Associations between atlantoaxial and craniomandibular anatomy.

Roentgen-cephalometric studies have shown that anatomical features of the craniocervical junction are associated with head posture, cranial base angulation, and mandibular shape and growth. The aim of the present work was to study relationships between atlantoaxial and craniofacial morphology based on macroscopical observations of skeletal material derived from 38 prehistoric Polynesian and 53 prehistoric Thai people. The two uppermost cervical vertebrae and the mandible of each individual were studied macroscopically and each skull base was analyzed on cephalometric X-rays in lateral projection. The height of the atlantal anterior and posterior arches displayed a significant negative correlation with the cranial base angulation, in that the higher the arches the steeper the flexure between the sphenoidal/clival and clival/foraminal planes. None of the axial variables were associated with the cranial base angulation. The height of the atlantal posterior arch was also associated with the mandibular length, ramal height and gonial angle. Thus, in general, a high arch was seen in conjunction with a long, high and square shaped mandible, whereas a low arch was usually found together with a short and low mandible characterized by an obtuse jaw angle. The anterior height of the axis (vertebral mass + dens) was significantly associated with mandibular length and ramal height. It is suggested that these results are evidence of the intimate ontogenetic development of the atlas and the cranial base, and a reflection of the functional relationship between atlas and cranium.