歯根未完成永久歯の移動に伴う歯根の発育, 根尖閉鎖に関する光顕的ならびに電顕的研究

Abstract

Immature permanent teeth of young adult dogs were displaced by placing force of 50g and 200g on them and the effect of displacement on root growth and apical closure was investigated light and electron microscopically. The results were as follows : 1. Change in the 50g group Although deformation of Hertwig's epithelial sheath was seen on the compression area light microscopically in short term cases, the root apex was closed by connecting cellular cementum and growth of dental root by formation of root dentine was observed in the end. Apposition of cementum however was decreased compared with the control group. Scanning electron microscopy showed large and small resorptive lacunae of the alveolar bone and apposition of new bone. Transmission electron microscopy showed marked destruction of cells one to two weeks after displacement. The tension area did not show deformation of Hertwig's epithelial sheath but showed root growth and apical closure light microscopically. Scanning electron microscopy did not show resorption of the dental root or of the alveolar bone. Transmission electron microscopy showed cementblasts, osteoblasts and fibroblasts of high cell activity. After maturation, however, cells of low activity were found. 2. Change in 200g group On the compression area, deformation of Hertwig's epithelial sheath was seen light microscopically and root growth and apical closure were delayed as compared with the 50g group. Scanning electron microscopy showed restoration of the resorption findings of the dental root and alveolar bone. Transmission electron microscopy showed marked appearances of osteoclasts, marked organelle, and active ruffled border. On the tension area, the light microscopic findings were about the same as those of the 50g group and deformation of Hertwig's epithelial sheath was not seen and apposition of new trabeculae in the alveolar bone in particular was marked. Scanning electron microscopy did not show resorption of dental root or of the alveolar bone. Transmission electron microscopy showed rough surfaced endoplasmic reticulum, cementblasts with developed Goldi apparatus, osteoblasts, and fibroblasts. Characteristic suggestive of high cell activity was seen. After maturation of dental root, organelle decreased. On the basis of the foregoing findings, although displacement of immature permanent teeth by continuous force of 50 to 200g caused deformation of Hertwig's epithelial sheath and poor formation of dentine and cementum in the apical region to some extent, it was clear that periodontal membrane fibers were functionally arranged between the teeth and the surrounding alveolar bone.