Research Of Computer-aided Design And Clinical Application For Mandibular Angle Osteotomy

Objectives1.To analyze the CT measurements of female prominent mandibular angle patients based on three-dimensional(3-D)skull image reconstruction.To compare the distance,angle and proportion related differences between different mandibular angle types,and to determine the morphologic features of mandibular angle in Chinese women.2.To analyze the 3-D skull CT images of attractive women,and to investigate the aesthetic features of female mandibular angle.To compare the 3-D measurements with those of female prominent mandibular angle patients,and to investigate the main differences between them.Our results could provide a reference for surgical planning of prominent mandibular angle.3.To apply digital technology in prominent mandibular angle patients to develop a pre-surgical planning and design.To evaluate the clinical application of 3-D digital technology in mandibular angle osteotomy based on data analysis of pre-operation,surgical simulation and post-operation measurements.Methods1.3-D CT images of 96 female prominent mandibular angle patients were reconstructed.We divided the mandibular angle into three types according to the position of gonion to the sagittal plane of the ramus.Distance,angle and proportion measurements were performed to identify the morphological features of different mandibular angle types.2.A 5-point Likert scale was used to quantify attractiveness of female volunteers,and 3-D CT images were reconstructed for attractive women with average score ? 4.Mandibular angle aesthetics related distance,angle and proportion measurements were calculated to compare those of female prominent mandibular angle patients,and to summarize the aesthetic features of mandibular angle in attractive women.3.According to the previous research of mandibular angle aesthetics,the length of mandibular body and ramus were calculated based on geometric formula,and two spheres centered at Co and Me points were generated in Mimic software with the radius of mandibular body and ramus respectively that calculated above.The new gonion was defined as the intersection point of the two spheres and the mandible.The osteotomy line was created based on the new gonion,and the surgical template was produced by a 3-D printer.The mandibular angle was resected according to the position template.3-D CT measurements of pre-operation,surgical simulation and post-operation were taken to evaluate the surgical outcome.Results1.Mandibular angle was classified into three groups,namely extraversion,introversion and normal group,based on the position of the gonion to the sagittal plane of the ramus.The extraversion group had the longest lower facial width(100.685mm±5.124mm)and the highest level of gonion divergence angle(71.827° ± 4.466°),compared to 91.297mm±4.795mm and 62.612°±1.88° in the introversion group respectively.The mandibular angle in the extraversion group(114.951°±5.356°)was significantly lower than that in the in the introversion group(119.451°±4.507°).2.There were significant differences between attractive women and female prominent mandibular angle patients in Co-Go-Me,FH-MP,Go-Me/Co-Go and Mf-Go/Co-Go.Chinese attractive women had a mandibular angle ranged from 112.76° to 125.06°,with an average level of 123.91°.The aesthetic FH-MP was ranged from 25.9° to 28.08°,with an average level of 27.03°.The Go-Me/Co-Go and Mf-Go/Co-Go ratios in attractive women were approximately to 2.0 and 1.4 respectively.3.19 female patients with prominent mandibular angle,including 4 patients who were diagnosed as microgenia simultaneously,underwent preoperative surgical design and mandibular angle osteotomy successfully.Results of 3-D CT measurements indicated an obvious improvement of Co-Go-Me,FH-MP and Go-Me/Co-Go after operation,and statistical analysis found a significant difference between the preoperative group and postoperative group.All the patients were satisfied with their facial outcomes.Paired t test showed that there were no difference in Co-Go-Me,FH-MP and Go-Me/Co-Go measurements between surgical simulation and postoperative groups.The mandibular contour of postoperative patients were much the same as those of surgical simulation.Conclusions1.In our study,we devised a novel,simple and efficient classification of prominent mandibular angle,and classified mandibular angle into extraversion,introversion,and normal types according to the position of the gonion to the sagittal plane of mandible ramus.Our study quantified the differences of mandibular angle types,and provided a reference for surgical treatment of prominent mandibular angle.2.The aesthetic features of mandibular angle in Chinese women could be summarized in three points:(1)The skeletal contour should be in harmony and symmetry.(2)The mandibular angle and FH-MP should be close to 124° and 27° respectively.(3)The Go-Me/Co-Go and Mf-Go/Co-Go ratios should be approximately to 2.0 and 1.4 respectively.Our study helped surgeons establish aesthetic standards for surgical planning of prominent mandibular angle patients.3.3-D digital technology was successfully applied to determine the new aesthetic gonion of female prominent mandibular angle patients,and this method has not been reported in the papers of domestic and international.With the application of digital technology to pre-surgical planning in prominent mandibular angle patients,there was a great improvement of the precision in mandibular angle osteotomy.Our study provided a safe and effective treatment for mandibular contouring surgery.