall distribution of mitoses was found to be similar to that described by other investigators for this and other species. Regional differences in the mitotic index and cellular density were noted in the internal enamel epithelium and the pre-odontoblast layer. Cells of the internal enamel epithelium and the stratum intermedium exhibited active proliferative capacity. Mitoses were also observed in those cells lying between the internal enamel epithelium and stratum intermedium, and in the linearly-oriented preodontoblast layer. Few mitoses were noted in stellate reticulum or external enamel epithelium. In general, mitotic activity in the internal enamel epithelium was greatest in young animals. In animals of the same age, mitotic activity in the internal enamel epithelium was higher in maxillary than mandibular incisors. No analogous age or positional differences could be demonstrated for the mitotic index in the pre-odontoblast layers. The axial distribution of mitoses, both in the internal enamel epithelium and the pre-odontoblast layer, was widest in the youngest animals. In the same animal, however, the axial distribution of mitoses in the mandibular internal enamel epithelium was wider than that found in the maxillary internal enamel epithelium. The pre-odontoblast layer did not exhibit a comparable positional difference.