Wu Jian-chao, Huang Ji-na, Zhao Shi-fang, Xu Xue-jun
Department of Orthodontics,School of Dentistry, Zhejiang University, Hangzhou 310006, Zhejiang Province, China.
Shanghai Kou Qiang Yi Xue. 2006 Dec;15(6):619-22.
The goal of this study is to analyse the stress distribution in the press-fit microimplant-bone interface and its indications for immediate loading of orthodontic microimplant.
Three-dimensional finite element models were created of a 20 mm section of posterior mandible simplified in isosceles trapezoid shape, 30 mm in height, 10mm in upper side width, 14 mm in lower side width,with a single microimplant, 1.2 mm in diameter, 6 mm in length embedded in the bone. The cortical bone thickness was assumed as 1.6 mm. Cortical and cancellous bone were modeled as transversely isotropic and linearly elastic materials. Titanium was modeled as isotropic and linearly elastic material. Perfect bonding was assumed at microimplant- bone interfaces. ANSYS 9.0 finite element analysis software was used to generate the simplified finite element models of the local mandible-implant complex. 0 mm, 0.05 mm and 0.1 mm press-fit were arbitrarily set to the implant-bone interface to mimic the situation of immediate placement of microimplant. Stresses in the microimplant-bone interface were calculated under these "press-fit".
Stresses distributed mainly in the cortical bone interface. At Omm press-fit, the stress was 0 MPa. For 0.05mm press-fit, the stress was 1648 MPa in mesio-distal direction, 1782MPa in occluso-gingival direction;and for 0.1 mm, it reached 2012MPa in mesio-distal direction, 2110MPa in occluso-gingival direction. As the "press-fit" increased, the stresses increased accordingly.
Values of initial stress in the microimplant-bone interface due to press-fit generated by immediately placed microimplant were very high in these limited and simplified three dimensional finite element models. It reminded us that the initial stress be taken into consideration when immediate loading of the microimplant is planned. Supported by Research Fund of Health Bureau of Zhejiang Province (2005B104).
本研究旨在分析压入式微型种植体与骨界面的应力分布情况及其对正畸微型种植体即刻加载的启示。
建立了一个简化为等腰梯形的下颌骨后部20mm节段的三维有限元模型，高30mm，上底宽10mm，下底宽14mm，其中植入一枚直径1.2mm、长度6mm的微型种植体。皮质骨厚度假定为1.6mm。皮质骨和松质骨被建模为横观各向同性和线弹性材料。钛被建模为各向同性和线弹性材料。假定微型种植体与骨界面为完美结合。使用ANSYS 9.0有限元分析软件生成局部下颌骨-种植体复合体的简化有限元模型。在种植体与骨界面任意设置0mm、0.05mm和0.1mm的压入量，以模拟微型种植体即刻植入的情况。在这些“压入量”条件下计算微型种植体与骨界面的应力。
应力主要分布在皮质骨界面。在0mm压入量时，应力为0MPa。对于0.05mm压入量，近远中方向应力为1648MPa，咬合龈向应力为1782MPa；对于0.1mm压入量，近远中方向应力达到2012MPa，咬合龈向应力为2110MPa。随着“压入量”增加，应力相应增加。
在这些有限且简化的三维有限元模型中，即刻植入微型种植体产生的压入力导致微型种植体与骨界面的初始应力值非常高。这提醒我们在计划微型种植体即刻加载时应考虑初始应力。由浙江省卫生厅科研基金资助（2005B104）。
