Background: The aim of this study was to verify the intra-individual reproducibility of natural head position (NHP) in centric relation (CR) position, to prove the inter-individual differences in the Frankfort horizontal plane and sella-nasion line compared with the true horizontal line, and to establish linear norms from A-point, B-point, Pog as well as soft tissue A-point, soft tissue B-point, and soft tissue Pog to nasion true vertical line (NTVL) in adult Indian subjects.
Methods: Lateral cephalograms (T1) of Angle's Class I subjects were taken in NHP and with bite in CR. A second lateral cephalogram (T2) of these subjects with ANB angle in the range 1-4° were taken after 1 week using the same wax bite and both the radiographs were analyzed based on six angular parameters using cephalometric software (Do-it, Dental studio NX version 4.1) to assess the reproducibility of NHP. Linear values of six landmarks were taken in relation to NTVL, and the mean values were calculated. A total of 116 subjects were included in this study.
Results: When the cephalometric values of T1 and T2 were analyzed, it was found that, the parameters showed a P < 0.001, indicating the reproducibility of NHP in CR. Mean values for point A, point B, Pog and their soft tissue counterparts were also obtained.
Conclusion: The study proved that NHP is a reproducible and accurate when recorded with the mandible in CR. Linear norms for skeletal Class I subjects in relation to NTVL were established.
Keywords: Centric relation; nasion true vertical line; natural head position.