When you're smiling : the role of different expressions in modifying facial 3D morphology

The introduction of modern 3D acquisition devices has strongly improved the chances of analysis facial morphology, since it allows the operators to perform more reliable metrical and statistical measurements. In addition, the 3D models can be superimposed and the distance between the two scans be estimated by mathematical models. This presentation aims at exposing an application of this potential to the assessment of modifications of facial morphology according to different expressions. The experimental project was performed on 10 male adults, aged between 32 and 39 years, without facial deformities, relevant pathologies or signs of previous surgery. The face from each individual underwent to four acquisitions by stereophotogrammetry (VECTRA-3D®: Canfield Scientific, Inc., Fairfield, NJ): in each scan the subjects have different facial expression (neutral, sad, happy, surprised). The 3D model focused on the facial oval area included between the trichion, the lower edge of the mandible and the line between gonion and tragion. On each 3D facial model, 9 landmarks (right and left endocanthion, exocanthion, cheilion: on the midline, selion, pronasale, subnasale) were identified using VAM® software; the neutral acquisition was then superimposed with the other ones of the same individual representing specific expressions. The superimposition was performed in order to reach the least distance between the corresponding landmarks. In all the cases, the RMS value (Root Mean Square) between the two models was calculated; in addition the maximum and minimum difference was evaluated. Results show appreciable differences in RMS values between various facial expressions: in addition, the chromatic assessment of facial superimposition was able to highlight areas where the modifications were more relevant in different conditions. This pilot study has therefore provided an example of the streong impact that 3D acquisition systems may have on the anatomical analysis of facial characteristics.