Prosthetic Complications in Fixed All-On-Four Prosthesis Reinforced with Poly Ether Ether Ketone (PEEK) Versus Cobalt Chromium (Co-Cr) Framework

Inclusion Criteria: * Any completely edentulous patient (mandible) with an old satisfactory denture requiring an implant-supported restoration. * Patients aged from 50 to 70, able to sign an informed consent will be considered eligible for this trial. * Implant sites must allow the placement of four implants. * Non- heavy Smokers will be included (smoking up to 10 cigarettes/day) * In case of post-extractive sites, they must have been healed for at least 3-month before being treated in the study. * Patients with no systemic condition that may interfere with implant placement (e.g., Immunosuppressed or immunocompromised patients, patients under treatment of intravenous amino-bisphosphonates) Exclusion Criteria: * Patients with poor oral hygiene and motivation. * Pregnancy or nursing. * Drug abusers. * Psychiatric problems or unrealistic expectations. * Patients with infection and or inflammation in the area intended for implant placement. * Patients participating in other studies, if the present protocol cannot be properly adhered to. * Patients with signs of hyperactive muscles.