桩核冠、髓腔固位冠和嵌体冠修复低矮磨牙残冠后产生的生物力学效应比较及其临床意义

目的：应用有限元分析对比桩核冠、髓腔固位冠和嵌体冠修复低矮磨牙残冠后的应力分布情况及固位效果，探讨低矮磨牙残冠的优选修复方案。方法：选择志愿者健康、完整的左侧下颌第一磨牙作为实验样本，应用锥形束CT（CBCT）扫描获得其影像学数据。利用Mimics、Geomagic和CATIA等逆向工程软件建立完整的下颌第一磨牙有限元模型。在此基础上构建3组低矮磨牙残冠模型（剩余临床牙冠的高度分别为1、2和3mm），并建立桩核冠、髓腔固位冠和嵌体冠3组修复体分别修复上述3组残冠的有限元模型，共9个实验组。在Abaqus软件中对模型施加垂直向及斜向静态载荷模拟咀嚼时牙齿受力，施加强制性旋转位移载荷模拟修复体旋转脱位。观察各组模型牙本质的von Mise应力峰值和分布云图，以及各组修复体为抵抗旋转脱位所产生的非轴向固位力和脱位时粘接剂的破坏情况。结果：von Mises应力峰值，垂直载荷下，嵌体冠 > 髓腔固位冠 > 桩核冠；斜向载荷下，髓腔固位冠 > 嵌体冠 > 桩核冠。应力分布云图，桩核冠的根尖1/3处、髓腔固位冠髓室底部和嵌体冠牙颈部及根部应力集中现象明显。非轴向固位力，1mm残冠组，桩核冠 > 嵌体冠 > 髓腔固位冠；2和3mm残冠组，嵌体冠 > 桩核冠 > 髓腔固位冠。刚度退化云图，旋转脱位时粘接剂开裂的面积由大到小依次为嵌体冠>髓腔固位冠>桩核冠。结论：从保护牙体组织及维持修复体长期稳定性的角度分析，桩核冠是修复低矮磨牙残冠较为理想的修复方式。

Comparison of biomechanical effects of repairing lower molar residual crowns among post-core crown,endocrown and inlaycrown and their clinical significances

Objective: To compare the stress distribution and retention effects of lower molar residual crowns restored by post-core crown, endocrown and inlaycrown using the finite element analysis, and to explore the optimized repair plan of lower molar residual crowns. Methods: The healthy and integral left mandibular first molar of volunteer was selected as the experimental sample. Their imaging data was collected by cone beam CT (CBCT) scanning. Then the complete finite element model of the mandibular first molar was reconstructed by reverse engineering software such as Mimics, Geomagic and CATIA. On this base, three groups of models of lower molar residual crowns with the clinical crown heights of 1, 2, and 3mm were constructed. Meanwhile, the finite element models of post-core crown, endocrown, and inlaycrown were established to repair the three groups of residual crowns mentioned above; there were nine experimental groups. In the Abaqus software, the vertical and oblique static loads were applied on the models to simulate the forces produced during chewing, and the forced rotational displacement load was applied on the models to simulate the dislocation of restorations. Then the stress peak and stress distribution cloud map of von Mises in dentin of the models in various groups, as well as the force generated by restorations to resist dislocation and the damage of adhesive during dislocating were all observed. Results: The von Mises stress peak results were inlaycrown > endocrown > post-core crown in vertical load and endocrown > inlaycrown > post-core crown in oblique load. According to the stress distribution cloud map, the root apical 1/3 of post-core crown, the pulp floor of endocrown and the dental cervix and root of inlaycrown was found obviously in the stress concentration. The non-axial retention force results were post-core crown > inlaycrown > endocrown in the 1 mm residual crown group, and inlaycrown > post-core crown > endocrown in the 2 and 3 mm residual crown groups. According to stiffness degradation contours of resin adhesive layer, the cracked areas of adhesive during dislocation was inlaycrown > endocrown > post-core crown. Conclusion: From the perspectives of protecting dental tissue and maintaining the stability of restorations, the post-core crown is an ideal restoration for repairing the lower molar residual crowns.