ラット下顎骨凍結が骨と下歯槽神経に及ぼす影響

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The inferior border of the mandible of ninety rats was frozen for three minutes with the rats grouped into freezing temperatures of -196℃, -100℃, and -25℃, and the histologic changes caused by freezing in the mandible and its related tissues were investigated histopathologically. The results are as follows : 1. Three days after freezing, the mandible showed hypochromatosis, and degeneration and disappearance of osteocytes. The extent of the changes was to the molar region of the alveolar bone in the -196℃ group, to the inferior border of the mandibular canal in the -100℃ group, and limited to the compact bone in the inferior border of the mandible in the -25℃ group. 2. Three days after freezing, osteoclasts appeared in part of the border in the -196℃ and -100℃ groups. On the fifth day, bone resorption and bone generation started in part. After two weeks, resorption and apposition of bone were observed extensively. At the sixth week, bone with osteocytes missing was found still remaining. 3. The medullary cavity showed bone formation in these two groups from the fifth day after freezing and marked networks of bone formation on the seventh day. It was filled with new trabeculae at the second week. 4. In the dental pulp of the incisor, degeneration and disappearance in part were seen in the pulp cell and odontoblasts three days after freezing. On the fifth day, hyaline degeneration was seen in the whole dental pulp at the frozen site. After two weeks, various cells began to be restored gradually and new dentin formation started. Periodontal ligament of the incisor showed plasmotomy and disappearance in part in an early stage of the experiment. In the next stage, direct bone fusion with the inner wall of the alveolar bone and stoppage of eruption were seen. 5. In the inferior alveolar nerve three days after freezing, hypochromatosis, swelling, plasmotomy, and granular degeneration were observerd in most nerve fibers in the -196℃ group and in part of the nerve fibers in the -100℃ group. In the -25℃ group, almost no changes were seen. 6. Seven days after freezing, the -196℃ and -100℃ groups showed minute nerve fibers crossing each other and extending among Schwann cells in the degenerated inferior alveolar nerve. After two weeks, the minute fibers extended to the peripheries beyond the frozen site, and increased in the number of fibers, in descending order of the -196℃, -100℃, and -25℃ groups. 7. After six weeks, the number of the regenerated nerve fibers distributed in the inferior alveolar nerve and incisal periodontal membrane approximated the normal in the -196℃ and -100℃ groups. 8. When the inferior border was frozen for three minutes at -196℃, -100℃, and -25℃, the temperatures in the mandibular canal were -22℃, -7℃ and 18℃, respectively. On the basis of the foregoing findings, nerve tissue was affected not only by the effect of freezing but also by the surrounding soft tissue. In the cases where bone tissue surrounds the nerve, regeneration of the nerve was found to be slightly delayed. In view of this, in performing cryosurgery, anatomical structure, freezing direction, and temperatures must be duely taken into consideration.
九州歯科学会の論文
1989-02-25

ラット下顎骨凍結が骨と下歯槽神経に及ぼす影響

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