Objective The purpose of this retrospective cephalometric study was to compare changes of the upper lip soft tissue in patients with Class Ⅰ malocclusion after extraction of either first premolars or second premolars. Methods The pretreatment and posttreatment records of 50 patients were used in the study. And 25 patients involved extraction of first premolars and 25 patients involved the extraction of second premolars. The lateral cephalometric radiographs taken before and after treatment were traced and measured. 15 typical values of soft tissue were measured in Winceph 7.0 software and statistical analysis was carried by SPSS 10.0 software. Results 1）The horizontal and vertical lines were not significant different in the two extraction group before the treatment. But after the treatment the vertical changes of upper lip（A′-X, UL-X） were more apparent in the second premolar extraction group （P0.05）. Conclusion The upper lips both changed remarkably after the treatment and there was no significant difference between the two premolar extraction groups.
