Tabriz University of Medical Sciences Journal of Dental Research, Dental Clinics, Dental Prospects 2008-210X 20 2 2026 06 30 Comparison of the Fracture Resistance and Fracture Patterns of Root-Filled Maxillary Premolars Restored with Different Post Systems and Composite-Based Post Space Restorations: An in Vitro Study 126 132 10.34172/joddd.44391 EN Sulhi Abidin https://orcid.org/0009-0001-7379-6295 Hanna Nadhirah Mohd Radzi Muhamad Sharifuddin Mat Daud Norfaezah Ahmad Izzuddin Ahmad Nadzirin https://orcid.org/0000-0003-3189-3633 Galvin Sim Siang Lin https://orcid.org/0000-0002-3996-5470 Journal Article 10.34172/joddd.44391 2025 11 14 2026 03 09 Introduction: Root-filled teeth are structurally and biomechanically weakened, and the choice of post-endodontic restoration is important. This study compared the fracture resistance and fracture patterns of root-filled maxillary premolars restored with different post systems and composite-based post space restorations. Methods: One hundred extracted maxillary second premolars were endodontically treated and randomly allocated to five groups (n=20): metal post (group A), fiber post (group B), flowable composite resin in the post space (group C), fiber-reinforced composite resin in the post space (group D), and composite resin restoration without post with a glass ionomer orifice barrier (control, group E). All the specimens received a standardized mesio-occluso-distal (MOD) cavity preparation with preservation of the buccal wall and were restored with nanohybrid composite before axial loading in a universal testing machine to determine fracture resistance. Meanwhile, fracture patterns were classified under a stereomicroscope. Results: Mean (±standard deviation) fracture resistance values were metal post (896.26±335.55 N), fiber post (1046.64±336.65 N), flowable composite resin (937.94±323.83 N), fiber-reinforced composite resin (799.90±244.43 N), and control (973.54±357.33 N), with no statistically significant differences between the groups (P=0.175). Metal and fiber post groups predominantly exhibited favorable, restorable Class 2 fractures, whereas flowable composite resin, fiber-reinforced composite resin, and control groups mainly demonstrated Class 3 or Class 4 fractures. Conclusion: Root-filled teeth restored with or without posts exhibited similar fracture resistance. Fiber and metal posts, however, produced more favorable fracture patterns, suggesting that posts can influence failure mode even without increasing overall fracture strength.