不同牙根形态对下颌第一磨牙即刻种植即刻负重影响的三维有限元分析

Effect of root morphology of first mandibular molar on its immediate loading after immediate implant: a 3-D finite element analysis

目的基于三维有限元的方法,分析下颌第一磨牙即刻种植即刻负重时,不同牙根形态对种植体及其周围骨界面生物力学分布的影响。方法用两组牙根解剖形态不同的下颌第一磨牙建立下颌第一磨牙即刻种植即刻负重的三维有限元模型。两组牙齿分别为牙根分叉角度(interradicular angle,IA)不同组、根柱高度(root trunk height,RT)不同组。每个模型以100N的力分别轴向(冠根向)、斜向舌侧45°、舌颊向、近远中向加载,应用ANSYS软件分析种植体的位移及种植体骨界面的应力值。结果成功建立了下颌第一磨牙即刻种植即刻负重的三维有限元模型;有限元分析结果显示:随根分叉角度增大,根柱高度变短,各加载方向上种植体的最大位移、种植体骨界面的最大应力都呈下降趋势。种植体的最大位移中最大值在近远中向加载RT=5.3 mm时出现达0.461 mm,最小值出现在轴向加载IA=42°时,为0.008 mm。骨界面的应力集中于颈部皮质骨及螺纹接触部位较薄弱的松质骨上。骨界面的应力最大值在近远中向加载IA=10°时出现,最小值在轴向加载IA=18°时出现。结论不同牙根解剖形态对下颌第一磨牙即刻种植即刻负重种植体骨结合的形成有一定影响,使牙根间隔骨量减少的解剖因素增加了第一磨牙即刻种植即刻负重失败的风险。

Objective To determine the effect of different root morphology of first mandibular molar on its immediate loading after immediate implant based on the three dimensional （3-D） finite element method. Methods Two groups of first mandibular molars with different root morphology were used to establish the model after immediate implant, and immediate loading of the first mandibular molars were built. The 2 groups of tooth were further divided according to their different interradicular angle （IA） and root trunk height （RT）. Load of 100 N was applied to the buccal cusps in 4 different directions, including axial, oblique 45°, lingual, and mesial directions. The displacements of implant and the Von Mises stresses of bone were analyzed with finite element analysis software ANSYS. Results The 3-D finite element model of immediate loading of first mandibular molar after immediate implant was established successfully. The results of the analysis indicated that with the increase of root separation and the shorter root trunk height, the maximum displacement of the implant and maximum Von Mises stresses of the implant bone interface were in a downward trend. The maximum displacement of the implant reached 0.461 mm when the mesial loading at RT of 5.3 mm, and the minimum displacement was only 0.008 mm when the axial loading at IA of 42°. The stresses concentrated upon the cortical bone of the neck of implant and the weak cancellous bone beside thread. The maximum Von Mises stresses of the implant bone interface was observed when the mesial loading at IA of 10°, while the minimum was when the axial loading at IA of 18°. Conclusion Different root anatomical morphology of mandibular first molar exert certain effects on the formation of osseointegration in the implant. The decrease of available bone in interradicular septa enhances the risk of failure in the immediate loading of mandibular first molar after immediate implant.