# Fresh Frozen Allogeneicic Bone Block in Maximly
## 1 Introduction  
Implant-supported rehabilitation of the atrophic posterior maxilla generally finds the maxillary sinus both as a boundary and an opportunity. In fact, bone regeneration in the Highmore antrum presents favorable conditions for an optimal bone-graft integration: a secluded defect surrounded by osteogenic surfaces, isolated from the occlusal forces and from the oral microbiological environment. Since its introduction in the early 1980s [1, 2], the surgical approach to access maxillary sinus and its clinical indications have greatly evolved. Nowadays, lateral sinus augmentation can be safely performed with piezoelectric instrumentation [3, 4, 5], and reliable alternatives (transcrestal approach, short implants) are available in selected cases [6, 7, 8]. Even if, in sinus floor elevation, autogenous bone is still the better material in terms of osteogenicity, osteoconduction, osteoinduction, and osteointegration, a robust body of evidence showed comparable results using an allograft, alloplastic, xenograft, and blood clot alone inthe outcomes of this surgical technique [9; 10; 11; 12; 13; 14]. However, limited conclusions should be drawn on bone grafting outcomes, when considering implant survival rate as the principal variable. Histomorphometric analysis should be considered as the gold standard measure to test the performance of different biomaterials, taking also in consideration that recent studies showed significant differences in terms of graft integration and substitution according to several variables, such as sinus buccolingual width, residual bone quantity, sinus walls thickness, membrane detachment from sinus walls, and overall graft volume [15; 16; 17; 18; 19; 20]. The anatomy of the posterior upper jaws, if dentulous, is clinically considered to be a difficult area for the dental implants positioning due to the atrophic ridge surgical management, the deficient bone quality, and sinus pneumaticization. In the last decades, with the development implant surface treatment, newly bone graft materials, and less invasive surgical techniques, the sinus lift surgery by crestal or lateral approach has been accepted as a common predictable treatment procedure in dentistry [9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Several published papers investigated the sinus lift surgical technique focusing on long-term absorption of the placed autogenous bone graft materials or mixed with other bone substitutes material in order to evaluate the bone graft residual at the time of dental implants placement. Retrospective studies at 60 months revealed how, even the surgical procedure works with the long- term dental implant stability and no signs of inflammation of the final prosthodontics crown restored over the dental implants, the residual of the applied biomaterials could be presented related to the kind of material used. However, today, the autogenous bone graft represents the gold standard for this kind of surgical procedure [18; 19; 20; 21; 22]. Moreover, the behavior and the modifications of the regenerated bone still remain unclear. Only a few isolated reports described the histologic characteristics of biopsies retrieved from augmented sinuses with long-term follow-up. Generally, the newly-formed bone surrounding and in contact with the biomaterial, which after 6 months of healing is mainly immature woven bone, with time is replaced by mature lamellar bone bridging the graft particles. Xenografts are the most investigated biomaterials: up to 14 years, inorganic bovine bone showed good osteoconnectivity between the grafting particles and the newly formed bone, without signs of inflammation [21; 22; 23]. This bone substitute is hardly resorbed by the osteoclasts and is still present with different percentages in all the biopsies taken at different time points in the various studies.