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

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 mm×13 mm×3 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.