 2. To evaluate and compare the cumulative survival rate CSR of NobelProceraTM Implant Bar Overdenture fixed-removable on four 4 NobelReplace CC implants in the mandible with the cumulative survival rate CSR of NobelProceraTM Implant Bar Overdenture fixed-removable on four 4 NobelReplace CC implants in the maxilla after 5 years. 