| Popis: |
This study aimed to evaluate the stress distribution of the mandibular first molar with different thicknesses and heights of the axial wall restored by the endocrown with two marginal designs and thus provide a theoretical basis for selecting clinical preparation through the finite-element method.Two marginal endocrowns of the mandibular first molar with different axial-wall thicknesses (t=1, 2, 3 mm) and heights (h=2, 3, 4 mm) were established. Group A was the butt-joint design, whereas group B was the shoulder-surrounded design. After applying vertical and oblique loads , the size and distribution of the maximum principal stress and equivalent stress of residual tooth tissue were recorded.The maximum principal stress and equivalent stress distribution of residual tooth tissue were similar among different models. Group A showed a lower maximum principal stress and equivalent stress than group B at the same thickness and height under vertical load. Meanwhile, under oblique load, the maximum principal stress values of groups A and B decreased with increased thickness at constant height. Group A showed lower equivalent stress than group B at the same thickness and height of 2 and 3 mm. However, when the height was 4 mm, the trend was reversed.In mastication, when bearing the vertical force, the retention of the butt-joint marginal endocrown preferred to the shoulder-surrounded one. Given the higher axial wall of the shoulder-surrounded marginal endocrown, it showed better ability to bear the oblique force than the butt-joint one.目的 采用有限元法研究下颌第一磨牙在不同的轴壁厚度和高度缺损时，两种边缘设计的髓腔固位冠受力时的应力分布情况，为临床髓腔固位冠预备方式的选择提供理论依据。方法 建立不同轴壁厚度（t，分别为1、2、3 mm），不同轴壁高度（h，分别为2、3、4 mm）的两种边缘设计（平面对接型为A组，包绕型为B组）下颌第一磨牙有限元模型，并行髓腔固位冠修复，对各模型进行垂直及斜向加载，记录在两种力学加载下剩余牙体组织最大主应力和等效应力大小及分布情况。结果 两组实验模型的牙体组织最大主应力及等效应力在两种力学载荷下分布相似；垂直载荷下，t、h相同时，A组最大主应力及等效应力值均小于B组；斜向载荷下，h一定时，A、B组最大主应力值随轴壁厚度的增大而减小；在t相同、h为2、3 mm时，A组等效应力值低于B组；当h为4 mm时，A组等效应力值高于B组。结论 咀嚼运动中，在承受垂直向的力时，平面对接型髓腔固位冠优于包绕型；当余留轴壁高度较高，包绕型髓腔固位冠比平面对接型能更好地承受侧向力。. |
