Stability of Resin Composite Materials Over Time

Objectives: To analyze the performance of nine resin composite restorative materials of five compositions over time through the analysis of flexural strength (FS), modulus of elasticity (ME), fracture toughness (FT) and microhardness (µH).
Methods: Specimens (n=10) of nine resin composites representing five categories (nanofilled - NF, microhybrid - MH, microfilled - MF, hybrid – HB, and nanohybrid - NH) were produced by incremental placement (1000 mW/cm²blue light output) to the final dimensions of 2 x 2 x 25 mm for FS (three-point bending) and 2 x 5 x 25 mm for FT. ME was determined using the linear portion of the stress-strain curve derived during the FS testing. Knoop hardness using post-testing FT specimens’ indentations were made using 100gF load over a 5-second duration and analyzed at 50X magnification. All specimens were stored under dark conditions (ISO-9917) in physiologic 0.02M phosphate-buffered saline (PBS) at 37°C until the appointed testing time: 24h, 12m, and 24m. Data were analyzed using a two-way analysis of variance and Tukey HSD (α=0.05).
Results: Microfilled materials presented the lowest FS, ME, FT, and µH after 24h. After 24m, nanohybrid and nanofilled composites also presented lower values for FS. Nanohybrid, microfilled, and hybrid materials remained stable at all times for FS. For ME, the microfilled composite was the only one that remained stable. There was a reduction in FT values after 24m for all materials except for the nanofilled composite. Nanofilled and hybrid groups were the only ones that µH remained stable at all times, although a nanohybrid composite presented a comparable result at 24h.
Conclusions: Overall, the microfilled composite presented the worst performance in comparison to other materials in all properties analyzed.