Sinus Floor Elevation Using Separately Two Different Xenografts - A Prospective Randomized Clinical Trial

Inclusion Criteria: 1. Patients who will present with a moderately or severely atrophic posterior maxilla with 1-6 mm residual alveolar bone . 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.