FEM Investigation on Formation Mechanism and Resolution of Wedge-shaped Defect Induced by Occlusal Form

楔形缺陷(WSD)的形成与材料的几何形状密切相关。有限元研究证实，加载过程中的应力集中区与经常观测到的WSD区是一致的。然而，由于建立复杂的解剖形态和咬合面的困难，这些有限元结果是通过二维有限元模型而不是三维有限元模型来获得的。本研究采用三维有限元模型，对不同咬合载荷作用下的颈椎应力分布进行了研究，并通过有限元方法求出了WSD的解析解。利用上颌前磨牙的显微CT图像建立三维有限元模型，并验证其有效性。在平行于牙轴方向或与牙轴成15、30、45度倾斜的加载条件下(加载点：舌尖尖端、近中缘脊和远中缘脊)，测量颈区牙釉质从近中、颊到远中(牙釉质-牙釉质交界处)的主应力分布。结果如下：1)利用显微CT图像成功地建立了牙齿的三维有限元模型，揭示了牙齿的解剖形态。2)三维有限元模型得到的应力分析值与安装在牙颈部的应变片测量值基本一致。3)牙釉质结合部的主拉应力随加载力倾角的增大而增大。但是，通过调整加载点的数目或这些加载点的加载比例，可以缓解拉应力。认为适当的接触方式不仅可以缓解WSD的形成，而且可以抑制WSD的形成。

Abfraction is known to have great deal with the formation of wedge-shaped defect (WSD). The finite element method (FEM) studies have confirmed that the stress concentration area during loading is consistent with the frequently observed WSD region. However, those FEM results were obtained by using 2-D FE model instead of 3-D FE model because of the difficulties in constructing the complex anatomical morphology and occlusal surface. This study used 3-D FE model to investigate the stress distribution by focusing on the cervical region under various occlusal loading and to find out the resolution for WSD by FEM. The 3-D FE model was constructed by using micro CT images of maxillary premolar and its validity was also examined. Furthermore, the distribution of principal stress occurred at cervical region enamel from mesial, buccal to distal surfaces (cemento-enamel junction) was measured under loading (loading points: tip of lingual cusp, mesial marginal ridge and distal marginal ridge) in a direction parallel to tooth axis or in an inclination of 15, 30, 45 degrees to tooth axis. The results were as follows.1) 3-D FE model was successfully reconstructed to reveal the tooth anatomical morphology by the use of micro CT images.2) The analytical value of stress obtained from 3-D FE model was consistent with the value detected by strain gauge that attached on tooth cervical region. It is indicated that the 3-D FE model is suitable to replace tooth for further FEM investigation.3) The principal tensile stress occurred around the cemento-enamel junction became larger with the increasing inclination of loading force. However, the tensile stress can be relieved by adjusting the number of loading points or loading ratio in those loading points. It is suggested that the appropriate contact patterns can not only relieve but also inhibit the formation of WSD.