Microtensile bond strength of two-step etch-and-rinse adhesive systems on sound and artificial caries-affected dentin

Purpose: To evaluate the microtensile bond strength of two-step etch-and-rinse adhesive systems on sound and artificial caries-affected dentin (CAD) produced by in vitro monoculture of Streptococcus mutans. Methods: 10 recently extracted non-carious human third molars were ground to expose a flat dentin surface. Each tooth was sectioned through the long axis with a diamond saw to create two similar halves. One half was used as control (sound dentin - SD) while the other was submitted to caries lesion induction in vitro, using 40 mL of Brain Heart Infusion broth containing 1% sucrose and 40 mu L of Streptococcus mutans UA159 inoculum (final bacterial concentration: 1-2 x 105 CFU/mL). The specimens were incubated at 37 degrees C for 4 weeks, and the culture medium was changed every 3 days for 4 weeks. Sound or CAD were alternatively restored as follow (n=5): Single Bond 2/sound dentin (SB-SD); Single Bond 2/artificial caries-affected dentin (SB-CAD); Prime&Bond NT/sound dentin (PB-SD); and Prime&Bond NT/CAD (PB-CAD). The adhesives were applied to dentin according to manufacturers' instructions, and build-ups of resin composite (Filtek Z250) were prepared and polymerized with a LED light-curing unit (Radii). The restored teeth were stored in distilled water at 37 degrees C for 24 hours and thereafter sectioned perpendicular to the bonded interface with a refrigerated low-speed diamond saw, obtaining three slices per half-tooth (n=15). The microtensile bond strength (mu TBS) test was performed in a universal test machine with a crosshead speed of 1 mm/minute. Bond strengths were calculated in MPa and analyzed by Kruskal-Wallis and Student-Newman-Keuls at a 0.05 level of significance. Failure patterns were examined with an optical microscope. Results: SD produced significantly higher mu TBS values than CAD for both adhesive systems. Furthermore, independently of the dentin condition, Single Bond 2 had higher values than Prime Bond NT (P < 0.05). Single Bond 2 showed higher mu TBS than Prime Bond NT, in both substrates, and application to CAD reduced the adhesion. (Am J Dent 2010;23:152-156).