Influence of frequency of mechanical traction on gene expression and angiogenesis in rabbit mandibular lengthening

Objective To evaluate the influence of the frequency of mechanical traction on gene expression and angiogenesis using a rabbit model of mandibular lengthening. Methods 80 adult New Zealand white rabbits were randomly assigned to the continuous distraction group and intermittent distraction group. A standardized surgical procedure used in our previous study was performed on all the rabbits. Unilaterally straight osteotomy was performed immediately anterior to the first premolar root. The custom-designed manual-driven or auto-driven distractor was adapted on the mandible along a plane perpendicular to the osteotomy and fixed by 2-mm diameter titanium screws. After a 3-day latency period, the distraction was activated. For the intermittent distraction group, distraction was performed once per day; in the continuous distraction group, distraction was achieved at a high frequency of 691,200 steps per day. 10 rabbits in each group were sacrificed at day 3, day 7, day 11 (end of active distraction) and day 18 (week 1 of consolidation) respectively. Bone healing were assessed by histological examination; angiogenesis was evaluated by the immunohischemical staining of collagen IV; mRNA expression of vascular epithelial growth factor (VEGF), basic fibroblast growth factor (bFGF), bone morphogenetic growth factor (BMP-2), transforming growth factor (TGF)-β and tissue inhibitor of metalloproteinase (TIMP)-1 were examined by real time PCR. Results All rabbits completed the experimental process uneventfully. Real time PCR examination demonstrated a significant upregulation of all the angiogenic and bone healing related growth factors in the continuous distraction group. Neo-vessel density in distraction regenerate was significantly increased by the high frequency traction. Conclusion High frequency mechanical traction creates a superior biological environment for bone regeneration by upregulating angiogenesis and bone healing related gene expression. Acknowledgement This study was supported by a grant from the AO Research Fund (05-C73).link_to_subscribed_fulltex