Effect of a Bonding Resin Layer Associated with a Self-etching Adhesive System on the Bond Strength of Indirect Restorations

The aim of this study was to evaluate the influence of a low-viscosity bonding resin applied over a self-etching adhesive system on the microtensile bond strength (microTBS) of indirect restorations. Comparisons were made using One Up Bond F (OB) self-etching adhesive system, Single Bond (SB) one-bottle adhesive system and Scotchbond Multi Purpose Plus (SMP) bonding component. Thirty bovine incisors were extracted and decoronated at the cementoenamel junction. The labial surfaces were ground so that superficial dentin and deep dentin were exposed. The specimens were randomized to three groups (n=10): G1- OB; G2- OB + SMP; G3- SB. In G2, a layer of the SMP bonding was applied over the OB adhesive system. Indirect composite restorations were bonded using dual-cure cement under 500 g load for 5 min. The specimens were serially sectioned with a bonding area of +/- 1.0 mm(2) in 3 regions: enamel (E), superficial dentin (SD) and deep dentin (DD). The sticks were fixed with cyanoacrylate adhesive and submitted to microTBS test at a crosshead speed of 0.5 mm/min in a mechanical testing machine (EMIC DL 2000). The fractured specimens were examined under scanning electron microscopy to determine the failure mode. Data were analyzed by one-way ANOVA followed by Tukey's test (p<0.05). microTBS means (in MPa) were: G1/E: 15.5 +/- 3.5b; G1/SD: 22.7 +/- 7.6a; G1/DD: 19.4 +/- 9.4a; G2/E: 15.9 +/- 5.8b; G2/SD: 19.9 +/- 6.9a; G2/DD: 15.3 +/- 4.9a; G3/E: 23.2 +/- 7.3a; G3/SD: 20.4 +/- 8.2a; G3/DD: 19.1 +/- 8.7a. The results showed that the use of a low viscosity bonding resin did not affect the microTBS means when associated with a self-etching adhesive system. The self-etching adhesive system was significantly more efficient in dentin than in enamel, while the one-bottle system was significantly more efficient in enamel when compared to the self-etching adhesive system.