Evaluation of Lip Cant Change by 2-Jaw Surgery in Class III Asymmetry Cases Using Three-Dimensional Facial Scan in Conjunction With Computed Tomographic Images:

The aim of our study was to evaluate the effect of cant correction in the anterior (AMXTOP) and posterior maxillary transverse occlusal planes (PMXTOP) on the change in lip cant (LC) using three-dimensional facial scan (FS) in conjunction with computed tomographic (CT) images. Thirty-five class III asymmetry patients treated with 2-jaw surgery were selected. Three-dimensional CT and three-dimensional FS images were taken before (T1) and after orthognathic surgery (T2). After obtaining the same head orientation between 2 images, bracket slot midpoints of the maxillary right and left canines as well as the first molars, point A, point B, and menton on three-dimensional CT images and the right and left lip commissures on three-dimensional FS images were located. Linear and angular variables of AMXTOP, PMXTOP, and LC were measured and statistically analyzed. At the T1 stage, linear and angular LC showed significant correlations with linear and angular cant of AMXTOP and PMXTOP, as well as menton deviation (all P < 0.001). During T1 to T2, significant linear and angular cant corrections were observed: ΔAMXTOP (1.3 mm, 1.9 degrees), ΔPMXTOP (1.9 mm, 1.7 degrees), and ΔLC (1.5 mm, 1.8 degrees) (all P < 0.001). Although angular change ratios of ΔLC/ΔAMXTOP and ΔLC/ΔPMXTOP did not exhibit a significant difference (1.0 vs 0.7), linear change ratio of ΔLC/ΔAMXTOP was higher than that of ΔLC/ΔPMXTOP (3.0 vs 0.5, P < 0.05). The vertical change in commissures was related to that in the maxillary right and left canines or maxillary right and left first molars and the extent of mandibular setback (all P < 0.01). To conclude, the use of three-dimensional FS images in conjunction with three-dimensional CT can provide more accurate information for changes in AMXTOP, PMXTOP, and LC.