Inclusion Criteria:  height of the residual bone crest <5 mm in both sites where implant placement was planned; age >18 years; written informed consent given.  Exclusion Criteria:  general contraindications to implant surgery smokers uncontrolled diabetes (HBA1c > 7.5%) treated or under treatment with intravenous antiresorptive drugs allergy to bovine collagen immunosuppressed irradiated in the head and neck area pregnant or breastfeeding substance abusers psychiatric problems or unrealistic expectations patient not fully able to comply with the study protocol. maxillary sinus conditions contraindicating sinus floor elevation poor oral hygiene and motivation (FMPS >25 and or FMBS>20) Schneiderian membrane perforation during surgery