Effect of changes to the manufacturer application techniques on the shear bond strength of simplified dental adhesives

Purpose: the aim of this work was to assess the shear bond strength (sbs) between a composite resin and dentin, promoted by two dental adhesive systems (one-step self-etching adhesive Easy Bond [3M ESPE], and two-step etch-and-rinse adhesive Scotchbond 1XT [3M ESPE]) with different application protocols (per manufacturer's instruction (control group); with one to four additional adhesive layers; or with an extra hydrophobic adhesive layer). Methods: Proximal enamel was removed from ninety caries-free human molars to obtain two dentin discs per tooth, which were randomly assigned to twelve experimental groups (n=15). After adhesion protocol, the composite resin (Filtek Z250 [3M ESPE]) was applied. Specimens were mounted in the Watanabe test device and shear bond test was performed in a universal testing machine with a crosshead speed of 5 mm/min. Data were analyzed with ANOVA followed by Student-Newman-Keuls tests (P<0.05). Results: The highest SBS mean value was attained with the Easy Bond three layers group (41.23±2.71 MPa) and the lowest with Scotchbond 1XT per manufacturer's instructions (27.15±2.99 MPa). Easy Bond yielded higher SBS values than Scotch-bond 1XT. There were no statistically signifcant differences (P>0.05) between the application protocols tested, except for the three and four layers groups, that presented higher SBS results compared to manufacturer's instruction groups (P<0.05). No statistically signifcant differences were detected between the three and four layers groups (P≥0.05). Conclusion: It is recommendable to apply three adhesive layers when using Easy Bond and Scotchbond 1XT adhesives, since it improves SBS values without consuming much time.