Glenoid Fossa Displaces Backward and Downward During Growth

Objectives: To examine the general relationship between mandibular growth and chin prominence during growth. Methods: As part of a general study examining determinants of changes in chin prominence during human growth we examined coordinate and angular data from a previously reported longitudinal study of Angle Class I and Class II children between the ages of 8.5 and 15.5 years. (JDR V86 Abstract 2995) This report focuses particularly on the displacements of Condyle within the glenoid fossa.  The data are from serial lateral cephalograms for a smoothed sample of 21 boys and girls and are reported relative to superimposition on anterior cranial base in the Frankfort frame of reference. Results:  Data for a selected subset of relevant parameters are reported in Table1. For each parameter, actual values are reported at 8.5 years and subsequent growth changes (Mean±1sd in millimeters, N=21) are reported at subsequent time points. Over the full 7 year time period all values except Y displacements of Nasion are statistically significant at the p<0.001 level.

Conclusion: In this sample, the backward displacement of Condyle is greater than the forward displacement of Nasion, offsetting to some extent the increase in body length as a contributor to the final forward positioning of Pogonion. In terms of chin prominence in the facial profile, the forward positioning of Nasion must be subtracted from the forward positioning of Pogonion.