LAUSR

INTRODUCTION This study aimed to compare the mechanical and metallurgical properties and shaping ability of different rotary systems using a multimethod approach. METHODS New NeoNiti A1, HyFlex EDM One File, ProTaper Gold F2, and ProTaper Universal F2 rotary instruments were tested regarding cyclic fatigue, torsional resistance, design and morphological characteristics by scanning electron microscopy (SEM), metal alloy characterization by differential scanning calorimetry (DSC) and energy-dispersive X-ray spectroscopy (EDS). Additionally, their shaping ability on the preparation of 48 canals of maxillary molars was evaluated using micro-CT technology. Mechanical and metallurgical analyses were compared using ANOVA post hoc Tukey tests while the independent Student t-test was used to compare the shaping ability of either ProTaper systems or the thermomechanically-treated instruments. Significance level was set at 5% RESULTS: The highest cyclic fatigue was observed with the NeoNiti and HyFlex EDM instruments (P > .05), while HyFlex EDM had the highest angular rotation to fracture (P < .05). SEM/EDS analyses confirmed similarities in the instruments' design and an almost equiatomic composition of the systems. DSC showed that ProTaper Gold had higher transformation temperatures than ProTaper Universal, while a similar transformation was observed between NeoNiti and HyFlex. Micro-CT analysis revealed that, despite none of the systems was able to prepare all root canal walls, no statistical differences were observed in either ProTaper systems (P > .05) or thermomechanically-treated instruments (P > .05). CONCLUSIONS Apart from differences in the mechanical tests and metallurgical characterization, systems with comparable instruments' dimensions and preparation protocols showed similar percentage of untouched surface areas in the root canal preparation of maxillary molars.