Influence of Water Storage on the Mechanical Properties of Short Fiber-Reinforced Dental Resin Composites

This study investigated the effects of 7-day water storage as an accelerated aging condition on the mechanical properties of short fiber-reinforced resin composites (SFRCs) and a bulk-fill resin composite (RC). Two SFRCs (everX Flow Bulk, EXB; everX Flow Dentin, EXD) and one bulk-fill RC (SDR) serving as a control were evaluated. Specimens were stored in distilled water at 37 °C for either 1 or 7 days. Flexural strength, flexural modulus, and Vickers hardness were evaluated. Fractured surfaces were observed using scanning electron microscopy (SEM). For statistical analysis, a two-way ANOVA and Tukey’s test were used (α = 0.05). After 7-day water storage, the flexural strength of SDR significantly decreased (p < 0.05), while SFRCs maintained their initial strength (p > 0.05). In contrast, the flexural modulus significantly decreased in all materials (p < 0.05). Vickers hardness remained unaffected by water storage for all groups (p > 0.05). SEM observation revealed fiber pull-out in SFRCs. Although water immersion induced matrix degradation reflected in a reduced flexural modulus, SFRCs demonstrated promising resistance to initial water aging by maintaining flexural strength after water storage. These findings suggest that SFRCs may be a promising option for biomimetic dentin replacement under short-term hydrolytic aging conditions.