| Summary: | 碩士 === 中山醫學大學 === 牙科材料研究所 === 90 === The corrosion resistance of different NiTi (Ormco, RMO, Orthodontic, SY) and stainless steel (Ormco, RMO, Orthodontic, 3M Unitek) orthodontic wires in an artificial saliva with various acidities (2.5, 3.75, 5.0, and 6.25) was investigated by using cyclic potentiodynamic polarization curve measurement and immersion test. Various corrosion parameters, breakdown potential, difference between breakdown and protection potential, and passive range, were obtained from the cyclic potentiodynamic polarization curves. Ions release after various immersion test periods (1, 3, 7, 14, and 28 day) was analyzed by using atomic adsorption spectrometer. Results of cyclic potentiodynamic polarization curve measurement showed that the manufacture of NiTi and stainless steel wires had a significant influence on the breakdown potential, potential difference between breakdown and protection potential, and passive range. The pH had a significant influence on the passive range of NiTi and stainless steel wires. The breakdown potential, as well as the potential difference between breakdown and protection potential, of NiTi and stainless steel wires produced by the same manufacture was significantly different. Furthermore, NiTi wire showed a better corrosion resistance than stainless steel wire. Results of immersion test showed that Ni ions release from NiTi wires were higher than that form stainless steel wires. After immersion test in pH 2.5 solution for 28 d, RMO had the highest quantity (38.7 g/cm2) of Ni ions release among NiTi wires. After immersion test in other pH (3.75, 5.0, 6.25) solution for 28 d, the quantity of Ni ions release from all NiTi wires was below 3.6g/cm2, while that from all stainless steel wires was below 3.2g/cm2. In pH 2.5 artificial saliva, Ni ions release from NiTi wires increased with increasing the immersion time, while the above phenomenon was not significant in higher pH solution. Regardless of the pH value, the highest quantity of Ni ions release from either NiTi or stainless steel wires was under the quantity assumed daily in the diet.
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