Date of Award
Summer 2014
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Dentistry
First Advisor
Berzins, David W.
Second Advisor
Bradley,Thomas G.
Third Advisor
Liu, Dawei
Abstract
Stainless steel wires have long been used in orthodontics. The austenitic stainless steel used in orthodontics contains approximately 18 wt% chromium and 8 wt% nickel. Nickel improves the corrosion resistance and helps maintain the austenite structure of stainless steel. Nickel is the most allergenic metal and is the most common metal associated with contact dermatitis in orthodontics. Nickel-free wires have been developed, and it was the goal of this study to compare nickel-free and nickel-containing stainless steel orthodontic wires to determine and compare their composition, phase structure, and corrosion properties. For each test, nickel-free and conventional stainless steel wires were compared from four companies: Acme Monaco, Dentaurum, Leone, and Scheu-Dental. Phase structure was determined using x-ray diffraction. Composition was measured using scanning electron microscopy with energy dispersive spectroscopy. For each wire, straight lengths were sectioned into 1-inch segments, arranged side-by-side, to create a 1-inch by 1-inch planar array of wires secured with sticky wax. Resultant XRD pattern peaks were indexed using standard methods or via ICDD files. Electrochemical corrosion tests were completed using a 3-electrode cell with a potentiostat and Gamry corrosion test software. Fusayama-Meyer artificial saliva solution was used as the electrolyte at room temperature. For each wire brand, wire lengths were isolated using nail polish, exposing a consistent surface area to account for varying diameters of the wires among brands. Open circuit potential, polarization resistance, and corrosion current density were determined. Data were compared using one-way analysis of variance (ANOVA) at a 0.05 significance value with a Tukey's Studentized Range (HSD) Test post hoc analysis, where required. Two nickel-free wires had detectable amounts of nickel. All nickel-free stainless steel wires had an increased amount of manganese, chromium, and molybdenum with decreased iron content. The orthodontic stainless steel wires are mostly austenitic, but martensite may be present in both types. Although there were significant differences among the wires for the three corrosion parameters, there was not a general difference between nickel-free and conventional stainless steel wires. Overall, despite composition differences between the nickel-free and nickel-containing stainless steel wires, they generally had the same phase structure and similar corrosion properties.