Robust and regional 3D facial asymmetry assessment in hemimandibular hyperplasia and hemimandibular elongation anomalies.

Hemimandibular hyperplasia (HH) and hemimandibular elongation (HE) anomalies present with facial asymmetry and deranged occlusion. Currently, diagnosis and assessment of the facial dysmorphology is based on subjective clinical evaluation, supported by radiological scans. Advancements in objective assessments of facial asymmetry from three-dimensional (3D) facial scans facilitate a re-evaluation of the patterns of facial dysmorphology. Automated, robust and localised asymmetry assessments were obtained by comparing a 3D facial scan with its reflected image using a weighted least-squares superimposition. This robust superimposition is insensitive to severe asymmetries. This provides an estimation of the anatomical midline and a spatially dense vector map visualising localised directional differences between the left and right hemifaces. Analysis was conducted on three condylar hyperplasia phenotypes confirmed by clinical and CT evaluation: HH; HE; and hybrid phenotype. The midline extraction revealed chin point displacements in all cases. The upper lip philtrum and nose tip deviation to the affected side and a marked asymmetry of the mid face was noted in cases involving HE. Downward and medial rotation of the mandible with minor involvement of the midface was seen in the HH associated deformity. The hybrid phenotype case exhibited asymmetry features of both HH and HE cases.