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

牙槽骨楔状缺损的形成与牙槽骨缺损的形成密切相关。有限元法（FEM）的研究已经证实，在加载过程中的应力集中区域是一致的，经常观察到的WSD区域。然而，这些有限元分析结果是通过使用二维有限元模型，而不是三维有限元模型，因为在构建复杂的解剖形态和咬合面的困难。本研究采用三维有限元模型，重点研究不同咬合力作用下牙颈部的应力分布情况，并探讨有限元法对WSD的解决方案。利用上颌前磨牙的显微CT图像建立了上颌前磨牙的三维有限元模型，并对模型的有效性进行了检验。在平行于牙轴方向和与牙轴成15 °、30 °、45 °倾斜方向加载（加载点：舌侧牙尖、近中缘嵴和远中缘嵴）的情况下，测量牙颈部釉质从近中面、颊面到远中面（牙骨质-釉质结合部）的主应力分布。结果表明：1）利用显微CT图像成功地重建了牙体的三维有限元模型; 2）三维有限元模型得到的应力分析值与牙颈部应变片测得的应力值基本一致。结果表明，所建立的三维有限元模型适用于替代牙体的有限元分析。3）牙釉质-牙骨质界面处的主拉应力随着加载力倾斜度的增大而增大。但是，通过调整加载点的数量或加载点的加载比，可以消除拉应力。结果表明，适当的接触方式不仅可以缓解而且可以抑制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.