IC measurement items. (A, C, E) CT slice images observed from the side, with sagittal sections of the IC at the middle. (B, D, F) Schematic diagrams of A, C, and E. a: IC length, distance between the midpoint of c and midpoint of d. b: Height of the anterior alveolar bone of the IC, distance to the alveolar crest from a line passing through the anterior nasal spine, in parallel with the virtual plane. c: Diameter of the nasopalatine foramina, IC diameter passing over a line connecting the anterior nasal spine and the floor of the nasal cavity, in parallel with the virtual plane. d: Diameter of the incisive foramen, maximum distance from the point (asterisk) where the superoposterior angle changes significantly. e: Width of the IC anterior alveolar bone, distance of the anterior alveolar bone parallel to the virtual plane. (e1: position of the anteroinferior point matching the diameter of the incisive foramen; e2: position of the intermediate part (asterisk); e3: position of 50% of the major axis of the upper IC). f: Total volume from c to d.