数種の硬組織疾患歯特に齲歯の分裂線について

Abstract

The research on the subject of splitting lines has a long history. Benninghoff and his school clarified the meaning of the splitting lines tentatively (1925). However, no interpretation has been presented by them about the irregular splitting lines that frequently appear and are observed in the line systems of the splitting lines. Prof. T. NAKAYAMA, M. D., (1957) attached special importance to the appearance of those irregular splitting lines and disclosed his study, offering the following opinion with regards to their significance. He concluded that the appearance of such irregular splitting lines is a direct functional manifestation that may be interpreted as a sort of defense reaction of the tissue, and insisted that the phase of growth of the organs and tissues should be grasped by the observation and investigation of both line systems and irregular splitting lines together. Based on the opinion of Dr. Nakayama, the author has made a series of study in order to investigate whether or not such special irritations to the human tooth as dental caries, abrasion, attrition or operative dentistry would cause irregular splitting lines to the dentin of tooth as a defense reaction. The study has led the author to the following views : 1. In the case of human tooth, too, the appearance of the irregular splitting lines as a defense reaction was observed partially in the dentin. 2. The appearance of the irregular splitting lines was not observed on the surface of the dentin. 3. In the cross section of the tooth, no irregular splitting line was obsered at the superficial layer of the dentin, while both cases of appearance and non-appearance of those lines observed at the deep layer. i) In the case of non-appearance, the reparative dentin formed as a defense reaction showed a small protuberance. ii) In the case of appearance, the formation of the reparative dentin was odserved as a large protuberance. As the cause of such difference, in the case ii) where the growth and formation of the reparative dentin is conspicuous, the growth force influences, as a component, the primary dentin insufficiently calcified in the course of development. The border line between the conspicuous reparative dentin and the deep layer of the primary dentin that come in contact with it makes a marked curvature, convex toward the superficial layer of the primary dentin. The splitting lines develop along this curvature and appear as the irregular ones, which is obviously odserved in the microscopic photo (fig. 8-b). 4. Appearance of the irregular splitting lines as a defense reaction, based on the Nakayama theory, is notably observed in the reparative dentin. There are two kinds of irregular lines that run to different directions seen among those lines, one of which is the lines developing along the edge of the rise of reparative dentin, and the others appear at a right angle toward the edge. When these two irregular splitting lines are observed togethor with the conditions of the caries, the former are seen appearing largely with the chronic, caries, while the latter appears oftener with the comparatively accute cases. 5. It is clearly observed in the microscopic photo (fig. 7, 8, 9) that the development of all these splitting lines corresponds to direction of the main arrangement of fibrils of the dentin matrix on the surface of the dentin of the individual teeth examined. From the way the irregular splitting lines appear in the dentin, the conditions of irritation the tooth sustained and the phase of growth of the reparative dentin formed as a defense reaction may be conjectured.