Abstract
Le FortⅠ osteotomy is one of the main methods in orthognathic surgery and allows movement in various directions. Superior repositioning of the maxilla is often required when treating maxillofacial deformities with vertical maxillary excess, for example in cases of long face or open bite, and protrusion of the menton. To be reliable and useful for accuracy and postoperative stability, horse-shoe osteotomy combined with Le FortⅠ osteotomy is often performed. However, when the distance between the palatine root apex of the maxillary molar tooth and the nasal cavity bottom is small, horse-shoe osteotomy cannot be performed due to the possibility of damaging the roots of teeth. In addition, if horse-shoe osteotomy is performed, superior repositioning becomes difficult due to strong bone interference depending on the width and inclination of the maxillary bone. The purpose of this study was to comprehend the tendency in the form of the maxillary bone of patients with facial deformity. The subjects were 274 patients who underwent surgery for facial deformity in our department for five years from April 2011 to March 2016. The measurement items were the distance between the palatine root apex of the maxillary first molar （6） and second molar （7） and the nasal cavity bottom, and the width and angle of inclination of the palatal side of the dentoalveolar part of the maxillary bone in coronal CT images. The results showed that the distributions of the distance, width, and angle of inclination were wide. The average value of root apex of 6 and the distance to the nasal cavity bottom was 9.68 mm and root apex root of 7 was 10.20mm. The median value of the thickness of the maxillary bone was 2.46mm （6） and 2.21mm （7）. The average value of the angle of inclination of the maxillary bones was 38.9 degrees （6） and 32.3 degrees （7）. Considering the distance between the root apex and the nasal cavity bottom of more than 6.0mm, and the thickness and inclination of the maxillary bone, 25.2％ of all cases were suitable and safe for horse-shoe osteotomy. In addition, about half of cases with facial asymmetry had a difference between the right and left in the distance between the root apex and the nasal cavity bottom. It is important to confirm the shape of the maxillary bone.
