Photoelastic Analysis of Biomechanical Behavior of Single and Multiple Fixed Partial Prostheses With Different Prosthetic Connections

The aim of this study was to evaluate the stress distribution on external hexagon, internal hexagon, and Morse taper implant in single and 3-unit implant-supported fixed partial prostheses (FPPs) using photoelasticity. Six models were fabricated with the photoelastic resin PL-2: 3 models for the 3-unit implant-supported FPP with implants of 4.0 x 10.0 mm in the region of the second premolar and molar including 1 model for each type of implant connection, and 3 models for the single prosthesis for each implant type. The prostheses fabrication was standardized. A circular polariscope was used, and axial and oblique (45 degrees) loads of 100 N were applied in a universal testing machine. The results were photographed and analyzed qualitatively. The internal hexagon implant exhibited better stress distribution and lower intensity of fringes followed by the external hexagon and Morse taper implants for the models with the 3-unit prostheses. For the single implants, the Morse taper implant presented better stress distribution, followed by the internal and external hexagon implants. The oblique loading increased the number of photoelastic fringes in all models. It was concluded that the internal hexagon implant exhibited better biomechanical behavior for the 3-unit implant-supported FPP, whereas the Morse taper implant was more favorable for the single implant-supported prosthesis. The oblique loading increased the stress in all models.