Influence of different primer application times on bond strength of self-etching adhesive systems to unground enamel

This study evaluated the influence of increasing the application time of acid primer on the bond strength of one- and two-step self-etching systems to unground enamel. Thirty-two human third molars were used in this study. Additionally, four self-etching adhesive systems: Clearfil SE Bond (Kuraray), AdheSE (Ivoclar-Vivadent), Futurabond NR (Voco) and One Up Bond F Plus (J Morita) were used in two conditions according to each manufacturer's recommendations and using double the application time of the primer recommended by the manufacturers. The teeth were randomly separated into groups and sectioned in their central region in the buccal-lingual direction perpendicular to their long axes, using a double-faced diamond disk. A 6-mm high block was then made with Rok (SDI) resin composite on the mesial and distal faces of each tooth. The samples were then serially sectioned from the resin composite in the occlusal-gingival and buccal-lingual directions at a distance of 1 mm between cuts using a high concentration diamond disk adapted to a precision cutter. The microtensile test was performed in a universal test machine at a speed of 0.5 mm/minute. The fractured specimens were analyzed by scanning electronic microscopy to determine failure modes. The data obtained were submitted to ANOVA and the Tukey Kramer tests. There was no statistically significant difference among the adhesive systems and primer application times. Failure modes varied among the groups and were influenced by the increase in acid primer application time.