Objective: To determine whether differences exist in the shape and position of the lips between Class II division 2 and Class I malocclusions.
Materials and Methods: Lateral cephalometric radiographs of subjects with Class II division 2 (n = 30) and Class I (n = 30) incisor relationships were scanned at 300 dpi to produce digital images. These were subsequently digitized in random order. Twenty-one landmarks characterizing the upper and lower lips and the maxillary and mandibular central incisors were digitized. Procrustes algorithms optimally superimposed the landmark configurations to standardize size, location, and orientation. Discriminant analysis of the principal components of shape determined the differences between the Class II division 2 and Class I groups.
Results: The shape and position of the upper and lower lips differed significantly between the Class II division 2 group and the Class I group (P < .001). Principal component (PC) 1 (46% of the variance) involved an increase in the thickness of the upper and lower lips in the Class II division 2 group. PC2 (11% of the variance) was characterized by a relatively higher lip line in the Class II division 2 group.
Conclusions: The shape and position of the lips differ between Class II division 2 and Class I malocclusions.