Natural head position and natural head orientation: basic considerations in cephalometric analysis and research.

Natural head position (NHP) provides the key for meaningful cephalometric analysis because an extracranial reference line is used instead of intracranial reference lines, known to be subject to considerable biological variation in their inclination. Although the principle of natural head position is being recognized in the orthodontic literature, its registration may contain an element of unavoidable error that requires correction. A new concept of natural head orientation (NHO) has been introduced to maximize the contribution of NHP to cephalometrics. It is defined as the head orientation of the subject perceived by the clinician, based on general experience, as the natural head position in a standing, relaxed body and head posture, when the subject is looking at a distant point at eye level. The present study was designed to determine the accuracy and validity of NHO, using lateral profile photographs cut in a circular shape, obtained from 27 orthodontic patients, 10-14 years old. Findings among four investigators showed a high correlation (r = 0.82-0.96), in orientating these profile photographs in estimated natural head position (NHP). Moreover, investigators showed good correlation (r = 0.57-0.84) in head orientation after a 3-week interval. Mean differences for the same period varied between 0.1 and 2.9 degrees. The validity of NHO was supported also by a panel investigation. Clinicians as well as auxiliary personnel can be trained to make a critical judgement of the recorded natural head position and correct head orientation, whenever indicated, to enhance the reliability of cephalometric analysis in clinical practice and research.