Effect of Inclination Angle on Fatigue of Veneered Zirconia Structures

Objectives: Ceramics restorations often fracture from repeated occlusal contact fatigue loading. The objective of this study is to elucidate the effect of cuspal inclination angle on fatigue damage in veneered zirconia (Y-TZP) structures.

Methods: Veneered Y-TZP plates (1mm porcelain on 0.5mm zirconia, LAVA, 3M/ESPE) were sandblasted and cemented (Rely X Unicem, 3M/ESPE) to a dentin-like composite (Z-100, 3M/ESPE) and subjected to Hertzian indentation fatigue in water with a WC spherical indenter (r=1.5mm) using a mouth-motion simulator (Elf-3300, EnduraTEC). Specimens were positioned at an inclination angle of 30° with respect to the loading direction, simulating tooth-tooth contact with cuspal inclinations. The applied fatigue load varied from 100 to 600 N (n=3). Specimens were sectioned and polished for post-mortem damage examination. Parallel studies were conducted on an in-house developed, stress free glass/Y-TZP/composite system where crack evolution was monitored using a video camera system.

Results: Fatigue fracture occurs exclusively in the veneer layer, as a result of the superior strength of Y-TZP. In the light of in-situ crack evolution studies of the model glass/Y-TZP/composite system, damage sustained in the porcelain/Y-TZP/composite system can be identified: distorted cone cracks (partial cone cracks) initiate at the occlusal-surface and propagate downward, ceasing at the porcelain/Y-TZP interface. These deep penetrating partial cone cracks are the product of a tangential force associated with loading of an inclined surface. The number of cycles for partial cone cracks to penetrate the entire veneer layer is much higher for glass than porcelain. This may due in part to the thermal property mismatch between the porcelain and zirconia.

Conclusion: Fracture in porcelain/Y-TZP all-ceramic system (LAVA) is limited to initiation and propagation of the partial cone cracks in the veneer layer, bulk fracture, common in veneered alumina layers is not found. Supported by NIH/NIDCR 1R01 DE017925 (Zhang) and P01 DE10976 (Rekow).