Background <p>The aim of this study was to comparatively evaluate the effects of fiber bundle posts and conventional fiber posts combined with different core materials on fracture resistance.</p> Methods <p>A total of 60 extracted human maxillary incisors with single-root, single-canal morphology were included in this in vitro study. The crowns were sectioned at the cementoenamel junction to standardize the root length to 15 ± 0.5&#xa0;mm. Following working length determination, biomechanical preparation was performed up to size 35/0.04, and the canals were obturated using 35/0.04 gutta-percha cones. Post space preparation was performed using a #3 Gates–Glidden drill while maintaining a 5-mm apical seal of gutta-percha. The specimens were randomly allocated into two experimental groups according to the post system used (<i>n</i> = 26): fiber posts and fiber bundle posts. Each group was further subdivided into two subgroups based on the core build-up material applied (<i>n</i> = 13): a condensable microhybrid composite resin or a flowable microhybrid composite resin supplied with the fiber bundle post system. Additionally, four specimens were assigned to the positive control group and four to the negative control group. All specimens were embedded in acrylic resin blocks and subjected to fracture resistance testing using a universal testing machine at a crosshead speed of 1&#xa0;mm/min.</p> Results <p>Although there was no significant difference in fracture resistance between post types in the specimens using flowable microhybrid composite cores (<i>p</i> = 0.72), a significant difference was observed between post types in the groups using condensable microhybrid composite (<i>p</i> &lt; 0.01). When fracture lines were assessed, the most reparable group was observed in specimens using fiber bundle posts and flowable microhybrid composite cores (62%).</p> Conclusions <p>Whilst the choice of post type directly affects fracture resistance when using condensable composite core materials, this difference is eliminated with flowable microhybrid composites. Furthermore, the combination of fibre bundle posts with flowable microhybrid composites provides the highest reparable fracture rate. For these reasons, from a clinical application perspective, fibre bundle posts have yielded more favourable results in terms of preserving dental tissue. These findings require support from in vivo studies to establish their clinical validity.</p>