Diagnosis and treatment outcome of facial asymmetry according to the maxillary roll pattern

Abstract

Facial asymmetry is one of the common craniofacial deformities, which requires 3-dimensional analysis for accurate diagnosis and correct treatment planning. Inclination of frontal occlusal plane (FOP) and lateral menton deviation are the main manifestations of the asymmetry of the maxilla and mandible, respectively. The FOP tends to incline toward the ipsilateral side of menton deviation, but there are patients whose FOP inclined toward the contralateral side of menton deviation. This study was performed to investigate morphological differences between the ipsilateral type of facial asymmetry, whose FOP inclined toward the same side of the menton deviation, and the contralateral type, whose FOP inclined toward the opposite direction, by using cone beam computed tomography (CBCT) images. Additionally, this study aimed to compare treatment outcomes of the two types of facial asymmetry. This retrospective study included a contralateral group (n = 12; 8 men and 4 women; mean age, 21.8 ± 2.2 years) and an ipsilateral group (n = 12; 8 men and 4 women; mean age, 21.2 ± 4.3 years). The subjects in the contralateral group were selected from a total of 296 patients who had been diagnosed as skeletal Class III malocclusion and facial asymmetry, had undergone bi-maxillary orthognathic surgery, and had taken serial CBCT before (T0), 1 month after (T1), and one year after (T2) surgery. The subjects in the ipsilateral group were selected from the same archive by matching age, gender, and degree of FOP cant with those in the contralateral group. CBCT images were reconstructed, and deviated and nondeviated sides were defined according to the menton deviation. Measurements for linear distance, angle, volume, and area were performed and compared between the deviated and nondeviated sides in each group and between the ipsilateral and contralateral groups 1. In the contralateral group, the mandibular body of the nondeviated side was longer than the deviated side (p = 0.024). 2. In the contralateral group, the asymmetry of vertical elements such as distances from the horizontal reference plane to gonion (p < 0.01) and mental foramen (p = 0.044) was more evident than that of horizontal elements such as distances from the midsagittal plane to gonion (p = 0.744) and mental foramen (p = 0.224). 3. Despite an improvement of facial asymmetry after the surgery in both groups, the improvement of menton deviation in the contralateral group was not statistically significant (p = 0.265). 4. In the contralateral group, the difference of hemi-lower facial area before surgery between deviated and nondeviated sides increased even after the surgery and did not improve one year after the surgery. 5. There were no other significant differences in the changes during retention period between the two groups. There were skeletal morphological differences between the two groups before surgery. The existing asymmetry was improved after surgery in both groups, but in the contralateral group, there was remained asymmetry in some aspects even after the surgery. Therefore, orthognathic surgery in the contralateral group should be planned to improve the vertical asymmetry rather than horizontal asymmetry and to prevent the horizontal asymmetry from being worsened after surgery. Moreover, clinicians should pay attention to the possibility of increase in the difference of bilateral hemi-lower facial area after surgery and consider the need of additional surgery when treating the contralateral type of asymmetry.