Effect of Surface Treatments and Bonding Agents on Microshear Bond Strength of Zirconia-Reinforced Lithium Silicate and Conventional Glass-Ceramics: Silane Versus Universal Adhesive

This in vitro study evaluated the effects of four surface treatments (no treatment, hydrofluoric acid [HF] etching, aluminum oxide [AlO] air abrasion, and tribochemical silica coating [TSC]) and two bonding agents (dedicated silane vs. silane-containing universal adhesive) on the microshear bond strength of four CAD/CAM glass-ceramic materials, including two zirconia-reinforced lithium silicate ceramics and two conventional glass-ceramics. Four CAD/CAM materials (Celtra Duo, IPS e.max CAD, IPS Empress CAD, and Vita Suprinity) were subjected to four surface treatments (no treatment, HF, AlO air abrasion, and TSC) and further divided according to bonding agent application: dedicated silane (Clearfil Ceramic Primer Plus) or silane-containing universal adhesive (Single Bond Universal). Microshear bond strength testing was performed after 24 h of water storage (n = 10). Failure modes were classified under stereomicroscopy, and surface topography was evaluated by SEM. Data were analyzed using three-way ANOVA and Tukey’s HSD test (α = 0.05). All three main factors and their interactions significantly affected bond strength values (p < 0.05; R2 = 0.863). HF etching with silane produced the highest values for most materials. However, IPS Empress CAD treated with TSC and silane yielded the highest overall bond strength (25.2 MPa). Dedicated silane consistently outperformed the universal adhesive across all combinations. ZLS ceramics showed intermediate values with distinct etching patterns compared with conventional glass-ceramics. Optimal bonding protocols for CAD/CAM glass-ceramics are material-dependent. Dedicated silane application is recommended over silane-containing universal adhesives for maximum bond strength.