Three-Dimensional Facial Soft Tissue Response to Premolar Extraction: Influence of Vertical Skeletal Change Analysed Using Geometric Morphometrics.

Abstract

Introduction: The three-dimensional (3D) facial soft tissue response to premolar extraction remains unclear, particularly in relation to vertical skeletal changes.

Methods: Thirty-three adult women who underwent orthodontic treatment with the extraction of four premolars were included. Homologous facial models were generated from facial soft-tissue surface data derived from CBCT images acquired before and after treatment. Principal component analysis (PCA) was performed to characterise variation in facial form using homologous model coordinates. Receiver operating characteristic (ROC) analysis was used to evaluate components nominally associated with pre- and post-treatment configurations within each vertical skeletal subgroup.

Results: Each vertical skeletal subgroup included 11 subjects. In the decreased-FMA group, PC5 showed the largest nominal AUC (0.79), followed by PC3 and PC11 (both 0.75), with morphological variation concentrated in the lower facial region. In the increased-FMA group, PC7 and PC12 showed nominal AUCs of 0.76 and 0.73, respectively, and were associated with lateral facial narrowing and facial slimming. No meaningful nominal discrimination was identified in the stable-FMA group. These findings indicated distinct group-level morphological tendencies depending on the direction of vertical skeletal change.

Conclusions: Three-dimensional facial soft-tissue changes following premolar extraction showed group-level patterns that appeared to vary according to the direction of vertical skeletal change. Patients with decreased FMA tended to show lower facialreorganisation, whereas patients with increased FMA tended to show lateral facial narrowing and facial slimming. Given the modest subgroup size and multiple nominal ROC comparisons, these findings warrant confirmation in larger cohorts.