The purpose of this study was to assess the soft tissue changes using twenty skeletal class Ⅲ malocclusion patients who treated with bimaxillary surgery for the correction of dentofacial deformities. Patients were devided into two groups. One was impaction and advancement of maxilla with mandibular set-back (Group 1), the other was downward and advancement of maxilla with mandibular set-back (Group 2). Preoperative and postoperative one year cephalometric data were analyzed and compared.
Results obtained were as follows :
1. The ratio of horizontal changes of soft tissue to hard tissue at Nt to ANS, Ls to UI, Li to LI, sPog to Pog were 1:0.60, 1:0.79, 1:0.47, 1:0.63 in group 1 respectively, and 1:0.59, 1:0.48, 1:0.83 1:1.09 in group 2 respectively. There were highly predictable in upper lip, lower lip, and chin.
2. The ratio of vertical changes of soft tissue to hard tissue at Nt to ANS, Li to LI were 1:0.72, 1:0.06 in group 1, and others showed no statistically significant differences.
3. The ratio of horizontal changes of Ls to hard tissue movements at LI(h) was 1:-0.82 in group 1 and at UI(h), LI(h) were 1:0.48, 1:0.01 in group 2. These ratios of group 1 were greater than those of in group 2.
4. The direction of horizontal change of Li was the same as that of hard tissue change. The ratio of horizontal changes of Li to LI was 1:0.47 in group 1 and others showed no statistically significant difference.
5. The changes of upper lip thickness and length were -1.6 mm, -1.4 mm in group 1, and -1 mm, -2.7 mm in group 2.
6. The ratios of thickness of upper lip to ANS, Ul, LI were 1:-0.83, 1:-0.37, 1:0.11 in group 1. There was similar trend in group 2, but there were no statistically significant difference.
These results suggest that prediction of changes in soft tissue of upper lip, lower lip, and chin were 79%, 47%,and 63% in group 1, and 48%, 83%, and 109% in group 2 after bimaxillary surgery. There was a tendency of decrease in thickness and increase in length of the upper lip.
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