A Study on the Linear and Angular Variability of the Sella-Nasion Reference Line Relative to the True Horizontal Line
Heewook Sohn1 , Janghoon Ahn2
1 Gai Orthodontic Clinic, Seoul
2 Department of Orthodontics, Kangnam Sacred Heart Hospital, Hallym University, Seoul, Korea
Purpose: The sella-nasion line (SNL) has various lengths and angles relative to the true horizontal line (THL), which results in false interpretations of the antero-posterior relationship of the maxilla and mandible. This study aimed to determine the variability of the SNL, commonly used in lateral cephalometric analysis.
Materials & Methods: A total of 109 Korean participants (52 male, 57 female) with a normal profile and occlusion were included in this study. Cone-beam computed tomography images of all participants were acquired in the natural head position (NHP) according to the Solow and Tallgren method. Linear S-N measurements and angular SNL-THL measurements were obtained.
Results: The SNL length and the SNL-THL angle were 65.92±3.03 mm and 8.87±3.64o , respectively, in the male participants and 61.78±2.66 mm and 8.95±4.96o , respectively, in the female participants. There was an effect of sex on the SNL length, but not on the SNL-THL angle. The SNL length in the present study differed significantly from previously reported values, but the SNL-THL angle did not.
Conclusion: The SNL length and SNL-THL angle revealed a variability in Korean adults with a normal profile and occlusion, which is the drawback of SNL as the reference line in lateral cephalometric analysis. To overcome this drawback, the THL has been presented as an alternative to the SNL. Several studies about the THL and NHP have reported excellent results in lateral cephalometric analysis and the measurement of maxillofacial structure.
Key words: NHP, SN line, True horizontal line
Korean J Lingual Orthod 2017;6(1):13-18
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