The Study Of Stress Distribution And Displacement Of The Mandibular Corpus Distraction Osteogenesis

After the first successful clinical results in 1992, distraction osteogenesis (DO) has become a powerful new technique for reconstructing the hypoplastic and malformed craniofacial skeleton. It has been widely used to treat hemifacial microsomia and mandibular deficiencies. Although many research works have been done on the biomechanics of distraction osteogenesis, there are some problems that need further study. Finite element method (FEM) is a valid, non-invasive and accurate method to predict different parameters of the complex biomechanical behaviour of the bone. But there are few reports of FEM study on DO. For the first time, a three-dimensional finite element model of human mandibular osteodistraction was established in this study with the CT scanned transverse sections and computer softwares(AutoCAD, PATRAN and NASTRAN). The stress distribution and displacement under different loads were evaluated. Results: 1. A whole three-dimensional finite element model of humanmandibular DO with improved biomechanical similarities to mimicthe situation in vivo was established.2: Von Mises stress accumulates in the distraction area, showing a linear relationship with DO force. The Mises stress was higher in bilateral DO or distraction parallel to the occlusial plane than in unilateral DO or distraction parallel to the inferior border of the corpus. Von Mises stress in symphyseal increases greatly during multifocal mandibular DO, while it changes .little in corpus.3. Displacements of the gnathion and right gonion show linear relationship with distract forces. Distractions parallel to the inferior border of the corpus make the mandible move backward and downward, while distractions parallel to the occlusial plane induce a forward and upward displacement of the mandible especially in bilateral distraction. Transversal shift to the other side was obvious under unilateral condition.4. DO in the corpus together with the midsymphyseal induce backward and downward mandible displacement.Conclusion:1. FEM provides a valid alternative for the study of mandibular DO.2. Von Mises stress accumulate in the DO areas and were higher during bilateral DO or distraction parallel to the occlusial plane. Von Mises stress in symphyseal increases greatly when the mandible was lengthened and widened at the same time.3. Transversal displacements to the opposite side were greater during unilateral DO, while displacements in the saggittal plane were greater during bilateral DO. Clinical complications such as open bite and divergent midsymphyseal will take place when DO parallel to the mandibular corpus.4. Lengthening and widening the mandible at the same time may induce open bite.