The study involved eighty-four freshly extracted human mandibular molars, prepared with standardized MOD cavities and endodontically treated. After thermocycling, fracture resistance was evaluated using a universal testing machine, and failure patterns were examined under a stereomicroscope. This study offers valuable guidance for dental professionals seeking evidence-based strategies to strengthen restorations and extend the longevity of endodontically treated teeth. Effect of combined use of reinforcement materials on the fracture resistance of MOD cavity restorations in endodontically treated teeth. 2025;29:481. doi:10.1007/s00784-025-06560-6Keywords: Fiber-reinforced composites, fracture resistance, MOD cavity, endodontically treated teeth, cervical segment, Lena Bal, Clinical Oral Investigations