How does temperature influence the properties of rectangular nickel-titanium wires?

Abstract

Thermodynamic nickel-titanium (NiTi) wires have become increasingly popular. The relationship between the temperature variation within the mouth and the force level delivered is, however, far from elucidated. The aim of this study was to evaluate the influence of possible intraoral temperature differences on the forces exerted by seven commercially available 0.019 x 0.025 inch NiTi archwires. As mouth temperature ranges from 33 to 37 degrees C most of the time, all wires were tested at five different temperatures between 30 and 40 degrees C in an orthodontic wire-testing device, a so-called Force System Identification (FSI) apparatus, placed in a climate chamber. In the FSI a two-bracket system using self-ligating Damon brackets simulated first order displacements up to 4 mm. At each temperature five samples of each archwire brand were tested. The following variables from the activation/deactivation curves were calculated: force and displacement at the yield point, maximum force level, total energy up to maximum displacement, energy loss after deactivation, force and displacement at the beginning and at the finish of the plateau, and the slope of the plateau. Any statistically significant differences in these variables for the different brands and temperature levels were analysed using one-way analysis of variance. The results showed that: (1) The behaviour of all wires was different. (2) Copper NiTi40 showed the lowest and the most constant force level, followed by NeoSentalloy 200 g. On the other hand, these wires may not work properly in mouth breathers as no forces were exerted below 35 degrees C. (3) If the use of superelastic characteristics and low force levels are the reasons for utilizing rectangular NiTi wires, austenitic NiTi wires should be avoided.

The effect of temperature on the mechanical behavior of nickel-titanium orthodontic initial archwires

“…Most of the research, though, was conducted on rectangular wires of significant size. 7,9 The aim of the present study, therefore, was to investigate the effect of temperature (55uC and 5uC) on the mechanical behavior of round NiTi wires, typically employed during the first stages of orthodontic treatment, during the discharge phase, evaluating the entity of displacement at which the average force is approximately constant, and to determine the effective degree of constancy of the plateau phase.…”

Propiedades mecánicas de tres marcas de arcos ortodóncicos de níquel-titanio termoactivados. Estudio in vitro

“…15 Por el contrario, obtuvo el menor valor de elongación alcanzada en la zona de activación constante, lo cual confirma lo obtenido por Gravina 1 , quien obtuvo el menor porcentaje de deformación en la zona de activación constante para los alambres de NiTi GAC. También se confirma lo investigado por Sakima y cols., 13 quienes observaron que los alambres termoactivados presentan mayores porcentajes de elongación en la zona de activación constante, en relación a los resultados obtenidos para los alambres superelás-ticos, lo cual es importante, pues los alambres termoactivados acumularían las mismas cargas por mayores intervalos de tiempo pudiendo ser deformados en mayor magnitud que los demás, acumulando fuerzas más uniformes durante las activaciones.…”

Torsional superelasticity of NiTi archwires

“…The superelastic effect was initially described in bending 8 and has been largely documented in this mode since. 9,10,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The literature, however, is less abundant when torsion is considered. [28][29][30][31][32][33] Some authors [28][29][30][31] were able to identify some degree of superelasticity at certain temperatures and above a certain value of twist, whereas Meling and Ødegaard 32,33 were not able to obtain a superelastic effect when wires were subjected to up to 25u of torsion at different temperatures.…”