Anteroposterior Movements of the Chin: Descriptions and Predictions

Purpose: To statistically evaluate circumpubertal changes in AP chin position and to predict the AP changes in chin position based on morphological indicators previouslyused to successfully predict true rotation. Method: A mixed-longitudinal sample of200 untreated subjects from the Montreal Growth Study was utilized, including 97females and 103 males between 10-13 and 12-15 years of age, respectively.Multilevel models were used statistically to determine the shape of the individuals' growth curves for the SNB and SNPg angles, and SPgH (horizontal mm movement ofpogonion from sella). Bivariate and multivariate analyses were performed todetermine the associations between the changes of these three outcomes variables and11 morphologic characteristics previously used to predict true mandibular rotation.The multiple regression equations were developed based on a randomly selected sample of 150 subjects; the remaining 50 subjects were used to validate the equations.The bivariate associations between the 3 outcomes and seven subjective morphologiccharacteristics of mandibular rotation were also evaluated. Results: SNB and SNPgangles showed small but consistent and statistically significant (p≤.05) increases overtime. Horizontal movements of the chin as measured by SPgH showed greater changes over time, but the patterns were also linear. Males were significantly moreprognathic than females and showed statistically greater rates for forward chinmovements than females. Bivariate correlations showed that, compare to subjects