The Influence of Structural Designs and Retainer Designs on the Fracture Resistance of Removable Partial Denture

The retainer with a framework is an important device for excellent function of the removable partial denture.However, prosthetic appliance fracture primarily occurs at the terminal abutment-cantilever junction. In this study, combinations of five structural designs (double structure consisting of six columns, or four columns, T-shapes, trusses and rectangular columns) and three retainer designs (full coverage, 4/5 coverage and mesiodistal rest) were subjected to the statical bending test. The fracture resistance of these frameworks were evaluated to measure maximum stiffness, yield load and strain of the retainer. The obtained results were as follows: 1.Maximum stiffness of the double structure consisting of six columns, trusses and T-shapes was approximately 10 times greater than that of rectangular columns. 2. Ultimate strength of double structure consisting of six columns was the greatest, followed by that of four columns, trusses and T-shapes. 3.Fracture resistance of full coverage and 4/5 coverage was about 4 times greater than that of mesiodistal rest. 4.When 20 kgf load was applied, the strain of the marginal and occlusal regions tended to increase according to the strength of the framework, whereas that of the proximal region decreased.