CBCT画像による顎顔面形態の３次元的評価とセファロ分析との関連性についての研究

The reproducibility of 3D facial bone measurements was examined using CBCT images of a dry human skull model. In addition, CBCT images of 38 adult female patients diagnosed with jaw deformity and temporomandibular joint disorder were used to perform 3D facial bone measurements and were compared with the results of cephalometric analysis of the same subject group. Then, changes in craniofacial, facial cranial, and lower facial volumes due to orthognathic surgical treatment were examined in patients with Class II and Class III jaw deformities. Patient consent was obtained for this study.
1. Measurement points were set four times a day on CBCT images of human dry skulls, and another four times by the same orthodontist on different days. Using a method based on spatial vectors, the volumes of 5 tetrahedrons in the neurocranium, of 6 tetrahedrons in the facial cranium, and 8 tetrahedrons in the lower face were calculated. The reproducibility of the measurements was examined by two-way analysis of variance and intraclass correlation coefficient, which confirmed the reproducibility of the 3D measurements of the facial bones.
2. Subjects were classified into Class I group, Class II group and Class III group by the value of angle ANB of lateral roentgen cephalometric measurements. There was no significant difference in the volume of the neurocranium among three groups. The volume of the facial cranium in Class III group was tended to be smaller than Class I and Class II groups. The volume of the lower face in Class III group was significantly (p < 0.05) larger than Class II. Whereas the volume of the lower face in Class II group tended to have smaller than Class I.
3. The changes of the volume of the neurocranium, facial cranium and lower face by the orthognathic surgical treatment was examined in two cases with Class II and Class III skeletal deformity. They have coincided with the findings of facial photos, plaster models and lateral roentgen cephalograms. For the correction of the cant of occlusal plane by upward displacement of the posterior teeth could be indicated with the difference in the volume of right and left tetrahedrons.
Since we can evaluate the volume of maxillofacial structures using the spatial vector coordinates of measurement points set on the 3D CBCT image, which allows us to evaluate more detailed 3D information by setting measurement points according to the purpose and significance.