Three-dimensional Analysis of Cranial Vault and Position of Mandibular Fossa Part 1: Analysis of Mandibular Protrusion Cases without Asymmetry

The relationship between the shape of the cranial vault and the position of the mandibular fossa is not clear. To clarify the relationship, three-dimensional analysis was performed using cases with mandibular protrusion but without facial asymmetry. Nineteen female patients with skeletal mandibular protrusion who had visited Meikai University Hospital were used in this study. The lateral deviation of mental spine was less than 4 mm in all cases. Genetic/congenital anomaly cases, endocrine disorders, or cases with severe trauma and TMD were excluded. Computed tomography (CT) images of the 19 cases were taken at the first visit. Three reference planes were defined in CT images. The horizontal reference plane was defined as the plane running through the right and left porion, and left orbitale. The mid-sagittal reference plane was defined as the plane running through the midpoint of the bilateral nasomaxillary suture and basion, and perpendicular to the horizontal reference plane. The frontal reference plane was defined as the plane running through the left porion, and perpendicular to the horizontal reference and mid-sagittal reference planes. There was a significant negative correlation between the bilateral difference in the sagittal length of the cranial vaults and the bilateral difference in the sagittal position of the mandibular fossas. This implies that posteriorly located mandibular fossas are seen in cases with asymmetric cranial vaults having longer A-P length on the same sides. In contrast, there was no correlation between the bilateral difference in the vertical length of the cranial vaults and the bilateral difference in the vertical position of the mandibular fossas. Also, there was no correlation between the bilateral difference in the transverse length of the cranial vaults and the bilateral difference in the transverse position of the mandibular fossas. Interestingly, there was a significant negative correlation between the bilateral difference in the sagittal position of mandibular fossas and the bilateral difference of mandibular body lengths, suggesting that the mandibular body length compensated the A-P position of the mandibular fossa to prevent facial asymmetry. The obtained findings indicate that the shape of the cranial vaults is related to the A-P position of mandibular fossas in patients with skeletal mandibular protrusion but without facial asymmetry. It is likely that the bilateral difference of the mandibular body lengths has a compensating effect on the bilateral A-P difference of the mandibular fossas in the present cases. 明海大学歯学部形態機能成育学講座歯科矯正学分野(主任:須田直人教授) Division of Orthodontics, Department of Human Development and Fostering, Meikai University School of Dentistry (Chief : Prof. Naoto SUDA) 32 日顎変形誌 2019 年 川尻 朱美,他