The Three-dimensional Finite Element Analysis On Mesial Movement Of Mandibular Second Molar By The Micro-impant

Objective To establish a three dimensional finite element model for mandibular,dentition, bracket, archwire and micro-implant without the lower left first molar.Byvarying loading forces and micro-implant positions, to appraise the optimal orthodonticforce and micro-implant anchorage effection on the mesial movement of lower secondmolar, to evaluate the therapy method for enhancing anchorage and mesial movement ofmolar. So supporting a biomechanical basic for applying orthodontic forces in clinic．Method1.Select a healthy young adult female volunteer with complete dentition asmodeling material. Obtain the430tomographic images by CT scan. Using the finiteelement modeling software to set up the three dimensional finite element model formandibular,dentition,bracket,archwire and micro-implant without the lower left firstmolar.One micro-implant Embedded into mandibular alveolar bone between firstpremolar and second premolar.2. Micro-implant connects the second molar buccal tube,to imitate the Ni-Ti tension spring by50g,100g,150g,200g and300g loading. Analysisthe initial stress of periodontal ligament and the initial displacement by different tension.Appraise the optimum orthodontic force in mesial movement of second molar.3.Fivedifferent loading conditions are based on the three-dimensional finite elementmodel.Condition one,the first premolar and second premolar are fixed by stainless steelwire,and the second premolar and second molar are connected by Ni-Ti tension spring,simulates the traditional oral anchorage.Condition two bases on the condition one,themicro-implant and premolar are fixed,simulates the enhanced micro-implant anchorage.Condition three,the micro-implant and second molar are connected.Conditionfour, the micro-implant is embedded into mandible alveolar bone between canine andfirst premolar, the micro-implant and second molar are connected.Condition five baseson condition three, the micro-implant and hook connected,simulates the micro-implantanchorage. Condition one and two,75g forces simulated by spring load on both thebuccal and the lingual. Condition three,four and five,150g forces simulated by springload on the buccal.Observe the displacement of teeth and the stress of periodontalligament,analyze the displacement graph of teeth and the stress graph of periodontalligament．Results1.The high precision FEM model,including MBT treatment system, micro-implant,mandibular dentition and periodontal supporting tissue was established.2.Thedisplacement of second molar and the stress of periodontal ligament were increasedby the loading force raise.When mesial movement of molar by50g,100g and150gloading, the maximum stress of Von-Mises are8.63KPa,17.26KPa and25.89KPa,lower than the maximum stress level for the periodontal ligament.When mesialmovement of molar by200g and300g loading, the maximum stress of Von-Mises are34.52KPa and51.77KPa, exceed the maximum stress level for the periodontalligament.3.The concentration of stress in condition3and4is the largest,exceed thecondition1and2,condition5is the least.Condition1and2, second molar is mesialinclination,condition3and4are inclination and rotation,condition5is approximatetotal mesial migration.The largest stress of periodontal ligament concentrates oncervical margin by inclining movement. Total movement is uniform.The stress byinclining movement is obviously move than total movement.The initial movement ofsecond premolar:model1＞model2＞model3,4,5.The initial movement of root apex:model3＞model4. The initial movement of root apex: model3＞model4.The initialmovement of buccal cusp,lingual cusp and root bifurcation: model4＞model3.The initial movement is uniform in model5.Conclusion1.Mesial movement of the second molar can safely loaded with150gforce.With the proper force,the change of stress and displacement on the groups are inthe rational range．2.The effect of micro-implant enhance anchorage isvisible.3.Application of both sides should try to choose in clinic.4.The father distancebetween the micro-implant and the second molar,the more benefit to mesial migration ofthe second molar.5.When the micro-implant connects hook, second molar approximatestotal movement.