The Le C Fort I osteotomy is the most commonly applied procedure in orthognathic surgery for the correction of various different types of maxillary deformities. In the past decades, scholars at home and abroad have conducted extensive studies on the anatomy of the region related to this procedure, and the studies were mostly anatomical measurements on cranial specimens, which had the deficiencies of small sample size and little measurement content. In recent years, with the development of CT imaging technology, especially the realization of 1:1 alignment with solids for accurate measurement, good conditions have been provided for the measurement of the maxilla. In this study, the cone beam CT (Conebeam computed tomography, CBCT) was used to measure the position of adult maxilla in Le Fort I osteotomy section to provide guidance reference for clinical maxillary Le Fort I osteotomy. 1. Subjects and methods 1.1 General data From the patients with non-dental and maxillofacial malformations treated in our maxillofacial center, 60 cases were selected for CBCT examination in our hospital between October 2008 and October 2010 and met the following criteria: age 18-40 years old; no dental and maxillofacial malformations, facial coordination and symmetry, orthognathic facial symmetry, three-equal coordination; neatly aligned upper and lower teeth, normal dental arch morphology The first molars were in neutral relationship, the anterior teeth were covered normally, the opening degree and opening type were in the normal range; there was no history of oral and maxillofacial trauma, tumor and surgery. There were 30 male and 30 female cases, aged 18-40 years, with an average age of 23.5 years. 1.2 CBCT scanning method CBCT examination was performed using the cone beam projection technique, with a single 360-degree rotational scanning angle and the patient in a sitting position, with 85KV, 8mA, 24 seconds continuous exposure, 36kHz bulb frequency, 0.1-0.3mm layer thickness, 180 seconds image reconstruction time, and 770.0mm distance between detector and X-ray focus. The data were acquired by an amorphous silicon flat panel detector (FPD) with a stereo pixel size of 270 M. The final 3D reconstructed images of the maxilla were obtained in standard coronal, sagittal and axial views, multi-planar reconstructed views and arbitrary tomographic views. 1.3 Measurement method and content The image was edited using image processing tools, and the measurement settings were equal to the actual distance. The transverse position image was selected on the traditional Le Fort I osteotomy plane, 3 mm from the base of the pyriform foramen, and parallel to the palatal plane. The distance from the rim of the pyriform foramen to the pterygopalatine canal, the distance from the zygomatic alveolar ridge to the pterygomaxillary union, the length of the nasal septum, the distance between the pterygomaxillary union and the pterygopalatine canal, and the angle between the inner wall of the maxillary sinus and the nasal septum were measured on the transverse image (Figure 1). The thickness of each bone wall was also measured by dividing each bone wall into three equal parts, including the width of the pterygomaxillary union, the thickness of the anterior, middle, and posterior parts of the medial wall of the maxillary sinus; the thickness of the anterior, middle, and posterior parts of the posterior wall of the maxillary sinus; and the thickness of the bone in the proximal pyriform foramen area, middle, and proximal zygomatic alveolar crest area of the anterior wall of the maxillary sinus. In the 3D reconstructed image, the distance from the upper margin point of the pterygomaxillary connection to the palatal plane and the distance from the lower margin point of the pterygomaxillary connection to the palatal plane were measured with the palatal plane as the reference line. After coloring the pterygopalatine canal by CBCT coloring technique, the course of the descending palatine artery in the posterior part of the maxilla was clearly shown, and the angle between the pterygopalatine canal and the palatal plane was measured. (Figure 2) 1.4 Data processing The SPSS13.0 statistical package was used to calculate each x±s, paired sample t-test was performed between the left and right measurement items, and the measurement data of each maxillary part in men and women were tested by statistical Levene chi-square test, and the corresponding data of men and women were equal variance, and then t-test was performed, and P0.05 was used as the test criterion for statistical significance of the difference, and the results of statistical analysis were derived . 2. Results 2.1 Bilateral comparison statistics of the data measured on the left and right side of each bone wall of the adult maxilla by paired t-test showed no statistically significant differences between the two sides of all measurements (P〉0.05), indicating that the corresponding measurements of the left and right side of the normal adult maxilla were consistent. See Tables 1 to 2. 2.2 Comparative statistics for men and women Statistical analysis of the measurements of the various maxillary components in normal adults of both sexes showed that the distance from the anterior margin of the pyriform foramen to the pterygopalatine canal and the thickness of the posterior portion of the medial wall of the maxillary sinus were statistically different between men and women for these two measurements, while the rest of the measurements were not statistically significant. 2.3 Specific measurements The distance from the rim of the pyriform foramen to the pterygopalatine canal was 35.18±2.56 mm in men and 32.90±1.40 mm in women, the distance from the zygomatic alveolar ridge to the pterygomaxillary union was 32.02±2.91 mm in men and 31.73±2.60 mm in women, and the distance from the anterior nasal spine to the posterior nasal spine was 49.13±2.79 mm in men and 47.41±3.70 mm in women. The distance from the anterior nasal spine to the posterior nasal spine was 49.13±2.79 mm in men and 47.41±3.70 mm in women. The distance from the inferior border of the pterygomaxillary junction to the palatal plane was 4.36±0.68 mm in males and 4.27±0.57 mm in females. The distance from the superior border of the pterygomaxillary junction to the palatal plane was 10.46±1.10 mm in males and 10.48±0.86 mm in females. The angle between the pterygopalatine canal and the palatal plane was 62.24±4.07° in males and 62.24±4.56° in females from the posterior oblique to the anterior oblique. 