A longitudinal study of the reproducibility of NHP

Objective: To investigate the reproducibility of nature head position (NHP) among the long facial type(LFT), short facial type(SFT) and average facial type(AFT) over time.Method: The material consisted of lateral cephalograms of 30 female subjects, taken at 6, 9, 12, 15, 18 years in nature head position. These subjects were selected randomly and divided into three groups based on the MP-SN angle at approximately 15years of age. Serial cephalometric roentgenograms traced upon the superimposition method based on the "best fit" of anterior cranial base structures. Results: 1) The craniovertical angles (NSL/VER) and craniocervical angles(NSL/CVT, NSL/OPT) in three facial types from 6 years to 18 years of age are stable and consistent. 2) the cervical inclinations angles(OPT/HOR,CVT/HOR) in three facial types from 6 years to 18 years of age are stable and consistent, except for the 6 to 12-year interval for the CVT/HOR angle in LFT. 3) the cervical lordosis angle (CVT/OPT) is stable and consistent, except for the 6 to 9-year inerval in SFT. 4) there were no significant differences in the change in NHP among three facial types.Conclusion: Irrespective of facial patterns over the age period 6 to 18 years in females, NHP is stable over time.