Quantifying Asymmetric Jaw Growth in Hemifacial Microsomia and Dentofacial Deformity

Objectives: This study compares longitudinal changes in asymmetry and growth of the facial skeleton in patients with an initial diagnosis of hemifacial microsomia (n=6), craniosynostosis (n=4), bilateral and unilateral cleft lip and palate (n=7) and dentofacial deformity characterized by asymmetry (n=12). Methods: We measured the three-dimensional (3D) growth of the maxilla and mandible in each group using two serial cone beam computed tomographic (CBCT) timepoints retrospectively from pre-existing records taken in the mixed dentition prior to bone grafting (T1), and at the completion of growth (T2). Pubertal growth prior to surgical correction was quantified using a regional automated, voxel-based registration of timepoints on the mandible and cranial base. Growth was quantified using a closest-point and spherical harmonic-based analysis (SPHARM) of displacement on segmented regions of the maxilla and mandible. Asymmetry was measured at both time points by creating mirror images of the maxilla and mandible and registering on the original image. Results: Methods for registration of longitudinal and mirror image timepoints in 3D were validated for asymmetric patients using regional superimpositions. Distinct patterns of asymmetric mandibular growth were measured in all four groups, with the hemifacial microsomia group having the most asymmetric growth in the transverse and coronal planes. Differences of up to 22% in condylar growth rates (mean=3.1± 0.9 mm/yr.) between right and left sides were measured over a two year time interval in the dentofacial deformity group. Asymmetric mandibular growth was characterized by compensatory remodeling of the gonial angle and corpus, and torquing of the condylar heads. Conclusions: Congenital anomalies of the craniofacial skeleton can impact the coordination of jaw growth, resulting in progressive facial asymmetry. In these cases, consideration for the asymmetric growth of the mandible and maxilla can greatly improve orthodontic and surgical treatment strategies.