Photoelastic analysis of stress distribution in single and three-unit implant-supported prostheses with different internal connections

Background: The accurate fit between the dental implant and the prosthetic abutment is crucial for the stability of the entire prosthetic-implant system, providing a better distribution of the occlusal load to the surrounding bone. To improve stress distribution between the implant and bone, various types of internal connection implants have been introduced. However, few studies are available on the biomechanical behavior of these connections. This study investigated the stress distribution in screwed implant-supported prosthesis with different implant‒abutment connections using a photoelastic analysis. Methods: Eight photoelastic models were fabricated in PL-2 resin and divided according to the different types of internal connections: Morse taper (MT), internal Morse hexagon (IMH), Morse taper hexagon (MTH), and frictional Morse taper (FMT) implants (3.75×11.5 mm), and the number of crowns (single and 3-unit pieces). Models were positioned in a circular polariscope, and 100-N axial and oblique (45º) loads were applied to the occlusal surface of the crowns using a universal testing machine. The stresses were photographically recorded and qualitatively analyzed using Adobe Photoshop software. Results: Under axial loading, the number and distribution of high-intensity fringes did not differ among groups for both crown types (single and splinted 3-element). Low stress values were noted at the implant apex. The oblique loading increased the number of fringes for all groups. In conclusion, the internal connection tested in this study did not affect the number and distribution of stress. Conclusion: The different types of internal connections provided better stability for the implant‒prosthesis set, which improved stress distribution when the prosthetic pillar was loaded, with the Morse cone friction system showing less stress. Oblique loading resulted in a higher stress concentration than axial loading.