| Objective: Malocclusion can affect the development of themaxillofacial,oral functions and can even cause psychological and mentaldisorders.Anchorage control is the key to the orthodontic treatmentsuccessfully in the majority of orthodontic cases.Existed Efforts whichenhanced the anchorage can not satisfy the clinical requirem-ents.Mini-implants emerged Recently have opened up a new field whichimproved the efficacy of the difficult cases. However, It main disadvantage isinstability,it was reported that a success rate of83-89%. Implant often failedbefore apply the orthodontic force or in the process of it, mostly result byimproper surgery of insert mini-implant and inappropriate stress distribution inthe implant-bone interface,which had a serious impact on the application ofmini-implant widely in clinical.Mini-implants is mainly implanted in buccal or lingual inter-radicular sites.Due to the limited distance between the roots and the differences of individualanatomical structure,the surgery request high accuracy.Mini-implants oftenclose to the root of teeth or contact it when implant in the placement.Reserchshowed that the failure rate of implant increased significantly as it is too closeto the root. It is necessary to determine the safe distance between mini-implantand the root. It is found in clinical that there is a high correlation betweenthe masticatory pain and implant failure, and masticatory pain occurs after themini-implant inserted in patients that is near the root in the X-ray. There is noliterature concerning that implant stability is affected by physiologic bite inthe situation of the implant close to the root and whether there is a joint effectof physiologic bite and stress distribution of implant loaded.This studyestablish implant-tooth-jaw model using three-dimensional finite element method to analyze the stress change of mini-implant bone interface when it istoo close to the root,to find out the influence of tooth mobility produced byphysiological occlusion on the implant's stability, and to explore a safedistance between the close root and the mini-implant,and to provide atheoretical basis for the clinical application of mini-implant.Materials and Methods：1EquipmentComputer: CPU:2.0; Memory:1G;Software:Mimics10.1software(Materialise companies), the Pro/E4.0software,ANSYS13.0software.2Establish the FEA models of maxillary with mini-implant2.1Establish FEA model of maxillaryA male with individual normal occlusion was scanned by spiral CT fromjaw to skull, and CT images were stored in DICOM,extracted in MIMICS,partial smoothed,set the periodontal membrane thickness of0.25mm,then thethree-dimensional finite element model containing the maxillary-teeth-periodontal ligament is created.2.2Establish the finite element model of mini-plantRegarding domestic implant size,set8mm deepth in the bone,diameter of1.6mm,pure titanium,cylindrical screw implant,3-D implant model isestablished in Pro/E.2.3Combination solid model2.3.1Implant location and angle:To simulate clinical situation,mini-implantwas inserted in the right side of the maxillary between the second premolarand first molar5mm from the top of alveolar crest, perpendicular to axis oftooth.2.3.2According to the distance between mini-implant and the adjacent root ofteeth, models are established as follow:Model1: Mini-implant contact the root surfaceModel2: Mini-implant embedded in the periodontal ligamentModel3: Mini-implant contact surface of the periodontal ligament Model4: Mini-implant1.0mm away from the adjacent periodontalligament surface3Loading condition3.1loading condition have two kinds of cases:Load A:teeth loaded but mini-implant unloaded;Load B:teeh and mini-implant both loaded;3.2Mini-implant loadedLoaded force:2N;Loading direction: loads are applied on the plane (which is perpendicularto the horizon passes though the straight line that parallel to the occlusalsurface passes though the site of mini-implant inserted) with the direction of30degrees of the occlucal surface.3.3Teeth loadedLoaded force:300NLoading direction:parallel to the long axis of teeth on the occlusal surface3.4calculating casesEight mini-implant cases were established:Model1-A,Model1-B,Model2-A,Model2-B,Model3-A,Model3-B,Model4-A,Model4-B.4Analysising the stress and displacement distribution of implant-boneinterface.Result:13-D models of jaw with mini-implant were established successfully, and allof them have well biological similarity,geometric similarity and satisfy therequirements of calculation of case,and all of them can meet the requirementsof biomechanics operation.2Stress distribution in implant-bone interface when teeth loaded2.1When implant placed contacts the root (in Model1),max Von-Mises stressof the part where is contacting the root(about3mm)on the implant-boneinterface is higher than that of other models which is tiny.In Model2,3,4,thestress on the implant-bone interface is tiny and nearly same level which isshown in Fig.1. 2.2When implant placed contacts the root (in Model1),stress on theimplant-bone interface is Obviously higher than others.Maximum peak of theVon-Mises stress on the implant-bone interface were33.86Mpa,1.67Mpa,1.38Mpa,1.09Mpa, respectively.2.3Von-Mises displacement in implant neck bone interface is lower,body ofthe roots tended to rise.When implant placed contacts the root (in Model1),displacement of the position where contacts is risen in a certainrange(Fig.1).2.4The maximum peak of the Von-Mises displacement in models is lower asfarther away from the root. Maximum peak of the Von-Mises displacementwere0.88μm,0.86μm,0.76μm,0.61μm, respectively.3Stress distribution of implant-bone interface when both teeth and implantloaded3.1Von-Mises stress is mainly distributed in the cervical part of implant2mmin all models, and that of model1was significantly higher than that of othermodels.The stress of model2,3,4is small and have not obviousdifference.Besides an significant high peak stress in bone interface of cervicalpart of implant, there is a second stress peak in the site of the implant touchesthe root which in the range of2mm and gradually decreases to the implantroot in model1,and the stress value in cancellous bone of model1is higherthan that of model2,3,4.(Fig.3).3.2The implant get closer to the root,the greater the stress peak becomes.Maximum peak of the Von-Mises stress stress peak were57.14Mpa,29.78Mpa,18.79Mpa,12.37Mpa, respectively.3.3Teeth and implant loaded produces synergistic effect on implant-boneinterface when mini-implant contact the root surface.(Fig3)3.4The distance closer between the implant and teeth,more influence on thepeak of displacement.The peak of the Von-Mises displacement were3.20μm,2.95μm,2.84μm,2.771μm,respectively.(Fig4)Conclusion：1When mini-implant contacts the root surface,the physiological occlusion can cause stress concentration of the implant-bone interface affecting the stabilityof the implant.2When mini-implant contacts the root surface,the physiological occlusion andloaded of mini-implant can produce synergistic effect on implant-boneinterface against the stability of implant.3The further the distance between the implant and teeth,mini-implant wasless effected by the physiological occlusion.Our results suggest that theimplant should be placed more than1mm far away from the cloest root. |
PDF Full Text Request