In vitro changes in clips and bars used to retain implant overdentures.

Although implant-retained overdentures are a less expensive alternative to fixed implant-supported prostheses in certain situations, problems with retentive clips fracturing and needing frequent replacement have been reported. This study compared baseline and posttest retention of metal and plastic clip-retained overdenture analogs and monitored surface changes in bars and clips throughout the testing process. A laboratory model was made with two implant analogs processed into an acrylic resin platform to which three bars were fitted. Two overdenture analogs were made and retained on the model with metal or plastic clips. Each bar-clip assembly was subjected to 5500 insertion and removal cycles to simulate 3 years of in vivo insertion and removal. Although the differences in retention between metal and plastic clips and between clips before and after testing were statistically significant, it is questionable whether they are clinically significant. Neither clip fracture nor loss occurred during this study, which suggests that it may be functional or parafunctional loading and not repeated insertion and removal of an implant overdenture that may cause the stated problems.