[Effect of silane coupling agent on composite-composite bond strength: an in vitro study]

Objective: To investigate the effect of silane coupling agent on composite-composite bond strength, and to provide experimental basis for improving composite-composite bond strength clinically. Methods: Self-etching adhesive Clearfil SE Bond (CSE) and silane-containing universal adhesive Single Bond Universal (SBU) were used as adhesives. A silane coupling agent (RelyX ceramic primer) was tested. P60 resin composite blocks were prepared and divided into 4 groups according to whether silane coupling agent was applied or the type of the adhesives: CSE group, in which CSE was applied as an adhesive; Silane + CSE group, in which the surface was treated with silane coupling agent followed by CSE; SBU group, in which SBU was applied as an adhesive; Silane+ SBU group, in which the surface was treated with silane coupling agent followed by SBU, then filling a new composite. All the composite blocks were cut into about twenty 1 mm×1 mm×14 mm samples to detect the micro-tensile bond strength. Fractographic analysis were performed under a three-dimensional laser scanning microscope. The micro-tensile bond strength data were analyzed statistically by one-way ANOVA and the failure pattern data were analyzed statistically by Chi-square test. Results: Silane + SBU group [(69.6 ± 3.3) MPa] showed a significantly higher micro-tensile bond strength than the other groups (P<0.05). Silane+CSE group showed a significantly higher micro-tensile bond strength [(63.9±3.7) MPa] than CSE group [(55.7±4.2) MPa] and SBU group [(55.4±4.0) MPa] (P<0.05); There was no significant difference in micro-tensile bond strength between the SBU group and the CSE group (P>0.05). Failure patterns in the 4 groups were adhesive failure, cohesive failure and mixed failure. There was no significant difference in the proportion of adhesive failure between the Silane+CSE group and the Silane+SBU group, and the proportion of adhesive failure in these two groups were significantly less than that in the CSE and the SBU group (P<0.05). Conclusions: Silane coupling agent pretreatment could improve composite-composite bond strength, however, the bond strength could not be higher when silane was mixed with adhesives in one bottle.