ラット臼歯の生後発育と enamel free area の発生に関する組織化学的研究

Abstract

The development of rat molars was investigated histologically from immediately after birth to the 35th days. Furthermore, a histochemical and scanning electron microscopic study was carried out concerning mainly the development of the tips of the cusps lacking of enamel, "enamel free area". The following results were obtained. 1. The sequence of development and eruption of rat molars was as follows : M_1, M_2, and M_3. There was little difference between upper molars and lower molars. The first molar in the lower jaw and the third molar in the upper jaw erupted slightly earlier. The second molar erupted in both upper and lower jaws at approximately the same time. 2. The cells at the center of the cusps where enamel free area occurred, morphologically showed similarity with the inner enamel epithelium cells in early stage. The cells at the inclined plane of the cusp differentiated into the long columnar ameloblasts, while the cells at the center of the cusp changed into the small cells. These small cells existed on the surface of dentin of enamel free area until eruption. The cells of stellate reticulum and outer enamel epithelium cells, which had transformated stratified squamous epithelium immediately before eruption, were observed on the dentin surface, connecting each other. 3. The stratum intermedium at the enamel free area showed slight development before the formation of predentin and these cells gradually dispersed and finally disappeared. 4. The histochemical study were made of phosphatase, dehydrogenase, glycogen and mucopolysaccharide before and after the development of cnamcl free area. Consequcntly, in the case of ALP, ACP, SDH, LDH, NADH and NADPH, the activity of inner enamel epithelium cells and stratum intermedium cells at the enamel free area showed difference in comparison with those of enamel forming inclined plane of the cusp. It was elucidated that the deficiency of these enzymes correlated well with the development of enamel free area. 5. The findings of enamel free area by the scanning electron microscope indicated a layer of adhesive material covering the surface immediately before eruption and generally reticular structure in the surface of dentin locating below it. However, the picture showed diversity, with moderate calcification or slight calcification.