title: The correlation between static and dynamic facial dysmorphology in unilateral cleft lip and palate (UCLP)
Creators: name: Wright, Christopher
Publisher: name: University of Glasgow
Year: 2024

description: Objective – The objective of this study was to assess the correlation between static (3D) facial dysmorphology at both rest and maximum smile and dynamic (4D) facial dysmorphology as represented by the frame of maximum asymmetry during a maximum smile in unilateral cleft lip and palate (UCLP). When maximum asymmetry occurs during a maximum smile was also analysed.

Design and setting – This study was designed as a retrospective cross-sectional study utilising quantitative methodology to assess a cohort of patients with a diagnosis of non-syndromic unilateral cleft lip and palate (UCLP). Patients had 4D imaging carried out at Glasgow Dental Hospital and School for audit purposes and as part of their routine care by the local cleft team working under the Managed Clinical Network (MCN) Cleft Care Scotland.

Materials and Methods – Thirty-one (31) patients between the ages of 13 to 17 years old with a diagnosis of non-syndromic unilateral cleft lip and palate (UCLP) had 4D images based on passive stereophotogrammetry captured at 60 frames per second (fps). Each patient was captured performing a maximum smile three times over a three second window. Data processing involved the conformation of a generic mesh containing over 7000 vertices or quasi-landmarks to the facial surface before tracking all the vertices during the facial expression. Partial ordinary Procrustes analysis was utilised to calculate an asymmetry score for each frame during the expression. The rest frame (3D), frame of maximum smile (3D), and frame of maximum asymmetry (4D) were used to determine the correlation between static and dynamic facial dysmorphology.

Results – Asymmetry scores were higher at maximum smile than at rest and maximum asymmetry was most frequently observed during the relaxation phase following a maximum facial expression (N=27/31; 87.1%). Asymmetry scores for maximum smile were less than but comparable to maximum asymmetry scores. Static (3D) asymmetry at rest and maximum smile was strongly correlated to dynamic (4D) facial asymmetry represented by the frame of maximum asymmetry during a maximum smile. The strongest correlation was seen with analysis using the frame of maximum smile focussing on the nasolabial region.

Conclusions – The use of 4D imaging combined with mesh conformation and dense correspondence analysis provides a valid objective measure of facial asymmetry. The fact that asymmetry scores for maximum smile were less than but comparable to maximum asymmetry scores highlights that assessment of facial asymmetry at maximum smile is still a valid assessment of facial dysmorphology despite not depicting the full extent of the asymmetry. Static (3D) asymmetry at rest and maximum smile is strongly correlated to; and likely highly predictive of, dynamic (4D) facial asymmetry represented by the frame of maximum asymmetry during a maximum smile. The strongest correlation is seen with analysis using the frame of maximum smile focussing on the nasolabial region. Future research could use linear regression modelling to predict dynamic (4D) asymmetry scores using static (3D) images.