Objective: This retrospective study was designed to show likely upper incisal and soft tissue lip changes accompanying Class II fixed appliance treatment with only two upper premolar extractions and to assess whether the lips, especially, are predictably and directly affected with such treatment.
Materials and Methods: Pretreatment and posttreatment lateral cephalograms and study casts from 61 growing Class II patients (aged 11 to 18 years; 39 division 1 and 22 division 2) were assessed. Upper and lower lip curve depths, nasolabial angle, and upper incisal position and angulation were all assessed and compared with changes in other cephalometric variables.
Results: A wide range of individual response in both lip and upper incisor behavior were noted. The observed soft tissue lip changes were most likely to be related to the preexisting morphology of the lips themselves, while upper incisal changes were mainly related to their own pretreatment positions and changes occurring with treatment in the underlying bony structures.
Conclusion: Orthodontic treatment involving the extractions of only two upper premolars is likely to result in a wide range of variation in lip and upper incisor behavior. The preexisting soft tissue morphology is likely to be the greatest determinant of lip behavior.