Combined effects of different heat treatments and alloying elements on transformation behavior of NiTi orthodontic wires

The shape memory nickel-titanium alloy has been applied in many fields due to its unique thermal and mechanical performance. One of successful applications of NiTi wires is in orthodontics because of its good characteristics providing low stiffness, high spring back, high stored energy, biocompatibility, superelasticity and shape memory effect. The mechanical properties of wires are paid special attention which can result in achieving continuous optimal forces and eventually causing rapid tooth movement without any damage. The behaviors can be controlled by chemical composition and thermo-mechanical treatment during the manufacturing process. In this study two kind of NiTi archwires of 0.016 in. diameter investigated: shape memory wire (Copper NiTi) and superelastic wire (TruFlex). The chemical analysis of Both wires was determined by EDS and shape memory wire contained copper and chromium in its composition. They exposed to different heat treatment conditions at the temperatures of 400 and 500°C for 10 and 60 min. Using differential scanning calorimetry, phase transformation temperatures were clarified and three point bending tests in the certain designed fixture in form of maxillary dentition were perfomed at 37°C to evaluate mechanical behaviors. Finally, the behaviors after aging treatment  were compared to as-received wires. The results showed presence of alloying additions gave distinctive transformation features to Copper NiTi wire.