健常家兎象牙質ならびに切削によるその形態変化に関する電子顕微鏡的観察

Abstract

Recently, many contributions has been given on the problem of the teeth grindings. The present study which applied to the rabbit was the electron microscopic observations to clear up ultrafine-structures of the normal dentin and morphological changes of the dentin occurred by using high speed dental engine for cavity preparation through the technique of undecalcified sectioning from the viewpoint of ultramicrophase. This observations for the normal dentin were conducted on the region just over labial alveolar crest of the incisors, as shown diagram, and for the experimental dentin, on the cases of three to twenty-four days after cavity preparation in the same region under the condition of the minimum irritation. The results were summarized as follows. On the normal dentin In the young dentin layer, the minimum diameter of dentinal tubules was approximately two microns and there were found within the tubules the odontoblastic process with network structures and vesicles, which were limited with delicate unit membrane. An inorganic fine granules accumulating on the typical collagen fibrils to some extent were observed in the matrix of this dentin layer. In the middle layer of calcified dentin, the minimum diameter of the tubules was about 1.5 microns. The dentinal fibers appeared to be surrounded by obscure limited membrane, and cytoplasm of the fibers changed into amorphous appearance different from the young layer. The characteristic periodicity of the collagen fibrils could not to be recognized completely because of fine granules accumulation in large quantities, and then obvious distinction between peritubular and intertubular matrices was shown. In the outward layer of the dentin, the fine containings within the tubules were found to be gathered in center or wall side of the tubules. The wall of the tubules showed various irregular appearances. The whole of the matrix appeared to be calcified similarly so that could not to be distinguished peritubular and intertubular substances. In the superfacial layer of the dentin, part of the terminal tips of the tubules could not to be recognized as they were filled with the hypercalcified matrix. On the experimental dentin Observations on the experimental dentin were undertaken on each cases of three days to twenty-four days at intervals of three days after the cavity preparation. There was not observed any changes in fine structure in young dentin of three and six days cases after the examination, that is, they were much the same as the findings of both of the tubules and the matrix in the normal dentin. During the duration of nine to fifteen days after the examination, variation in structure of the containings of the tubules were found, while the typical periodicity of the collagen fibrils was found obviously in part of the matrix. Middle layer of the dentin was demonstrated that the containings of the tubules was not only reduced, but also disappeared during the duration eighteen to twenty-one days after the examination. The matrix of the layer showed also reduce of the degree of calcification, since the typical periodicity of the collagen fibrils was found still obviously within limited region, whereby it was hardly possible to be distinguished peritubular and intertubular matrices. The outerward layer of the dentin underlying to the cavity floor did not indicate any clear changes. The dentinal fibers and matrix in the cases extended to twenty-four days after the operation was much the same structures as findings of those of the normal dentin. From the above findings, it was revealed that the reaction when the dentin was grinded by high speed dental engine under the condition of the least irritation, was not soon appeared, demineralization as related to the variations of the dentinal fibers occurred in the matrix after a certain period, and at twenty-four days after the operation the dentin was recovered completely from abnormal condition.