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Changes on NiTi orthodontic wired due to acidic fluoride solution.

The effect of acidic fluoride solution on NiTi arch wires was examined by testing crystal structure, tensile strength, morphology after fracture, and element release from wire under four different test solutions after 1 or 3 d immersion. Three-day immersion in a 0.2%/pH 4 solution did not form any new crystal structure. However, tensile strength after immersion was changed compared to the as-received wires. 3M wires showed increased tensile strength whereas G&H and Ormco wires showed decreased strength. Significant difference in tensile strength was associated with the immersion period. The fractured wires showed dimple patterns in the inner part of the wire, and ductile features on the outer part. Element release in the test solution increased as NaF concentration and the period of immersion increased, and as pH valued decreased. Wires immersed in a 0.2%/pH 4 solution released several-fold greater amount of elements than wires in a 0.05%/pH 4 solution. Tensile strength and element release were affected by acidic fluoride solution. In particular, NaF concentration, pH value, and the period of immersion were the factors affecting these properties.