Purpose: To evaluate peri-implant marginal bone loss in two immediately loaded narrow versus standard diameter implants retaining mandibular implant overdentures. Material and methods: Twenty completely edentulous patients were collected from Outpatient whom maxillary and mandibular dentures were constructed. Patients were randomly divided into two equal groups; N group which 10 received narrow (3x12 mm) and S group, 20 standard diameter implants (3.7x 12mm). Implants were immediately loaded

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... ng the previously constructed dentures, ball attachments for retention and silicone based resilient liner acting as female receptacle. Marginal bone loss was then assessed using standardized digital peri-apical radiographs at denture insertion, then 6 and 12 months later. Independent t test was used to study effect of group, while repeated measure ANOVA was used for studying effect of time on peri-implant marginal bone loss. Results were considered significant at p ≤0.05. Results: For both groups a significant difference was found among the different follow up intervals and between mesial and distal aspects of all implants at 0-6 and 0-12 months. N was associated with significantly higher bone loss if compared to S at all follow up intervals with the highest bone loss recorded at distal aspects of both groups after one year (N=1.485±0.215, S=1.062±0.125). Conclusion: Despite of the 100% one year survival rate found in both groups of the study, immediately loaded conventional diameter implants retaining mandibular overdentures are associated with lesser marginal bone loss if compared to immediately loaded narrow diameter ones.