[Longitudinal study of the stability and reproducibility of natural head position in adolescents with different facial types over time].

PURPOSE

The aim of this study was to investigate the stability and reproducibility of natural head position (NHP) in adolescents with three different facial types.

METHODS

The material consisted of intact lateral cephalograms of 30 male subjects and 30 female subjects, taken at 6, 9, 12, 15, 18 years in NHP. These subjects were selected randomly and divided into three groups based on the MP-SN angle at approximately 15 years of age. Serial cephalometric roentgenograms traced upon the superimposition method based on the "best fit" of anterior cranial base structures. The changes of NSL/VER angulation were analyzed statistically.

RESULTS

The standard deviation of the NSL/VER angulation at 6 year occasion, the mean incremental values, the standard deviation and the method error of NSL/VER angulation during the period from 6 years occasion to any other occasion were larger, the coefficient of reliability was much more lower than the others. The standard deviation and the mean incremental values among 9-year, 12-year, 15-year and 18-year occasions were lower. The coefficient of reliability range from 76% to 97% and the method error at these six periods ranged from 1.84 degrees to 3.48 degrees in three facial types. There was different natural head position in three different facial types with cross-sectional comparison. The angulation in LFT was significantly larger than AFT and HFT, and the values in HFT were the smallest. However, there were no significantly statistical differences in three facial types as the change magnitude of NHP over time was compared.

CONCLUSIONS

These suggest that the NHP of children at 6 years occasion or during the period from 6 years to 9 years of age is highly variable and this situation should be paid attention on while the facial growth studies and the cephalometric radiogram are made. The variance of NHP during any periods from 9 years to 18 years of age in three facial types (3.4 degrees to 12.1 degrees ) is much more less than the variance of intracranial reference planes to the vertical (25 degrees to 36 degrees ). Cephalometric analyses upon NHP in different facial types among these four occasional radiograms are rather highly valid. Supported by Research Fund (No.300411) from Zhejiang Province.