Filler amount influences long-term mechanical stability of experimental dental composites

This study evaluated the influence of real-time vs. accelerated aging protocols on the mechanical properties of experimental dental composites with varying filler contents, focusing on flexural strength (FS), flexural modulus (FM), and microhardness (MH).

Five Bis-GMA/TEGDMA-based composites containing Ba-glass microfillers and silica nanofillers with total filler amounts (wt%) of 55, 60, 65, 70, and 75 were prepared. Rectangular specimens (n = 20, 16x2x2 mm) were subjected to three real-time aging durations: 24-hour, 4-month, and 12-month water storage, or two accelerated aging conditions: 4-month water storage followed by 10,000 thermal cycles, and 4-month water storage followed by 10,000 thermal cycles and 5-day ethanol immersion. FS and FM were determined using three-point bending, and MH by the Vickers test. Fracture surfaces were examined by scanning electron microscope and the fractographic quantification was performed using R-based image analysis. Data were analyzed using two-way ANOVA and Tukey's post hoc test (α = 0.05).

Filler content and aging significantly influenced all properties. FS was unaffected by filler content until thermal cycling caused its deterioration in highest filled composites, while FM and MH increased with filler content (p < 0.05). Ethanol exposure transiently increased FS but reduced FM and MH (p < 0.05). After 12 months, all groups showed moderate decrease in FM, FS, and MH, with higher filler content showing the highest values (p < 0.05).

Real-time aging for 12 months resulted in lower FS, FM, and MH values than any of the accelerated aging protocols tested, except for FS of higher filled materials exposed to thermal cycling.