Labial Changes After One or Two Step Incisor Retraction

Objectives: To evaluate and to compare labial changes according to two standard protocols of space closure after premolar extraction.
Methods: Sample consist of lateral cephalometric radiographs originate from 48 patients with Class I malocclusion and biprotrusion treated with four first premolar extraction. The sample received standard fixed orthodontic treatment and by aleatory allocation, half of them (n=23) had their space close in one step (G1) and other half (n=23) had their space closed in two steps (G2). Cephalometric tracing of the pre-retraction (t1) and post-retraction (t2) were manually obtained by one operator and cephalometric points were digitalized in the software DFPlus^R (blinded for group and retraction phase). Were evaluated upper and lower incisor inclination, upper and lower lip protrusion, thickness and length, and nasolabial and mentolabial angles. After checking the normal distribution and homogeneity of variance (Levene test) of the t2-t1 variables, the t test for independent samples were applied at the 95% confidence level.

Results: There were no significant difference for upper incisor retraction among groups (mean of 13,6 ± 5,8 degrees) followed by upper lip retraction of 1,3±1,3mm and thickness decrease 1±1,5mm. The two step retraction produced significant greater lower incisor retraction than one step retraction (12,4±1,0mm for group 2 and 8,8±1,0mm for group 1) although without lower lip retraction (3,4±2,2mm) and thickness (1,7±1,7mm) significant differences among groups.
Conclusions: Lower incisor retraction is greater in two step than in one step retraction but the lower labial changes were not different. Upper incisor retraction and the upper labial changes were not different in the two treatment protocols.