치아색으로 코팅된 NiTi 와이어의 표면특성

Abstract

NiTi alloy has been used for orthodontic wire due to good mechanical properties, such as elastic strength and frictional resistance, combined with a high resistance to corrosion. Recently, these wire were coated by polymer and ceramic materials for aesthetics. The purpose of this study was to investigate surface characteristics of tooth colored NiTi wire usie uvarious instruments. Wires (round type and rectangular type) were used, respectively, for experiment. Polymer coatie uwas carried out for wire. CoWires (round specimenuwas investigated with field emission scanning electron microscopy(FE-SEM), energy dispersive x-ray spectroscopy(EDS), atomic force microscopy(AFM), and electrochemical tester. The results were as follows:

1. The phase transformation of non-coated NiTi wire from martensite to austenite occurred at the range of 14℃～15℃, in the case of coated wire, it occurred at the range of 16℃～18℃.

2. Polymer coating on NiTi wire surface decreased the surface defects such as scratch which was formed at severe machined surface.

3. From the AFM results, the average surface roughness of non-coated and coated NiTi wire was 13.1nm, and 224.5nm, respectively. From convetional surface roughness test, the average surface roughness of non-coated and coated NiTi wire was 0.046㎛, and 0.718㎛, respectively.

4. The passive region of non-coated NiTi wire showed largely, whereas, the passive region of curved NiTi wire showed shortly in anodic polarization curve. In the case of coated NiTi wire, pitting and crevice corrosion occurred severely at interface between non-coated and coated region.

5. The pitting corrosion resistance｜Epit-Ecorr｜of round and rectangular wire showed 650mV and 400mV, respectively.

6. From the AC impedance in 0.9% NaCl solution, polarization resistance(Rp) value of non-coated round and rectangular NiTi wire at curved part showed 5.10 × 105 Ω㎠ and 4.43 × 105 Ω㎠. lower than that of coated Ti-30Ta-xZr alloys. Rp of coated round and rectangular NiTi wire at curved part showed 1.31 × 106 Ω㎠ and 1.19 × 106 Ω㎠.

It is considered that the polymer coated NiTi wire can be used for aesthetics and corrosion resistant in the clinical orthodontic field. But, in this study, pitting and crevice corrosion can be severely occurred at interface between non-coated and coated region. For this problem, the elaborate coating method should be developed to increase the corrosion resistance at interface between non-coated and coated region.