Multimethod analysis of a novel multi-coloured heat-treated NiTi rotary system: design, metallurgy, mechanical properties, and shaping ability

Abstract

IntroductionThis study aimed to compare a new multi-colored rotary system with four heat-treated rotary instruments using the multimethod approach. MethodsThree-hundred instruments of RCS Rainbow, Rotate, RaCe EVO, OneCurve, and ProTaper Ultimate systems were evaluated regarding their design (stereomicroscopy, scanning electron microscopy, 3D surface scanning), metallurgy, and mechanical performance (cyclic fatigue, torsional resistance, bending and buckling resistance, cutting ability). Unprepared surfaces after canal preparation of maxillary molars were evaluated using micro-CT. Kruskal-Wallis and one-way ANOVA post hoc Tukey tests were used for statistical comparisons (α=5%). ResultsInstruments exhibited variations in active blade length, number of spirals, and cross-sectional designs. RCS Rainbow showed specific phase transformation temperatures, highest bending (400.5gf) and buckling (286gf) resistance values, and lowest mean angle of rotation (529º) (P<.05). OneCurve exhibited superior cutting ability (8.4mm) and longer time to fracture (112s). RaCe EVO displayed the lowest time to fracture (51s), maximum torque (1.2N.cm), buckling (174gf), and bending resistance (261gf) values (P<.05). ProTaper Ultimate showed the highest torque (1.6N.cm) and angle of rotation (611º) (P<.05), while its bending load (262gf) was comparable to RaCe EVO (P>.05). Rotate instrument showed intermediate values in the mechanical tests. No difference was observed regarding the unprepared canal surfaces (p>0.05) ConclusionsRCS Rainbow demonstrates a trade-off between flexibility and other mechanical properties. Its dimensions exceeded those of other instruments, affording it higher torque resistance, yet concurrently reducing its flexibility, angle of rotation, and cutting ability. OneCurve stands out as a well-balanced choice by integrating geometric design and mechanical performance.