Prediction of Soft Tissue Profile Changes after Sagittal Splitting Ramus Osteotomy and Genioplasty

Abstract

The purpose of this study is to improve the accuracy of predicting the soft tissue configuration from the change amounts of the hard tissue landmarks in the patients who underwent combined sagittal splitting ramus osteotomy (SSRO) and genioplasty for skeletal mandibular protraction. The samples for this study consisted of the lateral cephalograms records of 20 surgical orthodontics treated patients. The records of each subject were chosen on the basis of their having pre-treatment and post-treatment lateral cephalograms. Landmarks were traced from each film, and scaled to permit radiographic enlargement. The cartesian coordinates of these points were obtained with the use of calipers, where the coordinate set was first translated to bring the midpoint at sella turcica to the origin and then rotated to align the Frankfort horizontal plane with the X axis. Y axis was set perpendicular to the X axis. The means and standard deviations were estimated for each of the cephalometric variables in both the hard tissue and the soft tissue. There were significantly increased in the amount of change in Convexity, ANB, U1 to L1, on the contrary there were significant decreased in SNB, Facial angle, Gonial angle, IMPA. After SSRO and genioplasty there were significant decreased in the X-coordinates of the landmarks in the L1, Id, B, Pog and Me. Regarding the amount of those changes, in the soft tissue measurements, there were significant decreased in X-coordinates of Li, Sid, SB, SPog and SMe.

The results of the regression analysis suggested that the final positions of the points St

(X):0.80, St(Y):0.77, Sid(Y):0.78, SB(Y):0.73, and SPog(Y):0.87, which showed R square greater than 0.70(contribution%), could be predicted with confidence. On the contrary, in the measurement without corresponding hard tissue(Sn and Li), R square were more variable and could be predicted with less confidence.

The prediction of soft tissue profiles in combination with SSRO and genioplasty could be adequately predicted.