Resistance to thermo-mechanical stress of different coupling agents used as intermediate layer in resin-fiber post bonds

Purpose: To evaluate the microtensile bond strength (MTBS) of different coupling agents used in fiber post-composite bonds to withstand different in vitro challenging procedures. Methods: 63 fiber posts (DT Light Post) etched with 10% hydrogen peroxide were divided into three groups according to the silane/adhesive system applied: (1) Porcelain Bond Activator (PBA) + Clearfil SE Bond; (2) PBA + Clearfil Tri S Bond; (3) Monobond-S. A composite build-up (Clearfil AP-X) was performed around the post producing cylindrical specimens that were divided into three subgroups according to the different aging protocol: (1) 24-hour storage at room temperature; (2) Thermocycling (5000 cycles, 5°/55°C dwell time: 30 seconds); (3) Cyclic loading (45° angle, 20,000 cycles, load 5-50 N at 3.0 Hz). Samples were then cut obtaining sticks that were loaded in tension until failure. Bond strength values were statistically analyzed with two-way ANOVA and Tukey test (α = 0.05). Failure mode was recorded and the morphologic aspect of post/core interface after aging was evaluated under SEM. Results: Both post superficial treatment, thermocycling and cyclic loading influenced bond strength. After 24 hours, samples treated with silane/adhesive couplings attained higher MTBS than those bonded with conventional silane. No significant differences in the microtensile bond strength at the post/core interface were recorded between the different silane/adhesive couplings. After challenging, no differences were found between the tested groups.