Effect of different materials and canal filling methods in apexification of simulated immature teeth on fracture resistance–in vitro study

BACKGROUND: The restoration of immature teeth with thin dentinal walls remains a clinical challenge, and the choice of root canal filling material may influence their resistance to fracture. This in vitro study aimed to evaluate the fracture resistance and fracture patterns of simulated immature roots filled with different root canal filling materials and coronal backfilling strategies. METHODS: Sixty-four simulated immature maxillary central incisors were standardized and randomly allocated into eight groups: negative and positive controls, TotalFill RRM Putty or Biodentine used alone, or each material combined with either thermoplasticized gutta-percha or a dual-cure composite resin (Grandio Core). Following apexification procedures, fracture resistance was measured using a universal testing machine, and fractures were classified as restorable or unrestorable. Statistical analyses included Welch ANOVA with Games-Howell post-hoc tests and Fisher's Exact Test for fracture type evaluation. RESULTS: Significant differences in fracture resistance were observed among groups (p < 0.001). The positive control group demonstrated the lowest resistance. In contrast, the TotalFill RRM Putty + gutta-percha, Biodentine, and Biodentine + gutta-percha groups exhibited fracture resistance values comparable to those of the negative control (p > 0.05). Groups restored with gutta-percha showed higher fracture resistance than those restored with composite resin. Fracture mode distribution also differed significantly among groups (p = 0.047). CONCLUSIONS: Root canal filling materials and coronal backfilling techniques have a significant influence on the biomechanical behavior of immature teeth. Thermoplasticized gutta-percha demonstrated superior reinforcement compared with dual-cure composite resin, while Biodentine and TotalFill RRM Putty exhibited comparable mechanical performance. Material selection and obturation strategy play a crucial role in enhancing the structural integrity of immature roots during apexification procedures.