Natural head posture for horizontal reference planes in lateral cephalometrics

Abstract

Objectives: To find the relationship of common horizontal reference planes with true horizontal plane (TH) in natural head posture of 12-year old Southern Chinese. Methods: The material comprised lateral cephalograms of a random sample of southern Chinese (200 boys: 12.4 year, SD 0.7; 205 girls: 12.5 year, SD 0.38) in Hong Kong. The radiographs were taken in natural head posture and digitized twice. Results: The most commonly use of horizontal reference planes are Sella-Nasion plane (SN), Frankfurt horizontal plane (FH), constructed head posture plane (SN+7°), and Functional occlusal plane (FO). The mean angle between TH to SN is 7.7° (SD 4.8°, range 0.1° to 23.5°), to FH is 4.3° (SD 3.2°, range 0.1° to 16.7°), to SN+7° is 0.7° (SD 4.9°, range -13.9° to 16.5°) and to FO is 13.8° (SD 4.9°, range 0.3.° to 29.1°) respectively. Conclusion: The difference between any of the commonly used reference planes and the true horizontal plane for the individual subject might vary from none to substantial difference.