| Object The purpose of the present study was to creat a three-dimensional model of mandibular, analysis the mechanics property of varies fixed method. Tt will provide scientific evidencen for clinical. Method 1. 9 adult mandibles were choosed.and divided into three group random .They were operated sagittal split osteotomy. 2.Fixation (1)group 1 was fixed by two screw which was inserted (2)group 2 Three screw were inserted to stabilize the bone (3)group 3 The bone was stabilized by minipalate according to the themry of Champy .3 .The mandibles were placed in artificial joint fossa .of machinie .regulated them to transverse section . A observation wire placed in chin was to observe the displacement of distal of bone. Coracoids were splinted by two metal wires. Traction of wires wre modelling muscles force. Force was loaded on 13 functional point, molar,incicor.10 times every functional point. 4.Two JD-X2 microscopes were put two sides an- d afterwards of model. Displacement of bone could be measured by microscopes .Average value of each functional point was analysised by Origin software . And analysis the displacement of distal and mesial bone with T test. Results 1. After sagittal split osteotomy, there are some forces between two section of bone such as bening moment , torsion moment,shear force . They would make condylar and distal bone displacement. 2 Under the condition of functional loading ,the dispacement of the mesial and distal bone was larger in two-screw group than those in the other two groups. 3 The forward –backward displacement of condylar was less in the three-screw group than minipalate group .the right-left displacement of condylar was no obvious different. The displacement of distal bone was less in the three-screw group than minipalate group . Discussion The aim of the study was to analysis mechanics property of varies fixation methed of saggital split osteotomy. According to the results, the dispacement of the mesial and distal bone was larger in two-screw group than those in the other two groups. Several years most scholar applied three-screw fixation .but Souyris suggested that the effect of two-screw was reliability.we come to conclusion that the stablity of fixation in two-screw group was less than those in the other two groups. According to result , the stablity of fixation in minipalate group was less than that in three-screw group. But minipalate fixation was still utilized in clinic. The reason is that the shape of minipalate can be adjusted according to requirement . further more , nerves and blood vessel injury can be voided by this mean .and it can be easily operated. Compare to minipalate group three-screw group posses better stability.but we can not replace minipalate completely by three-screw in clinic. The reason followed. 1. Position of screw after saggital split osteomy , the position of screw have two type . One is that placed three screws all were above the inferior alveolar nerves .Another is that two screws were above the inferior alveolar nerves. The third was below the inferior alveolar nerves.Most study demonstrated that disperd distribution can provide better stability. But in clinic , dissection limited ideal position of screw. 2.The angle of screw and route of operation Spiessl suggested that operation entrance through cheek .but it can injury cheek . On the other side , entrance by mouth have many problem sunch as that operate was too complicated. Further more operation visual fiend was limited .Uckan contrast the angle of 90℃ a and 60 ℃,he got the result that 90 ℃ was better than 60℃.So as to get better stability ,operation must be improved. Conclusions 1. Rigid fixation can get better stability than wire fixation.2.Some scholar thought that two-screw can provide enough stability, but we can see that two-screw was less stability than other two fixation methed. 3.Three-screw processed better stability than minipalate. 4.Minipalate still utilized in clinic commonly because of its conven...
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