## 1 Introduction  
Fixed implant-supported prostheses are considered a successful and predictable treatment for the rehabilitation of edentulous patients in the presence of an adequate volume of available bone. In  edentulous atrophic jaws, bone deficiencies can prevent implants placement in the ideal prosthetic position with impairment of function and aesthetics. To overcome these limitations,augmentation procedures for improving bone dimensions are needed. To date, bony reconstruction approaches of advanced maxillary horizontal atrophy involve the use of guided bone regeneration, \"split\" ridge osteotomy, and block grafts with different types of materials [1; 2; 3]. Guided bone regeneration (GBR) is a well-documented surgical procedure that uses particulate autogenous bone or bone substitutes in conjunction with occlusive membranes to prevent undesirable competing migration of non-osteogenic cells into the bony defect. The stability of the graft and barrier membrane and the tension-free flap closure are essential to secure successful outcomes [4]. There is strong evidence for the effectiveness and predictability of GBR in promoting lateral bone augmentation for limited to moderate bony deficiencies [5]. Nevertheless, to achieve ridge augmentations in severe and extensive defects, the technique, requiring non-resorbable membranes or titanium mesh and a long-term healing period, is more prone to soft tissue dehiscence, with subsequent infection and possible failure of regeneration procedure [6; 7; 8; 9]. The ridge splitting/expansion procedure consists of a sagittal osteotomy and a controlled greenstick out-fracture of the buccal cortical plate, labially displaced to create the space that is filled with an interpositional particulate graft and covered with a membrane [3; 10]. This technique has proved to be a predictable and effective to correct alveolar width deficiencies of limited dedentulous areas with high implant survival rate, gain in horizontal alveolar ridge width, and few biological and technical complications [11]. In severe and extensive bony deficiencies, with the horizontal width less than 3 mm, treatment outcomes could be jeopardized since the alveolar ridge expansion predisposes to fractures of the buccal or palatal cortical plate and hampers a sufficient blood supply during the healing phase [3; 10; 11]. Autogenous bone block grafting is the best scientifically documented technique for the treatment of advanced horizontal atrophy in dedentulous jaws [1; 2]. However, this is a complex intervention and requires the need for general anesthesia, operation theater, and hospitalization because, in extensive and severe bone resorptions, block grafts are often harvested from the iliac crest or calvaria. Furthermore, the procedure is an operator-sensitive technique, which requires surgical skills in trimming and adapting blocks to the native bone, in achieving grafts immobilization, filling residual gaps, covering the grafted area with resorbable membranes, and suturing the flap tension-free [2]. The main drawbacks for the patients are the increased surgery invasiveness, longer surgical times, and more severe postoperative morbidity, mainly due to the extraoral donor sites. In the augmentation procedures, a variety of bone restorative materials with different characteristics may be used, including autogenous bone, allografts, xenografts, and alloplasts, as well as different barrier membranes or osteosynthesis materials [12; 13; 14; 15]. Autogenous bone, harvested from intra- or extraoral donor sites, is still considered the gold standard among the different biomaterials for bone thickness reconstruction due to its osteogenic, osteoinductive, and osteoconductive properties. Further advantages are a physical and chemical structure identical to that of the host site, a better vascularization potential, and the absence of immunogenicity and disease transmission capacity.