Characterization of the thermomechanical behaviour in correlation with structural aspects of Ni-Ti orthodontic arch wires

Abstract

In this paper, results of a study on commercial orthodontic arch wires (with square cross section) are presented. The samples selected include two conditions, before and after use. One of the main objectives of the paper considers the thermomechanical behaviour of the NiTi wire determined by a combination of differential scanning calorimetry (DSC) and measurements obtained through a specific experimental test developed for this study. The phase transformations in relation with temperature are also discussed. The thermodynamic stability of NiTi wire phases are predicted by simulation applying FACT SAGE 8.0 and corroborated with the structural information obtained by X Ray diffraction and observations by microscopy techniques. As it is known, clinical application requires a combination of shape memory effect at transition temperature range (TTR), superelasticity (that promotes tooth movement), suitable corrosion resistance, surface roughness characteristics, mechanical properties and biocompatibility. This paper presents results of surface roughness characteristics studied on wires in two conditions, before and after use. In addition, results of the thermomechanical behaviour of NiTi wires obtained by experimental tests at odontological treatment conditions are discussed. The transformation temperatures (TTR) of the samples were determined by differential scanning calorimetry (DSC). The information obtained is correlated with results of a thermodynamic simulation and microstructural aspects of the NiTi alloys systems selected for this study.