Three-dimensional analysis of face morphology by perspective transformation

Abstract

A new method for quantitative analysis of face morphology in three-dimensions was described and its clinical use efficacy discussed. The method consisted of calculating threedimensional values of reference points on the face by perspective transformation from twodimensional values of these and other nine standard points in two pairs of photographs taken simultaneously from both sides of the face with the head in a metal frame reference on which the standard points of known three-dimensional values were set and displaying a three-dimensional image of the face seen from any direction as a wire-frame model as well as its contour at any plane of section on a CRT and an X-Y plotter. All calculations were done with a personal computer.
The variation in the reconstructed three-dimensional coordinate values of nine reference points on a test plane in 20 trials was 0.36 mm at 1 SD at maximum and the mean error in each direction was within a 0.75 %range. The effect of angle in taking a pair of photographs on the error of reconstructed coordinate values which was highly correlated to the reciprocal of the angle (r=0.9996) was also found to be minimal when it was set at 20 degrees or more by a computer simulation analysis.
Clinical application of this analysis to six patients who underwent orthognathic surgery for mandibular prognathism showed that the characteristics of facial deformity and the postoperative change in facial appearance could be well visualized by superimposing pre-and post-operative images. In addition, quantitative evaluation of volume change in various areas of the face was also available. Thus, the method was found to be quite useful for diagnosis and analysis of postoperative changes in face morphology in jaw deformities.