effect of different formulations of dentin replacement materials and aging on the flexural strength of the overlying resin composite

Introduction: this study aimed to evaluate the flexural strength (fs) of dentin replacement materials, including; fiber-reinforced composite, bulk-fill flowable composites, and resin-modified glass ionomer (rmgi), layered with nanohybrid composite (nh) at different storage times. methods: a total of 100 specimens were prepared (n=10) and divided into five groups depending on the dentin replacement material used, and a control group with conventional nh incrementation. each group was further subdivided into two groups according to the time of the fs testing; 24 hours or 6 months. the specimens were subjected to a 3-point bending test till failure. the comparison between the base materials and time was made using the two-way anova, while the comparison between the base materials within each time interval was made using the one-way anova and the tukey’s post hoc test. additionally, the comparison between the immediate and aged fs within each group was made using the student’s t-test. results: after 24 hours, the resin-based, bulk-fill dentin substitutes layered with nh and the incrementally placed nh, showed a higher fs than the rmgi. however, after 6 months, all groups showed a significant decrease in fs, with the exception of the rmgi group, which showed a significant increase. conclusion: resin-based dentin replacements showed better or similar reinforcement effects compared to conventional composite incrementation, when tested immediately or after 6 months. aging over 6 months had a deteriorating effect on the fs of all composite resin materials, while it improved the fs of the overlying composite resin in the rmgi group