根未完成永久歯の根管中間位歯髄切断後の根尖閉鎖に関する光顕的ならびに電顕的研究

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Pulpotomy at the middle portion of the root canal was performed on immature teeth of young adult dogs. Healing process of the pulpal wounds, change in nerve fibers in the dental pulp, process of the formation of the dentin barrier, and apical closure including growth of the root were investigated under the light and the electron microscope. The results were as follows : 1. Three days after operation, a necrotic layer was formed extensively directly under the pulpotomied surface, and the nerve fibers in the inflammatory layer directly under the necrotic layer were degenerated. Observation under thc transmission electron microscope (TEM) of this region showed undifferentiated mesenchymal cells poor in cell organellae and nerve fibers with marked destruction of myelin of the myelin sheath. At the root apex, Hertwig's epithelial sheath was observed. 2. A week after operation, a calcified barrier was beginning to be formed on the pulpotomied surface and slight inflammatory cellular infiltration limited to the dental pulp directly under the surface was seen. Directly under the barrier, cells which were comparatively large in cell and nucleus sizes were found. The TEM observation of these cells showed cells which had nuclei with small depressions in part, were rich in rough-surfaced endoplasmic reticula, and showed wide intercellular space. 3. At the second week after operation, the formation of the dentin barrier was beginning to be seen directly under the pulpotomied surface. Observation of this region, viewed from the pulpal side, under the scanning electron microscope (SEM) showed large and small calcospherite-like structures fused together and piled. The TEM observation of the cells at this region showed large oval nuclei with gently sloped depressions, and many rough-surfaced endoplasmic reticula and mitochondria in cytoplasm around the nucleus, and odontoblast-like cells connected by junctional complex. The TEM observation of the nerve fibers showed normal nerve fibers of laminated structure with orderly formed myelin sheath. At the root apex from this time, addition of connecting cellular cementum was seen and the TEM observation showed active cementoblasts in both the control and experimental groups. 4. The cases from one to two months after operation showed the formation of the dentin barrier with dentinal tubules, on the pulpotomied surface, continuously from the periphery to the center of the pulp. The SEM observation of this region showed peritubular dentin on the coronal side, but its borders with matrix were distinct at some places and indistinct at other places. Dentinal tubules were not uniform. The TEM observation of the cells directly under the barrier showed, as in the case of odontoblasts of root dentin, large ovoid nuclei poor in chromatin, and uneven distribution of cell organellae such as mitochondria and many rough-surfaced endoplasmic reticula. As to the nerve fibers in the dental pulp, small nerve bundles and single nerve fibers were ascending toward the dentin barrier. Active apposition of cellular cementum was seen at the root apex and the TEM observation of this region showed cells with a large oval nucleus and rich in rough-surfaced endoplasmic reticula and mitochondria. 5. Six months after operation, the dentin barrier was thickened. The SEM observation of the dentin barrier showed that, on the pulpal side, calcospherites were orderly distributed, fused and increased in compactness, and had uniform dentinal tubules. The nerve fibers, at this time, reached near the dentin barrier with some running parrarel with the dentin barrier and terminating in the odontoblast layer and some infiltrating into the barrier together pulpal intrinsic tissue and blood vessels. At the root apex, slight internal resorption of dentin was observed in part and the formation of cementum with inclusion of cementocytes was seen in those sites. Calcification was completed and about the same degree of apical closure was seen as in the control group. The SEM observation of this region showed the formation a flat surface and highly calcified cementum lacunae. The TEM observation of cementoblasts on the surface of cementum showed resting cells poor in rough-surfaced endoplasmic reticula and mitochondria. Fibrous bundles of the periodontal membrane were arranged functionally.
1989-02-25

根未完成永久歯の根管中間位歯髄切断後の根尖閉鎖に関する光顕的ならびに電顕的研究

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