RESUMEN
OBJECTIVE: This study aimed to verify the intra-individual reproducibility of the natural head position (NHP) in adult Korean patients in the centric relation (CR) position and to prove the inter-individual variability of the Frankfurt horizontal (FH) plane and sella-nasion (SN) line compared to the true horizontal line (THL). In addition, the study aimed to investigate the correlations between linear measurements from A-point and B-point to the nasion true vertical line (NTVL) and angular measurements from A-point and B-point to the SN line. METHODS: Two lateral cephalograms were taken of 116 subjects (23 males, 93 females) with CR wax bites in a NHP at a one-week interval. RESULTS: Method errors of three variables and intraclass correlation coefficients of six parameters proved the intra-individual reproducibility of NHP (p 0.05), but it was clinically variable (SD 3.89degrees) on the inter-individual level. Conversely, the angle of the SN line to the THL was significantly different from 7degrees (p < 0.05). Very low correlation was found between the linear measurements and angular measurements of A-point and B-point (p < 0.01). CONCLUSIONS: The NTVL could be a useful reference line for assessing the antero-posterior position of the maxilla and mandibleof Korean adult patients in NHP and CR.