Microstructure and Mechanical Properties of Nickel-Free and Nickel-Containing Stainless Steel Orthodontic Wires
Date of Award
Master of Science (MS)
Bradley, T. Gerard
Introduction: In orthodontics, contact dermatitis caused by nickel allergy should be of concern with the number of nickel-containing appliances and wires used. Stainless steel archwires are commonly used throughout orthodontic treatment. With the release of nickel from these wires, some manufacturers have turned to nickel-free stainless steel alternatives. The goal of this research was to compare nickel-free stainless steel with traditional stainless steel archwires with regard to mechanical properties and microstructure. Materials and Methods: Nickel-free stainless steel and regular stainless steel archwires from four companies were included. Five random samples of each wire, vertically mounted in fast-set acrylic, were indented three times to determine their Vickers microhardness. Force deflection properties were investigated with the three point bending test in which fifteen random samples of each wire were tested. Wire samples were horizontally mounted in fast-set acrylic, acid-etched for variable amounts of time, and then analyzed with a metallurgical microscope to assess microstructure. All quantitative data were compared using one-way analysis of variance (ANOVA) at a 0.05 significance level with a Tukey's HSD (honest significant difference) test post hoc analysis, when necessary. Results: Vickers microhardness number, activation stiffness, elastic recovery, and activation bending force values were calculated for each sample. Activation modulus showed no significant differences between Dentaurum wires. All wires were statistically different when considering percent recovery. Scheu and Dentaurum stainless steel wires were statistically similar to the respective nickel-free alternatives when investigating activation stiffness. Scheu Chromium bending force values were always greater than Scheu Menzanium. Acme Monaco's nickel-free alternative had force values greater than Acme stainless steel. Force values for Dentaurum wires through 1.0 mm of deflection showed no significant differences. Nickel-free alternatives and stainless steel wires manufactured by Scheu, Acme-Monaco, and Pozzi/Leone showed no statistical significant difference with regards to microhardness values. Microstructure analysis revealed differences between grain structure and sizes between all wires. Conclusions: Dentaurum Remanium and Noninium archwires appear to have the most similarities with regards to the mechanical and microstructure properties investigated in this study. With regards to the mechanical properties tested, nickel-free stainless steel may be a viable alternative to traditional stainless steel archwires.