Development of a hollow orthodontic wire with functionally graded properties

对两种不同直径的医用钛镍中空合金丝(0.016和0.018英寸)和一种钛镍钴铬耦合丝在37ﾟC下的弯曲性能进行了三点弯曲试验。耦合丝是在钛镍中插入0.010英寸或0.012英寸钴铬丝制成的。从载荷-挠度曲线来看，在40o-600ﾟC的热处理温度范围内，表现出超弹性，塑性变形很小。但当温度超过600ﾟC时，出现了塑性相变。在450ﾟC热处理时，载荷水平最小，600ﾟC时，载荷水平最大。此外，该空心线材的载荷水平低于传统的钛镍合金线材，应力滞后仅为常规线材的65%。由此可见，该空心线材的应力滞后仅为普通线材的65%。在正畸治疗的初期，可以在不减小弓丝尺寸的情况下产生轻微的恒力来移动牙齿。将钴铬合金丝插入中空的超弹性钛镍合金丝中的耦合丝具有2倍的刚度。在正畸治疗的后期，当进行前牙后退和咬合抬高时，需要具有较高硬度的弓丝。目前，一种新的扭弯试验装置仍在研制过程中，计划对一根空心钛镍合金矩形导线的扭弯作用力进行评估。

Bending characteristics of two different diameters-O.016 and 0.018 inch-of hollow Ti-Ni alloy wire ; which are widely used in the medical field, and a coupling Ti-Ni and Co-Cr wire were investigated by three-point bending test at 37ﾟC.The coupling wire was made by inserting a 0.010 inch or 0.012 inch CO-Cr wire to a hollow Ti-Ni wire.First, heat treatment of the hollow Ti-Ni wires was performed in a nitrate salt bath for 30mm. The temperature ranged between 400-650ﾟC.From a load-deflection curve, in heat treatment temperature of 40O-600ﾟC, the super elastic property was shown and there was very little plastic deformation.However, when the temperature exceeded 600ﾟC, some plastic transformation was found.A smallest load level was obtained by heat treatment at 450ﾟC, and the biggest load level was obtained at 600ﾟC.Moreover, the load level of the hollow-type wire was lower than that of the conventional Ti-Ni alloy wire and the stress hysterisis was shown to be only 65% of the conventional wire.From the above, findings, the light constant force to move teeth can be generated during the initial stage of orthodontic treatment without the need to reduce an archwire size.A coupling wire that inserted Co-Cr alloy wire to a hollow super-elastic Ti-Ni alloy wire was shown to have stiffness of 2 times.In the later stage of orthodontic treatment, when retraction of anterior teeth and bite raising are performed, the archwire which has high stiffness is required. By using the coupling wire, it is possible to increase the stiffness without changing the archwire.At present, a new torquing and bending test device is still in developing process.Evaluation of the force produced by torquing and bending of a hollow Ti-Ni alloy rectangular wire is planned.