Date of Award
Master of Science (MS)
Objective: Alloys used in retention wires corrode in the oral environment. Previous studies have examined the effects of fluoride on archwires used in active treatment, but not on retention wires. The goal of this study was to determine what effect fluoride exposure has on corrosion of various lingual bonded retainer wires in the mouth. Methods: Twenty samples from six different wire types were tested in two solutions. Half were tested in Fusayama-Meyer artificial saliva, while the other half were tested in Fusayama-Meyer plus fluoride correlated to the concentration of toothpaste. A potentiostat was used to measure open circuit potential (OCP) for three hours, polarization resistance (Rp), and corrosion current (Icorr). A potentiodynamic curve was produced which revealed if pitting corrosion occurred in each wire. Results: In general, the OCP at three hours and Rp of the wires were significantly (p<0.05) greater in artificial saliva than artificial saliva plus fluoride. Icorr was significantly greater in the fluoride-containing artificial saliva. The solid stainless steel displayed the greatest OCP at three hours and the highest Rp of any wire in both solutions. The gold plated twisted had a significantly greater Icorr than any other wire in artificial saliva. Stainless steel twisted had the second highest value, which was also significantly greater than the remaining four wires. However, when fluoride was added the stainless steel twisted had the greatest Icorr, followed by gold plated twisted. Both of these wires had significantly greater Icorr values than the other wires in the fluoride containing solution. Gold plated solid had the lowest Icorr in this solution and was the only wire whose Icorr did not increase when fluoride was added. Pitting corrosion was present in the stainless steel twisted wire in both solutions and in both gold plated wires in artificial saliva. Conclusion: Twisted wires experience significantly greater corrosion rates than solid wires of the same composition. Conformation and composition are important in corrosion susceptibility. Gold plating increases a wire’s Rp and may lower its Icorr, reducing its susceptibility to corrosion in the presence of fluoride. Fluoride increases the susceptibility of most wires to corrosion.
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