Radiographic profile of the first cervical vertebra.

Lateral cephalographs from 220 normal adolescent white orthodontic patients, and of individuals with craniofacial dysostosis and oculodento-osseous dysplasia were studied. Variations were observed in the morphology of the posterior margins of the superior articular processes, vertebral artery canals being present in 8%. Posterior arch dehiscence was found in eight individuals, including seven cases in the midline. Three patients had accessory ossicles above the posterior arch of the atlas, and two showed evidence of fusion of the second and third cervical vertebrae. The profile of the atlas was well outside the normal range in both syndromes studied.