Bone resorption and sinus pneumatization, following tooth extraction, are common occurrences in the posterior maxilla. They may cause both a quantitative reduction and qualitative deterioration of bone, resulting in an inadequate bone volume for a standard implant placement. Sinus floor elevation with lateral approach had been described 35 years ago and widely studied afterwards, demonstrating an high predictability in regenerating bone, to allow for reliable implant supported rehabilitations. Maxillary sinus floor elevation with transcrestal approach represents a validated and effective alternative option to vertically enhance the available bone through an access created in the edentulous bone crest. Regardless of graft type, it is not yet well defined how three-dimensional anatomical sinus cavity characteristics may influence healing and mineralization process. An adequate Schneiderian membrane elevation in order to expose sinus floor, buccal and medial walls, seems to represent a crucial factor in influencing new bone formation, as the greatest part of the osteoprogenitor cells derives from these anatomical structures. It is not documented yet the efficacy of the different trnanscrestal sinus floor elevation approaches in exposing the internal bony walls of the sinus. Moreover, on the basis of the fact that only few articles correlated the size of the maxillary sinus with histologic outcome by lateral window and one retrospective radiographic study reported results in relation to the three-dimensional conformation of the sinus using a trans-crestal approach, the investigators conjecture that sinus bucco-palatal diameter could influence the newly-formed bone quality after a crestal sinus lift procedure. For example, the healing in a narrow maxillary sinus could result in a faster new bone formation, when compared to a larger and wider sinus. The aim of this study is to analyze neoformed bone after maxillary sinus lifting with transcrestal approach, in atrophic crests (≤5 mm residual bone height). Clinical and laboratory data will be related to maxillo breast anatomy. The present study has been designed as a multicenter prospective clinical trial. Five clinical centers will treat patients with two-stage transcrestal sinus floor elevation using a calibrated drills technique and a xenogeneic biomaterial. Implants will be inserted 6 months after sinus augmentation and bone-core biopsies will be harvested during the implant site preparation. Histological analyses will be performed in order to assess the quality of the newly-formed tissue and cone beam computed tomography scan examination will be used to evaluate graft resorption over time. For each inserted implant, collection of experimental parameters will be required up to 1 year after its placement.