Pseudoelasticity of NiTi Orthodontic Wires Modified by Current Methodologies : A Critical Comparison

It is well known that applications of NiTi alloys in orthodontics rely on the pseudoelastic properties developed at temperatures hgher than Af. That implies as a necessary condtion that the body temperature (Tb) be higher than Af; the level of reversion stress, or depends moreover upon the difference between Tb and Af. Nowadays the interest is directed to obtain an archwire with distinct or in different segments: that means to modify locally the properties ofthe wire by local thermal treatments. Current methodologies exploit either the joule effect or a hot air thermal treatment: both have been here used on NiTi archwires to modify (TbAf) and, as a consequence, the expected or. The properties detected along the archwires by means of Differential Scanning Calorimetry, have been found quite disuniform when the active procedure of the resistive heat treatment was used, whilst good uniformity has been found when adopting the passive hot air heat treatment method. At the light of the present results, the hot air treatment method, allowing a better local temperature control, appears more reliable than the resistive heat treatment method.