Inclusion Criteria:  at least one missing maxillary premolar or molar at least 7 mm crestal bone width confirmed by preoperative ConeBeam Tomography (CBCT) maximally 5 mm residual bone height at the sinus floor confirmed by preoperative ConeBeam Tomography (CBCT) full mouth plaque and bleeding scores (FMPS and FMBS) <20% satisfactory patient compliance (e.g. to participate in follow-up procedures) signed informed consent.  Exclusion Criteria:  clinically relevant diseases (e.g.: diabetes, rheumatism cancer) untreated periodontitis systemic steroid use bisphosphonate use acute or chronic inflammatory processes previous endoscopic sinus surgery previous sinus floor elevation GBR-treatment at the study site GTR-treatment at the study site tooth removal within 6 weeks prior to surgery