"Tunnel" Flap vs Trapezoidal Flap for Lateral Sinus Lift

The goal of this clinical trial is to evaluate the efficacy of the lateral sinus lift procedure using the tunnel technique flap in comparison to the traditional lateral sinus lift in partially or totally edentulous patients with loss of teeth in the maxillary premolar or molar areas and severe alveolar atrophy. The primary questions it aims to answer are: 1. Is the tunnel flap technique more suitable for lateral sinus lift than the trapezoidal flap technique in terms of post-operative symptoms? 2. Is the tunnel technique safer and more effective than the trapezoidal flap technique in terms of complication rate and the effectiveness of bone grafting? Participants will undergo the lateral sinus lift procedure using the tunnel technique, which involves making a vertical anterior incision. Patients will receive follow-up care, including phone contact the day after the procedure to detect any issues, and they will keep a diary during the week after surgery to record visual analog scale (VAS) pain values and analgesics taken. Follow-up surgical visits will be scheduled for suture removal and at 30 days after suture removal. After 6 months, dental implants will be inserted, and prosthetic rehabilitation will take place 6 months later. Implants will be monitored for up to 12 months after prosthetic rehabilitation. Researchers will compare the outcomes of tunnel flap technique lateral sinus lift with the trapezoidal flap sinus lift.