Soft-tissue thickness changes following bimaxillary surgery in skeletal class II malocclusion

Abstract

OBJECTIVES: This retrospective cohort study evaluated regional facial soft-tissue thickness changes after bimaxillary surgery in skeletal Class Ⅱ patients and assessed their associations with skeletal movement and patient-related factors. MATERIALS AND METHODS: Class Ⅱ patients treated with bimaxillary advancement surgery without genioplasty were included. Postoperative CBCT scans, acquired 16.7 ± 5.3 months after surgery, were registered to the corresponding preoperative scans using voxel-based superimposition. Skeletal displacement and corresponding overlying soft-tissue thickness were assessed at subspinale (A), supradentale (Sd), infradentale (Id), supramentale (B), pogonion (Pog), and menton (Me). Soft-tissue thickness was defined as the linear distance between each hard-tissue landmark and its corresponding soft-tissue landmark. Skeletal displacement was measured at the corresponding hard-tissue landmarks. RESULTS: 89 patients were enrolled, 33 male and 56 female, mean age of 30.3 ± 10.3 years. Significant postoperative soft-tissue thinning was observed at A (0.40 ± 1.51 mm), Id (2.20 ± 2.11 mm), B (0.33 ± 1.30 mm), and Pog (0.48 ± 1.29 mm), whereas soft-tissue thickness at Sd and Me did not change significantly. Pearson correlation analysis indicated that thickness changes were not associated with age, sex, or CBCT interval. Larger sagittal advancement at A and Id was associated with more pronounced thinning of the corresponding soft tissue (A: r = -0.650, p < 0.001; Id: r = -0.338, p = 0.001), with ratios of thinning to movement of 0.20 and 0.30, respectively. In contrast, larger downward vertical movement of B was associated with less thinning at B (r = 0.240, p = 0.023), with a ratio of thinning to downward movement of 0.05. CONCLUSION: Bimaxillary surgery in skeletal Class II patients without genioplasty resulted in region specific soft-tissue thinning, particularly affecting the lower lip. CLINICAL RELEVANCE: Postoperative soft-tissue thinning should be considered during surgical planning and patient communication.