Abstract

Introduction: The purpose of this study was to predict the lip changes in Class I adolescents and adults following non-extraction orthodontics treatment.

Methods: This longitudinal retrospective study evaluated the pre- and post-treatment lateral cephalograms of 40 adults and 72 adolescents with Angle Class I molar relationships and crowding in both arches. The horizontal and vertical changes of 15 landmarks, along with lip thickness and taper, were evaluated. The sample was randomly divided into two group; 76% of the subjects were used to develop the multivariate regression formulas; the remaining 24% served as a validation sample.

Result: Adolescent lips moved inferiorly and anteriorly during treatment; adult lips showed lesser inferior movement, little or no anterior movement and decreases in thickness. Males demonstrated significantly greater inferior and, mostly, greater anterior changes of lip position. The multivariate regressions explained 48-59% and 41-69% of the vertical and horizontal variation of the lip changes, respectively. When the prediction equations were applied to the validation sample, with correlations ranged from 0.60-0.84, indicating external validity.

Conclusion: The lip changes of Class I adolescents and adults treated with non-extraction orthodontic treatment can be predicted with fair to moderate accuracy. Adults’ lips became compressed and thinner, while the upper lip thickness of adolescents did not change or become slightly thicker.