[Effects of different surface treatments on the bonding strength between the lithium disilicate glass ceramic and resin cements].

Objective: To investigate the effects of different surface treatments protocol on the bonding strength between lithium disilicate glass ceramic and resin cements. Methods: Ceramic specimens of 15 mmx13 mmx3 mm were used to evaluate the effects of different surface treatments of hydrofluoric acid etching and silane coupling in current research. Firstly, the standard lithium ceramic specimens were divided into 8 groups (n=16), and were etched by 4.5% hydrofluoric acid for 0, 10, 20, 30, 40, 60, 120 and180 s. Then specimens in each group was further divided into two sub-groups. In one sub-group specimens were coated with coupling agents and in the other were not. Shear bonding strength (SBS) and failure mode were tested and analyzed. The surface morphologies of hydrofluoric acid-etched ceramic specimens were observed by the scanning electron microscopy (SEM). Secondly, after being etched by 4.5% hydrofluoric acid for 30 s, the lithium ceramic specimens were coated with coupling agents at different temperatures: room temperature (12 ℃) for 60 s, 60 ℃ hot air for 60 s and 100 ℃ hot air for 60 s (n=8). SBS and fracture mode were tested and analyzed. The infrared spectrum analysis was used to characterize the coupled surfaces of the ceramic samples. Results: The maximum SBS values were obtained after the specimens were etched for 30 s. The silane coupled group showed a higher SBS value [(25.91+/-4.30) MPa, P<0.05] than the no-silane-coupled group [(20.27+/-4.92) MPa]. SBS decreased with extended etching time (>30 s) and the SEM photos showed over-etching morphologies. The 60 ℃ hot air treatment resulted in the maximum SBS value [(28.70+/-5.32) MPa] than that of the room temperature [(20.08+/-3.64) MPa] or 100 ℃ hot air [(25.64+/-4.86) MPa, P<0.05]. And the cohesive failure mode was found in 60 ℃ hot air treatment group. The infrared spectroscopy analysis showed the highest amount of silicon oxide bond in the 60 ℃ hot air treatment group. Conclusions: In this study, for this product, the optimum etching time of 4.5% hydrofluoric acid was 30 s. Furthermore, an ideal SBS value could be obtained when the silane coupling agents were applied additionally. SBS could be increased substantially when the 30 s-etched-ceramic product was coated with silane coupling agents at 60 ℃ hot air for 60 s.