(1991) suggested that among the metal elements, nickel is toxic to animals and humans as well as being a carcinogen of the respiratory system and nasal cavity. In addition, the possible production of toxic corrosion products in the surrounding tissues is undesirable.
Toms (1988) reported that corrosion of orthodontic appliances could have serious clinical implications, ranging from a loss of dimension resulting in lower forces being applied to the teeth, to stress corrosion failure of the appliance. (1987) the corrosion of nickel-based orthodontic wires. (1981) studied the corrosion of nitinol and SS wires, and Lee et al. This is one reason why there are a limited number of materials used for making orthodontic appliances. Corrosion resistance is important when choosing a metallic orthodontic appliance. Some reports have shown that stress relief heat treatment for SS wires causes oxidation on the surface and creates an uneven oxide film, which eventually leads to localized corrosion ( Hwang et al., 2001 Oh et al., 2002). Nikolai (1985) reported that steel wires that have been deformed plastically by cold working experience greater stress relief and increased ductility, but that the effects can differ according to the type of wire, the diameter, and the degree of work hardening. Lane and Nikolai (1980) reported that heat treatment could affect the mechanical properties of SS wires, while Thurow (1982) showed that heating a SS wire decreases the danger of breakage due to residual stress and stabilizes the form of the steel wire by enhancing its elasticity. (1968) studied the relationship between stress relief heat treatment and the mechanical properties of a SS wire. In addition, Backofen and Gales (1952) reported the effectiveness of stress relief treatment, and Howe et al. Ingerslev (1966) found that heating 18-8 SS wire at 350 to 375☌ for 20 to 25 minutes was most effective, and Marcotte (1973) showed that the properties of springs made of SS improved after they were heated for 11 minutes at 400☌. Funk (1951) reported that stress relief for orthodontic SS wire is quite effective, and suggested 450☌ to be the optimum temperature for stress relief treatment. There have been numerous studies on orthodontic SS wires. Therefore, stress relief heat treatment, which enhances the elasticity and stability of the wire in terms of the form and the number of dislocations, must be applied. When orthodontic stainless steel (SS) wires are manipulated, their mechanical properties can change as a result of internal stress in their attempt to return to their original forms. The cytotoxicity was mild in all the experimental groups but the response index of the air groups was slightly higher than in the other groups.Īccording to these results, SS wires retain their high corrosion resistance and low ion release rate when heat-treated in a vacuum and cooled in a furnace. The concentration of dissolved nickel ions in artificial saliva was highest in the groups heat-treated in air ( P < 0.05), while the amount of nickel released was highest in the Remanium and Colboloy ( P < 0.05). In all groups, the concentration of dissolved nickel ions in artificial saliva was lowest for the vacuum heat treatment-furnace cooling group and a significant difference was shown compared with the other experimental groups. The concentration of dissolved nickel ions in artificial saliva was measured for a period of up to 12 weeks.
In each group, the amount of nickel released as well as its cytotoxicity was investigated. Four control groups and 24 experimental groups were classified according to the type of wires, heat treatment conditions and cooling methods. These wires were heat-treated in a vacuum, air, or argon environment, and were cooled in either a furnace or a water bath. In this study, four types of SS wires (Remanium, Permachrome, Colboloy and Orthos) with a cross-sectional area of 0.41 × 0.56 mm were investigated. The aim of this study was to investigate the influence of heat treatment and cooling methods on the amount of metal ions released and to examine the cytotoxicity of heat-treated wires. The quality and thickness of the oxide films formed on the surface of heat-treated wires can vary, and it is believed that these oxide films can influence the properties of heat-treated wires. Heat treatment is generally applied to orthodontic stainless steel (SS) wires to relieve the stresses that result from their manipulation by orthodontists.
0 kommentar(er)
