During his early years, Tweed found that large number of his cases experienced failures either due to relapse of the corrected dentition or poor facial esthetics. Tweed's failures occurred due to expansion of the arches. Tweed believed in keeping the mandibular incisors uprighted over the basal bone and thus he would expand the arches buccally. However, due to failures Tweed resorted to extracting teeth while keeping the mandibular plane to lower incisor angle at 90 degree +/- 10 degrees. The tides turned once more, however, in the 1990s, notably after the 1986 Brimm lawsuit, in which Tweed's approach was proven to lead to serious jaw disorder and the rate of extractions halved in the United States. Today in the US it is more common to try to expand the arches first, using palate expanders, rather than resort to extractions. The tendency of US orthodontists to avoid extractions grew more pronounced in the 2lst century, when peer reviewed research established that premolar extractions followed by retraction narrows the patient's pharyngeal airway, which can be a cause of Obstructive Sleep Apnea and other breathing disorders. The rate of the practice of extractions is still high in other countries, particularly in Asia where up to 80% of cases are still done with extractions.
