## 4 Discussion  
In the vast majority of cases, the quality of the new bone formation upon surgery is investigated through histology or densitometry, thus, implying a bone sampling from patient collected through a second operation. In our work, we have here proposed an innovative non-invasive method to establish a healthy bone volumetric increase after different time spans from the implant, which could be easily  
Figure 4: Clinical case #5; (**a**) CT slice immediately post-surgery, showing relatively low bone density, as highlighted in the graft are (red circle); (**b**) CT slice 2 years post-surgery, showing much higher signal, hence, higher bone density, due to new bone formation in the grafted region (red circle). Figure 5: Follow-up images of the six investigated clinical cases; the gray area evidences the grafted volumes, indicated as bone regenerated volumes. (**a**) Clinical case #1, 13 months post-surgery reconstruction, volume stability is high and symmetry almost perfect. (**b**) Clinical case #2, 8 months post-surgery reconstruction, high volume stability of grafted SB. (**c**) Clinical case #3, 6 months post-surgery reconstruction, high volume stability and remodeling already in progress. (**d**) Clinical case #4, 14 months post-surgery reconstruction, excellent results on all SB grafted sites. (**e**) Clinical case #5, 24 months post-surgery reconstruction, complete graft integration and good symmetry. (**f**) Clinical case #6, 24 months post-surgery reconstruction, complete bone remodeling and restoration of functional anatomy. used in follow up analyses. Specifically, to achieve this goal, the unique radiographic properties of SB have been exploited and were investigated to create 3D templates that faithfully mirrored the anatomy of the individual patient. The trickiest aspect of the applied method was to find the right way to make pre- and post- 3D models overlay accurately, because if the superimposition is precise, the volumetric increase should have respected the real anatomy. The overlay depends on the correct alignment of the 3D templates, and the pre-model reference system should change into the post-model reference one. We tested two different methods to evaluate the volumetric bone growth that took place following the SB implant. Both model-measuring methods used, by means of GOM and by Boolean subtraction with 3-matic, showed equivalent results and depended on the accurate creation of the models from the CT images. Hence, we decided to merge them. Indeed, the peculiarity of the final method is to create templates faithfully respecting the patient's anatomy by the two above mentioned alignments to obtain the best accurate overlapping, which could help us in the understanding the correct volumetric increase for all cases analyzed in the study. As reasonably expected, the quality of the CT played a primary role in this radiological approach: A good quality yield provided a better resolution and a greater discretization of tissues as it allowed to calculate 3D models identical to the bone anatomical region and, consequently, to reach a more accurate calculation of the possible volumetric increase. Importantly, it has to be taken into account that the SB has low density allowing an optimal CT quality to be recognized. The main technical aspects related to the acquisition and processing of CT images to obtain quantitative information on the skeletal system have recently been reviewed in [PERSON] et al. [49], providing recommendations finalized to maximize the repeatability and objectivity of measurements. It is particularly important to perform the scans on the same equipment, standardizing the X-ray tube settings, the field of view and the slice thickness. To properly evaluate bone mineral density and distinguish components of integral, cortical, and trabecular bone, a calibration phantom with known hydroxyapatite density standards should be scanned together with the anatomical district of interest.