Background: Accurate prediction of postoperative soft tissue behavior remains a critical challenge in Class III orthognathic surgery. However, existing estimates of soft-to-hard tissue correspondence are largely derived from 2-dimensional analyses or single-modality imaging, limiting their ability to characterize region-specific soft tissue responses after bimaxillary correction.
Purpose: The purpose of the study was to quantify region-specific soft tissue responses to skeletal repositioning following bimaxillary surgery via a hybrid cone-beam computed tomography -3-dimensional stereophotogrammetry approach.
Study design: This retrospective cohort study was conducted at the Department of Oral and Maxillofacial Surgery, Başkent University, between 2020 and 2023. Adult patients with skeletal Class III deformities, who underwent orthognathic surgery, had complete preoperative-postoperative cone-beam computed tomography and 3-dimensional facial scans were included. Patients with prior craniofacial surgery, syndromic conditions, or insufficient follow-up were excluded.
Predictor variables: The magnitude and direction of skeletal displacement at standardized landmarks following bimaxillary correction served as the primary predictor.
Main outcome variables: Primary outcome variables were postoperative soft and hard tissue displacement and soft-to-hard tissue correspondence ratios in the vertical (FH) and sagittal (VP) dimensions for the midface, perioral, and chin regions.
Covariates: No additional covariates were modeled. Age, sex, and surgical movement magnitudes were recorded to characterize the sample.
Analyses: Statistical analyses included paired t tests or Wilcoxon signed-rank tests, with P values adjusted for multiple comparisons using the false discovery rate (FDR) approach, alongside effect size estimation (Cohen's d) and intraobserver reliability assessment.
Results: The study included 20 patients [8 (40%) females; mean age 21.9 ± 2.7 years], with a median follow-up of 8 months (interquartile range, 6 to 9 months). In the chin region, sagittal soft tissue landmarks demonstrated high correspondence with underlying skeletal movements, particularly at pogonion (≈95%). In the sagittal dimension, maxillary advancement was associated with a statistically significant anterior displacement of the subnasale (mean + 2.0 mm; p_FDR = 0.040; d = 0.66) and the upper lip (2.3 mm; p_FDR≈ 0.05; d = 0.61), corresponding to 45 and 73% of skeletal movement at A-point, respectively. Mandibular setback resulted in a significant posterior displacement of B-point (-2.4 mm; p_FDR< 0.05; d = -0.55). All the significant measurements demonstrated good to excellent reliability (intraclass correlation coefficient≈ 0.75 to 0.95).
Conclusion: Soft tissue responses to skeletal repositioning following Class III bimaxillary surgery varied by anatomic region. Sagittal skeletal movements were more consistently reflected in the chin and perioral soft tissues, whereas nasal soft tissues demonstrated attenuated and variable responses.
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