Rui F. Martins

Aim: To comprehensively compare 12 nickel–titanium (NiTi) reciprocating single‐file systems from eight manufacturers by integrating geometric, mechanical, metallurgical and in silico analyses.Methodology: A total of 276 NiTi reciprocating instruments, representing 12 types across 8 brands, were selected, including Easy‐File Flex Regular 25, EdgeOne Fire Primary, Flash 25.06vt, One Files R25 and Blue R25, One RECI N25, Perfect RC R25 (Blue, Gold and Silver), Reciproc R25 (Blue and M‐Wire) and WaveOne Gold Primary. They were evaluated using stereomicroscopy, scanning electron microscopy, 3D optical scanning, energy‐dispersive X‐ray spectroscopy and differential scanning calorimetry to assess design and metallurgical properties. Mechanical performance was tested via buckling resistance and microhardness. A micro‐CT‐based premolar model was virtually prepared for each instrument to simulate canal shaping. Computational fluid dynamics (CFD) assessed irrigant penetration, wall shear stress and apical pressure. Finite element analysis (FEA) evaluated stress distribution in prepared roots. Data were analysed using the Shapiro–Wilk test for normality and the Kruskal–Wallis test for group comparisons (p < 0.05).Results: The systems differed considerably in spiral density, cross‐sectional design, size, volume and phase transformation temperatures. Instruments with larger apical cores (One Files and Reciproc M‐Wire) and austenitic‐phase dominance (Perfect RC Silver and One Files) showed greater buckling strength. Files with martensitic phases (Perfect RC Gold, WaveOne Gold and One Files Blue) or hybrid cross‐sections (One RECI and Flash) were more flexible. CFD revealed that conservative shaping (Easy‐File Flex, EdgeOne Fire, One RECI, WaveOne Gold) increased wall shear stress but reduced apical irrigant exchange. FEA showed similar stress patterns across all groups, with lower stress in restored roots.Conclusions: Substantial variation exists among current NiTi reciprocating systems in terms of design, mechanics, fluid dynamics and metallurgy. Instruments with large cores and austenitic‐phase structure provide superior buckling resistance. Conservative shaping improves shear stress but limits apical cleaning. Root stress remained consistent across systems. These findings highlight the importance of optimising instrument design and clinical protocols to balance shaping efficacy and irrigant delivery.

The current process for creating zirconia reconstructions for teeth is time-consuming, expensive, and results in tool wear and raw material waste. An alternative method, near-net shape additive manufacturing capable of producing samples with color gradient is presented as an innovative and more efficient solution. A low-cost robocasting system, which enabled the co-extrusion of two different ceramic inks, was designed and developed. Moreover, hydrogel-based ceramic inks, with rheological properties suitable for the present system, containing commercially available Yttria-stabilized zirconia (white and yellow) powders, were produced. Parts of different color shades and color gradients, with a high aspect ratio and good green body stability, were printed. In addition, precise color measurements were carried out, and co-extruded parts were compared with ultraviolet-C photofunctionalized parts. High fractions of binder in green bodies caused distortions in the samples during air drying and upon sintering. Debinding and sintering at 1500°C yielded parts of relatively low density (4.90–5.09 g/cm ³ ) and hardness (500 HV10–1100 HV10). A slightly different sintering behavior was observed for parts of different compositions. Density and hardness increased with the fraction of iron oxide-containing ink.

Selective laser melting (SLM) is an additive manufacturing powder‐bed fusion process that allows producing complex metallic parts with a relative density of up to 99.9%. Nevertheless, the mechanical properties of these components depend on numerous process variables, and there is a lack of systematic studies focused on SLM stainless steels. In the work herein presented, three specific printing strategies were X‐Y patterned to manufacture Compact Tension specimens transversally, longitudinally, or chess‐oriented, without any post‐processing heat treatment. The specimens were made of AISI 316L austenitic stainless steel. Thereafter, fatigue crack growth rate (FCGR) tests were carried out at room temperature, at constant amplitude loading (R = 0.2), to determine the fatigue crack propagation constants of the Paris Law associated with each print strategy. It was possible to conclude that transversal additively manufactured specimens showed the lowest FCGRs, and all results were well below the fatigue design curve given in ASME BPVC, Section XI.