الفهرس 
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Abstract
This study was aimed to study the effect of different bar clip materials (Poly etherether Ketone, Zirconia & Plastic) on retention in implant supported mandibular overdenture supporting structure .by using universal testing machine.
Three bar clips attachments were made from different materials (Poly Ether ether ketone, Zirconia & Plastic) and were constructed in acrylic model for implant supported mandibular overdenture and determine retention in implant and supporting structure by universal testing machine.
In this study, the maximum retentive force was measured at different cycles as following: at base line (to), 360 cycles (t₁), 720 cycles (t₂), 1440 cycles (t₃), 2880 cycles (t₄), and 4320 cycles (t₅) using universal testing machine. According to the literature approximately 1,000 to 1,500 insertion and removal cycles (3 or 4 removals a day) represent the clinical use of 1 year. Most other investigations simulated a clinical use between 1 to 10 years. In the present investigation, 4320 insertion and removal cycles were performed to receive suitable results.
The results of the present study showed a significant difference in the values of initial retention forces and at 2 years where the PEEK clip documented higher retention forces in comparison to the plastic and zirconia clip. However, at 3,6,12 months there was significant difference between the three materials; the highest retention was in PEEK followed by plastic and zirconia which showed insignificant difference between each other. But, at 3 years there was significant difference between the three materials; the lowest retention was in Zirconia followed by plastic and PEEK which showed insignificant difference between each other.