矯正的歯の移動がラットの臼歯歯髄内神経線維へ及ぼす影響
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概要
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Effect of tooth movement on the dental pulp is unclear in many respects and reports on changes in pulpal nerve fibers due to changes in orthodontic force, in particular, have been very few. In the present study as a part of a fundamental research, mesial movement of the first maxillary molar of the rats was made with use of two different initial loads and changes in pulpal nerve fibers resulting from the tooth movement were observed. The orthodontic appliance consisted of a closed coil spring connecting the first maxillary molar to the central incisors. The initial loads applied with the coil was 15 g as optimum force or 150 g as excessive force, and it dissipated with time. After 1, 3, 7 and 14 days, the animals were perfused after an overdose of anesthetic. Serial sections of the experimental and control jaws were ordinary prepared, given silver impregnation and Hematoxyline・Eosin stain, and observed under the light microscope. The results were as follows : 1. The experimental tooth was tipped mesially involving intrusion of mesial root and extrusion of distal root. The degree of intrusion and extrusion depended on the magnitude of the orthodontic force. 2. The two groups showed a common finding of slight reversible inflammation of the pulpal tissues. However, no significant difference in pulpal damage corresponding to the difference in the initial loads was found between the two groups. 3. The pulpal nerve fibers showed greater degeneration by root intrusion than by extrusion. The degree of degeneration depended significantly on compression caused by the initial load. Since the nerve fibers can fairy bear stretching, degeneration of pulpal nerve fibers showed low dependency on the stretching caused by the initial load. So intrusion caused more damage to the pulpal nerve fibers than extrusion. 4. Degeneration of pulpal nerve fibers differed due to the difference in susceptibility to compression and stretching, and due to the load on root apex. With interruption of axonal continuity at the root apex, however, degeneration can be classified into slight degeneration and axonotmsis. Slightly degenerated nerve fibers without axonotmsis showed morphological recovery with dissipation of the load. Nerve fibers with axonotmsis, on the other hand, showed Wallerian degeneration on the distal side. With dissipation of the load thereafter, regenerated nerve fibers appeared. It was suggested from the foregoing results that the use of excessive force in the daily clinical practice would be considered undesirable on the basis of changes in the pulpal nerve fibers.
- 九州歯科学会の論文
- 1994-02-25