In Vitro ion Release Property of Orthodontic Stainless Steels According to Stress Relief Heat Treatment Conditions

Heat treatment is applied to orthodontic stainless steel wires in order to relieve the stresses that result from the manipulation by orthodontists. The quality and the thickness of the oxide films formed on the surface of the heat-treated wires may be various and it is considered that the oxide films can influence on the properties of the heat-treated wires. The purpose of this study was to investigate the influence of the heat-treating conditions and cooling methods on the amount of metal ion release and cytotoxicity of the heat-treated wires. In this study, 4 types of stainless steel wires(Remanium, Permachrome, Colboloy and Orthos) in 0.41×0.56 ㎜ were selected for the experiments. These wires were heat-treated in vacuum, air, argon environment and were either cooled in a furnace or a water bath. Four control groups and 24 experimental groups were divided according to wires, heat-treating conditions and cooling methods. In each group, the amount of nickel ion release and cytotoxicity were investigated. The amount of nickel ion release in artificial saliva was measured for up to 12 weeks. In all groups, the amount of nickel ion release was lowest in the vaccum heat treatment-furnace cooling group and significant difference was shown compared with other experimental groups. The amount of nickel ion release was highest in the groups which were heat-treated in the air and significant difference was shown(p<0.05). The amount of nickel ion release was highest in Remanium & Colboloy and significant difference was shown(p