To Evaluate The Force Level And Strain Patterns On The Mandible During Bilateral Osteodistraction By Three Diamensions Finite Element Model

Purpose The purpose of this study was to evaluate the force level andstrain patterns on the mandible during bilateral osteodistraction withdevices oriented either parallel to the body of the mandible or parallelto the sagittal axis of distraction by FEM.Materials and methods: A three diamensions finite element model ofone unembalmed human cadaver mandible osteodistraction wasestablished in this study with the CT scanned transverse sections andcomputer program(AutoCAD and I-DEAS).The stress distraction andlateral forces were evaluated.Results: Greater lateral forces were seen when the devices wereoriented parallel to the madibular body.with this deviceorientation ,increased tnesile strains were seen at the labial symphysisand the medial neck of condyle ,and increased compressive strainawere found at the lingua symphysis and the lateral neck ofcondyle.However,when the devices were oriented were orientedparallel to the axis of distraction ,the forces and strains were notdetected.Conclusions:The results suggest that the device orienation hasimportant biomechanical effects on lateral forces and strains patternsduring mandibular osteodistraction The successful application ofdistraction osteogensis is dependent .For example,anteriorly directedforces are applied to the callus tissue forming between osteotomizedbone segment to generate new bone during mandibularosteodistraction.These forces stimulate peoliferation of the osteoblastprecursor cell population in the center of the distraction gap.At theedges of the host bone margins,differention and recruitment ofosteogenic cells provide the building blocks necessary for new ostoiddeposition and subsequent mineralization.The biomechanical factors can be categorized as eithertissue-related (intrinsic),distractor-related(extrinsic),or deviceorientation. Resently,Richards etal found that altering the orientationof the osteotomy (intrinsic)from 00to 450 caused an increased in shearstrain within the regenerate tissue with a consequent decrease in newbone quantity.Other have shown that unilateral distraction devices sancreat a stress shielding environment(extrinsic),thereby causingdecreased bone formation on the side closest to the distraction device.Finally,our group has demonstrated in a computer-generated modelthat distraction devices placed(oriented) parallel to the mandibularbody create lateral displacement tendencies at the bone-deviceinterface.Clinically this lateral displacement manifested as anundesired width increase at the anterior aspect of the proximalsegment ,lossening of fixation screws ,and localized pressureresorption of bone under the fixation plates.This device orienationmay also cause histologic condylar changes during symphysealwidening by osteodistration.However, when devices were orientedparallel to the common saggital axis of distraction ,these problemswere minimized.The force appliced to the mandible as a result of the previouslymentioned biomichanical factors all have the potential alter the tensileand compressive strains within the distraction gap and associated hostbone.these strains may not only affect the quantity ,but also thequanlity of the regenerate tissue.Therefore,it is important to have athorough understanding of the force vectors actived as a result of thedistraction process.This not only will aid in treatmentplanning,appliance design,and control of forces vectors during duiingosteodistraction,but it also may provide preliminary data for finiteelement analysis.The purpose of this study was to evalue the force level and strainpatterns produced on the mandible in response to osteodistractionusing 2 different device orienations by FEM.It was tested thatdistraction devices placed parallel to the the body of the mandiblewould increase the lateral force on the mandible proximal to thedistraction gap and affect the tensile and compressive strains at sitesproximal and distal to the axias of distraction would minimized anyalteration in lateral force or unfavorable compressive strains.