Comparison of the superelasticity of different nickel–titanium orthodontic archwires and the loss of their properties by heat treatment

Abstract

The aim of this work is to describe and compare mechanical properties of eight widely used nickel–titanium orthodontic wires under uniform testing conditions and to determine the influence of the heat treatments on the loss of the superelasticity. Ten archwires from two batches from eight different manufacturers were evaluated. A three-point bending test was performed, in accordance with ISO 15841:2006, on 80 round nickel–titanium archwire segments of 0.016 inch. To obtain a load-deflection curve, the centre of each segment was deflected to 3.1 mm and then unloaded until force became zero. On the unloading curve, deflection at the end of the plateau and forces delivered at that point, and at 3, 2, 1 and 0.5 mm of deflection, were recorded. Plateau slopes were calculated from 3 and from 2 mm of deflection. Data obtained were statistically analysed to determine inter-brand, intra-brand and inter-batch differences (P < 0.05). The results show that at 2 mm of deflection, maximum differential force exerted among brands [Nitinol SuperElastic (1.999N)—Sentalloy M (1.001 N)] was 0.998 N (102 gf). The Nitinol SuperElastic plateau slope (0.353 N/mm) was the only one that was statistically different from 2 mm of deflection, as compared with the other brand values (0.129–0.155 N/mm). Damon Optimal Force described the gentlest slope from 3 mm of deflection (0.230 N/mm) and one of the longest plateaus. Titanol and Orthonol showed the most notable intra-brand differences, whereas inter-batch variability was significant for Nitinol (Henry Schein), Euro Ni–Ti and Orthonol. Superelasticity degree and exerted forces differed significantly among brands. Superelasticity of Nitinol SuperElastic was not observed, while Damon Optimal Force and Proclinic Ni–Ti Superelástico (G&H) showed the most superelastic curves. Intra-brand and inter-batch differences were observed in some brands. In all cases, the heat treatment at 600 °C produces precipitation in the matrix. The precipitates are rich in titanium and this fact produce changes in the chemical composition of the matrix and the loss of the superelasticity. At 400 °C these precipitates are not produced and the forces delivered by the wires are very similar with wires untreated.

Effect of different bonding protocols on degree of monomer conversion and bond strength between orthodontic brackets and enamel

“…Orthodontics has evolved considerably in recent decades improving aspects such as treatment planning and diagnosis 1 , clinical performance 2 and patient comfort. 3,4 Factors that can influence clinical performance include bracket design and type 5 , composition of the orthodontic wire 6 , and, especially, the resins and adhesive systems used for bracket bonding. 7,8 Adhesion failures between bracket and tooth surface compromise the success of the orthodontic treatment, are costly, and cause inconvenience to the patient.…”

Bioinspired Superhydrophobic Ni–Ti Archwires with Resistance to Bacterial Adhesion and Nickel Ion Release

“…Flexural strength, one of the most important mechanical characteristics of orthodontic AWs, was investigated in a three‐point bending test . All AWs were tested according to ISO/CD 15841:2004, MOD standard, and stress–strain curves were drawn to visualize the flexural properties.…”

“…Mechanical Properties Measurement : Flexural strength was investigated in a three‐point bending test . The Bare‐LAWs (Control) and FAS‐AWs with different roughness were tested using a universal testing machine according to ISO/CD 15841:2004, MOD standard (short side of the cross‐section was selected as the driving face, with fulcrum distance 10 mm and loading rate 1 mm min −1 , under temperature of 36 ± 1 °C) and a stress–strain curve was drawn to visualize the flexural properties.…”

Evaluation of the Mechanical Properties and Surface Topography of as-Received, Immersed and as-Retrieved Orthodontic Archwires

“…In his recent study, Bellini et al [ 12 ] evaluated and compared the mechanical properties of eight widely used orthodontic Ni–Ti archwires, independently of trade houses and under the same standardized testing conditions. The effect of the thermal treatments on the mechanical behavior and the microstructure of Ni–Ti archwires of different compositions was also studied [ 12 ].…”

“…In his recent study, Bellini et al [ 12 ] evaluated and compared the mechanical properties of eight widely used orthodontic Ni–Ti archwires, independently of trade houses and under the same standardized testing conditions. The effect of the thermal treatments on the mechanical behavior and the microstructure of Ni–Ti archwires of different compositions was also studied [ 12 ]. Obaisi et al [ 13 ] determined the transformation temperatures of two brands of heat-activated Ni-Ti orthodontic archwires using both the Bend and Free Recovery (BFR) method and the standard method of Differential Scanning Calorimetry (DSC).…”