Can Coronal Restorative Choices Influence Root Strength After RET? A Fracture Resistance Evaluation in Simulated Immature Teeth In Vitro

Objective: This in vitro study investigated whether the use of different intraorifice barrier materials (IOBMs) in combination with tricalcium silicate-based cements affects the vertical fracture resistance of simulated immature mandibular incisors treated with regenerative endodontic protocols. Materials and Methods: A total of 128 extracted mandibular incisor teeth were standardized by removing 3 mm of their root ends and randomly assigned to four controls (CG, n = 8) and eight experimental groups (EG, n = 12): CG1: Intact immature teeth, CG2: Simulated immature teeth (retrograde preparation only, without access cavity), CG3: Simulated immature teeth restored with resin-based composite (RBC) only, CG4: Simulated immature teeth left unrestored, EG1: White Angelus MTA + RBC, EG2: White MTA + Riva LC HV + RBC, EG3: White MTA + Cention Forte (Alkasit) + RBC, EG4: White MTA + Zirconomer Improved + RBC, EG5: Biodentine + RBC, EG6: Biodentine + Riva LC HV + RBC, EG7: Biodentine + Cention Forte + RBC, EG8: Biodentine + Zirconomer Improved + RBC. Following access cavity preparation, all groups (except CG1 and CG2) underwent the RET protocol. Then, specimens were subjected to vertical fracture testing. Data were analyzed using two-way ANOVA (p < 0.05). Fracture patterns were categorized as repairable or non-repairable. Results: There was a significant difference in fracture resistance between CG1 and CG4 (p = 0.046). Samples restored with EG3 demonstrated significantly higher fracture resistance than the groups CG4 and EG7 (p = 0.044, p = 0.012, respectively). Across all groups, the majority of fractures were non-repairable. Conclusion: Within the limits of this in vitro model, most coronal restoration protocols after RET showed comparable fracture resistance. Combinations with Zirconomer Improved showed favorable trends, but clinical recommendations should remain cautious pending further standardized studies. Material choice at the cervical level may help reduce the risk of root fracture in traumatized immature teeth treated with regenerative endodontic therapy, improving long-term outcomes.