Initial Orthodontic Force Analysis of Shape Memory Polymer Arch Wire Based on Finite Element Simulation
1 Key Laboratory of E&M (Zhejiang University of Technology), Ministry of Education & Zhejiang Province，Hangzhou 310014, China
2 College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China
Abstract：In orthodontic treatment, metallic arch wire may produce potential toxic effect to human and can not satisfy the aesthetic requirements. In contrast, shape memory polymer (SMP) arch wire has attracted more and more attention for its good mechanical properties and aesthetic appearance. However, shape memory polyurethane (SMPU) as a typical kind of material, its effect in orthodontic treatment, including the force supplied by SMPU wire still remains to be explored. In orthodontic research, the intra-oral evaluation of the force supplied by appliances is difficult to achieve, and finite element method (FEM) has been widely applied as an alternative method. Aiming at these problems, based on the one-dimensional SMP constitutive equation built by Tobushi, a 3D constitutive equation of SMP is derived reference to the standard model of viscoelastic material, and user-defined material mechanical behavior (UMAT) subroutine used for ABAQUS is written by FORTRAN language. From clinical orthodontics data, a 3D model including teeth, brackets and SMPU arch wire were constructed. Taking a maxillary lateral incisor and a canine as examples, through exerting different deformation on arch wire, the initial orthodontic force of arch wire was acquired by FEM simulation. When deflection is 3 mm, the value range is 0.06～0.55N. The results revealed that the initial orthodontic force of SMPU arch wire is somewhat smaller than the optimal orthodontic force required in clinic, and is suitable in the first phase of orthodontic treatment. But the mechanics performances of SMP are still needed to be improved, which will promote a very high potential value on medical application in the future.
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