An In vitro Study on the Effect of Post Type and Core Material on the Biomechanical Behavior of Endodontically Treated Teeth Restored with Full-Coverage Crowns

Objectives: Restoration of structurally damaged endodontically treated teeth (ETT) requires post and core treatments to withstand functional forces. Post type selection together with core material substance determines the stress distribution patterns and breaks down resistance properties of teeth requiring treatment. Researchers conducted this in vitro study to assess different post and core combination models which received full-coverage crowns for their biomechanical outcomes in ETT teeth. Methods: Sixty endodontically treated single-rooted human mandibular premolars were distributed into six experimental groups (n = 10) according to the combination of post material and core cement: Group 1: Fiber post with composite core, Group 2: Fiber post with glass ionomer core, Group 3: Metal post with composite core, Group 4: Metal post with glass ionomer core, Group 5: Zirconia post with composite core, Group 6: Zirconia post with glass ionomer core. The dental specialists prepared all post spaces to 10 mm depth and cemented each post with resin-based luting cement. The core materials were placed following the manufacturer-specified guidelines. Zirconia crowns produced through CAD/CAM fabrication received their cementation from resin-modified glass ionomer cement. Laboratory tests of compressive strength included thermocycling the samples through 10,000 temperature changes between 5°C and 55°C before testing. The universal testing machine determined fracture resistance by testing at 135° inclination to the tooth axis at 1 mm/min cross speed. The assessment distinguished restorable from non-restorable failure patterns. Finite element analysis (FEA) provided data regarding the way stress distributed between components. Results: The group using Zirconia posts with composite core (Group 5) exhibited the highest fracture resistance at 1750±120 N, followed by metal post with composite core (Group 3) at 1620±110 N, while the lowest resistance was recorded for zirconia post with glass ionomer core (Group 6) at 980±90 N. Fiber post groups demonstrated more favorable failure modes, with 70% restorable failures in Group 1. Conclusion: Fiber posts with composite cores demonstrated superior stress distribution and favorable failure modes, making them clinically preferred for restoring endodontically treated teeth with full-coverage crowns, particularly in patients with high occlusal load.