Feasible Evaluation of the Thermo-mechanical Properties of Shape Memory Polyurethane for Orthodontic Archwire

In orthodontic treatment with fixed appliances, the use of nickel alloy for archwire may cause nickel allergy suffered from the release of nickel ions. In addition, esthetic concerns are a problem for many people. Shape memory polymer (SMP), as a functional material with the ability of thermo-driven shape change to produce force and with good biocompatible properties, possesses the potential to be used in orthodontic appliances. To investigate the feasibility of using polyurethane (PU) as orthodontic archwire, a kind of SMP, namely shape memory polyurethane (SMPU), a simulation via finite element method was conducted, based on a new three dimensional (3D) thermo-mechanical constitutive model and data acquired from some mechanics experiments related to temperature. Finally, a tooth-moving simulation with SMPU archwire on a wax model was performed. The results illustrated that SMPU wire shows good prospects in orthodontic application: the archwire with a 0.5 mm diameter can supply recovery force with magnitude 0.588-1.176 N (60-120 g), which is within the required range 0.49-2.94 N (50-300 g) for tooth movement. However, the force is smaller than that produced from metal wire, and more work related to material strengthening, such as filling SMPU with reinforcement material, is required in the future.