Three-dimensional morphometric analysis of facial units in virtual smiling facial images with different smile expressions

PURPOSE. Accuracy of image matching between resting and smiling facial mod-els is affected by the stability of the reference surfaces. This study aimed to in-vestigate the morphometric variations in subdivided facial units during resting, posed and spontaneous smiling. MATERIALS AND METHODS. The posed and spontaneous smiling faces of 33 adults were digitized and registered to the rest-ing faces. The morphological changes of subdivided facial units at the forehead (upper and lower central, upper and lower lateral, and temple), nasal (dorsum, tip, lateral wall, and alar lobules), and chin (central and lateral) regions were as-sessed by measuring the 3D mesh deviations between the smiling and resting facial models. The one-way analysis of variance, Duncan post hoc tests, and Stu-dent's t-test were used to determine the differences among the groups (alpha = .05). RESULTS. The smallest morphometric changes were observed at the upper and central forehead and nasal dorsum; meanwhile, the largest deviation was found at the nasal alar lobules in both the posed and spontaneous smiles (P < .001). The spontaneous smile generally resulted in larger facial unit changes than the posed smile, and significant difference was observed at the alar lobules, central chin, and lateral chin units (P < .001). CONCLUSION. The upper and central forehead and nasal dorsum are reliable areas for image matching between resting and smiling 3D facial images. The central chin area can be considered an additional reference area for posed smiles; however, special cautions should be taken when selecting this area as references for spontaneous smiles. [J Adv Prosthodont 2023;15:1-10]

Automated summary

This study investigated morphometric variations in different facial units during resting, posed, and spontaneous smiling. The results showed that minimal morphometric changes were observed at the upper and central forehead and nasal dorsum, while the largest deviation occurred at the nasal alar lobules. Spontaneous smiles resulted in larger facial unit changes compared to posed smiles, with significant differences observed in the alar lobules, central chin, and lateral chin units.