Bimaxillary protrusion in the Caucasian: a cephalometric study of the morphological features.

The skeletal morphology of bimaxillary dental protrusion has been investigated in a comparative cephalometric study. Because this is considered a subset of Class I malocclusions, the null hypothesis is that there should be no significant skeletal differences between this group and a Class I control group. There were 30 Caucasians in each group with no bias for age and sex differences between them. Eighteen radiographic landmarks were identified from which 33 skeletal, dental and soft tissue parameters were computed. The bimaxillary group had an average interincisal angle of 115 degrees versus the controls 135 degrees, and showed the following morphological features which persisted over a 5-year growth period: A shorter posterior cranial base. A longer and more prognathic maxilla. Similar mandibular dimensions and prognathism. A mild Class II skeletal pattern. A smaller upper and posterior face height. Diverging facial planes. A procumbent soft tissue profile with a low lip line. These findings indicate that there is a distinctive difference between the underlying skeletal patterns found in the two groups.