| Background Mandibular angle is one of important factors determining facial contour,oriental women regard ovoid or oval shaped facial contour to be beautiful.Wide mandibular angle makes female’s face in the shape of a square,which is considered to be lack of delicate beauty.Therefore,increasing number of patients chose to undergo mandibular angle surgery,and the osteotomy of mandibular angle has become one of the major cosmetic surgeries of facial contour.Reasonable design of osteotomy line is easy to lead to the second mandibular angle,neurovascular injury in the inferior alveolar neurovascular bundle,asymmetric mandibular angle,the fracture of mandibular neckcollum mandibulae and other complications.Therefore,it is a guarantee for the success of the operation to design a safe and reasonable osteotomy line.In this regard,this experiment,based on the observation of inferior alveolar neurovascular bundle,the measurement of mandibular angle after simulated osteotomy and bone thickness at osteotomy area,designd a safe and beautiful osteotomy line with the aid of three-dimensional finite element model for mechanical analysis and verification,to provide a theoretical basis for reducing clinical complications and achieving the best operation effect.Purpose To design a safe and reasonable osteotomy line for guiding the osteotomy of mandibular angle through collection and statistics of mandibular angles of patients,and measurement of relevant data and mechanical patients by three-dimensional reconstruction.To draw ideal osteotomy line for clinical application while ensuring the safety of operation.Methods Preoperative CT images of 20 cases of patients undergoing mandibular angle osteotomy in our hospital in recent years were collected(image provided by Radiology Department of Zhongda Hospital Affiliated to Southeast University).CT images were exported to Mimics 17.0 software in the form of DICOM format.3D images of mandibles were simulated and reconstructed in Mimics 17.0 software,and the arrangement of inferior alveolar nerve vascular bundle was marked according to CT images to design an ideal osteotomy line.C refers to front end point of the osteotomy line which is located just below mental foramen,A refers to end point of osteotomy line,which is determined by the intersection between horizontal extension line of alveolar arch and mandibular ramus,and M refers to turning point of inferior alveolar nerve vascular bundle.X refers to new mandibular angle points,which are located at the junction between lower alveolar end along inferior alveolar neurovascular bundle with mandibular angle point,i.e.,5mm,7mm,9mm and 11mm,13mm,15mm,17mm away from MX.Mandibular angles were measured after the osteotomy along four osteotomy lines,respectively,and bone thickness of major sites along the osteotomy line were measured,for guiding surgeons to master intervention depths in different positions.Finally,three dimensional finite element models constructed before and after osteotomy were input into Ansys software for mechanical analysis of occlusion experiment,to observe whether the mandibular occlusal function was normal after osteotomy.Results A total of 20 cases of patients were included into the experiment,and the analysis of osteotomy simulation showed that when MX was 13mm,the postoperative mandibular angle met aesthetic standards,and the bone thickness between the second and the third molar tooth become thinner and thinner at forward and backward directions,occlusal mechanical analysis showed that the stress distributions before and after osteotomy were almost consistent.Conclusion The method designed in this experiment can accurately determine osteotomy line,and mandibular angle after simulated osteotomy meets aesthetic standards and safety requirements,postoperative occlusal function is not affected,so the osteotomy line can be applied to clinical trials for guiding the surgery of mandibular angle osteotomy. |
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