Mechanical properties and micro-CT-based biomechanical performance of NiTi instrumentation systems in mandibular molars

This study evaluated the cyclic fatigue, torsional, and bending resistance of five nickel-titanium (NiTi) instrumentation systems and investigated the relationship between these mechanical properties and the biomechanical performance of root canal preparation in mandibular molars using micro-computed tomography (micro-CT). A total of 200 instruments were used. One hundred and fifty new instruments (n = 10 per group, per test) from the Blue Shaper (25.06), VDW Rotate (25.06), ProTaper Ultimate (25.08), ProTaper Next (25.06), and WaveOne Gold (25.07) systems were subjected to cyclic fatigue testing, torsional fatigue testing, and bending resistance evaluation. Fractured surfaces were analyzed under scanning electron microscopy (SEM). Additionally, 50 instruments (10 per group) were used to prepare 50 mandibular molars, which were analyzed by micro-CT to assess 2D and 3D shaping parameters. WaveOne Gold (WOG) and VDW Rotate exhibited the highest cyclic fatigue resistance. VDW Rotate presented the greatest flexibility and the best results related with shaping ability, with higher canal circularity and fewer unprepared walls, indicating a more conservative and centered preparation. Conversely, Blue Shaper (BS), characterized by lower fatigue resistance and greater stiffness, produced the largest dentin removal and volumetric increase. A significant positive relationship was observed between increased flexibility/fatigue resistance and more conservative shaping outcomes. The mechanical properties of NiTi instruments, especially flexibility as indicated by cyclic fatigue and bending resistance, play an important role in predicting biomechanical preparation performance. Systems combining enhanced flexibility through thermomechanical treatment and optimized cross-sectional design provide more conservative and centered shaping, improving clinical safety and efficiency.