Determinants of successful treatment of bimaxillary protrusion: orthodontic treatment versus anterior segmental osteotomy

The purpose of this study was to investigate the differences in initial skeletal, dental, and soft tissue characteristics of bimaxillary protrusion (BP) patients to determine poor or good results with orthodontic treatment (OT) or anterior segmental osteotomy (ASO) with extraction of four first premolars. Lateral cephalometric radiographs of 46 adult Korean females with BP were analyzed before treatment (T0) and after treatment (T1). According to the measurements at T1, patients were classified into group 1 (poor result with OT, n = 12), group 2 (good result with OT, n = 11), group 3 (poor result with ASO, n = 5), and group 4 (good result with ASO, n = 18). Sagittal, vertical, dental, and soft tissue variables were measured. The differences at T0 among the four groups were compared by one way analysis of variance test and verified by Scheffe's multiple comparison test. Stepwise discriminant analysis was performed to find decisive predictors. Skeletal class II malocclusion tendency, less developed chin, and vertical facial growth pattern were related with group 1. Overly uprighted and less protrusive upper and lower incisor, near normal interincisal angle (IIA), less protrusive upper lip, and more obtuse lower nasolabial angle (NLA) were related with group 3. IIA, U1-NA distance, combination factor, interlabial gap, lower NLA, pterygomaxillary fissure-N, and posterior nasal spine-anterior nasal spine were selected as significant variables for discriminating the four groups. The percentage of correctly classified cases was 91.3%. In particular, the discriminant function showed the highest accuracy in the prediction of group 4. These variables and discriminant functions contributed to the differential diagnosis on BP to make a procedural decision between OT and ASO.