Stability of flexural properties of experimental composites functionalized with bioactive glass under chemical and...

To evaluate flexural strength (FS) and flexural modulus (FM) of experimental composites containing bioactive glass (BG) 45S5 (C-series) or a customized low-sodium, fluoride-containing BG (F-series) after aggressive artificial aging.

A Bis-GMA/TEGDMA (60:40) resin was filled to 70 wt% total filler, comprising 5-40 wt% of either BG type, with the remaining filler fraction consisting of silanized barium glass and silica (2:1). Specimens (2 × 2 × 16 mm; NIST 4877) were artificially aged by immersion for 30 or 90 days in simulated body fluid (SBF; pH 7.4), lactic acid (pH 4.0), 75% ethanol or NaOH (pH 13.0), and by thermocycling (10,000 cycles; 5-55°C). FS and FM were measured by three-point bending test. Sample size was n = 20 per experimental group, and data were analyzed using three-way ANOVA with additional one-way ANOVAs at an overall significance level of α = 0.05.

The C-series showed a BG dose-dependent decline in flexural properties at baseline and after artificial aging, while the F-series, particularly F-20, maintained higher FS and FM than the C-series under all aging conditions. At baseline, FS decreased from 139.6 to 23.9 MPa across the C-series (5-40 wt% BG), while the F-series maintained values between 147.7 and 176.6 MPa. After 90 days, F-20 retained FS of 133.6-134.8 MPa compared with 41.2-47.2 MPa for C-20, and FM remained substantially higher in the F-series (9.5 vs. 3.7 GPa in SBF). The effects of artificial aging media varied in both severity and time-dependent pattern of change; SBF and lactic acid produced moderate degradation, ethanol induced a marked reduction that leveled off between 30 and 90 days, and NaOH produced the most extensive deterioration over the 90-day observation period. Thermocycling showed intermediate effects and maintained comparable differences between composites.

Reduced BG solubility improved tolerance to higher BG fractions under neutral and moderately acidic aqueous aging, whereas extreme ethanol and alkaline challenges primarily reflected matrix and interface vulnerability.

Customized low-sodium BG improved flexural property retention under clinically relevant aqueous challenges compared with BG 45S5, while extreme chemical aging reduced differences between the materials by shifting degradation toward matrix and filler/matrix interface. The improved flexural stability of composites containing customized low-sodium BG suggests their potential for use in restorations with higher functional filler loadings.