Changes Of Hard And Soft Tissue After Bilateral Sagittal Split Ramus Osteotomy(BSSRO)Setback Surgery Of Patients With Skeletal Class ? Malocclusion

Objective:1.To assess the changes of soft and hard tissues before and after BSSRO setback surgery of patients with skeletal class ? malocclusion through cephalometric measurements,and discuss the influence of the BSSRO setback surgery on mandibular corner area and condylar position;2.To analyze the correlation between soft and hard tissues movements,providing clinical data for accurate prediction of facial soft-tissue profile after BSSRO setback surgery;3.To evaluate the influence of soft tissue thicknessand setback distance on the ratio between soft and hard tissues changes,contributing to a better pre-BSSRO setback surgery plan-making.Materials and Methods:The sample consisted of 18 adult skeletal Class ? patients treated with BSSRO setback surgery.Lateral cephalograms were taken before surgery(T0)and six to twelve months after surgery(T1).These pre-operative and post-operative radiographs were imported into Dolphin imaging software.Selected sixteen hard and soft tissue points of facial profile were evaluated.The Student's t-test was used to assess the significance of differences between the pre-operative and post-operative hard tissue movements and soft tissue changes;Pearson' s correlation analysis was used to assess the degree of correlation existing between soft to hard tissue changes as well as the influence of the soft tissue thickness and hard tissue setback distance to generate soft tissue to hard tissue movement ratios;significance was set at p<0.05.Results:In the sample of 18 subjects,cephalometric tracing and measurements demonstrated that1.There were significant differences between pre-operative and post-operative hard tissue changes in the Go horizontal position,MP-HP angle,SNB,ANB,mandibular length and total mandibular length.Go went backward,ANBbecame positive from negative,SNB,mandibular length and total mandibular length reduced significantly(p<0.05);Co position and other points did not change significantly(p>0.05).2.Strong correlation occurred between corresponding soft and hard tissue movements:STB-to-B,andSTPog-to-Pog movement showed significant strong positive correlation(p<0.05),the Pearson coefficient wereboth0.95,theratio was separately 1.04:1 and 0.76:1.3.The ratio of STB to B movement decreased while therelative soft tissue thickness increased,but there was no significance(p>0.05),the ratio ofSTPog to Pog movement had no correlation with the relative soft tissue thickness;The ratio of STB to B movement had no correlation with the relative soft tissue thickness,the ratio of STPog to Pog movement decreased while Pog setback distance increased,but there was no significance(p>0.05).Conclusion:1.This study demonstrated that BSSRO surgery of patients with skeletal class ?malocclusion could achieve a correct maxilla-mandibular position and significantly improved oral function,and the method used in this research to reposition the condylar is effective.2.The soft to hard tissue movement showed high correlation.The ratio of soft to hard tissue movements derived from this study would contribute to the database for planning prediction.3.The soft tissue thickness and setback distance have no significant influence on the correlation between soft-to-hard tissue movement ratio.