Fracture Strength of CAD/CAM Endocrown and Post-Core Restorations with Fiber Strip Reinforcement in Mandibular Premolars

This study evaluated the effects of restorative material, restoration type, and fiber strip reinforcement on the fracture strength (FS) of endocrown (EC) and post-core (PC) restorations in endodontically treated premolars. Specimens were allocated according to restorative material [resin-nanoceramic (RNC) or feldspathic ceramic (FC)], restoration type (EC or PC), and reinforcement [fiber strip-reinforced (FR) or -non-reinforced (NF)]. FS was determined using a universal testing machine under axial loading. Statistical analysis was performed using three-way ANOVA and Bonferroni tests (α = 0.05). Material, restoration type, and reinforcement significantly affected FS (p < 0.05). RNC restorations exhibited higher FS than FC restorations (861 ± 181 N vs. 715 ± 212 N; p < 0.001). EC restorations exhibited higher FS than PC restorations (828 ± 173 N vs. 748 ± 236 N; p = 0.046). FR groups exhibited higher FS than NF groups (848 ± 180 N vs. 728 ± 222 N; p = 0.003). The highest FS was observed in the RNC–PC–FR group (965 ± 144 N), whereas the lowest occurred in the FC–PC–NF group (480 ± 177 N). Although EC restorations showed higher FS than PC restorations, the effect of restoration type depended on material and reinforcement.