A methodology is presented for registering three-dimensional preoperative and postoperative CT scan volumes and for evaluating their differences in selected areas of interest. The proposed method was applied to CT cone beam data from ten patients in order to assess the volume of augmented bone in the alveolar region. A 3D affine model was used to align the preoperative and postoperative data. The differences between the aligned sets were assessed through subtraction radiography. The volume of the differences was finally evaluated by defining regions of interest in each slice of the subtracted 3D data. Both quantitative and qualitative results were obtained after applying the method to all sets. The effectiveness of the volumetric assessment algorithm was verified by applying the algorithm to an object of known volume.