Fatigue performance and failure load of minimally-invasive occlusal veneers made of lithium disilicate and composition-gradient multilayered zirconia: An in vitro study

Abstract

PURPOSE To investigate the effect of ceramic material (lithium disilicate, LDS vs. composition-gradient multilayered zirconia [4Y-PSZ and 5-PSZ], Z) and ceramic layer thickness (0.5 mm, 1.0 mm, and 1.5 mm) on fatigue performance and failure load of occlusal veneers on molars. METHODS Seventy-two CAD-CAM-fabricated occlusal veneer restorations (IPS e.max CAD; IPS e.max ZirCAD Prime Esthetic, Ivoclar Vivadent) were divided into six groups (n=12, LDS-1.5, LDS-1.0, LDS-0.5; Z-1.5, Z-1.0, Z-0.5). Restorations were adhesively cemented (Variolink Esthetic DC, Ivoclar Vivadent) to dentin-analogue composite dies (Z100, 3M ESPE) and exposed to thermomechanical fatigue (1.2 million cycles, 49 N, 1.6 Hz, 5-55° C). Single-load-to-failure was tested with a universal testing machine. Data were analyzed using ANOVA with Tukey post-hoc tests and t-tests (P < 0.05). RESULTS The overall success rate across all materials and layer thicknesses was 91.7%. Half of the specimens of group Z-0.5 revealed cracks after chewing simulation. Occlusal veneers fabricated from LDS withstood significantly higher failure loads than gradient multilayered zirconia veneers in all tested thicknesses. The mean failure load values led to the following ranking: 3194 N (LDS-0.5)>2683 N (LDS-1.0)>2338 N (LDS-1.5)>1744 N (Z-1.5)>1310 N (Z-0.5)>1198 N (Z-1.0). CONCLUSIONS Ultrathin LDS occlusal veneers outperformed thin and standard thick counterparts, as well as gradient multilayered zirconia veneers at all thickness levels. Ultrathin gradient multilayered zirconia occlusal veneers were prone to cracks during thermomechanical fatigue. Individual mechanical properties need to be considered when aligning the restoration within the multilayered zirconia blank.