## 4 Discussion  
Given the constant updating of surgical bone grafting-techniques, the approach described in this short communication for the reconstruction of horizontal atrophic edentulous maxillae aimed to offer a potential alternative. In the recent years, the use of bone substitutes in the augmentation procedures has gained attention to overcome the drawbacks of the autogenous bone, including the additional surgery for harvesting,  
Figure 8: Histologic views: (**a**) some osteocytic lacunae of biomaterial block (P) appear to be filled by cells (black arrows); (**b**) close to the newly formed bone (NB) and biomaterial block (P), many blood vessels (V) are present. (Acid fuchsin-Toluidine blue 200X). Figure 9: CBCT, performed at a 2-year follow-up, shows no signs of inflammation and bone resorption at the grafted sites and around implants. the risk of donor site morbidity, the limited availability, the possible need of general anesthesia and hospitalization, and the unpredictable graft resorption [20]. An organic bovine bone substitute is one of the best-documented biomaterials, being commercially available in a wide range of products, and its osteeconductive properties and high biocompatibility have been tested in many clinical trials [21; 22]. The bovine-derived xenohybrid composite bone has proven to have effective integration and bone regeneration when it is used in oral and orthopedic fields [23]. Its composite structure is based on a deproteinized bovine-derived bone matrix reinforced with biodegradable aliphatic polymers and bioactive agents. The bovine-derived matrix, made of calcium hydroxyapatite (HA, Ca5(PO4)3(OH)), maintains an adequate 3D structure for strength. The biopolymers (poly(L-lactic acid) and poly(e-caprolactone) enhance mechanical properties. The bioactive agents (RGD-containing collagen fragments, obtained by purified gelatin) promote cell adhesion, proliferation, and high hydrophilicity. Furthermore, morphological analysis has shown a well-diffused open-porosity and microstructure comparable in terms of size and cell seeding spaces to human cortical bone. Furthermore, the possibility to custom-make scaffolds using CAD/CAM technologies speeds up the surgical procedure and limits any potential biological and technical complications. Indeed, the manual cutting and shaping of the blocks and the adaptation at recipient sites during surgery increase the risk of intraoral and extraoral contamination and result in a procedure that is time-consuming and highly dependent on the clinician's skill and experience. Additionally, the size and shape of the conventional bone grafts often are imprecise, and the difficulty of achieving a stable position on the native bone might jeopardize the integration process. Manufacturing of customized block grafts offers some advantages also compared to the grafts manually shaped on the 3D stereolithographic model of patients' jaws. The manual adjustment of the prefabricated block leads to less precise fitting, needs a greater quantity of material, and exposes to a risk of graft infection due to the prolonged contact to possible sources of contamination, such as the gloves of the surgeon, oral fluids of the patient, burs, and other environmental factors [24]. The therapeutic approach using bovine-derived bone blocks combined with 3D-CT and CAD/CAM technologies seems to be promising to overcome the above-mentioned limits of conventional bock grafting procedures. The use of deproteinized bovine bone, not requiring additional surgery for bone harvesting, avoids the risk of donor sites, reduces postoperative morbidity, and provides an unlimited biomaterial availability. 3D-CT and the surgical planning software allow virtually to analyze the patient's anatomical and prosthetic parameters, to plan the exact implant position and direction, to verify bone defects at implant sites, and to design the graft blocks.