Colorful dental arch wires are produced by anodizing the commercial beta-Ti and NiTi arch wires. Electrolytes of sulfuric acid, phosphoric acid, sodium sulfate, and trisodium phosphate are used. The anodization is conducted at a constant applied voltage, 10-60V, and at a constant temperature 25 degrees C. The colors of the wires vary with the applied voltages, and wires of a wide spectrum of colors are obtained. The anodized wires are metallographically examined. The compositions and the thickness of the oxide layers are determined by using electron spectroscopy for chemical analysis (ESCA) and Auger electron spectroscopy (AES). TiO2 layers are found on both kinds of anodized wires, and no nickel element is detected on the surface of the anodized NiTi wire. The colors of the wires are caused by light interferences through the oxide layers. The thickness of the oxide layers increases with the increasing applied voltages. The layer thickness also increases with the anodization time in the beginning, and it reaches a plateau after a certain period of reaction time at a constant applied voltage. The oxide layer is uniformly formed on the anodized beta-Ti wires. However, the surface roughness of the NiTi wires increases after anodization. (c) 2006 Elsevier B.V. All rights reserved.