1. Introduction: Titanium alloys are very reactive materials and react instantly with oxygen, forming an oxide film, which gives them excellent anticorrosive properties [??]. Thus, titanium alloys have proven to be the most tissue-compatible inorganic materials, especially for dentistry [???]. Nickel-titanium wires, which have a nearly equiatomic composition, were introduced into clinical orthodontic use by Andersen and colleagues in the early 1970s [???]. They have been very popular in dentistry because they have a much lower elastic modulus and a wider elastic range than other orthodontic wires such as those composed of beta-titanium, stainless steel and cobalt-chromium-nickel [?? ?]. NiTi alloys have excellent biocompatibility with living tissues and corrosion resistance in various simulated body fluids [???]. These properties originating from the spontaneously formed thin oxide passivation layer are mainly made of TiO2[???]. For patients with fixed orthodontic appliances, mouth rinsing with fluoride-containing products is an effective method for caries prevention because these appliances have complicated morphologies. [???]. However, reduced corrosion resistance of pure titanium and titanium alloys in fluoride-containing environments that attack the protective surface oxide layer and cause allergic reactions to NiTi wires after insertion had been reported [?? ??]. The corrosion resistance of pure titanium and titanium alloys depends largely on fluoride concentrations [???]. Some studies regarding the corrosion behavior of titanium alloys in fluoride-containing environments have been reported [????]. It is claimed that the solution containing fluoride with fluoride ions above 20 ppm can destroy the protective oxide in the middle of the paper......the active layer increases.5. ConclusionsThe corrosion resistance of NiTi was studied in Ringer's solution for different concentrations of chloride ions. Our results show that increasing the chloride ion concentration can accelerate the corrosion of NiTi alloy. OCP values ​​in solutions contained in KCl and NaCl are less negative at lower concentrations than at higher concentrations and corrosion resistance decreases as chloride concentration increases. According to EIS analysis, NiTi exhibits good corrosion resistance even at higher concentration of chloride ions, but the polarization resistance and capacitance value of the protective oxide layer decrease as the concentration of ions increases. AcknowledgmentsThe author acknowledges Shiraz University, School of Materials Science and Engineering for financial support. (Grant No. 89-GR-Eng-58)