Evaluation of the mechanical performance of different nickel-titanium files in straight and curved root canals and stress distributions in dentin: A finite element analysis (FEA)

The mechanical performance of nickel-titanium (NiTi) rotary systems used in endodontic treatments, which directly affects clinical success, varies depending on root canal morphology and operational conditions. This study aimed to evaluate the stress distributions of ProTaper Gold (PTG), Vortex Blue (VB), and TruNatomy (TRN) systems in straight (0°) and curved (60°) canals under different apical locking lengths (3 mm and 5 mm) and phase transformation states (martensite/austenite) using finite element analysis (FEA). This study analyzed three different NiTi rotary systems (PTG, VB, TRN) utilizing the finite element method (FEA). Each system was simulated in straight (0°) and curved (60°) canal configurations. The analyses were conducted under apical locking scenarios of 3 mm and 5 mm in both martensitic and austenitic phases, generating a total of 24 main models with 8 for each system. For PTG, the following models were assessed: PTG3mmMar0°, PTG5mmMar0°, PTG3mmMar60°, PTG5mmMar60°, PTG3mmAus0°, PTG5mmAus0°, PTG3mmAus60°, and PTG5mmAus60°. For VB: VB3mmMar0°, VB5mmMar0°, VB3mmMar60°, VB5mmMar60°, VB3mmAus0°, VB5mmAus0°, VB3mmAus60°, and VB5mmAus60°. For TRN: TRN3mmMar0°, TRN5mmMar0°, TRN3mmMar60°, TRN5mmMar60°, TRN3mmAus0°, TRN5mmAus0°, TRN3mmAus60°, and TRN5mmAus60°. Furthermore, in each canal configuration, two distinct scenarios were simulated in which the instrument was locked within the root dentin at 3 mm and 5 mm. According to the findings, in PTG files, the highest von Mises stress was observed in the 5 mm apical locking condition within straight canals, in both austenitic and martensitic phases. For VB files, the maximum stress was recorded in the austenitic phase with 5 mm apical locking in straight canals. In TRN files, the highest stress was detected in the martensitic phase, under 5 mm apical locking in curved canals. When maximum and minimum principal stresses in dentin were examined, in the martensitic phase, the highest stress value was observed in TRN files under the 3 mm apical locking scenario in curved canal models. In the austenitic phase, the highest maximum principal stress was also found in TRN files under 3 mm apical locking in curved canals. Conversely, in the austenitic phase, the lowest minimum principal stress was recorded in TRN files in the straight canal with 3 mm apical locking. In conclusion, it was demonstrated that file design, phase transformation characteristics, and canal morphology are decisive factors influencing the risk of instrument fracture and the development of cracks in dentin during clinical use. These findings emphasize that the selection of NiTi rotary systems should consider not only the material phase but also the apical locking length and canal curvature. Keywords: austenitic phase; finite element analysis; martensitic phase; nickel-titanium file