中文摘要
臨床上，鎳鈦矯正線長時間於應力狀態使用在口腔環境中，口腔環境的複雜與多變性對其腐蝕性質影響值得被考慮。關於評估鎳鈦矯正線在有、無應力應變存在時對於腐蝕性質的影響，鮮少有報告提出。本實驗目的在研究市售鎳鈦矯正線於應力狀態下，模擬口腔環境不同酸鹼值的腐蝕性質。
本實驗利用循環動電位極化法(cyclic potentiodynamic polarization test)分析兩種市售0.016英吋鎳鈦矯正圓線(Nitinol and Sentalloy)，在有、無應力(3mm 位移以及沒有位移)情況下，於恆溫37度、兩種不同酸性度(pH 5及pH 2)的人工唾液中的耐蝕性質，並與不鏽鋼矯正線比較之；之後，再利用電子顯微鏡觀察表面型態的改變。為了觀察表面氧化膜在有、無應力情況下改變的狀況，經過靜電位測試（potentiostatic test）後，藉由歐傑電子光譜儀(AES)進行鎳鈦矯正線表面元素的縱深分析。並且利用感應耦合電漿質譜分析儀(ICP-MS)測量鎳鈦矯正線在有、無應力下經過不同浸泡時間(1、3、7 及14天)的鎳離子釋出量。
實驗結果顯示在進行完循環動電位測試後，應力對於此兩種鎳鈦線的各項腐蝕參數在pH 5及pH 2的人工唾液中有負面的影響，特別是在鈍化區的電流密度有顯著的增加。同時注意到在電子顯微鏡的觀察中發現到不論是在pH 5或pH 2的人工唾液中，鎳鈦矯正線在受力下皆有局部腐蝕增加的現象。更進一步而言，表面氧化膜的縱深分析顯示在應力情況下氧化膜變的較薄，意味鈍化膜的保護功能有變差的傾向。此外，在浸泡實驗中於應力的狀態下鎳離子在第1天就可被偵測到，且隨著浸泡時間增加，鎳離子釋出量有上升趨勢；且在pH 2較pH 5的人工唾液有較高的鎳離子釋出量。因此，應力及酸性度可能導致存在鎳鈦合金上表面上保護性的鈍化膜的破壞進而產生孔蝕的現象。

In clinic, the Ni-Ti orthodontic wires are used under loading condition in oral environment for a long time. The corrosion behavior of NiTi wires that could be affected by complexity and variety of oral environment should be considered. The evaluation of the effect of corrosion behavior of Ni-Ti orthodontic wires with the presence or absence of stress is rarely reported. The aim of this study was to investigate corrosion behavior of commercial Ni-Ti orthodontic wires in stimulated oral environment at the different acidities under stress condition.
In this study the corrosion resistance of the two different commercial .016” round NiTi wires(Nitinol and Sentalloy)in two acidities(pH 5 and pH 2)of the artificial saliva, 37 ℃ with and without deformation(3 mm and no displacement)condition were evaluated by the cyclic potentiodynamic tests and were compared to the stainless steel wire, then the change of surface morphology was observed by SEM. To observe if the superficial oxygen film was changed or not with or without stress, the depth profile of the NiTi wires was analyzed with AES after the potentiostatic test. The amounts of Ni ion release of NiTi wires with or without stress during various immersion test periods(1,3 ,7 and 14 days)were calculated by ICP-MS.
The results showed that the stress had a negative effect on the various corrosion parameters of the two NiTi wires in the artificial saliva solution with two pH value after potentiodynamic test, especially in the current density of passive range with significant increasing. It was also noticed that a localized corrosion phenomenon of NiTi orthodontic wires under loading in the either pH 5 or pH 2 artificial saliva by the SEM examination. Furthermore, the oxygen film of wires became thinner under stress condition by the depth profile analysis of superficial oxygen film that implied the protective function of the passive film becoming poor. Besides, the Ni ion could be detected at the first day of the immersion test under stress condition, and the amount of Ni ion release had increasing tendency following the immersion time increasing. The more amount of Ni ion release under pH 2 than that under pH 5 artificial saliva. Therefore, the stress and acidity could evoke the breakdown of the protective passiviation layer that normally exists on the surface of NiTi alloy, and lead to pitting corrosion.

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