Comparative studies of the accuracy and stability of three dimensional measuring methods for facial configurations, especially the external nose

There are two accurate methods to measure facial configurations, especially the external nose, as three dimensional objects. One is laser-scanning which can immediately measure faces directly and without contact. The other method, which we usually use, measures plaster models, obtained from facial impressions made with dental impression materials, by means of a contact-type, high accuracy three dimensional coordinate measuring system (contact measuring system).This study was designed to assess the accuracy and stability of these two methods, an issue previously paid little attention. Four 25-year-old men without facial deformity were examined with these systems. Multiple plaster models were taken from each subject to investigate model stability. All data were integrated into three dimensional models, shown as computer graphics, and compared by the “best fit program, ” which can handle and superimpose the two sets of curved surface data to derive minimum differences in normal vector direction at every site of the surface.The two sets of curved surface data obtained from the same plaster model by each system were almost identical except for areas of the alar groove. In data derived from the laser-scanning system, more than 1.0 mm of distortion was noted around areas of overhang. Facial and plaster model data obtained by the laser-scanning system showed very good fit, with deviation between data being 0.2-0.3 mm.These results show the high accuracy of facial plaster models. The stability of plaster models was also examined with a contact measuring system and deviation between data was 0.1-0.2 mm. In conclusion, although the two systems employed in this study have different characteristics, both are highly accurate and useful for clinical measurement.