Bases for the analysis of cephalometric radiographs: intracranial reference structures or natural head position.

The inherent variability of intracranial cephalometric reference structures makes analysis based upon them potentially misleading with serious implications for orthodontic and orthognathic surgical treatment planning. These problems can be avoided by using natural head position and relating measurement to the true horizontal. The lack of suitable norms has been a barrier to this approach. This paper demonstrates that norms can be derived from existing data, enabling the clinical application of analyses related to the true horizontal.