Abstract: PURPOSE: To investigate the correlation between maxillary sagittal rotation and nasolabial soft tissue morphological changes during bimaxillary orthognathic surgery in patients with skeletal Class III malocclusion through accurate three-dimensional CT measurements in a small homogeneous patient cohort, so as to provide clinical evidence for surgical planning and postoperative soft tissue prediction. METHODS: A retrospective study was conducted on 21 patients with skeletal Class III malocclusion who underwent bimaxillary orthognathic surgery at our hospital from January 2017 to December 2024. Maxillofacial CT data were collected at 1 week preoperatively, 3-5 days postoperatively (after removal of drainage devices, defined as short-term postoperatively), and 12 months postoperatively, and imported into Mimics 21.0 software for three-dimensional reconstruction. The APP plane [constructed based on point A and the midpoints of the posterior edges of bilateral maxillary palatal plates PNS(l, r) on three-dimensional models] was innovatively introduced to quantify maxillary sagittal rotation, and three-dimensional displacements of hard and soft tissue landmarks were measured. The overall correlation between maxillary sagittal rotation and nasolabial soft tissue changes was observed. The patients were further divided into clockwise rotation group and counterclockwise rotation group according to postoperative changes in the APP-FH angle. Paired t test, Pearson/Spearman correlation analysis, and partial correlation analysis were performed using SPSS 27.0 software package. The confounding influence of mandibular movement on soft tissue was eliminated by controlling mandibular plane angle(MPA) and mandibular body length (Go-Gn). RESULTS: The APP plane showed favorable stability at different postoperative time points and could accurately reflect the magnitude of maxillary sagittal rotation. The maxillary rotation amount (ΔAPP-FH) was moderately negatively correlated with the horizontal displacement of Point AI(alar point) and Point Cm (columella point)(P<0.05). Partial correlation analysis indicated that this effect was jointly influenced by anteroposterior mandibular movement. Clockwise maxillary rotation independently affected the vertical displacement of point AI and the sagittal displacement of point Ch (cheilion) and point LL' (lower lip edge) (P<0.05). No significant correlation was found between counterclockwise maxillary rotation and soft tissue changes(P>0.05). CONCLUSIONS: The APP plane is a reliable osseous reference plane for evaluating maxillary sagittal rotation. Clockwise maxillary rotation exerts significant influence on nasolabial soft tissue independent of mandibular movement, whereas counterclockwise rotation shows no significant effect on soft tissue.

Key words: Orthognathic surgery, APP plane, Skeletal Class Ⅲ malocclusion, Nasolabial soft tissue, Three-dimensional measurement