Bond strength, biaxial flexural strength and flexural modulus of dentin bonding systems exposed to water

Purpose This study evaluated the effects of storage time on dentin bond strength, biaxial flexural strength, and flexural modulus of four adhesive systems. Materials and Methods The following adhesive systems were tested: Easy Bond, Scotchbond SE, Single Bond Plus, and Scotchbond Multi-Purpose. Sixty human third molars were used for the microtensile bond strength test (n=15). The adhesives were applied to flat occlusal dentin surfaces according to the manufacturers' instructions and a Filtek Supreme resin composite block (6 mm high) was incrementally built up. After 24 h, the teeth were prepared for the bond strength test. The specimens were stored for one week, six months, and one year in distilled water. At the end of each storage period, the specimens were tested under tension (0.5 mm/min) until failure occurred. For the biaxial flexural test, resin discs of each adhesive (0.6 mm thick and 6.0 mm in diameter) were prepared in silicon molds (n=10). The discs were stored for the same storage periods in distilled water prior to testing in a universal testing machine (1.27 mm/min). Data were analyzed using two-way analysis of variance and Tukey's test (α=0.05). Results Bond strength values decreased significantly after six months and one year of water storage only for Scotchbond SE (from 48.1±11.0 to 24.5±15.3 MPa after one year). The storage time did not affect the flexural strength or modulus for any adhesive tested. Conclusion Water storage for six months or one year can reduce the dentin bond strength of adhesives; however, the results are product-dependent. No changes in flexural strength or modulus of the adhesives tested were observed after storage of any duration.