Objectives: The aim of this study was radiographic evaluation of bone level around dental implant of mandibular over denture versus fixed denture supported by four implants placed according to ‘All-on-Four^® Concept Materials and methods:Six completely edentulous patients, each patient received four implants in the mandible; two implants in canine area and two implants in second premolar area. Three patients received implant supported screw-retrained fixed prosthesis and the other three patients received a milled-bar overdenture, Radiographic evaluation will be performed in terms of Peri-implant alveolar bone loss using (CBCT). Results: FP recorded significant VBL than MB at T6 and T12 for distal sites of anterior implants. MB recorded significant higher VBL than FP at buccal site of anterior implants. For anterior and posterior implants at other sites and surfaces no significant differences in VBL between groups were noted. For FP no significant difference between anterior and posterior implants were noted at all implant surfaces at T6 and T12. For MB at distal site at T6 posterior implant recorded higher VBL than anterior implant and at buccal site anterior implant recorded higher VBL than posterior implant. MB recorded significant HBL than FP at T6 and T12 for buccal sites of posterior implants. For anterior and posterior implants at other sites and surfaces no difference in HBL between groups were noted. . For FP and MB, at all implant sites at T6 and T12, no difference in HBL between anterior and posterior implants except at buccal site of posterior implants of MB group at T6 where posterior implants recorded significant higher HBL than anterior implants. Conclusion:Within the limitation of this short-term study, taking the small patient cohort into account, it could be concluded that both FP and MB could be used successfully for All on four implant rehabilitations of edentulous mandible as both prostheses were associated with acceptable peri-implant bone resorption after 6 months of prosthesis insertion. However, MB may be advantageous than FP in terms of vertical peri-implant bone preservation and FP may be advantageous than MB in terms of horizontal peri-implant bone preservation.