Hoop Stress and the Conical Connection
Dental implant-abutment connection design has developed into the use of a conical, shank and socket connection between the implant abutment and fixture. The connection between these two elements is, in effect, a conical wedge that may exert lateral forces under load that may result in fracture of the coronal implant socket fixture walls. This study evaluated the axial loading on a conical connection and found that axial loads were well tolerated but off-axial loads were not. Fracture of the implant coronal socket fixture wall occurred under off-axial loading.
Figure 1. A fractured anterior implant supported fixed partial denture. Figure 2. The abutment screws fractured. Figure 3. The socket fractured under off-axial loading. Figure 4. The socket fractured, referred to as “flowering.”
Figure 5. Strength-number of stress cycles curve developed by combining results of multiple fatigue tests. Figure 6. Goodman diagram created for titanium 6Al-4V. Figure 7. The graph demonstrates that if the alternating and mean stresses on the test specimen are below the line, the test specimen should never fail. Above the line, the specimen should eventually fail. Figure 8. Cross-sectional view of dental implant and abutment, the conical socket, and shank design. Figure 9. Alternating and mean stresses shown graphically. Figure 10. Deformation plot for cantilever beam using ANSYS, finite elemental model design, and finite elemental model design.
Figure 11. Free body diagram of cantilever beam test case. Figure 12. Three pieces were modeled in the CAD program SolidWorks: the implant, an abutment, and a medium to hold the body of the implant. The assembly of parts can be seen; the orange part is the abutment, the gray part is the implant, and the blue part the structural steel. Figure 13. A finite elemental analysis (FEA) of the cylindrical beam, a tetrahedral mesh represented the implant with 59 000 elements and 138 000 nodes. Figure 14. Stress plot for geometry 1 from ANSYS. Figure 15. Goodman diagram displaying the alternating and mean stress for geometry 1 loaded with 200 N vertically. Figure 16. Cross-sectional view of the 2 different test implants. The walls of geometry 1 were 0.25 mm thick and for geometry 2 0.5 mm thick. Figure 17. Test rig that delivered the test loads. Figure 18. Implant after 332 000 cycles. Figure 19. Image of bending moments on dental implants.
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