Soft tissue thickness changes in the lower face following bimaxillary surgery with advancement genioplasty in skeletal Class III malocclusion

BACKGROUND: In patients with skeletal Class III malocclusion, additional genioplasty is frequently required to enhance lower facial esthetics after orthognathic surgery. This study aimed to evaluate soft tissue thickness changes in the lower face before and after bimaxillary surgery with advancement genioplasty in patients with skeletal Class III malocclusion. METHODS: Ninety-four patients were included: 57 patients underwent bimaxillary surgery alone (Group N), and 37 patients underwent bimaxillary surgery with advancement genioplasty (Group G). Changes in hard tissue landmarks and soft tissue thickness before and after surgery were analyzed from reconstructed three-dimensional cone-beam computed tomography (CBCT) images. CBCT images were taken pre-surgery (T0) and at least 6 months post-surgery (T1). Within- and between-group changes were tested with paired and independent t-tests; Pearson correlations assessed associations between skeletal advancement (Pogonion and Menton) and soft tissue thickness. RESULTS: After surgery, soft tissue thickness at Pogonion (Pog–Pog’) increased in Group N but decreased significantly in Group G (− 1.90 ± 3.93 mm; p = 0.006), with a significant intergroup difference (p = 0.014). In contrast, soft tissue thickness at Menton (Me–Me’) did not change significantly in Group N but increased significantly in Group G (3.14 ± 8.87 mm; p = 0.038), with a significant intergroup difference (p = 0.034). Pearson correlation analysis indicated that skeletal advancement was negatively associated with Pog–Pog’ (p < 0.05) and total chin soft tissue thickness (p < 0.01), whereas B–B’ and Me–Me’ showed no significant correlations. CONCLUSIONS: In skeletal Class III patients undergoing bimaxillary surgery with advancement genioplasty, soft tissue thickness decreased at Pogonion and increased at Menton; Pogonion thinning scaled with skeletal advancement. While genioplasty can counteract mandibular setback-related thickening, excessive advancement risks over-thinning. Clinicians should anticipate these responses, calibrate advancement magnitude, and consider selective adjunctive soft tissue procedures.