Class II restorations bond strength after thermal-mechanical cycling

Objectives: The aim of this study was to evaluate the effect of restorative techniques on tensile bond strength (TBS) of class II restorations after thermal and mechanical stresses. Methods: Proximal cavities with dentin gingival margins were prepared on ninety bovine incisors. The teeth were randomly assigned into 9 groups (n=10), according to the combination of bonding agent + layer of the flowable composite resin Filtek Flow (FF/3M): G1- Single Bond (SB/3M) without FF; G2-SB+1mm of FF; G3-SB+2mm of FF; G4-Optibond Solo Plus (OB/Kerr) without FF; G5-OB + 1mm of FF; G6-OB + 2mm of FF; G7-Prime & Bond NT (NT/Dentsply) without FF; G8- NT + 1mm of FF, and G9-NT + 2mm of FF. The adhesive systems were applied according to the manufacturers' instructions, the samples were restored with Filtek Z250 (3M) composite resin and submitted to thermal (1,000x, 5-55°C, 60s/bath) and mechanical stresses (100,000x, 80N). Teeth were vertically sectioned to obtain 1mm thick slabs, which were trimmed to an hour-glass shape with a cross sectional area of 1mm2. The specimens were tested in tension in a universal testing machine (0.5mm/min-Instron 4411) and the failure mode of the tested specimens was analyzed by SEM. Results: The means (SD) of TBS were (MPa): G1-18.7(7.9); G2-18.3(11.4); G3-19.3(6.9); G4-15.4(5.0); G5-12.7(4.2); G6-12.77(4.8); G7-19.3(7.5); G8-14.9(3.1), and G9-17.83(3.8). Statistical analyses (ANOVA/Tukey, alpha=5%) did not exhibit significant difference between the use or not of FF layers. The bond strength of SB and NT was higher than that observed when OB was used (p<0.05). Conclusion: Results varied by the type the bonding agent but not by the use of a flowable composite resin layer. Acknowledge: FAPESP-03/06089-1 / CNPq-130666/03-3.