Evaluation of the effect of fluoride-containing acetic acid on NiTi wires.

The possibility of the formation of hydrofluoric acid by the reaction of fluoride with acetic acid seems natural in the oral cavity. The effect of an acidic fluoride solution on NiTi wires was investigated by testing microhardness and color changes on wires. For aesthetic reasons, the color change on wires was also evaluated. Wires were immersed in four different test solutions for 1 or 3 days. As-received wires were used as a reference. After immersion for 3 days, the microhardness of the tested wires increased 1.8% to 10.4% compared to that of their as-received state. Wires immersed in a higher NaF concentration, lower pH solution with longer immersion yielded a more corroded surface than those of the counter cases. Wires showed a different color after immersion. However, after 3 days in solutions of pH 4, wires showed an appreciable color change regardless of the products. In test solutions, 3M wires showed the highest volumetric and percentage (0.59 for 0.05%; 1.19 for 0.2% solution) weight loss and G&H wires showed the least volumetric and percentage (0.43 for 0.05%; 1.05 for 0.2% solution) weight loss among tested wires. In pH 6 solutions, wires lost weight and were under the detection limit of the testing machine. Copyright 2004 Wiley Periodicals, Inc.