Mechanical properties of contemporary resin composites determined by nanoindentation

Objective The objective of this study was to evaluate the Young’s modulus (E) and nanohardness (H) of recently developed high viscosity bulk‑fill and self‑adhering resin composites by using nanoindentation technique. The effect of water aging on these properties was also studied. Materials and methods Four resin composites that fall into the categories of conventional (Filtek Z250 XT; FZ), high viscosity bulk‑fill (Filtek Bulk‑Fill Restorative Posterior), flowable (Filtek Supreme Ultra Flowable), and self‑adhering flowable (Vertise Flow) were evaluated in this study. Ten disc specimens (5 mm × 2 mm) were prepared from each material. After polishing, half the specimens of each material (n = 5) were dry stored and the other half stored in distilled water for 30 days at 37°C. The E and H were determined by nanoindentation test using Bruker CETR‑Apex nanoindenter. Ten indentations were made on top surface of each specimen. Statistical analysis was performed using one‑way analysis of variance and paired t‑test. Results All materials were significantly different from each other regarding both E and H in both testing circumstances. A 30‑day water storage caused a significant decrease in E and H of all tested composites except for Filtek Bulk‑Fill Restorative Posterior, where its E increased and its H not affected. There was a positive correlation between E and H. Conclusion Generally, both E and H were significantly increased when the filler content increased and they were significantly affected by 30‑day water aging. E and H were affected not only by the filler content but also by the quality of resin matrix particularly after water storage.