In the present study, we used the superior spatial resolution of CBCT to measure changes over time in (a) the volume of the bone graft (BV) and (b) the height of the bone surrounding the implant (BH).

The method of calculating the volume of the implant site is shown below (Fig. 2).

The slice thickness (voxel value) was resized (0.146 mm → 1 mm) to derive the volume of the grafting agent on the basis of CBCT data. After setting the slice interval to 1 mm and specifying the output range (FOV option), the DICOM server for storing data was selected and registered.

Next, image data of four time axes from prior to surgery, immediately after surgery, 6 months after surgery, and 2.5 years after surgery was simultaneously imported into a multi-data image analysis system. For confirming that the four images had the same positional relationship, we implemented synchronized scrolling after identifying similar anatomical reference points. The area of the implant site was measured using the polygon tool which was dragged around the perimeter of the target site to measure area. It allows measurements up to two places after the decimal point. It is operated by dragging the cursor only around the bone graft material site and avoiding the implant itself. In cases in which it was impossible to determine the margin between the implanted bone and the existing bone after 1-year examination, the entire bone was measured and the preoperative measurement was subtracted from the postoperative measurement.

Then the images were taken at 1-mm increments mesio-distally, and the volume was calculated by adding the entire area of the bone grafting material. BoneVolume (BV) cm³ = area cm² × N (number of images)

The method of measuring the height of the bone surrounding the implant (BH) is described below (Fig. 3).

The measurements were taken at the long axis of the implant and on the frontal plane of the perpendicular frontal plane. In the event that there was grafted bone above the implant, the distance was measured from the point of intersection of the line connecting the buccal and palatal side of the maxillary sinus floor and the medial axis of the implant to the implant tip (+mm). Moreover, in the event that absorption of the grafting material exceeded the implant tip, the distance was measured from the point of intersection of the medial axis of the implant and the line connecting the most apical part of the grafted bone-to-implant contact (BIC) to the implant tip (−mm). In addition, the liner valuables (RBH, SW, IL) that may effect the outcomes of BH were measured. The following are the explanations of the linear valuables.