Wang Raorao, Lu Chenglin, Arola Dwayne, Zhang Dongsheng
The Tenth People's Hospital of Tongji University, Shanghai, PR China.
J Prosthodont. 2013 Aug;22(6):456-64. doi: 10.1111/jopr.12035. Epub 2013 Apr 1.
The aim of this study was to compare failure modes and fracture strength of ceramic structures using a combination of experimental and numerical methods.
Twelve specimens with flat layer structures were fabricated from two types of ceramic systems (IPS e.max ceram/e.max press-CP and Vita VM9/Lava zirconia-VZ) and subjected to monotonic load to fracture with a tungsten carbide sphere. Digital image correlation (DIC) and fractography technology were used to analyze fracture behaviors of specimens. Numerical simulation was also applied to analyze the stress distribution in these two types of dental ceramics.
Quasi-plastic damage occurred beneath the indenter in porcelain in all cases. In general, the fracture strength of VZ specimens was greater than that of CP specimens. The crack initiation loads of VZ and CP were determined as 958 ± 50 N and 724 ± 36 N, respectively. Cracks were induced by plastic damage and were subsequently driven by tensile stress at the elastic/plastic boundary and extended downward toward to the veneer/core interface from the observation of DIC at the specimen surface. Cracks penetrated into e.max press core, which led to a serious bulk fracture in CP crowns, while in VZ specimens, cracks were deflected and extended along the porcelain/zirconia core interface without penetration into the zirconia core. The rupture loads for VZ and CP ceramics were determined as 1150 ± 170 N and 857 ± 66 N, respectively.
Quasi-plastic deformation (damage) is responsible for crack initiation within porcelain in both types of crowns. Due to the intrinsic mechanical properties, the fracture behaviors of these two types of ceramics are different. The zirconia core with high strength and high elastic modulus has better resistance to fracture than the e.max core.
本研究旨在结合实验和数值方法比较陶瓷结构的失效模式和断裂强度。
用两种陶瓷系统（IPS e.max ceram/e.max press - CP和Vita VM9/Lava氧化锆 - VZ）制作12个具有扁平层结构的试件，并用碳化钨球对其进行单调加载直至断裂。采用数字图像相关（DIC）和断口分析技术分析试件的断裂行为。还应用数值模拟分析这两种牙科陶瓷的应力分布。
在所有情况下，瓷质材料中压头下方均发生准塑性损伤。总体而言，VZ试件的断裂强度大于CP试件。VZ和CP的裂纹起始载荷分别确定为958±50 N和724±36 N。从试件表面的DIC观察可知，裂纹由塑性损伤引发，随后在弹塑性边界处由拉应力驱动，并向下朝饰面/核界面延伸。裂纹穿透e.max press核，导致CP冠严重的整体断裂，而在VZ试件中，裂纹发生偏转并沿瓷质/氧化锆核界面延伸，未穿透氧化锆核。VZ和CP陶瓷的断裂载荷分别确定为1150±170 N和857±66 N。
准塑性变形（损伤）是两种类型冠中瓷质材料内裂纹起始的原因。由于固有机械性能，这两种陶瓷的断裂行为不同。具有高强度和高弹性模量的氧化锆核比e.max核具有更好的抗断裂能力。
