Sagittal Soft-Tissue Changes of the Lower Lip and Chin Associated with Surgical Maxillary Impaction and Consequent Mandibular Autorotation

A retrospective cephalometric study was undertaken to assess the sagittal soft-tissue changes of the lower lip and chin in 22 patients who exhibited autorotation of the mandible after surgical vertical impaction of the maxilla. Lateral cephalometric radiographs were taken immediately before surgery and on average 15 months after surgery. Sixteen cephalometric landmarks were digitized by the use of a Kontron Videoplan Image Analysis System (Kontron Messgerate, GmbH, Image-analysis-systems, Eching/München, West Germany). The comparison between those cases that received maxillary elevation only and 6 cases that had additional advancement genioplasties revealed statistically significant proportional differences in the changes in the chin area, but not in the lower lip response, between the 2 groups. Therefore, when studying the lower lip changes, the 2 groups were pooled, but when changes in the area of the chin were considered, the 6 advancement cases were omitted from the study. In the horizontal plane, soft-tissue contours of the chin responded to changes to the underlying hard tissue at a ratio of 0.9:1. In the vertical dimension, soft-tissue gnathion also followed hard-tissue gnathion at a ratio of 0.9:1, whereas soft-tissue menton responded to hard-tissue menton at a ratio of 1:1. The lower lip in the horizontal dimension responded at a ratio of 1:1 with the lower incisor tip and lower incisor anterius at a ratio of 1:1, the associated correlation being strong (r = 0.84). In the vertical dimension, stomion inferius followed lower incisor tip at 1:1 and lower incisor anterius in a ratio of 1.3:1, whereas labrale inferius followed lower incisor anterius in a ratio of 1.5:1. Multiple regression analyses revealed that presurgical tissue thickness exerted no influence on the strength of the relationships between changes expressed at corresponding soft- and hard-tissue landmarks.