Reproducibility of Smiling Efforts Using 3D Facial Topograph

Objectives: To evaluate the reproducibility of facial expression with 3D facial topography using surface-based analysis.
Methods: Ten adult volunteers (5 male, 5 female) from among university students were enrolled. They were instructed to produce three facial expressions (rest posture, posed smile, and maximum smile; Okamoto, 2010). These expressions were recorded using a three-dimensional image-capturing device (3dMD cranial System, USA) at two separate occasions, i.e. the Session 1 (S1) and the Session 2 (S2) with an interval of one week. The S1 and S2 images in the rest postures were superimposed on the basis of 19 square regions located on the forehead. Two kinds of paired images the rest and posed smiles and the rest and maximum smiles were also superimposed on the forehead, which were assumed to be immobilized during facial expression. For each participant and for each facial expression, a wire mesh fitting based on the assignment of landmarks to each 3D facial image was performed. This method generated 10431 points on the wire mesh (i.e., the nodes of the fitted mesh). The differences between the paired images were calculated for each patient. Significant difference between paired images was statistically tested by a paired t-test (p<0.01).
Results: The inter-individual variation regarding the repeated measures exhibited a range between 0.66 mm to 1.73 mm (mean, 1.07 mm). For the posed smile, inter-individual variation ranged from 0.79 mm to 1.94 mm (mean, 1.21 mm), which was greater than the maximum smile. Neither the posed smile nor the maximum smile showed significant differences between the repeated measures.
Conclusions: The inter-individual variation was greater in the posed smile than in the maximum smile. Overall reproducibility of the maximum smile, in terms of intra-individual variation, was approximately 1 mm, and this was clinically acceptable.