TP Laboratories, Inc. (TP) (plaintiff) was an orthodontics supplier. TP developed orthodontic devices for its own practice and sold devices to other orthodontic practices. In 1956, one of TP’s orthodontists created a device that helped position teeth to correct orthodontic irregularities. The device featured springs to hold teeth in a desired location, and patients would wear the device for several hours a day over a span of years. In 1956, the device was used on a patient for the first time for two months. Another patient was treated with the device in 1959, and the device was used intermittently for over two years. A third patient was treated with the device in 1961. In 1962, the orthodontist filed a patent application for the invention, and the patent was assigned to TP in 1965. TP later brought a patent-infringement suit against Professional Positioners, Inc. (defendant), but the district court found that TP’s patent was invalid under 35 U.S.C. § 102(b) due to public use of the device prior to the critical date, which was one year before the application date. TP appealed the decision, arguing that TP’s prior use of the device was merely experimental and did not trigger the public-use bar to patentability.