Congenital and acquired mandibular asymmetry: Mapping growth and remodeling in 3 dimensions

Abstract

Introduction Disordered craniofacial development frequently results in definitive facial asymmetries that can significantly impact a person's social and functional well-being. The mandible plays a prominent role in defining facial symmetry and, as an active region of growth, commonly acquires asymmetric features. Additionally, syndromic mandibular asymmetry characterizes craniofacial microsomia (CFM), the second most prevalent congenital craniofacial anomaly (1:3000 to 1:5000 live births) after cleft lip and palate. We hypothesized that asymmetric rates of mandibular growth occur in the context of syndromic and acquired facial asymmetries. Methods To test this hypothesis, a spherical harmonic-based shape correspondence algorithm was applied to quantify and characterize asymmetries in mandibular growth and remodeling in 3 groups during adolescence. Longitudinal time points were automatically registered, and regions of the condyle and posterior ramus were selected for growth quantification. The first group (n = 9) had a diagnosis of CFM, limited to Pruzansky-Kaban type I or IIA mandibular deformities. The second group (n = 10) consisted of subjects with asymmetric, nonsyndromic dentofacial asymmetry requiring surgical intervention. A control group (n = 10) of symmetric patients was selected for comparison. A linear mixed model was used for the statistical comparison of growth asymmetry between the groups. Results Initial mandibular shape and symmetry displayed distinct signatures in the 3 groups (P < 0.001), with the greatest asymmetries in the condyle and ramus. Similarly, mandibular growth had unique patterns in the groups. The dentofacial asymmetry group was characterized by significant asymmetry in condylar and posterior ramal remodeling with growth (P < 0.001). The CFM group was characterized by asymmetric growth of the posterior ramus (P < 0.001) but relatively symmetric growth of the condyles (P = 0.47). Conclusions Forms of CFM are characterized by active and variable growth of the dysplastic side, which has a distinct pattern from other disorders of mandibular growth.

3D superimposition of craniofacial imaging—The utility of multicentre collaborations

“…The Dental and Craniofacial Bionetwork for Image Analysis (DCBIA‐https://sites.google.com/a/umich.edu/dentistry-image-computing/) group is composed by researchers, clinicians, computer scientists and engineers with the aims to (a) develop image analysis tools specifically to answer dentistry‐related clinical questions; (b) train researchers interested in those tools. These efforts resulted in international collaborations with South America, Europe, Asia and Oceania, not to mention other centres within the United States, with a large variety of application of the tools as follows: craniofacial anomalies, asymmetry, surgical outcomes and growth changes . Strengthening the relationship with other centres may eventually facilitate the development of big data that require secure but easily accessible de‐identified databases, with storage, mining and analytics capabilities.…”

Utilizing three‐dimensional data in orthodontic practice and research

“…Structures presumed to be stable in profile view, such as the mandibular canal and follicles of erupting permanent molars, may be displaced by transverse growth . For this reason, recent efforts have evaluated and tested individual approaches for superimposition or “registration” on a specific region . Analogous to structural superimposition methods, a volume of reference can be selected to align multiple timepoints.…”

“…For the interpretation of most clinical changes in orthodontics and orthognathic surgery, three types of superimposition are generally required: a superimposition on the cranial base, maxilla and mandible. In recent research, target volumes of reference have been evaluated for each type of superimposition in growing patients. In general, larger regions of reference result in improved accuracy for voxel‐based registration .…”

“…In recent research, target volumes of reference have been evaluated for each type of superimposition in growing patients. In general, larger regions of reference result in improved accuracy for voxel‐based registration . For general superimposition in non‐growing patients (generally older than age 18), the entire cranial base should be used for maximum accuracy.…”

“…Recent studies have also evaluated regions of reference in the mandible for voxel‐based registration . Three regions were validated, specifically a volume incorporating the internal border of the mandibular symphysis, inferior alveolar canal and follicles of the developing mandibular molars (Figure ).…”