Comparative Study on Cyclic Fatigue Resistance of Two Series of Rotary Instruments: Austenitic NiTi versus Thermally Treated NiTi Alloys (Gold, Blue, and Pink)

Objectives: Evaluate the fracture-free cutting efficiency of different NiTi alloys by testing Mtwo (Sweden & Martina) and BlueShaper Pro (Zarc4endo) endodontic instruments for cyclic fatigue strength and length of separated fragments. Materials and methos: The study examined a sample of 160 files, all of the same length, used at the manufacturer-recommended speed and torque in continuous rotation. The files were tested in custom-designed curved artificial canal made of stainless steel, operated by an endodontic motor fixed in place to prevent axial movement. The experiment was conducted at a constant, continuously monitored temperature. The number of cycles to failure (NFC) was recorded with a stopwatch, and the lengths of the separated fragments (FL) were measured using a digital caliper. To identify statistically significant differences between groups, a P-value of < 0.05 was considered. Results: In the first two comparisons, the austenitic alloy Mtwo demonstrated better cyclic fatigue resistance with higher NFC values (p < 0.05). In the second and third comparisons, the heat-treated martensitic alloy BleuShaper Pro showed higher NFCs than the austenitic alloy at the chosen experimental standards (p < 0.05). Conclusions: No endodontic instrument is completely immune to separation at the point of maximum stress; however, some tools offer superior strength (NFC) in relation to cross-section, taper, and alloy. Clinical relevance: The results obtained in this study suggest that the use of endodontic instrument series composed of both austenitic and martensitic alloys represents a gold standard in clinical practice.