Bond strength and degree of conversion of flowable bulk-fill composites for fiber post cementation after aging: a comparative in vitro study

This study aimed to evaluate the use of flowable bulk-fill composites for cementing fiber posts by assessing the degree of conversion (DC) and bond strength (BS) to root dentin. Endodontically treated bovine roots were prepared for fiber post space, and cementation was performed using conventional resin cement (CC), self-adhesive resin cement (SAC), light-cured flowable bulk-fill composite (LCB), and dual-cured flowable bulk-fill composite (DCB). Samples were sectioned into cervical, middle, and apical thirds and stored in distilled water for 24 h or 6 months. DC was analyzed after 24 h using Raman spectroscopy ( n = 3), while BS was evaluated by push-out tests ( n = 10), followed by failure pattern analysis. Data for DC (%) and BS (MPa) were subjected to two-way ANOVA and three-way, respectively, and Tukey’s test (α = 0.05). SAC showed the highest DC, with the other materials showing no significant difference among them. After 24 h, DCB had higher BS than the others, which did not differ from each other. After 6 months, SAC demonstrated superior BS compared to DCB, and both were statistically similar to CC and LCB. All materials except SAC exhibited a reduction in BS over time. The apical third consistently showed lower BS, regardless of storage time. A decrease in BS was observed in all post-root regions after water storage. Adhesive failures predominated across all groups, regardless of material, root region, or storage duration. In conclusion, while dual-cure bulk-fill composites provide high initial bond strength, self-adhesive resin cement maintains superior long-term performance. These findings highlight the significance of material selection for achieving durable fiber post retention in clinical practice.