 Surgical procedures Once all patients have been enrolled in the study, the surgeries will be scheduled within the same week. Antibiotics will be prescribed 1 day before surgery and continued for 5 days. Three calibrated and confirmed surgeons will place 4 Narrow Neck NN or Regular Neck RN Roxolid tissue level implants Institut Straumann, Basel Switzerland according to the surgical protocol recommended by the manufacturer. The implant positions have to be determined previously at the time of CT scan evaluation by an agreement between the 2 operators and according to the bone availability. Two implants have to be placed in the lateral or canine region and 2 implants as distal as possible. The implants have to be placed with as parallels as possible. A maximum divergence of 10 will be tolerated. The flap design will be determined according to the available bone quantity and in order to emphasize an adequate quantity of keratinized tissue around the implants. A Cone Beam Computed Tomography CBCT scan will be done directly after surgery. Sutures will be performed with silk sutures and removed after 1 week. The removable conventional prostheses will be adapted to avoid any contact with the implants. Patients will be followed up at 4 and 8 weeks post-surgery, respectively. At 8 weeks, a panoramic x-ray will be done. If osseointegration is successful, the removable prostheses will be connected to the implants. 