an additional biocompatibility problem furthermore the anodizing treatment according to the present invention only oxidizes the surface of the material such that the mechanical strength of the orthodontic archwire will not be affected conspicuously in other words an anodizing treatment can alter the outlook color of an orthodontic archwire without significantly changing the biocompatibility and mechanical strength thereof wherein the former might be increased slightly while the later might be decreased or increased slightly an orthodontic archwire of u03b2 ti alloy having ti 77 79 zr 6 06 mo 11 27 and sn 4 88 code no 101 009 ortho organizers inc was used as a specimen 0 017 inch u00d7 0 025 inch in an anodizing treatment wherein the electrolytic solution used was an aqueous solution having 0 25 m h 2 so 4 0 15 m h 2 o 2 0 075 m h 3 po 4 and 0 0075 m hf the anode was said orthodontic archwire the cathode was a platinum plate and the power supply was a lps 305 from the motech co said orthodontic archwire was polished in sequence with sic sandpapers of 1000 1200 2400 and 4000 and alumina powder the polished orthodontic archwire was immersed in 0 5 m naoh aqueous solution and under an ultrasonic oscillation for 10 minutes this alkaline washing treatment removed esters on the surface and activated the surface of the metal in order to achieve a uniform surface property next said orthodontic archwire was immersed in a hydrochloric acid solution 0 2 m and subjected to an ultrasonic oscillation for 2 minutes in order to remove oxides on the metal surface followed by washing with a large quantity of distilled water and drying by blowing the above cleaning steps were all carried out at room temperature.