Functionally Graded Orthodontic Archwires - Production And Characterization

The introduction of graded functionality in commercial superleastic orthodontic archwires was analyzed (Morelli SE). There are few studies concerning the manufacturing of the functionally graded Ni-Ti orthodontic archwires reported in the literature. The superelastic orthodontic archwire transformation temperatures were obtained by DSC analysis. The load developed by these wires depends on the geometrical properties, the temperature and level of strain. Normally, the conventional archwires generate constant forces in a wide range of displacement during the orthodontic treatment.

A functional gradient was introduced in the superelastic Ni-Ti orthodontic archwire (Morelli - SE) by localized heat treatment (by Joule effect). From the DSC measurements at different positions of the wire, it can be inferred that a microstructural gradient is present in this treated archwire. But DSC technique is not able to provide a localized analysis along the heat-treated archwire. To identify the microstructure of the heat-treated archwire with a finer spatial resolution, the synchrotron radiation based X-ray diffraction (SR-XRD) was performed. Tensile tests were performed and in situ analysis by SR-XRD to analyze the superelastic behavior. Specific steps performed, were previously selected in accordance with displacement during the orthodontic treatment. During these tests the SR-XRD 2D images were in-situ collected along the Ni-Ti orthodontic archwire heat treated. This structural analysis has been complemented by thermal, mechanical and thermomechanical tests.