Studies In Craniofacial Sutural Morphology, BMP-2 Expression And The Infraorbital And Palatine Nerves After Trans-sutural Distraction Of Midfacial Skeleton: Experimental Studies In Dogs

PartⅠThe possibility of external rigid framework and trans-facial pin for trans-sutural distraction of midfacial skeletonObjective:An external fixation retractor was applied on experimental animals to study the method of Sutural Distraction Osteogenesis on craniofacial skeleton. Method:Rigid external distractors were fixed on experimental animals.Kirschner wire was penetrated bilateral maxillary bones as force-borne device and a elastic traction of 800g was exerted on them for 20 days.Result:3 dogs survived to predicted observation period.The external fixation retractor had an excellent retention and were not loose.The experimental animals appearances a progressively maxillary antelocation without obvious stationary period.The clinically visible maxillary antelocation could be observed 2～3 days after distraction.Edge-to-edge occlusion relationship appeared 7～8 days after distraction.The occlusal relationship turned into Angle ClassⅡfrom Angle ClassⅢfrom then on.The maxillary complex showed parallel anterior displacement and there was no obviously change in the basilar-maxillary angle.Conclusion: The external fixation retractor has an excellent retention.The micro surgical trauma,suitable tractive force and excellent distraction effect make the experiment can exactly mimic the process of treating midfacial hypoplasia clinically.PartⅡThe histologic and morphologic changes of craniofaciai sutures after trans-sutural distraction of midfacial skeletonObjective:To explore the effect of midfacial sutural distraction osteogenesis on the reconstruction of craniofacial sutures by observe the histologic and morphologic changes of craniofical sutures.Methods:Eighteen mongrel dogs were used and randomly divided into the experimental group(n=12)and the control group(n=6).Rigid external distractor was used for sutural distraction of the midfacial skeleton in the experimental animal.Two experimental and one control dogs were sacrificed at each interval(in the 5th,10th and 15th day of distraction,the 10th and 20th day of consolidation,60th day after completion of consolidation.).To observe the sutural histologic and morphologic changes under the light microscope.Results:During the period of distraction and consolidation, the width of sutures become large,the cells differentiate and proliferate,the amount of vessel increase,and the sutures reconstruct and shape the new structure. Conclusion:The craniofacial sutures appear adaptive reconstruction under distraction.PartⅢThe expression of BMP-2 after trans-sutural distraction of midfacial skeletonObject:To study the expression of BMP-2 after midfacial sutural distraction osteogenesis in dogs and to probe the mechanism of sutural distraction osteogenesis.Methods:Eighteen mongrel dogs were used and randomly divided into the experimental group(n=12)and the control group(n=6).Rigid external distractor was used for sutural distraction of the midfacial skeleton in the experimental animal.Two experimental and one control dogs were sacrificed at each interval(in the 5th,10th and 15th day of distraction,the 10th and 20th day of consolidation,30th day after completion of consolidation.).The expression of BMP-2 was observed by means of immunohistochemistry.Results:During the period of distraction and consolidation,the positive stain of BMP-2 was found in the proliferative preosteoblasts,the mesenchymal cells and the newly formed bone matrix at the sutural margin of the experimental dogs.Weak expression was also found in the control dogs.Along with the distraction,The expression of BMP-2 in the experimental group increased significantly and reached the peak in the 15th of distraction,then gradually decreased.The level of BMP-2 was higher than that in the control group.Two months after the removal of the distractor,the expression of BMP-2 recovered to nearly nomal.Conclusion:The mechanical strain can lead to the generation of endogenous BMP-2,BMP-2 maybe play an important role in the new bone formation.PartⅣInfluence of midfacial sutural distraction osteogenesis on dog infraorbital and palatine nervesObjective:To observe the histological changes of the dogs infraorbital and palatine nerves at different time during and after midfacial sutural distraction,and to investigate the influence of sutural distraction on infraorbital and palatine nerves.Methods:The animal model was established with thirteen 12-week mongrel dogs,which were randomly divided into the experimental group and the control.Rigid external distractor was used in experimental dogs for midfacial skeleton protraction.Distraction protocol included 15 days distraction and 20 days consolidation.The force used for midfacial protraction was 800 gram.The experimental animals were sacrificed at different time points postoperatively. Bilateral infraorbital and palatine nerves were obtained from the experimental and the control dogs,made thin section,and observed under light microscope and electronic microscope.Results:The midfacial skeleton moved forward obviously in experimental dogs.Pathological changes were observed in the infraorbital and palatine nerves in experimental dogs.At the end of distraction,the changes of the infraorbital and palatine nerves became more obvious.During the period of consolidation,the infraorbital and palatine nerves began to recover.Two months after the removel of the rigid external distractor,the nerves were observed as normal.Conclusion:Along with the midficial skeleton advancement by sutural distraction,deleterious changes appeared in the infraorbital and palatine nerves, but it is temporary and reversible.