Longitudinal post-eruptive mandibular tooth movements of males and females

Unbiased estimates of post-eruptive eruption and migration of the mandibula r teeth for large representative samples are presently unavailable. The pur pose of this study was to evaluate pure tooth movements of untreated childr en and adolescents longitudinally. Lateral cephalograms of 214 French-Canad ians, followed bi-annually between 8 and 15 years of age, were traced, and the positions of the mandibular permanent central incisors and first molars were digitized. Temporal changes in tooth position were evaluated relative to naturally stable mandibular reference structures, using the mandibular reference line for orientation. The statistical analyses included t-tests t o assess gender differences and Pearson product-moment correlations to eval uate associations. The results showed that the incisors proclined significantly more for males (6 degrees) than females (3 degrees). The incisor tips displayed early mes ial movements that were countered by later distal movements. The incisor ap ex showed a consistent pattern of distal migration between 8 and 15 years. Mandibular arch length decreased over the 7-year observation period. Rates of mesial molar migration accelerated until 11 years of age and then decele rated. There was no significant change in the mandibular occlusal plane ang le between 8 and 15 years of age. Incisor eruption showed the greatest rate s during adolescence, attaining peaks at approximately 12 years for females and 14 years for males. The molars erupted approximately 5 mm between 8 an d 15 years of age. The greatest gender differences occurred at the older ag es, with males showing greater eruption potential than females. It was concluded that the mandibular teeth show significant migration and e ruption during childhood and adolescence, with gender differences in the am ount, direction, and timing of movement.