Retrusion of the mandible is characterized by posterior displacement of the entire lower jaw. It may be a unilateral or a bilateral deformity but is more frequently the latter. In all such defects of the lower jaw there is some degree of bony hypoplasia; often there is an actual loss of bone with much distortion of the anatomic structures of the mandible. Malocclusion is invariably present, and underdevelopment and recession of the symphysis may accentuate the deformity. The most conspicuous feature in all cases of mandibular retrusion is retraction of the chin; this may or may not be associated with shortening of the upper lip (Figs. 1 and 2).
Retrusion of the mandible may be due to (1) malocclusion alone or (2) arrested growth of the lower jaw complicated by malocclusion.
In all patients having mandibular retrusions resulting from malocclusion and characterized by a distal relationship of the lower to