Pneumatization of the maxillary sinus may lead to insufficient bone volume for dental implant placement in the edentulous posterior maxilla. Sinus floor elevation (SFE) surgery with the lateral window technique is a safe and predictable surgical intervention to restore bone height in the maxillary premolar and molar areas. According to the literature, several bone graft materials may be successfully applied for SFE surgery. There is a lack of evidence regarding the application of biphasic calcium sulfate (BCS) for SFE. The healing period following staged SFE is 2-9 months. The aim of this study is: * to evaluate the success of SFE surgery using BCS as graft material, * to compare the microarchitecture of the augmented bone depending on the healing period, * to evaluate the success of dental implants placed in the augmented bone and that of the prostheses delivered on the dental implants.