Clinical Relevance The degree of conversion of contemporary universal adhesives positively correlates with the bond strength to dentin. The correlation is more marked after thermocycling, suggesting that a high degree of conversion is required for long-term dentin bonding durability. SUMMARY Purpose: The objectives of this study were to evaluate the micro-tensile bond strength (μTBS) of five contemporary universal adhesives to dentin after 24 hours and thermocycling (TC), to measure their degrees of conversion (DC) and to test the correlation between μTBS and DC. Methods and Materials: Four commercially available universal adhesives, Prime&Bond universal (PBU), Ecosite Bond (EB), G-Premio Bond (GPB), and Clearfil Universal Bond Quick (UBQ), and one experimental adhesive, UBQ without an amide monomer (UBQ-A), were used in this study. For the μTBS test, midcoronal dentin of 50 human molars was exposed, ground using 600-grit SiC paper, and the adhesives were applied according to the manufacturers’ instructions. After resin-composite buildup and 24-hour water storage, one-half of the specimens were subjected to 15,000 thermal cycles. The specimens were sectioned into beams and stressed in tension at a crosshead speed of 1 mm/min until failure. The DC of adhesives applied to dentin was evaluated using attenuated total reflectance Fourier-transform infrared spectroscopy immediately after light-curing. All data were statistically analyzed at a significance level of 0.05. Results: The highest μTBSs were obtained with UBQ, UBQ-A, and PBU, which were not significantly different from each other both after 24 hours and TC. The μTBS of GPB was lower compared with the aforementioned adhesives, but significantly only after TC, and the lowest μTBSs were obtained with EB. TC did not affect the μTBSs of UBQ, UBQ-A, and PBU significantly, but a significant decrease was observed with GPB and EB. The highest DC was obtained with PBU and UBQ, followed by 2-hydroxyethyl methacrylate–rich adhesives UBQ-A and EB, which exhibited significantly lower DCs. The DC of GPB could not be determined because the reference peak at 1608 cm −1 was not detected in its spectra. A significant positive correlation was shown between μTBS and DC after 24 hours ( r =0.716) and TC ( r =0.856). Conclusion: μTBS and DC were positively correlated, more markedly after TC, which suggests that DC may be an important factor for bond durability.

Clinical Relevance The bond strengths of fiber posts to root canal dentin could be affected by the characteristics of the fiber post and its bonding quality. The failure patterns of fiber-post bonded root canal dentin were dependent upon the post system. SUMMARY This study evaluated the regional bond strengths of fiber posts to root canal dentin luted with dual-cure resin composite. Twelve extracted human premolars were decoronated and post spaces prepared to a depth of 8 mm. The root canal dentin was treated with Clearfil SE Bond and light-cured for 20 seconds. Three posts from each of the following four types of fiber posts—Snowlight, FibreKor, DT Light-Post and GC Fiber Post—were surface-treated with a mixture of Porcelain Bond Activator and Photobond, then luted into the post spaces with Clearfil DC Core Automix and light-cured for 60 seconds. After 24-hour water storage, each specimen was serially sliced into eight 0.6 × 0.6 mm-thick beams for the microtensile bond strength (μTBS) test. Failure modes were observed using SEM. The μTBS data were divided into coronal and apical regions and statistically analyzed. The highest bond strengths were obtained from FibreKor posts. Regional factors had no effect on bond strength. FibreKor and DT Light-Post specimens primarily failed at the post-resin composite interface, whereas Snowlight and GC Post cohesively failed within the post.