Comparative Buckling Strength and Metallurgical Analysis of Five Classic NiTi Endodontic Rotary Files

Objective: Nickel-titanium (NiTi) rotary instruments have revolutionized endodontic practice through continuous advancements in metallurgy and design. Despite these improvements, mechanical failure remains a clinical concern. This study aimed to evaluate and compare the design features, metallurgical properties, and buckling resistance of five widely used NiTi rotary endodontic systems.b Methods: A total of 250 new NiTi rotary instruments from fi e systems (ProTaper Next, Mtwo, ProFile, EndoSequence, and GT Series X) were analyzed. Design features were assessed using dental microscopy and scanning electron microscopy. Metallurgical properties were evaluated through energy-dispersive X-ray spectroscopy and differential scanning calorimetry. Buckling resistance was measured using a universal testing machine equipped with a 1 kN load cell, applying a compressive load at 1 mm/min until 1 mm of lateral displacement was achieved. Statistical analysis was performed using the Shapiro–Wilk test to assess normality, followed by the non-parametric Kruskal-Wallis test to compare groups. A signifi e level of p<0.05 was adopted. Results: ProFile instruments exhibited the highest number of spirals (19) and spiral density (1.19 spirals/mm), while GT Series X featured the shortest cutting blade length (≤12 mm). All systems demonstrated near-equiatomic nickeltitanium ratios. ProTaper Next and GT Series X showed higher R-phase and austenitic transformation temperatures. Buckling resistance was significantly greater in the ProFile (0.04 and 0.06 taper) and EndoSequence 35/.06 and 40/.06 instruments (p<0.05). In contrast, EndoSequence 0.04 files, Mtwo, and ProTaper Next exhibited lower resistance. Conclusion: Design features, taper, and metallurgical composition significantly influence the buckling resistance of NiTi rotary endodontic instruments.