Comparison of repair protocols for veneered zirconia as a function of surface conditioning parameters, ceramic primer types and defect sizes

This study assessed the effect of surface conditioning methods and ceramic primers on the repair strength of resin-composite to zirconia-veneering ceramic with different defect sizes. Zirconia (IPS e.max Zir-CAD) (n = 30) and veneering ceramic (Creation) (n = 30) alone acted as control groups. In the 1st part of the study, zirconia was silica-coated (SC) and treated with 3 different ceramic primers (Monobond Plus + Helibond (MBP), Clearfil Ceramic Primer Plus (CCP), Z-Prime Plus (ZPP)). Feldspathic ceramic was etched with 9.6% hydrofluoric acid (HF) and primed. After repairing with resin-composite (Empress Esthetic) and testing for shear bond strength (SBS), the best performing adhesive system (MBP) for both substrates (N = 60, n = 10 per group) was tested for defect sizes of (a) 3.2, (b) 4, (c) 5 mm with zirconia (diameter: 1.7 mm) being in the center (N = 60, n = 10 per group). Half of the specimens were repaired employing HFSC and the other half with SCHF. The specimens were stored in distilled water (37 , 24 h) and thermocycled (5-55 , 5000 cycles). The resinsubstrate interface was loaded under shear force (1 mm/min). Data (MPa) were analyzed using two-way ANOVA and Tukey's tests ( = 0.05). In the 1st study, MBP resulted in significantly higher SBS (MPa) for both zirconia and veneering ceramic (Zirconia: 14.2 3.6; Veneer: 11.0 3.7), compared to those of CCP (Zirconia: 9.4 2.2; Veneer: 7.5 3.4) and ZPP (Zirconia: 5.0 0.9; Veneer: 5.9 2.1) (p < 0.01). Neither the size of the defect (p > 0.05) nor repair sequence showed a significant effect (p > 0.05) on the repair bond strength with mainly mixed type with cohesive fracture in the veneering ceramic.