Corrosion behavior of orthodontic archwire coupled to bracket under bending stress

• Main Authors: Yueh-chun Yen, 嚴月君
• Other Authors: Chuan-yang Chang
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/30025574922306197186

碩士 === 國立成功大學 === 口腔醫學研究所 === 97 === Bracket coupled to wire systems are commonly used in modern orthodontics to move teeth. Practitioners can choose from a wide range of wires and brackets made from different alloys. Oral environment is a particularly suitable environment for corrosive attack on metals as there exist various microorganisms and enzymes in mouth. In orthodontic treatment, not only galvanic interaction commonly exists between the archwire and brackets but also its stress will induce corrosion process. The aim of our study is to provide a quantitative assessment of the galvanic corrosion behavior of archwire alloys coupled to bracket alloys under the effect of stress, then to analyze the oxide layer of wire, and finally to detect the amount of nickel ion release from galvanic and stress corrosion. All of our experiments were performed at 37℃ with modified Fusayama artificial saliva with pH 2 and 5, respectively. At first, cyclic potentiodynamic test was carried out to gain corrosion parameters and surface topography was analyzed by means of scanning electronic microscopy (SEM) of nickel titanium wire coupled to bracket. The current density in passive region under stress condition was greater than that of unstressed specimens. Up to present, in the absence of stress, the corrosion mechanism in Nitinol Classic® and Sentalloy® was dominated by uniform corrosion; in brackets, two corrosion patterns were noted, including pitting corrosion in wing and grain boundary as well as crevice corrosion in the slot. In the presence of stress, Sentalloy® showed uniform corrosion, whereas Nitinol Classic® has uniform and pitting corrosion at stress area, no mater if wing or slot in brackets were of pitting corrosion and grain boundary corrosion. In potentiostatic test under the stimulated oral potential, the passive film of bracket and wire were spoiled. The current density in passive region was found unstable and higher in loaded mode. Greater release of nickel ion from loaded specimen was evident. We can conclude that the more the acidity, the more easily the corrosion reaction initiates, as well as stress can accelerate the corrosion rate.