Photoelastic Analysis on Different Retention Methods of Implant-Supported Prosthesis
The aim of this study was to evaluate the stress distribution of different retention systems (screwed, cemented, and mixed) in 5-unit implant-supported fixed partial dentures through the photoelasticity method. Twenty standardized titanium suprastructures were manufactured, of which 5 were screw retained, 5 were cement retained, and 10 were mixed (with an alternating sequence of abutments), each supported by 5 external hexagon (4.0 mm × 11.5 mm) implants. A circular polariscope was used, and an axial compressive load of 100 N was applied on a universal testing machine. The results were photographed and qualitatively analyzed. We observed the formation of isochromatic fringes as a result of the stresses generated around the implant after installation of the different suprastructures and after the application of a compressive axial load of 100 N. We conclude that a lack of passive adaptation was observed in all suprastructures with the formation of low-magnitude stress in some implants. When cemented and mixed suprastructures were subjected to a compressive load, they displayed lower levels of stress distribution and lower intensity fringes compared to the screwed prosthesis.

Demonstration of the results after installation of the suprastructures (passive fit). (a) Screwed suprastructures; (b) cemented suprastructures; (c) mixed suprastructures 1; and (d) mixed suprastructures 2.

Demonstration of the results observed after application of a 100-N compressive load. (a) Load application on screwed suprastructures; (b) load application on cemented suprastructures; (c) application of mixed load 1; and (d) application of mixed load 2.
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