[An immunohistochemical study on the response of nerve fibers in the periodontium of rat molars during experimental tooth movement].

It is well known that orthodontic forces induce pain during tooth movement. However there have been few neurohistological studies on sensational periodontal tissue response to orthodontic tooth movement. So we have many unknown problems about reactions of periodontal nerve fibers during tooth movement. The present study deals with the response of nerve fibers in periodontal ligament of rat molar during experimental tooth movement by means of immunohistochemical method for calcitonin gene-related peptide (CGRP). The results obtained in this study were as follows: 1. In control sections, CGRP-immunopositive nerve fibers were observed both around the root apex and in the intermediate region of the periodontal ligament. Although most of those fibers was distributed around the blood vessels, a few nerves were recognized to terminate in the periodontal fibers. 2. At three days after tooth movement, the CGRP-positive nerves gradually increased in number around the blood vessels. After that, the number of CGRP-positive nerves decreased and no difference of distribution of CGRP-positive nerves was observed between the control sections and the experimental sections at seven days. 3. Especially, at three days when active remodeling of alveolar bone was taking place, a few nerve fibers showing CGRP-immunoreactivity were observed to concentrate around osteoclasts or to migrate Howship's lacunae. These findings showed the dynamic changes of CGRP-immunoreactive nerves in the periodontal ligament during tooth movement, and suggested that this reaction of the periodontal nerves might induce pain in patients. In addition to neurotransmitter function, it was supposed that CGRP directly or indirectly effected the cellular elements and surrounding tissues on peripheral organs such as vascular system and osteoclasts.