Journal of International Dental and Medical Research ISSN 1309-100X Stainless Steel and Nickel-Free Brackets http://www.jidmr.com Natsinee Pipatvadekul and et al Volume ∙ 15 ∙ Number ∙ 3 ∙ 2022 Page 984 In Vitro Corrosion of Stainless Steel and Nickel-Free Brackets after Exposure to Fluoride Agents Natsinee Pipatvadekul 1 , Kanlaya Insee 1,2 *, Samroeng Inglam 2,3 , Awiruth Klaisiri 4,5 1. Division of Orthodontics, Faculty of Dentistry, Thammasat University, Pathumthani, Thailand. 2. Thammasat University Research Unit in Dental Biomechanics, Thammasat University, Pathumthani, Thailand. 3. Division of Oral Diagnostic Sciences, Faculty of Dentistry, Thammasat University, Pathumthani, Thailand. 4. Division of Restorative Dentistry, Faculty of Dentistry, Thammasat University, Pathumthani, Thailand. 5. Thammasat University Research Unit in Restorative and Esthetic Dentistry, Thammasat University, Pathumthani, Thailand. Abstract This in vitro study aimed to analyze the nickel ions release, surface morphology and surface roughness of stainless steel, and nickel-free brackets after exposure to fluoride agents. Twelve samples of stainless steel and nickel-free brackets were used and divided into three groups for exposing different fluoride agents by following each product’s instructions; acidulated phosphate fluoride (APF) solution, fluoride varnish, and artificial saliva without fluoride as a control group. After that, all brackets were detracted from their respective solutions and submerged in artificial saliva for seven days. Inductively coupled plasma mass spectrometry was used to determine the amount of nickel ion concentration. A scanning electron microscope and a non- contact optical 3-dimensional profilometer were used to evaluated surface morphology and surface roughness, respectively. The Shapiro–Wilk test was used to determine the distribution of nickel ion concentration and surface roughness values. The data were presented as means and standard deviations. Differences between groups of each type of bracket were analyzed by one-way analysis of variance (ANOVA) followed by Dunnett’s test. The results were considered significant at P < 0.05. Nickel ions concentration and surface roughness from stainless steel brackets significantly increased after exposure to fluoride products. In contrast, nickel-free brackets released similar amounts of nickel ions among groups. There were no significantly different in the amounts of nickel ions and the surface roughness between groups of nickel-free brackets. Nickel-free brackets are a choice for orthodontic patients who need a topical fluoride supplement. APF gel and fluoride varnish should not be used with stainless steel brackets in orthodontic patients for minimal clinical side effects. Experimental article (J Int Dent Med Res 2022; 15(3): 984-989) Keywords: Nickel, stainless steel, brackets, corrosion, surface roughness. Received date: 04 June 2022 Accept date: 02 August 2022 Introduction The most frequently metallic bracket material used in orthodontics is austenitic stainless steel, for example, type 304 and 316L of the American Iron and Steel Institute (AISI), which contains around 8–12 % nickel and 17– 22 % chromium. 1,2 The corrosion resistance of stainless steel alloys is based on chromium oxide layer along the surface. Nickel is cooperated into alloys to compete with chromium for the formation of salts, providing more chromium to create a passive layer. Nickel enhances ductility, stiffness, and resistance to crevice corrosion. 3 However, the link between the nickel atoms and the intermetallic compounds is so weak that the nickel is removed from the alloy surface. 3,4 Moreover, nickel is frequently known as an immunologic sensitizer that causes both short- and long-term sensitivity reactions. 5 Nickel- induced contact dermatitis is a hypersensitive immunological response that takes at least 24 hours to manifest. 6 Orthodontic appliances must be retained in the oral environment for a long time, two years *Corresponding author: Asst.Prof. Kanlaya Insee, Division of Orthodontics, Faculty of Dentistry, Thammasat University, 99 M. 18, Paholyothin road, Klongluang, Pathumthaini 12120, Thailand. E-mail: ikanlaya@tu.ac.th