Development of a hollow orthodontic wire with functionally graded properties

两种不同直径（0.016和0.018英寸）的空心Ti-Ni合金丝的弯曲特性其广泛应用于医疗领域，并且通过在37 ℃下的三点弯曲试验来研究耦合Ti-Ni和Co-Cr线。通过将0.010英寸或0.012英寸的Co-Cr线插入中空Ti-Ni线来制造耦合线。首先，在硝酸盐浴中对中空Ti-Ni丝进行30 mm的热处理。温度范围为400-650 ℃。从载荷-挠度曲线来看，在400 -600 ℃的热处理温度下，显示出超弹性性能，并且几乎没有塑性变形。但是，当温度超过600 ℃时，发现了一些塑性转变。在450 ℃热处理获得最小载荷水平，在600 ℃获得最大载荷水平。此外，中空型线材的载荷水平低于常规Ti-Ni合金线材的载荷水平，并且应力滞后仅为常规线材的65%。从以上发现，在正畸治疗的初始阶段可以产生轻微的恒定力来移动牙齿，而不需要减小弓丝尺寸。弹性钛镍合金弓丝的刚度约为2倍，在正畸治疗后期进行前牙内收和上牙合时，需要使用刚度较高的弓丝。目前，一种新型的扭转和弯曲试验装置仍在研制中，拟对钛镍合金空心矩形丝扭转和弯曲所产生的力进行评价。

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.