Cranial base, maxillary and mandibular morphology in Down syndrome

To test the null hypothesis that there is no difference between craniofacial measurements of individuals with Down syndrome (DS) and normal controls.

A cephalometric analysis including additional landmarks and measurements to study specific craniofacial features was undertaken on pretreatment cephalograms of 25 patients with DS (12 male, 13 female; mean age 15.1 years) treated at The Hospital for Sick Children, Toronto. Measurements were compared with those from cephalograms of racial groups age and gender matched, normal, Class I children, available from the Burlington Growth Center. Data were analyzed using paired t-tests.

Large reductions were measured in the size and spatial relationships of craniofacial structures in the DS group. The greatest differences included a larger cranial base angle; reduced elevation of sella from FHP; reduced anterior and posterior cranial base lengths; reduced anterior and posterior face heights; smaller maxilla with reduced anterior basal and apical dimensions; and smaller mandibular ramus, body and symphyseal dimensions and proclined symphysis. Maxillary incisors were severely proclined and undererupted, while mandibular incisors were undererupted. Alveolar heights were reduced. Anterior open bite was frequently noted. Maxillary and mandibular planes exhibited forward rotation patterns, promoting overclosure. Mandibular hypoplasia was less severe than cranial base and maxillary hypoplasia. Hypodontia of one or more permanent teeth was found in 92% of the sample.

The null hypothesis was rejected. Significant hypoplasia in endochondral, mesodermal, and ectomesenchymal derived structures of the cranium and face in subjects with DS was clearly evident. More severe platybasia than previously reported was found.