A comparison of dentin bond strength and degree of polymerization of bulk-fill and methacrylate-based flowable composites

OBJECTIVE: This study aimed to evaluate the dentin bond strength and degree of polymerization of bulk-fill and methacrylate-based flowable composites. MATERIALS AND METHODS: Dentin bond strength of composites was evaluated using the microtensile bond strength (μTBS) test. Five different composites were applied on flat dentin surfaces with self-etch and etch-and-rinse adhesives. Twenty microspecimens with a 1 mm(2) cross-sectional area were prepared for each group (n = 20). The μTBS test was then applied. To measure the degree of polymerization of composites, eight cylindrical blocks were prepared (n = 8) from each composite. The surface microhardness of each composite was measured on the bottom and top surfaces, and a hardness ratio (HR) was calculated. Data were analyzed using one-way ANOVA and the Tukey's honestly significant difference test (α = 0.05). RESULTS: According to the μTBS test results, the SDR Etch-and-Rinse group exhibited the highest dentin bonding strength and the Aelita self-etch group exhibited the lowest (P < 0.05). HR measurement showed that all composite groups had a sufficient degree of polymerization at a 2-mm thickness, while only the SDR and Xtra-Base groups had sufficient polymerization at a 4-mm thickness. CONCLUSIONS: Bulk-fill composite demonstrates an even higher degree of polymerization of methacrylate-based flowable composite when applied in a 4-mm thickness.