62.24±4.56° in males and 62.24±4.56° in females. The measurement of each bone wall showed that the thickest area was in the junction area of adjacent bone walls, such as the zygomatic alveolar ridge, the margin of the pyriform foramen and the pterygomaxillary joint area, and the middle part area of each bone wall was significantly thinner than the sides, while the posterior part of the inner wall of the maxilla differed greatly from the posterior part of the posterior wall individually. CBCT and spiral CT are both volumetric scans. CBCT has a spatial limit resolution of 50 LP/cm, a minimum layer thickness of 0.1 mm, and voxel isotropy to ensure a clearer and more delicate image. Because the image quality of multi-layer spiral CT is affected by many factors such as pitch, exposure parameters, and reconstruction parameters, while CBCT only needs to select the correct exposure conditions, there are no other influencing factors, and the image quality is stable. CBCT images can be called repeatedly on the image workstation or computer system, and the multi-view and multi-profile display of craniomaxillofacial three-dimensional structure provides us with “Brown et al [1-3] showed that the consistency of CBCT measurements with solid measurements and the 1:1 ratio between the projected object and the actual measurement can be performed; this fully illustrates the high accuracy of CBCT image measurements. The key to maxillary Le Fort I osteotomy is accurate positioning of the descending palatal artery, accurate osteotomy site, osteotomy depth, and control of angular direction. The current clinical positioning is mainly based on the curved tomography film and positioning cranial lateral film, and the surgical osteotomy depth is also based on previous experience. The average distance from the edge of the pear-shaped foramen to the pterygopalatine canal is 35.25 mm in domestic studies, and the average distance from the edge of the pear-shaped foramen to the pterygopalatine canal is 38.4 mm (34-42 mm) in men and 34.6 mm (28-43 mm) in women in foreign studies. Too shallow a surgical osteotomy can leave too much bone connection and cause high fractures or poor force transmission in the posterior maxillary wall, leading to ocular symptoms; too deep can damage the descending palatal artery or break the pterygoid plate, leading to serious complications such as bleeding. This study utilized the CT tomography function of the CBCT system and its measurement function with a 1:1 ratio between the projected illumination, allowing for actual measurement and thus preoperative accurate positioning of the distance from the margin of the pyriform foramen to the pterygopalatine canal. The study measurements showed 35.18±2.56 mm in males and 32.90±1.40 mm in females. the angle between the pterygopalatine canal and the palatal plane of the jaw specimen was measured by domestic and foreign scholars as 58. 47° [4] and 57.33±4.54°, respectively. In the present study, the measurements using CBCT were 62.24±4.07° for males and 62.24±4.56° for females. The angle between the medial wall of the maxilla and the median sagittal plane has been little studied, but we found that the angle between the medial wall of the maxilla and the median sagittal plane is certain through a lot of clinical observations and preoperative CBCT measurements, and this study showed that the angle was 10.30±1.36° in males and 9.52±1.97° in females, further suggesting that when the medial wall of the maxilla is truncated, the bone gouge should be slightly abducted posteriorly, with about 10° to the median sagittal plane of the face. sagittal plane with an inclination of about 10°, combined with the specific measurement of depth from the edge of the CBCT pear-shaped foramen to the pterygopalatine canal, which ensures adequate osteotomy and improves safety accuracy. As maxillary orthognathic patients, there are maxillary developmental deformities, their bone wall distance, all vary, although there are normal values for reference, but if preoperative CBCT examination can make accurate localization of specific differences in the descending palatal artery, the surgery is safer and more effective. Another key to maxillary Le Fort I osteotomy is the dissection of the pterygomaxillary junction. otterloo [7] counted 8 intraoperative hemorrhages in 410 cases of Le Fort I osteotomy, 2 from the descending palatine artery, 3 from the internal maxillary artery, and 3 of unknown origin, all of which occurred during the dissection of the pterygomaxillary junction. Therefore, it is more important to be able to accurately grasp the height and width of the pterygomaxillary union. The average height of the pterygomaxillary union in the domestic study was 13.15 mm, and the shortest was 6.76 mm. It is recommended to use a 10 mm curved bone gouge to perform osteotomy of the pterygomaxillary joint. The average height of the pterygomaxillary joint in foreign studies was 15.14±2.46 mm [6] and 14.6±3.1 mm [8], and it is recommended that the height of the pterygomaxillary joint osteotomy should not exceed the hard palate plane by more than 10 mm. Therefore, in this study, the distance between the upper edge of the pterygomandibular joint and the palatal plane was measured using the palatal plane as the reference plane, and the distance between the lower edge of the pterygomandibular joint and the palatal plane was measured. The results showed that the distance from the superior border of the pterygomaxillary junction to the palatal plane was 10.46±1.10 mm in men and 10.48±0.86 mm in women, and the distance from the inferior border of the pterygomaxillary junction to the palatal plane was 4.36±0.68 mm in men and 4.27±0.57 mm in women. 5 mm below the palatal plane was safe and effective for osteotomy of the pterygomaxillary junction. The maxilla contains the maxillary sinus cavity, and the thickness of the bone wall is closely related to the development of the maxillary sinus and the development of the teeth, and there are no studies on the thickness of the bone wall in different areas of the maxilla in China or abroad. The posterior part of the medial wall of the maxilla and the posterior part of the posterior wall of the maxilla had greater variation, and the posterior part of the posterior wall had greater variation due to the growth of the maxillary third molar and the development of the maxillary sinus. The posterior part of the medial wall of the maxilla is the area of fusion between the palate and the maxilla, and is also the most common area of maxillary sinus separation, and the study statistics show that the thickness of the bone wall in this area is significantly greater than that in the anterior and middle parts. These two areas are also the key areas of maxillary Le Fort I osteotomy, and it has been reported in the literature that the thick wall of the junction between the medial wall and the posterior wall makes it difficult to lower the osteotomy fracture, which leads to serious intraoperative and postoperative complications.