US Patent 4,900,251
United States Patent and Trademark Office
University of Iowa Research Foundation (Iowa City, IA, US)
Mesial-distal slippage of an orthodontic archwire is deterred by manufacturing a parabolic archwire with a bend at its vertex. The bend has a height incapable of entering the wire-receiving slots of the brackets on a patient's teeth.
Andreasen, George F. Orthodontic archwire, apparatus, package and method. US Patent 4,900,251 filed April 29, 1988 and issued February 13, 1990. https://ir.uiowa.edu/patents/72