Bond Strength of CAD/CAM Restorative Materials Treated with Different Surface Etching Protocols

Purpose: To evaluate the effect of different surface treatments on the surface morphology of CAD/CAM ceramics and on their bond strength to cement. Materials and Methods: Sixty cubic sections were cut from each of three materials (lithium disilicate glass-ceramic [DL], leucite-based glass-ceramic [LC], resin-matrix ceramic composite [RMCC]) and were treated as follows (n = 10): 1. no treatment (C); 2. 5% hydrofluoric acid applied for 20 s plus silane (HF5% 20 s); 3. 5% hydrofluoric acid applied for 60 s plus silane (HF5% 60 s); 4. 10% hydrofluoric acid applied for 20 s plus silane (HF10% 20 s); 5. 10% hydrofluoric acid applied for 60 s plus silane (HF10% 60 s); 6. Self-etching ceramic primer (MBEP). Ceramic cubes were bonded to pre-polymerized composite resin cubes with a composite cement. Each set was cut into stick-shaped specimens (1 ± 0.3 mm2). After 24-h water storage, microtensile bond strength (µTBS) was measured. Data were analyzed using two-way ANOVA and Tukey's test (α = 0.05). Failure pattern and surface morphology were assessed using scanning electron microscopy (SEM). Results: Both factors significantly influenced µTBS, while no interaction between factors was found. RMCC presented statistically higher µTBS values than LC and DL, while the surface treatments HF5% 20 s, HF5% 60 s, HF10% 20 s, HF10% 60 s and MBEP, did not show statistical differences between them, although they resulted in statistically significantly higher bond strengths than did C groups. A high number of pre-test failures were detected in the control groups for all materials. MBEP produced less extensive surface alterations than did all HF treatments. Conclusion: All of the hydrofluoric acid treatments tested showed similar cement-ceramic bonding efficacy. The self-etching ceramic primer produced less surface alterations and comparable bonding efficacy compared to separate hydrofluoric acid/silane primer application. Keywords: bond strength, CAD/CAM, hydrofluoric acid etching, self-etching ceramic primer, ceramics, silane