Enhancement of Flexural and Compressive Strength of Methacrylate-Based Composites Through Glass Fiber Reinforcement

The phase-down of mercury-containing amalgam under the Minamata Convention has created a need for mercury-free restorative materials capable of withstanding high masticatory forces in posterior teeth. Resin-based composites are the preferred alternative; however, those formulated with bisphenol A-glycidyl methacrylate and urethane dimethacrylate often exhibit high water sorption, polymerization shrinkage, and cytotoxicity, compromising their long-term clinical performance. Bisphenol A ethoxylated dimethacrylate (BisEMA) offers reduced water sorption and lower cytotoxicity, yet its mechanical strength may be insufficient for posterior applications without reinforcement. This in vitro study aimed to enhance the flexural and compressive properties of a BisEMA/triethylene glycol dimethacrylate (80:20 wt%) composite through E-glass fiber incorporation at 3 wt% and 5 wt%. Specimens were fabricated according to ISO 4049 standards for flexural (25 × 2 × 2 mm) and compressive (4 × 6 mm) testing, with Tetric N Ceram, Charisma Smile, and Brilliant NG serving as controls. The 5 wt% fiber group achieved significantly higher flexural strength (82.94 ± 4.64 MPa) than the 3 wt% fiber group (75.52 ± 6.70 MPa, p = 0.0109), with values comparable to Tetric N Ceram and Charisma Smile. Compressive strength for the 5 wt% fiber group (124.31 ± 27.69 MPa) exceeded Brilliant NG but was not significantly different from the 3 wt% fiber group (101.97 ± 22.50 MPa, p = 0.0639). One-way ANOVA showed no statistically significant differences in flexural strength among all groups (p > 0.05), while compressive strength differences were more pronounced. These results indicate that E-glass fiber reinforcement improves the mechanical properties of BisEMA-based composites and supports its potential for the development of biocompatible, high-performance posterior restorative materials that address the limitations of existing formulations.