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

Abstract

Objective: The aim of this 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.

Materials and Methods: Thirty-five class III asymmetry patients treated with two-CT surgery were selected. Three-dimensional CT and three-dimensional FS images were taken before (T1) and after orthognathic surgery (T2, mean= 5.5 ± 1.6 months). 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 AMXOP, PMXOP, and LC were measured and statistically analyzed.

Results: 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-T2, significant linear and angular cant corrections were observed: △AMXTOP (1.3mm, 1.9°), △PMXTOP (1.9mm, 1.7°), and △LC (1.5mm, 1.8°) (all P < 0.001). Although angular change ratios of △LC/△AMXTOP and △LC/△PMXTOP did not exhibit a significant difference (1.0 vs. 0.7), linear change ratio of △LC/△AMXTOP was higher than that of △LC/△PMXTOP (3.0 vs. 0.5, P < 0.05). The vertical changes in commissures were related to that in MXC or MXM1 and the extent of mandibular setback (all P < 0.01).

Conclusion: The three-dimensional approach using three-dimensional FS images in conjunction with three-dimensional CT revealed more precise change ratio of △LC/△AMXTOP and △LC/△PMXTOP than traditional two-dimensional approach. With the linear regression analysis, the vertical positions of lip commissures were shown to be related to the vertical change in the maxillary teeth and the setback amount of mandible.