Changes in facial profile during orthodontic treatment with extraction of four first premolars

The present study was designed to evaluate soft tissue profile changes after the orthodontic treatment of class I bimaxillary dentoalveolar protrusion in adult cases. Pre- and post-treatment cephalograms of 20 Caucasian female class I bimaxillary dentoalveolar protrusion patients were selected from private practice. All of them were treated by extraction of four first premolars, and banded and bonded by 022 × 028 standard edgewise technique. t-Test was used to analyze pre- and post-treatment cephalograms. This study showed that upper and lower lip protrusions were decreased respectively 2.7 ± 2.9 mm (p < 0.001) and 2.8 ± 2.8 mm (p < 0.001). The mean changes of upper and lower lip thickness and length, as well as nasolabial and labiomental angles were not significant. Significant positive correlation was found between changes of maxillary and mandibular incisors with changes in upper lip (r_UI = 0.70, p < 0.001, r_LI = 0.59, p < 0.006) and the lower lip positions (r_UI = 0.64, p < 0.002, r_LI = 0.72, p < 0.001). By using stepwise regression it was found that a ratio of 0.63:1 was obtained between upper lip retraction and maxillary incisor retraction and a ratio of 0.62:1 was obtained between lower lip retraction and mandibular incisor changes. This study concluded that, a strong correlation exists between anterior tooth retraction and the position of both lips.