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 buccal. however, due to failures tweed resorted to extracting teeth while keeping the mandibular plane to lower incisor angle at 90 degree +/- 10 degrees.