hlstopathologic al and Immunohistochemical Background of Orthodontic Treatment

摘要

It is important to establish the biological basis of immunohistochemical characteristics of mandibular bone and cartilage, as well as periodontal tissue reaction to mechanical stress for orthodontic treatment. The mandible is composed of mandibular bone and cartilage. This cartilage is classified as secondary, together with condylar, coronoid and angular cartilages. The mandibular bone formation pattern attracts many researchers because it suggests large possibilities for orthodontic treatment. Mandibular condylar cartilage has bone characteristics which are more significant than cartilaginous characteristics. In general, Runx2 is a transcription factor necessary for osteoblast differentiation and bone formation. Therefore, we focused on Runx2 and investigated the distribution of Runx2 in developing mouse mandibular condylar cartilage, with Jagged-Notch signaling, using immunohistochemistry and in situ hybridization techniques. These IHC and ISH results suggest that Runx2 plays an essential role for mandibular condylar cartilage development, especially that Runx2 is essential for the onset of secondary cartilage differentiation. In addition, to establish an immunohistochemical basis for orthodontic treatment, we examined early changes of Runx2 and Msx2 immunohistochemical expressions by immunohistochemistry in mouse periodontal ligament exposed to mechanical stress. At 20 minutes, 1 hour, 3 hours, 9 hours and 24 hours, relevant parts of the mouse tissues were histopathologically evaluated, and they were examined for Runx2, Msx2 and alkaline phosphatase (ALP) expressions. Strong expressions of Runx2 arid Msx2 were seen in periodontal fibroblasts of the tension side at 20 minutes after mechanical stress. Expressions of Runx2 and Msx2 became stronger in parallel with time, and at 24 hours after mechanical stress, the periodontal fibroblasts, cementoblasts, and osteoblasts showed strong expression. Moreover, ALP has also demonstrated similar strong expression. All these results strongly suggested that Runx2 promoted differentiation of osteoblasts at an early stage and Msx2 worked as an activator of Runx2 function. Furthermore, because Heat Shock Proteins (HSPs) serve as molecular chaperones to maintain homeostasis in tissues, we examined the immunohistochemical profile change of one such protein, HSP70, in periodontal ligament cells after receiving mechanical stress during orthodontic treatment in the course of up to 24 hours. We thought that the mechanical stress for orthodontic treatment might cause dynamic histological change occurred within a short time and might also cause expression of HSP70 in periodontal ligament tissue.