This study was conducted to clinically and radiographically evaluate the effect of retaining mandibular overdenture, by retention silicon material, on the bone level and mobility of the abutment teeth. Eighteen patients were selected from the outpatient clinic in the department of prosthodontics, faculty of oral and dental medicine, Cairo University. All the selected patients had a completely edentulous maxilla and only two canines in the mandible. All patients were completely free of any systematic diseases or conditions that might affect the bone quality or quantity around the abutment teeth or the mobility of the teeth. In this stage the selected 18 patients were randomly divided into two groups A and B. All patients were treated by upper conventional complete dentures opposed by tooth supported lower complete overdentures. In group A, the overdenture abutment teeth were covered by post and copping carrying an attachment. Retention Silicon act as housing by relining the denture base in the area of the attachment. In group B, the overdenture abutment teeth were covered by post and copping only with no attachment mechanism. Patients were clinically and radiographically evaluated at the time of the prosthesis insertion and after 3 and 6 months. Radiographic evaluation was carried out by measuring the amount of change in alveolar bone height around the abutment teeth using the Digora radiographic system. Clinical evaluation was done by measuring the mobility of abutment teeth using the periotest. The results of the study showed a significant alveolar bone loss around the abutment teeth in both groups. The group with attachment showed more alveolar bone loss. The amount of bone resorption was nearly 3 times more in the attachment group than the group without attachment by the end of the 6 months follow up period. In terms of abutment teeth mobility, there was an increase in mobility in both groups, but this increase was minor and had no clinical effect as the mobility of the abutment teeth at the end of the follow up periods was grade zero according to miller’s classification in all abutment teeth in both groups. Conclusion Within the limitation of this study, it can be concluded that using retention silicon material as housing with attachments doesn’t reduce forces transmitted to the abutments to the level that eradicate alveolar bone resorption around the abutment teeth. However, it showed minimum effect on the mobility of the abutment teeth that is clinically insignificant.