CBCT analysis
The CBCTs were imported into Dragonfly software (version 4.3, Objects Research Systems, Montreal, QC, Canada) in DICOM format for analysis.
Alignment based on voxel information.CBCT of T0 was set as a “fixed module”. CBCT of T2 was aligned to the T0 through manual rotation and translation until the teeth and bone contour were overlapped exactly. Although the maximum occlusal position was asked during CBCT acquirement, occlusion position variation of the same patient occurs occasionally. Therefore, the upper and lower jaws were aligned separately.
Region segmentation.Through the threshold segmentation method, cortical bone and dental tissues were selected and saved as regions of interest (ROIs) of T0 and T2, Fig. 
CBCT region segmentation, Boolean subtraction, and HTVC region division. The green region is the result of region segmentation. The orange region is the HTVC region of the maxilla, which the volume is calculated by pixel counting
Boolean subtraction and volume change region selection.With the Boolean subtraction of ROIs (T2-T0), the three-dimensional voxel model of the changing area of the hard tissues can be obtained. As the maxilla and mandible were aligned separately, two cubes were drawn in the space which selected the volume change regions, containing the wisdom teeth of the maxilla or mandible as well as the alveolar bone around the wisdom teeth, Fig. 
Voxels counting and HTVC measurement.By counting the number of voxels, the volume of the selection region can be calculated directly (the orange region in Fig. 