## 4 Discussion
Therefore, the esthetic result sometimes may be unsatisfactory [46]. Autogenous bone is the ideal biomaterial, thanks to its biocompatibility and osteogenicity. Regarding bone graft procedures, autogenous bone blocks remain the 'gold standard'; intraoral block grafts harvested from the symphysis or the mandibular ramus can be used to reconstruct horizontal and vertical ridge deficiencies prior to implant placement. If the amount of bone needed exceeds what is available intraorally, extraoral sites, such as the iliac crest and calvarium, can be considered [47; 48]. The main disadvantage of autologous bone grafts is the morbidity of the donor site; another complicating factor is the additional surgical time necessary to harvest the bone block. As an alternative to this type of grafting, allogenic, xenograft and alloplastic materials have been developed, but they can only provide osteoconduction or osteoinduction, not osteogenesis, and none of them guarantee the healing and bone replacement that autogenous block grafts can provide [49; 50; 51; 52; 53; 54; 55]. The successful integration of a bone graft depends on numerous factors, which are all associated with a good surgical technique. In the receiving site, the cortical plate should be perforated to induce bleeding, which is fundamental to the healing process. There should be intimate contact between the bone block and the recipient site; precise measurements or a template of the recipient site can help to ensure that the harvested bone block is adequate in size and form. The bone graft must be completely still during the healing process, because any movement causes its failure: for this reason, the blocks should be secured through mini screws to the host site. Once the block is screwed, a tension free flap closure and a primary healing must be obtained. Strict asepsis protocols must be respected [56]. Implant primary stability, whenever possible, should be researched in the native bone of the patient, even basal bone: when the native bone ensures the primary stability and the graft only works as a coverage for the implant, implants can be placed 4 months after the graft procedure; otherwise, when there is no residual native bone, it is recommended to wait 6-8 months from the graft procedure before placing the implants, because new bone must form inside the graft in order to have primary stability for the implant. Bone augmentation could also be performed simultaneously with implant placement, but it is associated with increased failure rates [57]. Ridge splitting technique can increase the width of bone by splitting and expanding the existing residual ridge. Indications of this technique include the ridge deficient in width with an adequate amount of height, with no vertical defects. The maxilla is preferred in the mandible because the expansion of bone is easily achieved without any complications thanks to the cancellous nature of bone. Advantages include no second surgery required to place implants simultaneously inserted during the ridge splitting procedure, reduced overall treatment time and increased implant stability because of new bone formation between cortical plates. Disadvantages include more severe ridge defects in case of procedure failure and primary closure being difficult to achieve [58; 59; 60]. Distraction osteogenesis is based on the principle of secondary wound healing. Osteotomy removes a bone segment from the basal bone, and the distraction gap is filled with callus that forms a new bone segment. This procedure demonstrates many advantages such as decreased bone resorption, no donor site morbidity and simultaneous lengthening of the surrounding soft tissues. This technique requires a delayed implant placement (at least 4 months from the end of the distraction) to wait for the consolidation of distracted bone segments.