The Influences Of Distraction Osteogenesis On Intramusucular Tissue And Nerves In Rabbits' Mandible

Distraction Osteogenesis (DO) is a new technique to reconstruct bone malformation or defects by inducing the development of callus then lengthening and widening the bone, by means of exerting mechanical force at certain rate to the bone which is cut but maintained blood supply. Because the DO technique do not need the supplying of bone, avoid second surgery and the soft tissues can be prolonged simultaneously, it has been used widely in clinic today since it has been imported into the field of oral and maxillofacial surgery by McCarthy firstly.. To study the optimal distracting procedure to decrease the side effect of distraction osteogenesis on soft tissue related for providing fundamental theory to clinic application, we established mandibular model of distraction osteogenesis bilaterally of rabbit, discussed the changes of the thickness , percentage of collagen type Ⅰ and Ⅲ and microstructure of the perimysium and observed the changes of transforming growth factor-beta (TGF-β) expression at various timeafter distraction at different distracting rate.According to the Law of Tension-Stress and being acquainted with the anatomic structure of the mandible and the course of inferior alveolar nerve, we established the model of distraction osteogenesis bilaterally in rabbits' mandible, advanced the mandible bilaterally effectively and studied the effect of osteogenesis of various time by histochemical method. It was proved that this kind model was stable and reliable and it was feasible to be used to study the principles and the influence on soft tissue related of distraction osteogenesis.Based on this model we studied the changes of the thickness of the perimysium, the acreage of cross section of the muscles , percentage of collagen type I and type III and the ratio of the acreage of cross section of the collagen and fascicles at different distracting rate by picrosirius-polarization and image analysis method. At the rate of lmm/d, the perimysium and the muscles were injured slightly, the percentage of collagen type III increased temporarily. At 4 week after distraction, the percentage of collagen type III decreased to normal level while the perimysium and the muscles became thickened slightly. The ratio of the acreage of cross section of the collagen and fascicles had not obvious changes. Nevertheless the perimysium was harmed severely , became thinner and the muscles atrophied at the rate of 2mm/d.. The percentage of collagen type III persisted a higher level. At the end of the experiment the acreage of cross section of the muscles had been recoverd but the perimysium became thicker than normal level and the ratio of the acreage of cross section of the collagen and fascicles increased. It was implied that there was the formation of excessive fibrous tissue of the intramuscular connective tissue which would produce bad influence on the function of the muscles. So it was appropriate for the perimysium to be distracted at the rate of 1mm/d.The samples of muscles for Scanning Electron Microscopy were made simultaneity to look into the changes of the microstructure anterior and posterior distraction osteogenesis. It showed that normally the collagen of the perimysium arranged orderly, compactly and undulately. But when the muscles were stretched longer the collagen became straighter and inclined to the long axis of the muscle. The perimysium was scathed slightly and its spatial arrangement was recovered eventually at the rate of 1mm/d. At the rate of 2mm/d, the perimysium not only lost its undulate arrangement, but also became loosen, even having lacuna some in part, and had not reverted ultimately at the end of this experiment. It implied that at upper distracting rate the perimysium was damaged badly and its spatial arrangement changed obviously. In a word it was fitting to distract at the rate of less than lmm/d.In this experiment we also observed the changes of transforming growth factor beta (TGF-p) expression in rabbits' inferior alveolar nerve (IAN) suffering distraction at different rate by histological immunhistochemical method. After the distraction was finished, the number of Schwann cells and the staining score of TGF-p became to increase, reached the tip afterwards and then decreased gradually almost simultaneously. But the number of Schwann cells and the staining score of TGF-P increased more distinctly and went on for a longer time at the rate of 2mm/d, so that even in the end of this experiment the staining score of TGF-P still had obvious statistical significance. This showed us that during the course of rehabilitation of the injured nerve the number of Schwann cells and the staining score of TGF-P were synchronous and they both regulate the rehabilitation and regeneration of the injured nerve. Furthermore at the rate of 2mm/d, IAN was injured badly, and the persistent highness of the staining score of TGF-P might cause the excessive sediment of...