Method: Composite resin cylinders (N=100) (Tetric N-Ceram, IvoclarVivadent; diameter:1mm; height:3mm) were prepared. Zirconia ceramic specimens (3mm×3mm×3mm) (IPS e.max ZirCAD,IvoclarVivadent) and LDC blocks (IPS e.maxCAD,IvoclarVivadent) were prepared (n=10/group). Luting surfaces of the composite and zirconia specimens were air-abraded with alumina (30µm), while LDC surfaces were etched with 4.9% hydrofluoric acid (IPS Ceramic Etching Gel, IvoclarVivadent). Specimens were ultrasonically cleaned in ethanol and randomly divided into five silanization protocols: 1- Control (C; silanization+60s waiting), 2- Hot air-drying (HAD; silanization+60s waiting+15s hot air-drying), 3- Furnace heating (FH; holding time: 15 min. at 100°C+silanization+60s waiting), 4- No silanization (US; no surface-conditioning), 5- Water-rinsing (WR; silanization+60s waiting+water-rinsing+15s. air-drying). A universal primer (Monobond Plus,IvoclarVivadent) was used as the silane. After surface-conditioning, composite specimens were silanized, adhesive resin was applied (Syntac) and bonded to each treated surface with luting resin cement (Variolink II, IvoclarVivadent). Micro-shear bond strength (MSBS) tests were performed in a Universal Testing Machine (0.5mm/min). Data were statistically analyzed (One-way ANOVA, Tukey`s, α=0.05). Failure types were analyzed using optical microscope and SEM.
Result: Mean MSBS values (MPa±SD) were as follows: C:30.8±7.3; HAD:24.15±6.8; FH:31.1±8.4; US:9±2.2; WR:31.2±5.2 and C:30.3±9; HAD:30.9±7.2; FH:31.3±7.5; US:25±9.1; WR:8.2±8 for zirconia and LDC groups, respectively. US group showed the lowest SBS values for zirconia (p<0.05) but not for LDC (p>0.05). WR group delivered the lowest results for LDC (p<0.05). Failure types were exclusively adhesive.
Conclusion: Universal primer showed no significant positive effect on adhesion of resin-cement to acid-etched LDC but to zirconia. The most practical silanization mode was immediate silane application and waiting for the recommended period of 60 s.