Creating lip seal by maxillo-facial osteotomies. A retrospective cephalometric study.

Lateral head films taken immediately pre-operatively and at least 6 months postoperatively were analysed in 99 selected orthognathic surgery patients to study soft and hard tissue ratios in relation to lip seal creation. The patients were grouped according to the osseous correction carried out. In maxillary advancement patients, the overall position of stomion superius was difficult to predict when important horizontal and vertical movements had been made. The vertical movement of stomion superius was 30% of that seen at the anterior palate point, and 25% of that at the upper incisal point, when the main vector of maxillary repositioning was vertical (either intrusion or extrusion). There was a weak linear correlation between mandibular advancement at pogonion and vertical changes at stomion inferius. The correlation increased if vertical movement at menton and mentolabial angle were added as independent variables. Good linear correlations between vertical changes at stomion inferius and vertical changes at lower incisal point and menton were observed in mandibular set-back surgery. In mandibular autorotation, the best linear correlation with single predictors was found between vertical changes at stomion inferius and those at menton (about 80% + 1 mm upward movement), and vertical changes at stomion inferius and horizontal changes at lower incisal point. Vertical changes at stomion inferius were mainly determined by vertical changes at menton in genioplasties, the change at stomion inferius being 40% of that at menton. The horizontal component at pogonion had almost no influence. In combined genioplasty and Le Fort I procedures, the vertical changes at stomion inferius were 50% of those at menton + 1 mm upward movement, this difference being due to mandibular autorotation.