Abstract
The present research compared the design, metallurgical properties, and mechanical characteristics of the ProTaper Ultimate instruments with five multifile systems. A total of 469 new nickel-titanium rotary finishing instruments, all 25 mm in length but varying in size, taper, and metal alloy composition, from six different multifile systems (ProTaper Ultimate, ProTaper Next, ProFile, Mtwo, EndoSequence, and GT Series X), were inspected for irregularities and analyzed for their spiral density (spirals per millimetre), blade design, surface finishing, alloy composition, phase transformation temperatures, and mechanical performance (microhardness, torsional, and bending resistance tests). Group comparisons were performed using Kruskal-Wallis and one-way ANOVA with post hoc Tukey's tests (α = 5%). ProFile instruments exhibited a greater number of spirals and a higher density of spirals per millimetre compared to the other systems. Microscopic analysis revealed distinct tip geometries and blade designs among tested instruments. All of them displayed parallel marks from the machining process, but the EndoSequence system had the smoothest surface finish. The alloys of all instruments consisted of an almost equiatomic ratio of nickel to titanium. At the testing temperature, the ProTaper Ultimate system exhibited a complete R-phase crystallographic arrangement, while the ProFile and Mtwo systems were fully austenitic. The ProTaper Ultimate F2, F3, and FX instruments demonstrated the highest maximum torque values (1.40, 1.45, and 3.55 N.cm, respectively) and the lowest maximum bending loads (202.7, 254.9, and 408.4 gf, respectively). EndoSequence instruments showed the highest angles of rotation, while the highest microhardness values were recorded for GT Series X (407.1 HVN) and ProTaper Next (425.0 HVN) instruments. The ProTaper Ultimate system showed a high spiral density per millimetre and a complete R-phase crystallographic arrangement at room temperature, which significantly contributed to its superior flexibility and torsional strength when compared to the other tested systems.