الفهرس 
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Abstract
Study was conducted to compare the effect of two different treatment modalities mandibular overdenture on marginal bone height changes around straight and angled implants placed using All on Four concept & four straight implants placed in interforamina space during the follow up period of 6 months and 1 year.
Fourteen patients were selected from the outpatient clinic of prosthodontic Department, Faculty of Dentistry, Ain Shams University. Two groups were randomly divided, each group contains seven patients.
group 1: Seven completely edentulous patients were rehabilitated with upper complete denture and lower implant supported overdenture using All on Four concept.
group 2: Seven completely edentulous patients were rehabilitated with upper complete denture and lower implant supported overdenture using four straight implants in anterior intra foraminal space.
The selected patients were free from any systemic diseases, parafunctional habits, smoking habits and temporo-mandibular joint disorder. Intra and extra oral examination were done for all patients.
Guided Surgery was done by flapless technique using tissue supported surgical guide. Immediate loading was done after implant insertion from the first day of surgery with provisional prothesis over the implants.
Patient’s own denture was converted into fixed provisional prosthesis on the day of surgery by creating access holes which was filled by pick up material to pick up the temporary sleeves later on.
Using CBCT for measurement of marginal bone loss of straight and angled implants in all patients on the day of implant insertion, six and one year after implant insertion for measurement of marginal bone changes in implant over one year.
Results were recorded, collected, tabulated, and statistically analyzed.
Although the amount of marginal bone loss around posterior implants in All on four group was found to be higher than posterior implants of straight group after 6 months of functional loading, but this difference was statistically non significant.
However, after 12 months of functional dynamic loading the amount of marginal bone loss around posterior implants in All on 4 group increased significantly to exceed the amount of marginal bone loss around the posterior implants in straight group. In both groups average peri-implant bone height changes were greater in the first six months .