[Microtensile bond strength of a three-step etch-and-rinse adhesive two years after the expiration date]

Can adhesives still be safely used two years past their expiration date? In an experimental laboratory study, the bond strength of the etch-and-rinse adhesive OptiBond FL was measured two years after its expiration date. Microtensile bond strength testing was performed on 1 1 mm specimens of human enamel and dentin. Statistical analyses were conducted using an independent t-test or a Mann-Whitney U-test. Three specimens were excluded due to air bubbles and testing errors, while 20 dentin specimens in the expired adhesive group failed pretest (0 MPa). The enamel groups were analyzed and showed no significant difference in bond strength between the in-date and expired adhesives (p = 0.77). For dentin, a Mann-Whitney U-test revealed a significantly lower bond strength with the expired adhesive (p = less than 0,001). The conclusion of this study is that an expired etch-and-rinse adhesive may still be effective for enamel bonding, whereas bonding to dentin is significantly weakened.