RESUMO
PURPOSE: To investigate the effect of firing times on the fatigue properties and failure modes of posterior occlusal veneers made of lithium disilicate glass ceramics. METHODS: According to the number of times of firing (1, 3, 5, 7 times), IPS e.max CAD(IC) and IPS e.max Press(IP) occlusal veneer restorations with a thickness of 1.2mm were prepared, and then cemented to the maxillary molar composite resin dies. Each group was subjected to thermo-mechanical fatigue(TMFT) test (5-55 â, 5000 cycles, 30-300 N, 10 Hz, sinusoidal wave, 500 000 cycles) and compressive loading. The maximum force at fracture was recorded. Stereomicroscope and scanning electron microscope(SEM), energy dispersive X-ray spectroscopy(EDX) and X-ray diffraction(XRD) were adopted to analyze the failure modes and microstructural features. Statistical analysis was performed with SPSS 20.0 software package. RESULTS: The highest average loads (N) at fracture for IC groups were (1546.73±192.85) N after one firing time; in IP group, the highest average loads were (1504.46±138.56) N after three firing times. There was no significant difference in the fracture load with different firing times for IC/IP(P>0.05). EDX and XRD analysis showed no significant difference in the composition of two materials. SEM showed that the size of crystal was shorter and the porosity increased after multiple firing. CONCLUSIONS: After repeated firing, the fatigue loading of lithium disilicate glass ceramics has a decreasing trend of fracture load value without any significant difference, and it meets clinical requirements.
