Influence Of Fluoride On Corrosion Behavior Of Nickel-titanium Orthodontic Wires In Vitro

Objective To observe the performance changing of nickel-titanium (Ni-Ti) orthodontic wires induced by fluoride, and evaluate the influence of fluoride on corrosion behavior of Ni-Ti orthodontic wires.Methods Prepared the artificial saliva, and artificial saliva with sodium fluoride at different F~- concentrations(0.05%,0.10%,0.15%) . Selected the straight parts of four kinds of Ni-Ti orthodontic wires, put them into artificial saliva. Dislodged the species and immersed them into artificial saliva with sodium fluoride for 3 min, then washed them with deionized water, and put back to artificial saliva , this course should be repeated 3 times per day. The whole immersion test lasted for 28 days, and the control groups without immersion in fluoride solution. After immersion test, we observed the color changing, microstructure with scanning electron microscope, friction performance and tensile strength with universal test machine, then detected the amount of releasing Ni~+ in artificial saliva.Results 1 The color changing in fluoride solution came to be more serious as the F~- concentration growing ,there was statistical significance between different F~-concentration groups, different Ni-Ti wires got different results at the same F~-concentration. 2 In control group, there were more defects on the surface of IMD and YY, and the surface of TP and SL were smoother. The surface morphosis of species in control group was different from that of fluoride treated groups. As the concentration of F~-increasing ,the corrosion of species came to be more serious. Different to the others, TP group was more sensitive to uniform corrosion. 3 In TP and SL group, the friction between wire and brackets increasing as the increasing. When the concentration of F~-≤0.10%, the IMD and YY groups show the same trend as the other two groups, and when it came to be 0.15% , the friction of IMD and YY groups were even lower than the control group. 4 The tensile strength of all species decreased as the concentration of F~-increasing. Different materials show different decreasing speed, and the IMD group got the highest speed. 5 When the F~-≤0.05%, the concentration of Ni~+ in artificial saliva was less than 0.05 mg/l. The concentration of Ni~+ in 0.10% and 0.15% group were higher than that of control and 0.05% group, even to be 0.50 mg/l. Conclusions 1 Fluoride can change the color and micro-morphosis of Ni-Ti wire. 2 Different Ni-Ti wires don't show same changes of color and micro-morphosis at same F~- concentration. 3 The friction performance can be influenced by fluoride, but there is no linear relationship between them. 4 Fluoride makes the fracture of Ni-Ti wire more frequently. 5 At the common F~- concentration we used daily, we believe that Ni-Ti wires won't be harmful to human. But we still suggest that don't prescript fluoride agents to the patients with fluorine allergic who is taking orthodontic appliance with Ni-Ti wires.