The Correlation Between Static and Dynamic Facial Asymmetry in Unilateral Cleft Lip and Palate.

Objective: Assess the relationship between static and dynamic facial asymmetry in unilateral cleft lip and palate during maximum smile.

Design: Retrospective cross-sectional study.

Setting: Multidisciplinary dentofacial planning clinic.

Participants: Thirty-one surgically managed non-syndromic unilateral cleft lip and palate patients between the ages of 13 to 17 years.

Materials and methods: Dynamic three-dimensional (3D) facial images (four-dimensional [4D]) throughout the course of a maximum smile were captured using video stereophotogrammetry at a rate of 60 frames per second, which generated 180 3D images/expression. A generic facial mesh containing more than 7000 vertices was superimposed onto the 3D facial images to quantify and track facial asymmetry throughout the captured sequence. Partial ordinary Procrustes analysis was utilized to calculate an asymmetry score at the rest position, maximum smile, and at the point of maximum mathematical asymmetry. The relationships between the asymmetry at rest and the asymmetry at the point of maximum smile (static 3D), and the maximum mathematical asymmetry (dynamic 4D) were evaluated.

Results: Asymmetry scores were higher at maximum smile than at rest. Maximum mathematical asymmetry was observed in most cases during the relaxation phase. Static asymmetry at rest and maximum smile was strongly correlated with the maximum mathematical asymmetry (r = 0.941, P < .001).

Conclusions: Static 3D asymmetry at both rest and maximum smile are strongly correlated with dynamic 4D facial asymmetry. The use of 4D imaging, combined with generic mesh conformation and dense correspondence analysis, provides a valid objective measure of facial asymmetry.