Mechanical Properties Comparison of Nickel-Titanium and Novel Titanium-Niobium Orthodontic Wires.

Objectives: To compare the mechanical properties (flexural and tensile strengths) of three superelastic orthodontic wires with a novel Titanium-Niobium wire (Gummetal®).
Methods: 24 orthodontic arches were distributed in four groups of six arch wires each, depending on the alloy: Nitinol® (3M Unitek), Heat Activated Nitinol® (3M Unitek), Cooper Ni-Ti® (Ormco) and Gummetal® (Rocky Mountain). Sample size and testing methods were determinate according ISO 15841 standard. Flexural and tensile strength (crosshead speed 1.7mm/min) tests were performed using the universal testing machine (AG-IS, Shimadzu, USA). Additionally, chemical composition and surface characterization were evaluated by spectrometry with a x-ray fluorescence spectrometer (Geminis, EDAX-DX4, USA) and a scanning electron microscope (XL30, Philips, Holland). After tensile tests, eight samples (2 per group) were observed using an optical microscope (Epiphot-200, Nikon, Japan) in order to determine the fracture mode. Statistical analysis was performed using Shapiro Wilk, Kruskal-Wallis, Mann-Whitney, one-way ANOVA and Tukey tests.
Results: Flexural strength was statistically different (p<0.05). Nitinol® was significantly higher than the other three alloys. Heat Activated Nitinol® reported the lowest values. No statistical differences were observed between Gummetal® and Cooper Ni-Ti®. Tensile strength showed statistical significant differences between the four groups (p<0.05). Gummetal® showed significantly higher tensile strength values than the three Nickel-Titanium alloys evaluated. (Nitinol®, Heat Activated Nitinol® and Cooper Ni-Ti®) Nitinol® was significantly higher than the other two Nickel-Titanium alloys. However, Heat Activated Nitinol® and Cooper Ni-Ti® were not statistically different. Chemical composition of the four wires evaluated was consistent with the manufacturer´s information reported. Cup-cone ductile fractures were observed in all wires evaluated.
Conclusions: Titanium-Nobium had similar flexural behavior than Cooper Ni-Ti alloys. However, Gummetal® tensile resistance was higher than the values reported by all superelastic Ni-Ti alloys evaluated. Titanium wires alloys evaluated are useful for the beginning of treatment. However, novel Titanium-Niobium is more resistant to tensile stress and favorable nickel-free.