# Morphological Evaluation of Cranium Facial Asymmetry in Class III Malocclusion Patients
## 1 Introduction  
Many patients present to the orthodontic practice with complaints of facial asymmetry as well as bite malfunction. For such patients, frontal, lateral, and axial cephalometric radiographs are taken, and cephalometric analysis is performed to find the cause of the asymmetry. Skeletal malocclusion with significant malpositioning of the jawbone, either vertically or horizontally, is diagnosed as a jaw deformity and is an indication for orthodontic treatment with surgical intervention. Facial asymmetry is also included in the diagnosis of jaw deformity [1]. [PERSON] [2] and [PERSON] et al. [3] reported that asymmetry of the jaw angle has the greatest influence on the judgment of the symmetry of frontal appearance by a third party other than a dentist, and [PERSON] et al. [4] reported that the difference in the bulge of the contour line from the chin to the left and right jaw angle is involved in asymmetry. Indeed, patients themselves often point to mandibular asymmetry as a factor in their perception of asymmetry. However, in the process of diagnosis, the maxillofacial surface of patients with facial asymmetry is often deformed in three dimensions, not only inthe mandible but also in the entire maxillofacial region, including the maxilla. Therefore, to understand the morphology of facial asymmetry, it is essential to measure the maxillofacial region centered on the upper and lower jawbones as well as the mandible [5; 6; 7]. [PERSON] et al. reported that more than half of the studied patients with facial asymmetry had deformities of the maxillofacial region, including the maxilla [8]. On the other hand, patients with facial asymmetry often have deformities not only in the maxillofacial region but also in the head region. The head region consists of the cerebral cranium and the facial cranium. The cerebral cranium is further divided into the cranial base, which supports the brain from below, and the cranial crown, which surrounds the brain from the outside. The cranial base grows via growth at the cartilaginous joints, bone addition at the sutures, and bone remodeling on the inner and outer surfaces of the basal bone. On the other hand, the cranial crown shows sutural growth and periosteal growth on the external and internal surfaces of the bone [1]. The cranial crown, which surrounds the brain from the outside, includes the temporal bone that forms the mandibular fossa [9; 10]. The mandibular fossa is part of the structure of the temporomandibular joint, which develops at 8 weeks of fetal age and is shaped by fetal jaw movement. During postnatal growth, the mandibular fossa becomes visible from infancy to childhood, i.e., with the eruption of the primary teeth. The position of the mandibular fossa in the temporomandibular joint is also known to be involved in the anteroposterior, lateral, and vertical position of the mandible [11]. In cranial studies, it was also reported that children attempt to compensate for abnormal head structures, such as cranial asymmetry and plagiocephaly, with a displacement of normal organs. [12] Abnormal structures of the head, if present, cause damage to the mouth and vestibule. When accompanied by distortion of the orbit, this creates pressure on the suborbital muscles and nerves, causing sensorimotor deficits. One study also reported that anterior and posterior deformities of the cranium might cause deviations in the surrounding structures, including the temporomandibular joint, and that mechanisms may be at work to compensate for this [13]. Some studies have also compared such left-right skull deformities by measuring left-right differences in skull distance and area [14; 15]. Thus, it has been suggested that there may be a close relationship between cranial deformity and deformation of the maxillofacial region and mandible. However, there are only scattered reports on the relationship between facial asymmetry and cranial deformity, and much remains unknown.