The reproducibility of natural head posture: a methodological study.

Current clinical interest in natural head posture (NHP) derives from studies correlating NHP to craniofacial morphology, future growth trends, and to respiratory needs. It has also been argued that NHP is the logical reference and orientation position for craniofacial analysis and the publication of illustrations. The individual or group is presented as they naturally appear in life. Hence, lateral cephalometric radiographs recorded routinely in NHP would be more meaningful for the clinician. Underpinning all these potential clinical benefits is the incompletely answered question of the clinical reproducibility of NHP. In this study a natural head posture, the orthoposition, was defined and standardized for clinical use. The effects of ear posts, an external source of eye reference (a wall mirror), sex and time were evaluated in relation to the reproducibility of recording lateral cephalometric radiographs in this natural head posture. The sample comprised 217 randomly selected 12-year-old Chinese children in Hong Kong. Boys looked up more when changing from the self-balance position to the mirror eye reference position (mean change 2 degrees, P less than or equal to 0.001). No other significant male-versus-female differences were detected. NHP reproducibility was better with a mirror (with mirror, method error = 1.9 degrees, without mirror, method error = 2.7 degrees). No significant differences in reproducibility were detected between NHP recordings taken with and without ear posts. However, without ear posts the radiographs tended to be of poor quality. The reproducibility of same-day repeat radiographs recorded with ear posts and with a mirror (after 4 to 10 minutes and 1 to 2 hours) was 1.9 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)