The present study was conducted to investigate, clinically and radiographically , the effect of two different mandibular prosthetic designs : Fixed –detachable implant overdenture prosthesis (Screw –Retained prosthesis) and Conventional implant supported overdenture prosthesis (Dome –shaped prosthesis) on the implants and the implant supporting structures . For each patient, 4 implants were placed in the mandibular canine-molar area. Conventional loading of these implants was carried out after 3 months of implant placement. Patients were divided randomly into two equal groups, each of five patients. Patients of group I received Fixed –detachable implant overdenture prosthesis (Screw –Retained prosthesis), while patients of group II received Conventional implant supported overdenture prosthesis (Dome –shaped prosthesis). Evaluation was carried out clinically and radiographically at the time of prostheses insertion (0-time, baseline), 3 months, 6 months, 9 months and 12st months later. Results revealed that for the implants in the 1 molar location, the difference in the ISQ change between both groups is statistically insignificant for all the follow up periods with Group I showing higher values of change for the ISQ than Group II, while those in the canine location, difference in the ISQ change between both groups is statistically significant for all the follow up periods with Group II showing higher values of change for the ISQ than Group I.