Aims: (1) To determine the variability of S-N and Frankfort planes, (2) to establish the reproducibility of natural head position, (3) to establish norms for five cephalometric parameters in natural head position. Materials and methods:A sample of 31 young adults from dental student population was selected under certain criteria. Two lateral cephalograms in natural head position (NHP) for each subject were taken within a span of 5 to 10 minutes following standardized procedure. All cephalograms were developed and traced by the same clinician under standard conditions. A true horizontal line drawn on film was transferred to tracing paper.The conventional cephalometric planes were drawn. Subsequently, five angles were measured between true horizontal (HOR) and these conventional cephalometric planes. Results:The above observations were subjected to statistical analysis to establish the variability of conventional intracranial reference planes and consistency of NHP. Statistical norms for five cephalometric parameters with respect to NHP were also established. Conclusion:Since there is considerable variation in the inclination of conventional S-N and FH planes, a true horizontal extracranial reference line in NHP should substitute, or at least supplement, the use of intracranial reference planes for efficient orthodontic diagnosis and treatment planning. The new norms established for the five cephalometric parameters provide data that more closely describes morphology as it appears in real life. Hence, this data is more meaningful in clinical practice.

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