ラット切歯の発生および初期発育過程における神経分布に関する研究

抄録

The relationship between development and innervation in the early developmental stage of the incisor teeth of the rat was investigated in a period from 13-day fetus, initial development of tooth germ, to 10-day old, beginning of tooth eruption. The results obtained were as follows : 1. At 13-day fetus, the early configuration of trigeminal nerve ganglion was observed and endings of their nerve fibers were short. However, at 14-day fetus, development of the origin of tooth germ was observed with the thickening of epithelium. At this period, no nerve fibers reaching near the tooth germ were observed. 2. At 15-day fetus, the ending of nerve fibers were densely distributed around mesenchymal tissues which were present inside of epithelial tooth germ at cap stage. 3. At 19-day fetus, the tooth germs were in the bell stage. The nerve fibers were observed entering mesenchymal tissues of dental sac and they were rich, especially on the palatal side of maxillary incisors and lingual side of mandibular incisors. 4. At 1-day old, enamel was formed and at the same time small single nerve fibers were first recognized entering the dental pulps of mandibular incisors. On the other hand in the maxillary incisors they were observed at 3-day old. 5. Vascular and nerve canal, where nerve fibers distributed to the maxillary incisors passed through, were gradually displaced toward the incisal ridge as the development of the tooth germs progressed. As a result, the nerve bundles, distributing to the basal portion of the tooth germs and labial periodontium through the vascular and nerve canal indicated a sharp bend to the posterior and superior direction. 6. The nerve fibers in the dental pulp increased in number and amount with time, in addition, their branches increased. After 7-day old, nerve fibers, reaching the odontoblast layer, were rarely observed. 7. At 10-day old nerve fibers in the dental pulps were abundantly observed and elongated to the direction of incisal ridge up to the superior position than the intermediate one and their tips were located around the alveolar ridge ; however, no nerve fibers were observed in the superior portion of the pulp. 8. The nerve fibers in the periodontium elongated with time and were abundant, and at 10-day old they reached at the level of alveolar ridge.