The Change of ANB- and Gonion-Angle during Ageing

Objectives: The ANB-angle is commonly utilized to describe the sagittal relationship between the maxilla and the mandibula in cephalometric analysis. As there is only few data available on the change of the ANB during the process of ageing for large populations this cross-sectional study should investigate the ANB of orthodontic patients' cephalograms at different stages of life. Additionally the Gn-tgo-Ar (Gonion-) angle as a both sagitally and vertically relevant value was measured. Methods: 10925 cephalograms out of 12147 cephalograms were selected and the ANB- and Gonion-angle were measured. Groups of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ,17, 18, 19 to 24, 25 to 30, 31 to 35, 36 to 50 and 51 to 75 year old patients were formed. Descriptive and comparative statistics were applied to the different groups (SPSS13.0) to show changes and interindividual variabilities for the different ages. Results: The mean value for the ANB (Gn-tgo-Ar) starts at the age of six at about 5,4° (130°) to decrease to about 2° (122°) at the early twenties. Then it increases again to values of about 3° (124°). The 95% confidence interval of the mean value narrows from the age of 5 to 19-24 and broadens with ageing again. Standard deviation and the curve through the mean values followed nearly the same pattern for both the ANB- and the Gonion-angle. The Speaman-rho-test showed high two-tailed significance of correlation between the two angles. Conclusions: This cross sectional investigation shows that there are changes of the mean values and interindividual variability of the ANB- and the Gonion-angle at the different stages of life. It can be concluded that during growth the ANB-angle changed from a skeletal distal to a neutral relationship in the analysed group of orthodontically treated and non-treated individuals.