Mandibular Overdentures vs All-on-4 With PEEK

Inclusion Criteria: Adults aged ≥40 years. Completely edentulous mandible for at least 6 months prior to implant placement. Treated with either: Four-implant-retained mandibular overdenture with a PEEK framework, or Mandibular All-on-4 fixed prosthesis with a PEEK framework. All implants placed in the lateral incisor and first premolar regions (per respective protocol). Restorations fabricated via CAD/CAM-milled PEEK framework with acrylic denture teeth. Prosthesis delivered with a delayed loading protocol. Minimum clinical and radiographic follow-up of 4 years. Availability of standardized baseline and follow-up periapical radiographs for marginal bone level assessment. Treated by the same surgical and prosthodontic team. Exclusion Criteria: History of uncontrolled systemic diseases that could affect bone healing (e.g., uncontrolled diabetes, osteoporosis under bisphosphonate therapy). History of head and neck radiotherapy. Active periodontal or peri-implant infection at the time of implant placement. Insufficient bone volume in the interforaminal region requiring grafting beyond minor augmentation. Heavy smoking habit (\>10 cigarettes/day) at the time of treatment. Parafunctional habits (e.g., severe bruxism or clenching) documented in patient records. Use of medications known to affect bone metabolism (e.g., high-dose corticosteroids, antiresorptive drugs). Pregnancy at the time of implant placement. Incomplete clinical or radiographic records. Follow-up period of less than 4 years.