【作者】 郭娜；

【导师】 单丽华；

【作者基本信息】 河北医科大学 ， 口腔临床医学， 2012， 硕士

【摘要】 目的：错牙合畸形可以影响牙合颌面的发育、口腔功能等，甚至造成心理和精神障碍。支抗的控制是多数正畸病例治疗成败的关键。现有的各种加强支抗的方法不能满足临床使用要求。近年来出现的微型种植体为提高疑难病例的疗效开拓了一个新的领域。但稳定性不足是其主要缺点，据报道成功率为83-89%。种植体脱落大多发生在正畸加力前和加力过程中，多由于种植体植入手术不当及种植体-骨界面不合适的应力分布造成，严重影响了种植体在临床中的普及应用。微型种植体主要植入在牙槽骨颊舌侧牙根间的部位，由于牙根间距离有限和个人解剖结构差异，对手术的准确性要求很高，常常发生种植体植入后距离临近牙根很近或触及牙根的情况。研究表明种植体植入后距离牙根过近时脱落率明显增加。因此有必要明确微种植体植入后距牙根的安全距离。临床应用发现，种植体植入后拍摄平行投照牙片怀疑距离邻近牙根较近时，患者常有咬合痛的表现，且咬合痛与种植体脱落有较高相关性。目前种植体植入后距离牙根过近时生理性咬合对种植体稳定性的影响及牙齿的生理性咬合与种植体载荷的应力分布是否产生联合效应未见报道。本研究拟用三维有限元方法建立微型种植体-牙-颌骨的模型，分析微型种植体植入后距离牙根过近时种植体周围骨组织应力改变，牙齿生理性咬合产生的动度对种植体稳定性的影响，探讨微型种植体植入后距临近牙根的安全距离，为微植体支抗的临床应用提供理论依据。材料与方法：1实验设备计算机：CPU：2.0；内存：1G软件：Mimics10.1软件（Materialise公司）、Pro/E4.0软件、Geomagic Studio逆向工程软件、ANSYS13.0软件。2建立微种植体-颌骨的三维实体模型2.1上颌骨三维有限元模型的建立采用螺旋CT对一牙齿排列整齐的健康志愿者进行扫描，CT图像以DICOM格式存储，在Mimics软件中切除，进行局部光滑处理，设定牙周膜厚度0.25mm，建立含有上颌骨-牙-牙周膜的三维有限元模型。2.2微种植体有限元模型的建立参照国产纯钛、微型圆柱状螺纹种植体的几何形态，设定骨内段8mm，直径为1.6mm，在Pro/E中建立种植体三维模型。2.3装配实体种植体颌骨三维模型2.3.1植入位置和角度：模拟临床情况，将微种植体植入在上颌骨的右侧第二前磨牙和第一磨牙之间，距离牙槽嵴顶5mm处，植入方向为垂直于牙体长轴。2.3.2根据微种植体距临近牙根的距离，设计模型如下：Model1：微种植体植入后接触牙根表面Model2：微种植体植入后进入牙周膜Model3：微种植体植入后接触牙周膜表面Model4：微种植体植入后距临近牙周膜表面为1.0mm3加载条件3.1加载分两种情况Load A：牙齿载荷，微种植体不载荷Load B：牙齿、微种植体同时载荷3.2微型种植体加载加载大小：2N加载方向：通过种植体植入点做一平行于咬合平面的直线，通过此直线做一垂直于地平面的平面，在此平面上沿与咬合平面成30度角的方向载荷(模拟内收上前牙时的正畸力)。3.3牙齿加载加载大小：300N加载方向：在牙齿牙合面上，平行于牙长轴加载。3.4计算工况所建模型共有8种工况：Model1-A，Model1-B，Model2-A，Model2-B，Model3-A，Model3-B，Model4-A，Model4-B。4计算并分析各模型种植体-骨界面的应力分布、应变规律。结果：1成功建立了微种植体-颌骨的三维有限元模型，所建模型具有良好的几何相似性和生物力学相似性，能满足生物力学运算的要求。2牙齿加载时种植体-骨界面的应力分布2.1种植体植入后触及牙根时（Model1），接触牙根部位（约3mm范围）的种植体-骨界面Von-Mises应力峰值较其他模型明显增高，其余部分受力很小；Model2,3,4种植体-骨界面受力很小，且变化不明显，见Fig.1。2.2种植体植入后触及牙根时（Model1），骨界面应力峰值明显高于其他模型。各模型种植体-骨界面Von-Mises应力峰值分别为33.86MPa，1.67MPa，1.38MPa，1.09MPa。见Fig.1。2.3种植体颈部骨界面位移值较低，体部及根部趋于上升，但种植体植入后触及牙根时（Model1），接触牙根部位的种植体-骨界面Von-Mises位移在一定范围内有一定程度的增高，见Fig.2。2.4随着种植体距离牙根越远，位移峰值越小。各模型种植体位移峰值分别为0.88μm，0.86μm，0.76μm，0.61μm。3牙齿和种植体均加载时种植体-骨界面的应力分布3.1各模型的Von-Mises应力主要分布在种植体颈部皮质骨2mm范围内，Model1的应力峰值明显高于其他模型，Model2,3,4差别不太大。其中Model2,3,4松质骨内应力很小，且变化不大。而Model1除了在种植体颈部骨界面内有一个明显高的应力峰值外，在种植体触及牙根的部位出现第二个应力高峰，范围约2mm，向种植体根端方向逐渐减小，且松质骨内应力值相应高于Model2,3,4应力值。见Fig.3。3.2种植体距离牙根越近，应力峰值越大。各模型种植体-骨界面的Von-Mises应力峰值分别为46.12MPa，8.79MPa，12.25MPa，7.63MPa。3.3种植体植入后触及牙根时，牙齿加载与种植体加载对种植体-骨界面应力值有叠加效应，见Fig.3。3.4种植体距离牙根越近，位移峰值受到的影响越大（位移峰值降低）。各模型种植体-骨界面的Von-Mises位移峰值分别为1.02μm，1.57μm，1.96μm，2.21μm。见Fig.4。结论：1种植体植入后触及邻近牙根时，牙齿的生理性咬合可以造成种植体-骨界面应力明显集中，影响种植体的稳定性。2种植体植入后触及邻近牙根时，牙齿的生理性咬合与微型种植体载荷在种植体-骨界面可以产生应力的叠加效应，不利于种植体的稳定性。3种植体植入后距离牙根越远，受到牙齿生理性咬合的影响越小。本实验结果建议种植体植入后距离邻近牙根在1mm以外。更多还原

【Abstract】 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.更多还原