The performance of sol-gel silica coated Y-TZP for veneered and monolithic dental restorations

Objectives: The purpose of the study was to characterize the microstructure, constituents, and mechanical properties of mono and bilayered zirconia specimens infiltrated with silica by the sol gel method. Methods: 180 zirconia discs (14-mm diameter) were divided in 3 groups (n = 60) according to thickness (1.2, 0.5 mm) and further divided in two groups (n = 30) according to treatment (infiltrated or not). Disk thickness was 1.2 mm for the control samples. Veneering feldspathic porcelain had two thicknesses (0.5 mm and 1 mm) at the tops of the zirconia discs. All groups were subjected to the biaxial flexural test in an aqueous medium. Weibull analysis was performed for determination of the Weibull modulus (m) and characteristic strength (GO). The specimens were characterized by SEM and EDS and XRD. Hardness and elastic modulus were measured by nano-indentation and pulse-echo methods, respectively. Fracture toughness was determined by the nano-indentation technique. A scratch test was used for evaluation of the adhesion between the zirconia and porcelain. Results: There was less variability (higher Weibull modulus) in the infiltrated monolithic specimens; biaxial flexural strength was not statistically higher in the veneered infiltrated specimens and was decreased for the 1 mm veneered infiltrated group. The diffractograms showed formation of ZrSiO4 crystal phase. Hardness also increased in the infiltrated monolithic zirconia, whereas fracture toughness decreased. Adhesion between zirconia and porcelain was superior in the non-infiltrated monolithic specimens. Conclusions: Infiltration increased the structural homogeneity and hardness of the monolithic zirconia, but it reduced fracture toughness, and the adhesion to porcelain. Clinical significance: Within the limitations of the present study, it is possible to recommend the infiltration of silica gel in zirconia only for monolithic restorations.