<p>This study compared the effects of polyethylene and glass fibers in reinforcing artificially induced notches in dentin. In this in vitro study, standardized 0.4&#xa0;mm deep notches were created in dentin specimens prepared from 45 extracted human molars. Specimens were randomly divided into three groups (<i>n</i> = 15) and restored with a microhybrid composite: Control (composite only), Glass Fiber, and Polyethylene Fiber. Specimens were sectioned into standardized bars and subjected to a three-point bending test to determine flexural strength, apparent fracture toughness, and elastic modulus. Fracture patterns were qualitatively examined using light microscopy. Data were analyzed using one-way ANOVA and Tukey’s post hoc test (α = 0.05). No significant differences were observed among the groups for flexural strength (<i>P</i> = 0.218) or apparent fracture toughness (<i>P</i> = 0.098). However, significant differences were found in the apparent elastic modulus at both peaks (<i>P</i> &lt; 0.05), with the control group showing the highest stiffness. Qualitative fracture-pattern assessment suggested predominantly abrupt, single-step fractures in the control group, whereas fiber-reinforced specimens more frequently exhibited two-peak fracture behavior and fracture patterns consistent with slower crack propagation. Fiber reinforcement did not significantly enhance the flexural strength or apparent fracture toughness of notched dentin–composite specimens but appeared to influence fracture behavior. Differences in apparent elastic modulus were observed, whereas findings related to the second peak should be viewed with caution because of the limited number of control specimens contributing to that analysis.</p>