This clinical study is designed to compare the regenerative outcome of using separately two different Xenografts during sinus floor augmentation.

Aim of this prospective randomized-controlled clinical trial is to compare the regenerative results of Alpha-Bio's GRAFT Natural Bovine Bone versus commercially available bone graft after two-step sinus floor elevations by clinical and histological analysis.

Clinical Parameters are wound healing parameters, radiological volume stability and implant survival rates. Histological parameters are based on a histomorphometrical analysis of trephine cores harvested in progress of implant bed preparation.

Inclusion Criteria:

1. Patients who will present with a moderately or severely atrophic posterior maxilla with 1-6 mm residual alveolar bone will be selected for the study.
2. Men and women over the age of 18 years.
3. Patient has signed the Informed Consent.

Exclusion Criteria:

1. Chronic steroid therapy,
2. Uncontrolled diabetes,
3. Cardiovascular disease,
4. Past irradiation of head and neck
5. Maxillary sinus cysts,
6. Active chronic sinusitis,
7. Smoking more than ten cigarettes per day during the 3 months preceding this study .
8. Malignant disease in the 5 years preceding this study
9. Uncontrolled bleeding disorders such as: hemophilia, thrombocytopenia, granulocytopenia
10. Disease that compromise the immune system
11. Psychiatric disorder
12. Hypersensitivity to titanium, collagen or bovine bone.
13. Women who are pregnant or nursing.
14. Patients with non-treated periodontal disease.
15. Medical and/or general contraindications for intraoral surgical procedures