Effect of zirconia type on its bond strength with different veneer ceramics

The bond strength between veneer ceramic and the zirconia framework is the weakest component in the layered structure. This bond was proven to be sensitive to the surface finish of the framework material and to the type of the veneer ceramic and its method of application. New colored zirconia frameworks were introduced to enhance the final esthetics of the layered all-ceramic restoration. The aim of this study was to investigate the effect of zirconia type, white or colored, and its surface finish on the bond strength to two veneer ceramics.

Five commercial zirconia framework materials (Cercon white and yellow, Lava white and yellow, Procera zirconia) received either of the following surface treatments: CAD/CAM milled surface, airborne-particle abrasion, and liner application. Two veneering ceramics were used to veneer the specimens: Noble Rondo and Ceram Express. The disc-shaped layered specimens were cut into microbars, and microtensile bond strength (MTBS) test was conducted. Structural and chemical differences between the white and colored frameworks were evaluated using scanning electron microscopy (SEM) and energy dispersive analysis. Two-way ANOVA and Tukey post hoc tests were used to analyze the data (p < 0.05 was considered significant).

The type of zirconia framework had a significant effect on the core-veneer bond strength, which was material dependent. The bond strength to colored zirconia was significantly weaker compared to white zirconia frameworks. Different surface treatments had different effects on the core-veneer bond strength according to the zirconia material used. Although no marked chemical differences between the examined zirconia materials could be found, there were structural differences, especially between white and colored zirconia and for different zirconia frameworks of different manufacturers, which significantly affected core-veneer bond strength values.

The addition of coloring pigments to zirconia frameworks resulted in structural changes that require different surface treatment before veneering. To prevent delamination and chipping failures of zirconia veneered restorations, careful selection of both framework and veneer ceramic materials, in addition to proper surface treatment, are essential for maintaining good bond strength.