ラット臼歯の多根形成と髄室床の発生に関する研究

Abstract

A histomorphological and histochemical study was undertaken to clear the first stage development of the root bifurcation and to observe the enzymatic histochemical detections of alkaline phosphatase, acid phosphatase, adenosine triphosphatase and lactate dehydrogenase activity in the multirooted formation and the floor development of the pulp chamber in the upper first molars of rats. The following results were obtained. 1. In rat, the epithelial thickening for the multirooted bifurcation occuring from epithelial diaphragm started to be formed immediately after birth at the three spots on the palatal side and two spots on the buccal side. They gradually grew up into the epithelial interradical process and formed the original type of orifice of root canal after joining. The original type of five orifices of the root canal was completed with the epithelial interradical process at ten days after birth. 2. It was appered that each of the tips of the above-mentioned epithelial interradical processes was fused not with the one directly opposite but with one in interlacing position. 3. In the neighborhood of the center of the basal area of the dental papilla, namely in the places where the floor of the pulp chamber will be formed in the future, the accumulation of the cells in the dental papilla adjacent to the epithelial diaphragm and the epithelial interradical process was seen from about eight days after birth. At about ten days after birth, the odontoblasts differentiated from those cells formed a thin layer of dentin, and the first stage of floor development of the pulp chamber was observed. 4. It appeared that the significant factor of the collateral branch formation of the pulp floor was the surrounding of the blood vessel connecting between the dental sac and dental papilla in the growth process of the epithelial interradical processes. 5. In alkaline phosphatase, the epithelial diaphragm and the epithelial interradical process did not show the enzymatic activity, but the island-like areas with activity in the dental papilla adjacent to the epithelial interradical process in the neighborhood of the center of basal area of dental papilla at six days after birth. 6. From the beginning stage of the formation of the enamel matrix the epithelial diaphragm and the epithelial interradical process showed acid phosphatase activity, but did not show polarity. In the coincidence with the time when the activity appeared in this epithelial diaphragm and the epithelial interradical process, the accumulation of the cells with activity was seen in the dental papilla adjacent to a part of the epithelial interradical process. When the dentin was formed on the epithelial diaphragm and the epithelial interradical process, the activity in the coincident area showed a tendency to decrease and disappear. 7. In adenosine triphosphatase, the activity was seen in the epithelial diaphragm and the epithelial interradical process together with in the stratum intermedium cells predominantly with the intense activity at the tip. When the dentin was formed, the epithelial diaphragm lost the continuity and a band of the activity area disappeared. 8. In lactate dehydrogenase, the epithelial diaphragm and epithelial interradical process showed the intense activity, but did not show polariity. From about seven days after birth, the accumulation of the cells with the activity was seen in the dental papilla adjacent to the epithelial interradical process in the center of the basal area of the dental papilla.