Effect of Different Heat-treated Nickel-Titanium Files on Vertical Root Fracture Resistance

Abstract

Objective: This study aimed to evaluate the fracture resistance of teeth instrumented with rotary files manufactured from different heat-treated nickel-titanium (NiTi) wires. Materials and Methods: One hundred extracted single-canal mandibular premolar teeth were sectioned, leaving a standard root length of 13 mm. Samples were matched with respect to the buccolingual-mesiodistal diameters. They were randomly divided into four experimental groups and one control group (n=20): Control group, no preparation or obturation; ProTaper Universal (PTU) group, prepared with the PTU system as a universal NiTi; Twisted File (TF) group, prepared with the TF system as an R-phase treatment; ProTaper Next (PTN) group, prepared with the PTN system as an M-Wire thermal treatment; and HyFlex Controlled Memory (HCM) group, prepared with the HCM system as a CM-Wire thermal treatment. After preparations, samples were obturated with gutta-percha and sealer. Samples were subjected to a vertical loading force of 1 mm/min until fracture occurred. Data were subjected to statistical analysis using One-way ANOVA (p=0.05) and Tukey tests. Results: Although the control group had the highest root fracture resistance value, the differences between the control group and HCM group was not significant (p>0.05). Except for the control group, the differences among the study groups were not significant (p>0.05). Conclusion: Different heat treatments of instruments have no effects on vertical root fracture resistance.