Abstract
Changes in soft tissue profile following mandibular set back were investigated with lateral cephalograms of 40 patients initially having mandibular prognathism. Soft tissue profiles were evaluated using the analysis methods reported by Legan and Burstone, Ricketts, and Merrifield. Differences of the measurements before and after surgery were calculated as changes in profile produced by surgery, and following studies were made.1. The average changes in profile were analysed and the results were as follows: 1) Facial convexity improved, 2) Mandibular prognathism decreased, 3) No change in maxillary prognathism, 4) Posterior displacement of the upper lip with elongation and increase in upper lip protrusion, 5) Nasolabial angle increased, 6) Decrease in lower lip protrusion, 7) Lower facial height decreased, 8) Vertical lip-chin ratio improved, 9) Labiomental sulcus depth increased.2. The principal component analysis was employed in order to qualify the changes in profile as composition of several patterns.The analysis resulted in four principal components having 85% of accumulated contribution ratio.1) The first component (37.9%) is indicative of over-all quantitative change in profile by surgery.2) The second (23%) is indicative of displacement of the upper lip and change in lower lip protrusion.3) The third (14%) is indicative of changes in height of the lower lip and lower facial height and in the nasolabial angle.4) The fourth (10%) is indicative of change in the depth of the labiomental sulcus.Since there is no correlation among components in a principal component analysis, the second and third components in this study suggest the qualitative patterns of profile change. Therefore, changes in profile vary in the height of the lips and lower face and lower lip protrusion, based upon the averaged over-all changes.
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