| Part1A serial histological study for tissue response to rapidmaxillary expansion in the midpalatal suture of the goingrabbitObjective To study the continuous process of tissue response andregularity of midpalatal suture expansion osteogenesis for maxillaryexpansion.Methods For the chronic experiment, a total of 52 male,8-week-oldNew Zealand White rabbits were randomly allocated 13 groups . 5 groupswere experimental groups, 6 groups were matched groups .In addition ,fluorescence labeling groups consist of a experimental groups and amatched groups .A Haas appliance was used for rapid expansion of themidpalatal suture at a rate of 0.25mm/ 12h for 14 days. 4 animals ofexperimental group and 4 animals of matched group were sacrificed onOd, 7d ,14d ,21d ,28d, 42d after the start of activation respectively. 8animals of fluorescence labeling groups were killed on 42d. Sutural tissuechanges were examined histologically. Laser scanning confocalmicroscopy and fluorescence labeling in bone were used to observenewly mineralized bone.Results rapid maxillary expansion induced significantly greatermidpalatal sutural widths for experimental group than sham control on 7d,14d. Then a great amount of osteoblasts and fibroblasts proliferated, new bone deposited along the bone front. Signs of intramembranous bone formation and remodeling were found in the expanded suture. Fluorescent labeling of newly formed sutural bone demonstrated more osteogenesis on a experimental group in comparison with a control group . Conclusion The new bones formation belongs to intramembranous osteogenesis. During different period, the degree of calcification has been different. The remodeling of suture expansion is a process of bone tissue regeneration and fibrous tissue repair.Key words : rapid maxillary expansion ; suture distraction; remodeling Part 2Expression of VEGF mRNA during sutural distraction osteogenesis in rabbitObjective To investigate the expression of VEGF mRNA during midpalatal suture expansion osteogenesis for rapid maxillary expansion . Methods For the chronic experiment, a total of 44 male,8-week-old New Zealand White rabbits were randomly allocated 1 i groups . 5 groups were experimental groups, 6 groups were matched groups. A Haas appliance was used for rapid expansion of the midpalatal suture at a rate of 0.25mm/ 12h for 14 days. 4 animals of experimental group and 4 animals of matched group were sacrificed on Od, 7d, 14d, 21d, 28d, 42d after the start of activation respectively. Then the levels of VEGF mRNAwere detected by RT-PCR.Results The expression of VEGF mRNA in the experiment groupincreased significantly at 7 day's group and reached peak at 21 day'sgroup ,then gradually decreased. The level of VEGF mRNA was higherthan that in the control groupConclusion Mechanical strain created by rapid maxillary expansionregulated the expression of VEGF at transcription level.Key words : rapid maxillary expansion ; suture distraction -, VEGF ;mRNA ; RT-PCRPart 3The correlation between neovascularization and boneformation in the midpalatal suture Expression of VEGFduring sutural distraction osteogenesisObjective To investigate the temporal pattern of expression of VEGF(vascular endothelial growth factor) and new bone formation duringmidpalatal suture expansion osteogenesis for rapid maxillary expansion.Methods For the chronic experiment, a total of 44 male,8-week-oldNew Zealand White rabbits were randomly allocated 11 groups . 5 groupswere experimental groups. 6 groups were matched groups. A Haasappliance was used for rapid expansion of the midpalatal suture at a rateof 0.25mm/ 12h for 14 days. 4 animals of experimental groups and 4animals of matched groups were sacrificed on Od, 7d, 14d, 2Id. 28d. 42dafter the start of activation respectively. The tissue of the midpalatal suture was harvested at different time points to do immunohistochemical research on VEGF protein. Sections were prepared and stained with Periodic acid and schiffs reagent (PAS) to observe the pattern of new bone formation.Results Higher expressions of VEGF were observed following midpalatal sutue distraction osteogenesis. Positive staining for VEGF was mainly seen in the vascular endothelial cells and the active osteoblasts at the edge of newborn trabecular bone. Their strongest expression was noted on the 14th and 21th day after expansion. After the 28th day of expansion , moderate staining for VEGF was observed in the osteoblasts at remodeling sites. Only weak VEGF expression was detected in those cells in the controlled group. The expression of VEGF in the experiment group increased significantly at 7 day's group and reached peak at 21 day's group, then gradually decreased. The level of VEGF in the experimental groups was always higher than that in the control group, and the amount of newly formed bone in the experimental groups was always higher than that in the control group. The amount of newly formed bone in the experiment group increased significantly at 7 day's group and reached peak at 28day's group. The highest increase of VEGF expression preceded that of new bone formation. Conclusion Mechanical strain created by rapid maxillary expansion... |
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