Department of Conservative Dentistry and Periodontology, University Hospital, Ludwig-Maximilians-University Munich, Goethestrasse 70, 80336 Munich, Germany.
Faculty of Computer Science, University of Applied Sciences, Friedberger Straße 2a, 86161 Augsburg, Germany.
Dent Mater. 2022 Apr;38(4):646-654. doi: 10.1016/j.dental.2022.02.003. Epub 2022 Feb 18.
The fracture resistance of ultrathin computer-aided design and computer-aided manufacturing (CAD/CAM) occlusal veneers with different preparation designs was investigated under cycling mechanical loading and via finite element analysis (FEA).
Eighty molars were prepared with a circular enamel ring until complete exposure of the occlusal dentin occurred. Forty were prepared via additional circular chamfer preparation. The teeth were restored with 0.5 mm-thick occlusal veneers. Each group received a CAD/CAM fabricated occlusal veneer with a low modulus of elasticity (composite, CeraSmart) and a high modulus of elasticity material (ceramic, Celtra Duo). The restorations were adhesively luted and underwent 2000 thermocycling cycles. The samples were loaded at 50 N under 1,000,000 cycles in a chewing simulator and were checked for failure after various cycles. A visible crack was defined as failure, and the Kaplan-Meier survival rate was used for data analysis. One sample per group was digitized using microcomputed tomography, and FEA was performed using open-source software. The comparative stresses were analyzed for specimens with and without chamfer preparation.
The survival probabilities were 60% for occlusal ceramic veneers without preparation and 40% for veneers with chamfer preparation, with no statistically significant differences. Composite veneers achieved 95% survival probability regardless of the preparation method. The main principal stress in ceramic restoration was visualized via FEA. In composite veneers, stress was also visible in the luting composite and dentin.
The preparation method had no influence on mechanical fatigue. Minimally invasive preparation can be recommended. The restoration material is crucial for survival.
通过循环机械加载和有限元分析（FEA）研究不同预备设计的超薄计算机辅助设计和计算机辅助制造（CAD/CAM）牙釉质贴面的抗断裂能力。
80 颗磨牙制备有圆形釉质环，直至完全暴露牙本质。40 颗磨牙进行额外的圆形倒角预备。牙齿用 0.5 毫米厚的牙釉质贴面修复。每组均使用低弹性模量（复合材料，CeraSmart）和高弹性模量材料（陶瓷，Celtra Duo）制作 CAD/CAM 牙釉质贴面。修复体通过黏接方式黏合，并经过 2000 次热循环。在咀嚼模拟器中以 50N 的载荷施加 100 万次循环，在不同循环后检查失效情况。出现可见裂纹定义为失效，采用 Kaplan-Meier 生存率进行数据分析。每组一个样本使用微计算机断层扫描进行数字化，使用开源软件进行 FEA。分析有无倒角预备的样本的比较应力。
无预备的牙釉质陶瓷贴面的存活率为 60%，有倒角预备的贴面存活率为 40%，无统计学差异。无论预备方法如何，复合贴面的存活率均为 95%。通过 FEA 可以观察到陶瓷修复体的主要主应力。在复合贴面中，黏接复合层和牙本质也可以看到应力。
预备方法对机械疲劳没有影响。可以推荐微创预备。修复材料对存活率至关重要。
