Mechanical Performance and Biomechanical Implications of a Reduced-Taper Reciprocating Instrument Compared With 6...

To evaluate and compare the geometric characteristics, metallurgical properties, mechanical performance, and biomechanical behaviour of a reduced-taper reciprocating instrument with six commercially available systems.

A total of 441 new nickel-titanium (NiTi) instruments from seven reciprocating systems (Excalibur 25/.05, Flash 25/.06vt, One RECI N25, Reciproc R25, Reciproc Blue R25, Reciproc Minima M25, and WaveOne Gold Primary) were analysed. Geometric design was assessed through photographic analysis, scanning electron microscopy, and high-resolution three-dimensional optical scanning to obtain dimensional measurements along the active blade. Metallurgical characteristics were investigated using energy-dispersive X-ray spectroscopy and differential scanning calorimetry. Mechanical performance was evaluated through cyclic fatigue, torsional resistance, bending resistance, buckling resistance, cutting efficiency, and microhardness tests (n = 10 per parameter). In addition, finite element analysis was conducted using a micro-CT-derived mandibular premolar model to assess maximum principal stress distribution and deformation following simulated canal preparations produced by each instrument. Data distribution was analysed using the Shapiro-Wilk test, and intergroup comparisons were performed with the Kruskal-Wallis test (α = 0.05).

All instruments presented nearly equiatomic NiTi composition and distinct phase transformation temperatures. Reciproc Minima M25 showed smaller blade volume and surface area compared with the other systems. Significant differences were detected among instruments for all mechanical parameters (p < 0.05). Reciproc Minima M25 demonstrated the longest time to fracture during cyclic fatigue testing and the highest angular rotation before fracture, as well as the lowest bending load, indicating greater flexibility. Reciproc R25 exhibited the highest torsional and buckling resistance. Flash 25/.06vt showed the lowest cyclic fatigue resistance, whereas One RECI N25 presented the highest cutting efficiency. Finite element analysis revealed similar stress patterns across models; however, larger preparation volumes tended to generate higher dentinal stresses, whereas conservative preparations were associated with lower stress concentrations.

The reduced-taper Reciproc Minima M25 exhibited high cyclic fatigue resistance and flexibility while maintaining a high torsional performance comparable to other instruments. Its reduced taper and smaller blade volume were associated with slightly lower stress values in the surrounding dentine.