Influence of crystal structure on debonding failure of zirconia veneered restorations

Delamination of porcelain from intact zirconia framework was recently reported as the most common failure mode of these restorations. The aim of this study was to investigate the influence of different laboratory surface treatments on crystals structure and fracture strength of zirconia veneered restorations.

Zirconia discs received airborne particle abrasion with either 50 or 120μm alumina particles then half of the specimens were annealed to remove surface pre-stresses, while assintered discs served as a control. Crystal structure of each group was evaluated using X-ray diffraction analysis (XRD). The discs were then veneered with porcelain and biaxially loaded to fracture with the veneer surface in tension (α=0.05).

Regarding debonding failure, 50μm particle abrasion significantly increased biaxial flexure strength compared to as-sintered specimens. On the contrary 120μm particle abrasion resulted in significant reduction in flexure strength and was associated with higher percent of monoclinic phase (7%). However for both types of particle sizes, annealing reduced initial failure load as it led to complete reverse transformation of the monoclinic phase which was associated with zirconia grain pull-out at the critical crack location.

Paying attention to the surface treatment of zirconia before veneering could reduce chances of delamination and significantly improve the strength of the bilayered restorations.