中文摘要：

目的研究隐裂下颌第一磨牙受力后裂纹的变化情况，以及裂纹存在对牙齿受力后整体位移的影响。方法建立包含不同深度和长度裂纹的隐裂下颌第一磨牙的三维有限元模型以及无裂纹对照模型，模拟咬合过程，确定6种加载方式，通过有限元计算，求得不同裂纹的变化情况以及裂纹存在对牙齿整体位移的影响。结果随着裂纹深度和长度的增加，袷面裂纹的宽度亦变大，载荷4的影响最大。开裂时裂纹边缘不齐，相邻节点不在同一平面上。邻面裂纹在载荷621-况下开裂最大。裂纹存在时牙齿整体位移增加，但对牙齿整体位移的影响是有限的。结论裂纹的变化与初始裂纹形式和载荷工况密切相关。

英文摘要：

Objective To study the change of the cracks and the influence on overall displacement of the cracked first mandibular molar under different loadings. Methods Three-dimensional finite element models of first mandibular molar with cracks of different depth and length and a control model with no crack were created firstly. Then six loading conditions were applied to the models simulating the real mastication. The changes of the cracks and displacement of the teeth under the six loadings conditions were obtained by finite element method. Results The length and depth of the cracks increased, the cracks of the occlusal surface become wider, and the crack was the widest under the fourth loading condition. Moreover, the edge of the cracks was irregular. The adjacent nodes were not in the same plane. The crack of the distal surface was the widest under the sixth loading condition. Compared to the teeth without cracks, the overall displacement of the teeth with cracks increased, but the increment was limited. Conclusion The change of the cracks is closely related to the initial crack forms and loading conditions.