The Influence of Clip Material and Cross Sections of the Bar Framework Associated with Vertical Misfit on Stress Distribution in Implant-Retained Overdentures

Purpose: The aim was to evaluate the stress concentration caused by different cross sections of bar frameworks and clip materials used to retain overdentures. Materials and Methods: Three-dimensional models of a severely resorbed arch, an overdenture retained by two implants, and a bar-clip attachment system were made. A total of twelve models were made according to the cross section of the bar framework (round, oval, or Hader), clip material (gold or plastic), and presence of misfit. A vertical misfit of 100 μm between the implant and the bar framework was made on the right implant. Finite element models were obtained by importing the solid model into mechanical simulation software. The base of the mandible was set to be the fixed support, and a pressure of 100 MPa was applied to the right mandibular first molar. The analysis was made by means of von Mises stress for the prosthetic components and microstrain to the bone tissue. Results: Round bars led to lower values of stress in the clip and prosthetic screw of the ill-fitted component and lower microstrain values in the periimplant bone tissue. The lowest values of stress in the bar were observed in the Hader groups. Plastic clips reduced the stress concentration in all structures compared with gold clips. Conclusion: The clip material and the cross section of the bar framework influenced the stress distribution in overdentures retained by a bar-clip system presenting vertical misfit. Int J Prosthodont 2014;27:26-32. doi: 10.11607/ijp.3627