The reliability and fatigue behaviour of three dental CAD/CAM ceramics

Abstract

OBJECTIVES New CAD/CAM ceramic-based dental prosthesis has become a popular choice for their advantages, e.g. more materials availability, more aesthetics, higher strength and biocompatibility, and saving processing time, in comparison to other kinds of restorations. Measuring their static and dynamic mechanical properties could help dentists to choose and evaluate the appropriate material for specific applications, since the long-term clinical data might not be available when the materials had been launched. Thus, in this study, the reliability and fatigue behaviour of three CAD/CAM dental ceramics were evaluated, and envisaged to reduce the clinical risk of damage for CAD/CAM restorations. METHODS Three CAD/CAM blocks, i.e. zirconia (Cercon, DeguDent, Germany), hybrid ceramics (Enamic, Vita Zahnfabrik, Germany) and lithium disilicate (e.maxCAD, Ivoclar Vivadent, Liechtenstein), were cut, sintered (if necessary according to manufacturers’ instruction), and surface polished (Ra<0.2microns). The final sizes of bar specimens were ~4.0×1.2×12.0mm and subjected to three-point bending. For flexural strength test (n=15, cross-head speed 1mm/min), Weibull statistics were used to analyse and characterize the strength. For cyclic fatigue loading test, sinusoidal loading (8 Hz, minimal load 3N) was applied to the specimen (n=15). S-N fatigue diagram was used to predict and fitted with basquin curve on fatigue data points. Microstructural analysis was conducted using SEM on the fracture surfaces. RESULTS The hybrid ceramics showed the highest Weibull modulus (18.90) whilst lithium disilicate the lowest (7.01). For one million cycles, zirconia showed the highest fatigue limit (247.07MPa) than lithium disilicate (81.20MPa) and hybrid ceramics (33.90MPa). However, the lithium disilicate showed the lowest S-N slope (-0.012) than others. The SEM revealed that all tested CAD/CAM ceramics under fatigue loading gave a smoother fracture surface than monotonic loading. CONCLUSIONS Hybrid ceramics deemed to be the most reliable material under static loading. All the tested ceramics seems able to withstand certain fatigue failure.