Shear bond strength and interface analysis of different veneering ceramic applications over CAD/CAM zirconia substructure

The interest of all-ceramic restoration in prosthodontic dentistry has been increasing due to many advantages especially esthetics. Among all-ceramic materials, yttria tetragonal zirconia polycrystalline (Y-TZP) ceramic has shown the highest strength, which is suitable for restoration in highly stressed area. However, the opacity of Y-TZP leads to the need of veneering ceramic application. The most recent application technique introduced in the market is pressing. This technique allows more convenience and saves time for the dental technicians to build up the restorations. However, there are not many studies for the bond strength between veneering ceramic and Y-TZP substructure. The aim of this study was to compare the shear bond strength (SBS) of different veneering ceramic applications over Y-TZP substructure.;The study was performed with a total of 45 Y-TZP discs. The samples were divided into 3 groups according to the type of veneering ceramic as followings: base liner group (NobelRondo(TM) Zirconia, Nobel Biocare, Goteborg, Sweden), conventional layering group (NobelRondo(TM) Zirconia, Nobel Biocare, Goteborg, Sweden) and pressing group (NobleRondo(TM) Press Zirconia, Nobel Biocare, Goteborg, Sweden).;The SBS was tested with universal testing machine (Dillon Quantrol TC 2, Fairmont, USA). Then results were analyzed by One-way ANOVA followed by Tukey's post hoc test at significance level alpha = .05. The surfaces of the samples after tested were examined by light stereomicroscope in order to determine the fracture mode.;One-way ANOVA showed a statistically significant difference among groups, F2, 42 = 11.558, p < .005. Tukey tests indicated statistically significant difference between the base liner group and both conventional layering (p = .02) and pressing (p < .005) groups, while there was no significant difference between conventional layering and pressing groups (p= 0.719). Baseliner and conventional layering groups exhibited combined cohesive/adhesive failure while pressing group failed cohesively. According to the findings of this study, pressable veneering ceramic has comparable SBS to conventional veneering ceramic.