Effect of Different Formulations of Dentin Replacement Materials and Aging on the Flexural Strength of the Overlying Resin Composite

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.

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.

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.

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