Evaluation of Soft Tissue Compensations in Subjects With Facial Asymmetry Using Cone Beam Computed Tomography (CBCT): A Retrospective Study

Introduction Facial asymmetry influences aesthetics and can involve either hard or soft tissues or both. Underlying skeletal asymmetry can be compensated by differential expression of soft tissue thickness on either side. Orthognathic surgical planning needs to take the interaction between the hard and soft tissues into account. The aim of this study was to assess the bilateral thickness of hard tissues and the corresponding facial soft tissue in asymmetric subjects to assess the compensation using cone beam computed tomography (CBCT) imaging. Materials and methods CBCT measurements of 30 skeletal Class l asymmetric untreated patients with menton deviation greater than 4 mm were included in the study. The side towards which the menton deviated was considered as the deviated side and taken as the control group (GC). The contralateral side of the menton deviation was considered as the non -deviated side and was taken as the test group (GT). The greatest width of both hard and soft tissues was measured at the head of the condyle; the centre of the ramal upper, middle, and lower thirds; furcation of the first molar; and apices of the first premolar and canine. Each landmark was precisely positioned on all three planes and the measurements were correlated. An independent t -test compared the difference of both hard and soft tissues between deviated and non -deviated sides. The correlation between the hard and soft tissues of both non -deviated and deviated sides was performed using the Pearson correlation two -tailed test. Results In the condylar and mid ramal regions, significant differences between the hard and soft tissues were noted in the GT (p < 0.05). In the non -deviated side, at the condylar region, it was noted that with an increase in hard tissue thickness, there was a decrease in soft tissue thickness, while in mid and lower ramal regions, it was noted that with a decrease in hard tissue thickness, there was an increase in soft tissue thickness. No significant difference was seen in the tooth -bearing section of the mandible (p > 0.05). Pearson's correlation showed a highly significant negative correlation between the hard and soft tissues of the GT at the level of the condyle and the ramus (p < 0.05). Non -significant correlation was seen between the hard and soft tissues at the molar, premolar and canine areas of the GT. No significant correlation between the hard and soft tissues was seen at any level in the GC (p > 0.05). Conclusion In the non -deviated side, the non -tooth -bearing segment of the mandible (condyle and ramus) showed differences between the hard and soft tissue thicknesses. With an increase in the hard tissue thickness, there was a corresponding decrease in the soft tissue thickness and vice versa which is attributed as compensation. The tooth -bearing segment of the non -deviated side did not show compensation. There is no compensation seen on the deviated side in both segments.