Natural head position, posture, and prognathism: the Chapman Prize Essay, 1986.

Natural head position and natural head posture are terms which have been used synonymously to describe the spatial relationships of the head with reference to the true vertical, the cervical column, or both. This is confusing, and it would seem logical to ascribe one term to one reference and consider the phenomena separately. For the purposes of this prospective cephalometric survey, natural head position will describe the relationship of the head to the true vertical, while natural head posture will describe the relationship of the head to the cervical column. In order to investigate these two relationships of the head, five groups were formed, three representing horizontal discrepancies selected on ANB differences (class I, II and III dental base relationships) and two representing vertical discrepancies selected on Bjork's posterior angles ('high angle' and 'low angle' groups). Despite the marked differences in 'skeletal' pattern shown between the five groups, the values obtained for the saddle angles (N-S-Ar) showed no significant difference. However, the natural head positions and natural head postures were significantly different (P less than 0.01). Natural head position affected cranial base orientation and this alone produced class II or III effects. Natural head position was also associated with maxillary prognathism whilst natural head posture appeared more closely related to mandibular prognathism. These phenomena may help to explain an apparent class II or III tendency in cases where the saddle angle is normal.