Adaptation of overdenture-bars casted in different metals and their influence on the stress distribution: a laboratory and 3D FEA.

Adaptation at the implant/abutment interface is important to the long-term success of prosthetic rehabilitations. The aim of this study was to evaluate the adaptation of overdenture bar frameworks casted with different materials and the stress distribution of ill-fitted frameworks placement through 3-D finite element analysis (FEA). Thirty overdenture bar frameworks (n=10) were casted in different materials (Co-Cr, Ni-Cr, Ti). Vertical misfit of both abutments was examined using a single screw test and, after both screws were tightened, using a scanning electron microscope (SEM). The misfit values of each group were used to construct 3-D models, and a displacement with the same extent observed in SEM was applied to the non-tightened abutment to simulate the effect of prosthetic tightening. von Mises stress for prosthetic components, and the maximum principal stress and microstrain for bone tissue were evaluated. The misfit in the non-tightened abutment during the single screw test ranged from 145 to 211 µm. Different bar framework materials did not present significant differences in regard to adaptation. An increase in the misfit values in the other abutment was observed after the final settlement of the bars in Ni-Cr and Ti frameworks. The stress values on prosthetic screw and implant were not influenced by the bar framework material. However, Ti caused lower stress in the bar framework itself and strain in the bone tissue. The bar framework material does not affect the implant/abutment adaptation. Titanium frameworks presented the best behavior for the bar framework itself and bone tissue compared to the other materials.