Water sorption and bond strength of graphene oxide-added universal adhesives

To evaluate the effect of adding graphene oxide (GO) to HEMA-containing and HEMA-free universal adhesives on water sorption/solubility and bonding effectiveness to dentin. GO was incorporated into universal adhesives (Scotchbond Universal and G-Premio Bond) at three weight percentages (0.5, 1, and 3%) and characterized by SEM. Clearfil SE Bond was used as the reference adhesive. Disk-shaped specimens were prepared to evaluate water sorption and solubility (n = 10). Microspecimens were prepared from ninety extracted human third molar. The µTBS of half of the specimens was tested after 24 h, and the remaining specimens were aged for 6 months. Failure mode was analyzed using a stereomicroscope. Statistical analyses were performed with one-way ANOVA, Duncan, and paired t-tests (p = 0.05). Adding 3% GO increased water sorption of the adhesives (p < 0.05). Clearfil SE Bond exhibited the lowest water sorption and solubility (p < 0.05). 1% GO significantly increased the immediate µTBS of the adhesives, whereas 3% resulted in a significant decrease (p < 0.05). 0.5 and 1% GO significantly increased the aged µTBS of Scotchbond Universal, while only 1% improved the aged µTBS of G-Premio Bond (p < 0.05). 3% GO reduced the aged µTBS of the adhesives (p < 0.05). The highest immediate and aged µTBS were recorded for Clearfil SE Bond (p < 0.05). The bonding performance of universal adhesives improved with 0.5% and 1% GO additions, whereas 3% GO had a detrimental effect on both bond strength and water sorption. Adding GO to adhesives may improve the long-term durability of bonded restorations.