OBJECTIVES The rapidly increasing use of zirconia-based CAD/CAM multi-layer structures in dentistry calls for a thorough evaluation of their mechanical integrity. This work examines the effect of the multi-layering architecture as well as variations in composition and inclusion of pigments among the layers on the flexural strength of multi-layer zirconias. METHODS A modified 4-point bending test, aided by a Finite Element Analysis (FEA), was used to probe the interfacial strength of 3 classes of yttria-partially-stabilized zirconia: Ultra Translucent Multi-Layer (UTML-5Y-PSZ), Super Translucent Multi-Layer (STML-4Y-PSZ), Multi-Layer (ML-3Y-PSZ). In accord with the size limitation (22-mm height) of CAD/CAM pucks, test samples were prepared in the form of "long" (25×2×3mm) and "short" (17.8×1.5×2mm) beams. Homogeneous beams (both long and short) were produced from either the Enamel (the lightest shade) or Dentin (the darkest shade) layer, whereas multi-layer beams (short beam only) were obtained by cutting the pucks along their thickness direction, where the material components of various shades were stacked. RESULTS The Enamel and Dentin layers exhibited similar flexural strength for a given material class, with ML amassing the highest strength (800-900MPa) followed by STML (560-650MPa) and UTML (470-500MPa). The 3 classes of multi-layer zirconia showed a trade-off between strength and translucency, reflecting different yttria contents in these materials. The failure stress of the cross-sectional multi-layer beams was, however, ∼30% lower than that of their Enamel or Dentin layer counterparts, regardless of material tested. SIGNIFICANCE The weakness of interfaces is a drawback in these materials. Additionally, when measuring strength using short beam flexure, friction between the specimen and supporting pins and accuracy in determining loading span distances may lead to major errors.

中文翻译：

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探索新型多层氧化锆的界面强度。

目的牙科中基于氧化锆的CAD / CAM多层结构的快速增长使用要求对它们的机械完整性进行全面评估。这项工作研究了多层体系结构的影响，以及各层之间颜料组成和夹杂物的变化对多层氧化锆抗弯强度的影响。方法采用有限元分析（FEA）进行改进的4点弯曲测试，以探测3种氧化钇部分稳定的氧化锆的界面强度：超半透明多层（UTML-5Y-PSZ），超透明多层（STML-4Y-PSZ），多层（ML-3Y-PSZ）。根据CAD / CAM圆盘的尺寸限制（高度22mm），以“长”（25×2×3mm）和“短”（17.8×1.5×2mm）梁的形式制备测试样品。从搪瓷层（最浅的阴影）或牙本质层（最暗的阴影）产生均质光束（长光束和短光束），而多层圆盘（仅短光束）是通过沿圆盘的厚度方向切割圆盘而获得的，其中各种阴影的材料成分被堆叠在一起。结果对于给定的材料类别，牙釉质和牙本质层表现出相似的抗弯强度，其中ML的最高强度（800-900MPa）最高，其次是STML（560-650MPa）和UTML（470-500MPa）。3类多层氧化锆显示出强度和半透明性之间的权衡，反映了这些材料中不同的氧化钇含量。但是，无论采用何种材料，横截面多层梁的破坏应力均比搪瓷或牙本质层的破坏应力低约30％。重要性界面的缺点是这些材料的缺点。此外，在使用短梁挠曲测量强度时，样品与支撑销之间的摩擦以及确定载荷跨度的精度可能会导致重大误差。