UCLA

Introduction:Craniofacial microsomia (CFM) is the second most common craniofacial congenital defect after cleft lip and palate. It is a congenital deformity characterized by hypoplasia of derivatives from the first and second pharyngeal arches. Clinically, patients who have CFM usually express the phenotype of facial asymmetry. The condition has a wide spectrum of involvement and expresses in a variety of clinical features which may affect patients’ zygoma, orbit, trigeminal nerve, facial nerve, mastication muscles, facial muscles, external ear, maxilla, and mandible. It is essential to reconstruct maxilla-mandibular symmetry to achieve better facial skeletal harmony. Correction asymmetry and occlusion of CFM patients involves orthodontic treatment combined with orthognathic surgery to correct most of the asymmetry. Orthognathic surgery is either just in the mandible or involves bi-jaws surgery. The asymmetry expression becomes more obvious where it meets the lowest part of the skull. Previous studies show significant relapse when surgery was limited to the mandible with longitudinal follow-up. Patients look asymmetrical again after long-term follow-up. Previous studies also identify the reason for the relapse as a larger amount of growth in the non-affected side. However, a significant amount of dentoalveolar compensation is found after mandibular surgery. The dentoalveolar compensation is accomplished by dental extrusion, which is the most unstable type of tooth movement. This movement has a higher chance of relapse. During the past ten years, the surgical methods to correct facial asymmetry in CFM patients has tended to involve surgery on both jaws; however, optimal correction techniques remain unclear. Previous articles related to CFM patients focus on analyzing mandible asymmetry, and not much attention has been paid to the maxilla. Growth is one of the reasons for relapse after surgical intervention, and not many articles include long-term follow-up results. Nevertheless, after high levels of dental alveolar compensation, the risk of relapse is significant and might be another reason for the relapse observed in long-term follow-up patients. This study addresses these gaps in the research and investigates the extent to which the maxilla contributes to the asymmetry that can affect the treatment result and long-term stability of the treatment. This study is based on cone beam computed tomography (CBCT) images of CFM patients and the normal population. It evaluates the pattern of maxillary asymmetry in three dimensions—anteroposterior, transverse, and vertical.

Methods: This is a retrospective study. Initial CBCTs of patients with severe CFM (14 patients), mild CFM (16 patients), and the control group (16 patients) before orthodontic treatment were compared using Dolphin image 11.95software. Asymmetry indices were calculated from linear measurements obtained from dentoskeletal landmarks to three reference planes (coronal, axial, midsagittal). Additionally, angular measurements were obtained from each landmark to the axial plane.

Results: In the vertical direction of linear measurements in patients with craniofacial microsomia, the non-affected side is longer than the affected side (p<0.05). This difference is not statistically significant if the landmarks are higher than the orbital rim. All the lines connected by the same landmarks on both sides have the same canting direction trend and are canted upward to the affected sides. However, in patients with a severe condition of craniofacial microsomia, the line connects both sides of the condyles and is canted up in the opposite direction toward the non-affected side. There is no statistically significant difference for the maxilla landmarks in the anteroposterior direction. For the skeletal landmarks of the mandible angle (Ag, Go, Gop), the affected side is more forward than the non-affected side in the anteroposterior position. In the transverse direction, the affected side is wider than the non-affected side in the maxilla. Landmarks at the anterior part of the skull all showed statistically significant differences (P<0.05). The landmarks in the mandible all showed the same result between the severe and the control groups. For the angular measurements, all lines connectedboth sides of landmarks canted up toward the affected side and showed statistical significance except the condyle canted up toward the non-affected side. The severe group (type IIb, type III according to Pruzansky’s classification) showed significant differences in its asymmetry index in the vertical and transverse directions. If the patient needs early surgical intervention, the direction of the deformity and simultaneous bi-jaw surgery should be considered.