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Objective: To compare the fracture mode of lithium disilicate ceramics and zirconia ceramics through a single-load-to-failure test, and reveal the cause of failure through the fractographic analysis of fracture morphology. Methods: Based on the standardized preparations, 10 IPS e.max disilicate ceramic crowns (IPCs) and 10 monolithic zirconia ceramic crowns (MZCs) were designed and fabricated. All the specimens were placed on a universal material testing machine for a single-load-to-failure test. The fracture load was recorded, and two independent sample $t$-tests were performed. Additionally, the type of fracture under a stereo-microscope was observed, and the morphological characteristics of the fracture with a scanning electron microscope (SEM) were investigated. Results: The fracture load of the IPC group was $1819.29\pm 108.13$N, and that of the MZC group was $4347.41\pm 739.90$N, with a statistically significant difference ($t=-10.69$, $p<0.001$). The fracture types of the IPC group and the MZC group were similar, namely, types II and III. The fracture modes of the two groups were all ceramic layer fracture. Through SEM, the origin of the crack on the occlusal surface could be traced back. The crystal fracture of IPC group had a rock sugar-like pattern, and the crystal distribution of MZC group was uniform. Conclusions: Zirconia ceramics have higher fracture load and a denser crystal structure compared to lithium disilicate. Fractographic analysis method could be a better way to analyze the failure mode of single-layer porcelain materials and reveal the origin of fracture.

In this study Al₂O₃-SiC nanocomposites have been fabricated by mixing of alumina and silicon carbide nano powders, followed by hot pressing at 1700°C. The mechanical properties and fracture mode of Al₂O₃-SiC nanocomposites containing different volume fractions (5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. Al₂O₃-SiC powders were prepared by planetary milling in isopropanol. Fracture mode of specimens was investigated by means of scanning electron microscopy. Nanocomposites were tougher than alumina when they were hot pressed at the same temperature, and the values of nanocomposite's flexural strength and hardness were higher than those of alumina. Flexural strength, hardness and fracture toughness of the nanocomposites increase by increasing the volume percent of SiC up to 10% and then decrease slightly. The Scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for nanocomposites. Finally X-ray diffraction analysis couldn't detect any chemical reactions between Al₂O₃ and SiC particles.