Microtensile Bond Strength of Resin Composite Bonded to Caries-affected Dentin with Three Adhesives

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This study evaluated the ability of two self-etching adhesives (a two-step and a one-step) and a conventional 3-step adhesive to bond composite to both intact and caries-affected dentin with and without thermocycling. Thirty extracted human teeth with occlusal caries were randomly assigned to three groups according to the adhesive used: Scotchbond Multi-purpose (3M) (SBMP), ClearfilSE Bond (Kuraray) (SE) and Xeno IV (Dentsply) (XEIV). The occlusal surfaces of the teeth were sectioned to expose dentin. The adhesives were applied according to manufacturers' instructions, and a composite material (Herculite XRV, Kerr) was applied and cured in increments to form a core 3 mm high. The teeth were stored in distilled water for 24 hours, then sectioned using a micro-slicing machine to obtain sections 1 mm thick. The sections were further cut to obtain rods 6 mm long and 1 x 1 mm in thickness, with dentin/composite interface located at the center. The specimens were examined microscopically to separate the caries-affected (AD) and sound dentin (SD) into two groups. Half the specimens from each group were subjected to 3,000 thermocycles (5 degrees C to 55 degrees C) prior to testing. All the specimens were then subjected to microtensile bond strength (microTBS) testing in a special apparatus. Mean microTBS was determined for each group, and data were statistically analyzed with ANOVA and Tukey's tests. Mean microTBS and standard deviation values in MPa were: SBMP-SD = 22.19 (4.6), SBMP-SD-thermocycled = 15.7 (5.55), SBMP-AD = 18.6 (2.89), SBMP-AD-thermocycled = 16.62 (6.23), SE-SD = 24.25 (5.7), SE-SD-thermocycled = 22.3 (6.7), SE-AD = 20.7 (5.55), SE-AD-thermocycled = 20.23 (6.1), XEIV-SD = 21.43 (7.6), XEIV-SD-thermocycled = 18.3 (7.11), XEIV-AD = 15.45 (6.62), XEIV-AD-thermocycled = 14.8 (3.89). ANOVA revealed a significant difference among the groups (p < .0001). The two-step self-etch adhesive resulted in highest mean microTBS values under all test conditions. However, these mean values were significantly higher than the mean values obtained with the other two adhesives under some, but not all test conditions.