An association of photoelastic and finite element analysis in overdenture

Objective: The aim of this study was to evaluate the load transmission of a mandibular implant retained overdenture under occlusal forces with the association of two different stress analysis methods: photoelasticity and three-dimensional finite element. Method: A photoelastic model and a similar 3D geometrical mathematical model were manufactured simulating an edentulous mandible with two screw-type implants (3.7 x 10 mm with 4.1 mm diameter abutment platform) embedded in the interforaminal region positioned parallel to each other and vertically oriented. The implants, in both models, were splinted with a bar system, an overdenture was connected to the bar by a clip and, under the prosthesis, a silicone rubber was used to simulate a mucosa. The materials used for the finite element model were evaluated as being homogenous, isotropic and linear. A force of 44.2N was applied to the mandible base and the resultant stresses developed in the supporting structure were monitored. Results: The photoelastic method supplies a visual result and the finite elements analysis provides visual and numerical results; in both methods these results are analyzed by their fringes. Results:The photoelastic mandibular model demonstrated peaks of stress values around the implant apex, supporting structures like molar region and mandibular trigon, although the prosthesis boundaries do not reach this last area. The mathematical mandible model showed stress concentration in the implant apex (approximately to 0.188 a 0.113 in a scale from 0 to 0.2 MPa) and in the supporting structures in the boundaries of the prosthesis (from 0.138 to 0.113 MPa). Conclusions: Within the limitation of this in vitro study, in both models a higher stress level in the implant apex and supporting structures was observed, so that no differences of stress distribution were detected demonstrating the advantages in the association of these two methods to facilitate the comprehension of stress analysis.