Bond strength of three different universal adhesives after different thermal cycling protocols

The purpose of this study was to examine the bond strength of three different universal adhesives on enamel after different aging periods. Ninety enamel specimens were prepared and randomly assigned into three groups according to different universal adhesive systems (n = 30): iBOND Universal (IB), G-Premio Bond (GP), Clearfil Universal Bond Quick (CU). All adhesives were applied at etch&rinse mode. A cylinder-shaped resin composite was placed on enamel surfaces and light cured. Then all specimens were stored in distilled water at 37 degrees C for 24 h and divided into 3 thermal cycling protocol groups (n = 10): No thermal cycling (NTC), 10,000 thermal cycles (10TC), 40,000 thermal cycles (40TC). Specimens were subjected to shear bond strength (SBS) test at a universal testing machine. Failure modes were determined and SEM analyses were performed for each failure mode. Data were analyzed using two-way ANOVA followed by Tukey HSD test. The highest SBS values were observed at NTC groups. The 40TC groups showed significantly lower SBS values than other groups (p < 0.05). The highest mean SBS values were obtained in IB at NTC group (p < 0.05). After 10TC, all universal adhesives exhibited similar SBS values (p > 0.05), however after 40TC, CU showed higher SBS than GP. The mean shear bond strength to enamel was significantly affected by thermal cycling (p < 0.05). The enamel bond durability of universal adhesives dractically decreased after 10,000 and 40,000 thermal cycling periods. The universal adhesives tested showed different SBS values at NTC and after 40TC.