Objectives: this research was carried out to evaluate two different attachment material retainers bar supported overdenture regarding the peri-implant crestal bone level changes.   materials and methods: Twenty edentulous female patients participated in this study For each patient 3 endosteal implants were inserted in the interforamenal region using computer guided surgical Stent. Four month later implants were uncovered, healing abutments were secured and then transfer coping with long heads were used to make open tray impression technique. Plastic abutments were secured to implant analogue then plastic bars was attached to plastic abutments using durallay with two semi precision attachments at the distal ends of the bar. Then the bar was casted. Patients were divided into two groups. Group one the CAD CAM wax pattern of housing and the female part of the attachments were casted using nickel chrome alloy. Group two patients the CAD CAM wax pattern of housing and the female part of the attachments were transferred into Acetal resin using the injection molded technique. Then per implant crestal bone level were assessed using long cone parallel technique after six, twelve and twenty four months and then statistically analyzed.   Results: This study showed that there was a statistically insignificant difference in between follow up periods for each group and between groups in between follow up period in interval 12-24 and significant difference between two groups after 24 months. Conclusion: Based on the results obtained from this study it can be concluded that acetal resin is favorable long term solution for implant retained mandibular overdentures