発育初期の歯牙に及ぼす機械的損傷の影響に関する実験的研究

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Various forms of experimental traumatic injuries were exerted on 146 unerupted permanent teeth of 50 dogs aged 50 to 120-days after birth. Following the radiologic observation made on these teeth over the period from 4 to 324 days after the operation, the animals were sacrificed, and the teeth were studied histologically. The findings were summarized as follows : In the first group of animals in which the superficial layer of enamel with incomplete calcification was filed away experimentally, the finding was as follows. The enamel substance lost by the expeirmental injury could never be restored in any way. After the injury the enamel epithelium proliferated in strands or in networks, and in the two cases of teeth examined at 26 and 93 days respectively after the injury formation of small cysts was observed. Thers was, however, no retardation of tooth eruption in this group of teeth. The second group of teeth in which the hard tissues were surgically fractured showed the following picture. The enamel substance lost by the injury could never be restored thereafter. However, in the dentinal layer, apposition of newly formed dentin was observed which started at the fractured surface of the tissue. The tissue regeneration was shown to be generally complete with those teeth which elapsed more than 67 days after the operation. Of eleven cases of teeth observed until to the expected time of eruption, only three were observed to erupt. The third group of teeth in which the total hard tissue of the crown was removed showed the following picture. On the fourth day after the operation there were observed on the surface of the exposed tissue of dental papillae a layer of arranged odontoblasts and progressive formation of the primary dentin-like tissue. In this group of teeth eruption was observed to take place in 4 out of 5 teeth which were kept under observation until to the expected time of eruption. However, the crown portion of the erupted teeth was shown to be imperfectly formed. The fourth group in which the hard tissue of the crown and a part of the adjoining dental papillae were surgically removed, showed the following picture. That is, in the teeth observed 4 to 7 days after the operation there was shown a calcified tissue being formed at the junction between the remaining tissue of the dental papillae and the surrounding mesenchymal tissue. These teeth, however, eventually showed abnormal development and all failed to erupt. The fifth group of teeth in which the superficial layer on the lower margin of dental papillae was scarified, showed the following picture. That is, in those teeth in which the Hertwig, s epithelial sheath suffered the injury there was seen temporary formation of the irregular dentin at the site, which, however, failed to impair the normal course of the tooth development and eruption in any member of this group. The sixth group in which the lower ends of calcified tissue of the crown and the adjoining dental papillae were simultaneously removed showed the following picture : that is, according to varying degrees of damage given the teeth by the operation, the tooth roots showed different degrees of growth and this in turn directly affected on their prospect of eruption. Thus, eruption was possible in all 6 teeth where the mesial and distal roots had been normally developed. In the seventh group of teeth where major part of the dental papillae was excised, following picture was observed. Development of the enamel substance in the crown was only barely observed taking place at the residual part of dental papillae. There was never seen any sign of tissue regeneration of the dental papillae at the site of removal, and instead, there was filled by irregular osteoid-dentin proliferating from the inner wall of dentin and from the lower ends of hard tissue, and by osseous tissue proliferating from the base of dental crypt. All the teeth in this group remained impacted in the mandibles. It was revealed from the above experiment that the most essential factor for the normal development and architecture of tooth enamel is the presence and integrity of enamel epithelium as well as of dental papillae with equal importance. It was further considered of importance for the normal eruption of teeth to occur that a well-balanced relation should exist between the teeth and the surrounding alveolar bone throughout their growth stage.
九州歯科学会の論文

発育初期の歯牙に及ぼす機械的損傷の影響に関する実験的研究

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