ラット切歯反復切断後の変化に関する実験的研究

Abstract

The incisal edges of the right mandibular incisor teeth of rats were repeatedly cut above the gingival margin at least seven times at three-day intervals. A visual comparison was made between the operated right mandibular incisors and the unoperated left mandibular incisors. The changes in the eruption rate, in radiographic, histopathological and neurohistological findings were examined and the following observations were made : 1. The operated teeth gradually assumed a white chalky appearance which resembled enamel hypoplasia. Some of the operated teeth showed a thinner enamel morphologically. 2. Radiographically and histopathologically, the operated teeth gave evidence of expanded pulp cavities, with resultant thinning of both dentin and enamel. 3. The eruption rate of the operated teeth was accelerated. The eruption rate was 1.3-1.6 times that of unoperated teeth. 4. Histopathological examination showed severe hypocalcification in the enamel with evidence of less thickness. This was noticed to a lesser extent in the dentin. 5. The scanning electron microscope examination of the operated teeth revealed an irregular arrangement of enamel rods, whereas the unoperated teeth showed a regular arrangement of rods. Granular or soluble sections of the operated teeth were observed, clearly indicating hypocalcification. 6. Morphological changes were not observed in the enamel organs at the base of the incisors. However, an increase in cell proliferation was observed in the operated teeth, substantiating the acceleration of the eruption rate. 7. It was observed that the pulp cavities of the operated teeth expanded to the incisal edge. A slight irregular arrangement of odontoblasts was noted, and that calcific tissues like the dentin bridge, which covered the vital pulp were formed at the cutting site. 8. No differences were noted in the nerve distribution around the pulp and the enamel organ ; therefore, it should be noted that the repeated cutting at the incisal edge of the teeth did not influence the nerve distribution.