Align Corporation (“Align”) (plaintiff) held the ‘611 and ‘548 patents for a type of braces that straighten teeth. Align’s invention, called Invisalign, used a series of three retainers, each moved an individual’s teeth from one position to another. When the first retainer moved the teeth from one position to the second, it was discarded. Then, a second retainer moved the teeth from the second position, to a third, etc. Ormco Corporation and its subsidiary, Allesee Orthodontic Appliances, Inc. (collectively “Ormco”) (defendants) invented a different type of teeth straightening product. Align brought suit against Ormco for patent infringement in the U.S. District Court for the Central District of California. Ormco argued that claims 1-3 and 7 of Align’s ‘611 patent were invalid because they were obvious or anticipated under 35 U.S.C. §§ 102(a) and 103(a). In support of its argument, Ormco presented two orthodontists as experts, Drs. Traux and Rains, who each used slightly different methods to incrementally straighten a patient’s teeth using three retainers. The district court granted summary judgment to Align that its patents were not invalid. Align did not challenge the district court’s determination that other claims of the ‘548 patent were invalid. Ormco appealed.