Two-Stage Transcrestal Sinus Lift With Osseodensification: Allograft vs Autogenous-Xenograft

This study is a prospective, randomized, controlled clinical trial comparing two grafting approaches used during two-stage crestal sinus lifting with osseodensification in patients with severely atrophic posterior maxillae (residual bone height ≤ 4 mm). Participants will be randomly allocated in a 1:1 ratio to receive either allograft alone (Group A) or a mixture of autogenous bone and xenograft (Group B). During the first stage, crestal sinus elevation will be performed using osseodensification drills, and the assigned graft material will be placed lncrementally. Cone-beam computed tomography (CBCT) will be performed immediately postoperatively and again after a six-month healing period to assess vertical bone height At the second stage, during implant placement, bone-core biopsies will be harvested for histomorphometric analysis, and implant primary stability will be recorded using insertion torque values.

Eligibility Criteria Inclusion Criteria: Participants must: 1. Be 18-70 years old. 2. Have a severely atrophic posterior maxilla with RBH 0-4 mm confirmed by CBCT. 3. Have adequate bone width of minimum 7 mm. 4. Be in good health status and able to undergo surgery. 5. Provide informed consent and agree to follow study instructions. Exclusion Criteria: Patients with: 1. Uncontrolled systemic diseases, immunosuppression, history of head \& neck radiotherapy or chemotherapy. 2. Use of bisphosphonates, antiresorptive\*\*,\*\* or antiangiogenic drugs. 3. Pregnancy. 4. Heavy smoking (\>10 cigarettes/day). 5. Active sinus disease, oral infection, untreated periodontal disease, or severe bruxism. 6. Poor oral hygiene. 7. Anatomical issues such as sinus septa or inadequate ridge width preventing the OD approach. 8. Previous sinus lift or implant failure in the same site.