치과교정용 NiTi 합금계 선재의 탄성과 상변태 거동에 대한 열처리 효과

Abstract

Due to unique property of superelasticity, NiTi has been used widely since their introduction(1971) to the orthodontic specially by Andreasen and Hillmann. But sufficent evaluation of superelasticity for domestic marketed wires has not yet been made. It has been known that heat treatment causes changes not on]y of elastic behavior but also of phase transformation behavior, an important factor of superelasticity. So, this study was investigated into varied ways of heat treatment of wires for orthodontic force proper for each clinical case. Each elastic behavior of 6 commercial NiTi alloy orthodontic arch wires(LG's ORTHOLLOY, G & H's Nickel Titanium arch wire, ORMCO's NI-TI and COPPER NI-TI, TOMY's SENTALLOY and 3M Unitek's Nitinol)were examined, and in order to study the effect of heat treatment on elasticity and phase transformation behavior, 3-point bending test, differential scanning calorimetry and X-ray diffraction with each wire heated at 350℃, 450℃ and 550℃ for lhour were carride out compared with a as-recieved group. The results are as follows ; 1. As a result sf 3-point bending test in a control group, all wires had superelasticity and COPPER NI-TI showed the lowest maximum load as well as minimum(p<0.05). 2. Except Nitinol and COPPER NI-TI, the wires in the group heated at 450℃ had lower maximum and minimum load than that of a control group, and higher maximum and minimum load than that of COPPER NI-TI in control group, and had superelasticity without any permanent deformation(p<0.05). 3. Phase transition temperature of all wires heated at 350℃, except COPPER NI-TI, became higher but it became lower when they were heated at 450℃ and 550℃. 4. All wires in a control group had austenite structure and when they were heated, martensite phase increased, and R phase appeared when heated at 550℃ The wires used in this study were changed in phase transition temperature, structure and elastic behavior as well by heat treatment. So this study showed that even the same kind of wire could be varied and used after heat treated, choosing proper load in accordance with each clinical orthodontic case.