The Study Of Surgically Assisted Unilateral Anterior Maxillary Expansion

Maxillary hypoplasia is a common skeletal malocclusion,including transverse and sagittal deficiencies.In the past,serious skeletal deformities,often need to be treated by orthognathic surgery.Distraction osteogenesis(DO)is a kind of endogenous bone tissue engineering technique,which has been applied to the congenital and acquired craniofacial deformity.Compared with the conventional orthognathic surgery,DO has advantages of less surgical trauma,less operation difficulty,and and better long-term stability.Patient’s velopharyngeal function is not affected,and additional bone grafting is not needed.Moreover,DO can provide more space for orthodontic alignment,that is an ideal treatment methods.Previously,most of the researches on the DO were focused on the long bone and mandible,and there were few experimental studies on the maxillary sagittal DO.However,there are significant differences in the anatomical structure among maxillary,long bone and mandible.In this study,we designed the distraction device to expand the unilateral anterior maxillary of the swine model,and observed the feasibility of the device and the swine model.The distraction area is observed using histological examination and computed tomographic.New bone’ quantity was scanned by Micro-CT constructing the microstructure to evaluate its quantity and quality,and from the molecular level studying morphogenetic protein-2(BMP-2)expression pattern during new bone formation.Thus to further understand maxillary DO process and lay down basis for further clinical application.The full text is divided into 3 parts:1.Establishment of a unilateral anterior maxillary expansion model in swine4 female Bama swine at 10 months of age were chosen undergoing unilateral anterior maxillary expansion.Results showed that the distraction device fixed well,swine can well tolerate anesthesia and operation procedure and all experimental animals in distraction group were successfully lengthened.Therefore,swine is a good candidate for maxillary distraction.With the extension of the fixation period,the distraction zone was gradually filled with new bone and the new bone mature along the time.The newly formed bone had certain characteristics: extending from bilateral sides of distraction area to the central part,gradually blending and remodeling.At the 8 week of fixation,the remodeling of the distraction zone is still in progress and its density showed in CT image was still lower than that in the control side,indicating that the fixation period of maxillary DO should be longer than 8 weeks.2.Micro-CT study of new bone qualityMaxillary bone samples were obtained from both the control side and the distraction side on the fixed period of 2 weeks,4 weeks,and 8 weeks.The Micro-CT scan results showed during the healing process of DO,the bone mineral density(BMD)of new bone density increased with the extension of the fixed period,and the mineralization rate of the palatal side was higher than that of the buccal side.In the first 8 weeks of fixation,the new bone was formed continuously,and the trabecular bone in the distraction zone grew from bilateral sides to the central part,and remodelled from rod-like shape to plate-like shape.At the 8 week of fixation,the "quality" and "quantity" of the new bone were lower than those of the normal maxillary,which suggested that the fixation period of maxillary DO should be more than 8 weeks.3.Study on the changes of BMP-2 level in serum during maxillary DOSerum samples of both distraction group and control group were obtained before the surgery,at the end of latency,at the end of distraction,at the fixation of 1 week,and 2 weeks,using ELISA method for BMP-2 concentration evaluation.The results showed that the serum BMP-2 concentration of distraction group was higher than the control group.concentration of BMP-2 increased at the end of latency,and reached the peak at the end of distraction,then during the fixation it decreased rapidly.The serum BMP-2 concentration of control group among all time points had no significant different.These results suggest that BMP-2 plays an important role in the early healing of DO,and it can directly or indirectly stimulate the synthesis of endogenous BMP-2.