DSC and three-point bending test for the study of the thermo-mechanical history of NiTi and NiTi-based orthodontic archwires

It is a known fact that the NiTi orthodontic archwire is one of the first and most diffuse biomedical applications of shape memory alloys. In the last years, none deep study about orthodontic archwires has been conducted from the material point of view. In general, the clinical response is the principal aspect that has been investigated for this application. Nonetheless, the accurate mechanical and physical characterization of the archwires can be very important to add new developments to this biomedical product and to give a substantial contribution to the indispensable evolution that is crucial for better clinic results. In fact, the principal aspect that it is needed for further improvements is the study of the optimal force that does not cause damage to the surrounding tissues. According to this statement, a deep study about the thermo-mechanical characterization of several pseudoelastic commercial archwires used in the straight-wire low-friction techniques is presented. In detail, flexural mechanical tests in the three-point-bending configuration were conducted to assess the archwires unloading force, while differential scanning calorimetry was used to study the phase transition temperatures, and the thermo-mechanical history of each specimen. Both NiTi and NiTiCu commercial archwires were tested, and different geometries were considered. For all the archwires, an excellent repeatability of the results has been found. This series of characterizations provides a complete view of the thermo-mechanical properties of the material, and therefore it shows the possibility to modulate the functional properties developed by the device as a function of the biological field.