Fracture and Crack Behavior of Weakened Incisors Restored With Fiber Posts, Polyethylene Reinforcement, or 3D-Printed Endocrowns

Background To evaluate the biomechanical performance of weakened maxillary incisors restored with glass fiber posts (GFPs), polyethylene fiber reinforcement, or CAD/CAM (computer-aided design/computer-aided manufacturing) endocrowns (ECs), focusing on fracture resistance, failure mode, and crack formation after thermomechanical aging. Methods Fifty maxillary central incisors were allocated into five groups (n = 10): sound tooth (ST, control); glass fiber post (GFP) + CAD/CAM crown; polyethylene fiber in a "U" pattern (PFU) + CAD/CAM crown; polyethylene fiber in a "C" pattern (PFC) + CAD/CAM crown; and CAD/CAM EC. All experimental groups underwent root canal treatment and weakening. Specimens were subjected to 1.4 million thermomechanical cycles and loaded to fracture. Fracture mode was examined under stereomicroscopy, and cracks were analyzed via micro-CT. Fracture resistance (N) was analyzed with ANOVA and Tukey's HSD (α = 0.05), while failure and crack types were compared using Kruskal-Wallis tests. Results ST had the highest fracture resistance (990.8 ± 107.8 N), followed by PFC (800.5 ± 139.1 N). PFU (649.4 ± 146.8 N) and GFP (616.6 ± 122.3 N) showed intermediate values; EC had the lowest (461.1 ± 146.3 N). Most failures were favorable, but 30% of EC samples failed catastrophically. PFC and PFU preserved more crack-free roots (70% and 60%), while GFP exhibited multiple vertical cracks. Conclusion Polyethylene fiber reinforcement, regardless of fiber orientation, significantly improves fracture resistance and reduces root cracking in endodontically treated incisors. This technique may provide a reliable alternative to fiber posts and CAD/CAM ECs in the restorative dentistry of anterior teeth.