A 3-D Finite Element Study Of Mandibular Second Molar Mesial Movement By Using Customized Lingual Appliance With Mini-implant

ObjectiveTo establish left mandibular with first molar extraction 3-D finite element models included customized lingual brackets,stainless steel lingual arch wire,buccal buckles,micro-implants,lower dentition,periodontal ligaments(PDL),alveolar bone The aim was to analyze the biomechanical characteristics during mandibular second molar mesial movement by using micro-implants with customized lingual appliances,which sets a reference for clinic appliance.MethodsThe study was designed for three sections:3-D finite element models were established in section 1,the method is as following.256-row computed tomography was applied to scan volunteer’s mandibular.Mimics,Geomagic Studio and ANSYS were employed to fabricate 3 customized lingual brackets for mandibular second molar with different slot lengths(3.5mm、4.0mm、4.5mm)firstly,then extract the first molar on the mandibular and develop 3 volume models included customized lingual brackets,stainless steel lingual arch wire,buccal buckles,micro-implants(located at 5mm from the alveolar ridge crest of the buccel side between mandibular canine and first premolar),lower dentition,periodontal ligaments(PDL),alveolar bone.Finally 3-D finite element models were established after dividing FEM mesh,setting the material mechanics par ammeters and constrainting the experiment boundary condition.The changing regularity of the dentition displacement was studied in section 2.Four different loading conditions were based on the 3-D finite element models at the slot length of 5.0mm.The Force of 1.5N was loaded at the lingual side only under the condition one.And the Force of 0.5N,0.75 N,1.0N was loaded at the both buccal and lingual sides respectively under the condition two to four.The changing regularity of initial displacements of the dentition and stress distribution on the periodontal ligaments were studied.Von Mises stress,major principal stress and minor principal stress were observed and analyzed.The changing regularity of the slot lengths was studied in section 3.The force of 0.75 N was loaded in the models builded in section 1 at the both buccal and lingual sides respectively under the condition one to three.The items were observed and analyzed same as these in section 2.ResultsIn section 1,three left mandibular with first molar extraction 3-D finite element models including customized lingual brackets,stainless steel lingual arch wire,buccal buckles,micro-implants,lower dentition,periodontal ligaments(PDL),alveolar bone were successfully established.In section 2,more uniform relatively were the stress distributions of periodontal membrane of left mandibular second molar when the mesial force were loaded at both buccal and lingual sides than the force loaded at lingual side only.The potential increased of mesially inclined second molar while decreased of distally lingual rotated second molar when the feature could happen.The increase of potential of mesially inclined second molar,the initial movement of molar and the stress of periodontal membrane could be found under the force loaded increasingly.The maximum stress values of von Mises superior to safe stress of periodontal membrane could be obtained at the value of 5.72*10-2Mpa under the mesial force of 1.0N loaded at both buccal and lingual sides.In section 3,the stress distributions were relatively more uniform under the slot length of 4.5mm than of 3.5mm while there were no differences about the inclined movement of second molar.The more the slot length increased by 0.5mm,the more the difference of initial movement between the molar crown and root decreased Conclusions1.The 3-D finite element models of mandibular second molar mesial movement with customized lingual brackets from interdental micro-implants were built,which has not been report in the current journal.Their perfect biological fidelity and clinical similarity laid the foundation of further research.2.In the model,the optimal loading pattern should be a mesial force of 0.75 N loaded at both buccal and lingual sides.3.There would be moderate influences decreasing the potential of mesally inclined mandibular second molar when mesially moving through lengthening the slot length.Some other inclination performance should be provided for the clinic appliance.