Three-Dimensional Nonlinear Contact Finite Element Analysis of Mandibular All-on-4 Design
The All-on-4 design was used successfully for restoring edentulous mandible. This design avoids anatomic cripples such as inferior alveolar nerve by tilting posterior implants. Moreover, tilting posterior implants of All-on-4 design had a mechanical preference than the conventional design. On the other hand, the anterior implants are parallel at the lateral incisor region. Several researches showed favorable results for tilting posterior implants. However, research did not study the influence of the anterior implant position or orientation on the mechanical aspects of this design. This study analyzes the influence of varying anterior implant position and orientation of the All-on-4 design using nonlinear contact 3D finite-element analysis. Three copied 3-dimensional models of the All-on-4 design were classified according to anterior implant position and orientation. The frictional contact between fixtures and bone was the contact type in this finite element analysis. Finally, von Mises stress and strain at implant and bone levels were recorded and analyzed using finite element software. Stress concentrations were detected mainly around the posterior implant at the loaded side. Values of the maximum equivalent stress and strain were around tilted implants of design III followed by design II, then design I. Changing the position or orientation of the anterior implants in All-on-4 design influences stress-strain distribution of the whole design.
Figure 1. Isometric view of the 3-dimensional (3D) model of the mandibular bone including cancellous (orange color) and compact bone (light blue color). Figure 2. 3D models of the 4 implants (angled and paralleled) designed according to manufacturer's dimensions and configurations. Starting from right to left fixture 1 (F1) to fixture 4 (F4). Figure 3. Assemblies of the 3 designs seen in computer-aided design (CAD) software showing changes in the position and orientation of the anterior implants. Figure 4. Meshing of the models was performed using 3D tetrahedron element type with 4 node element shape. Figure 5. Boundary conditions were selected using fixed support constrains (blue areas) and force applied (red arrow and areas).
Figure 6. Graph showing maximum equivalent stress of components of different designs. Figure 7. Graph showing maximum equivalent strain of components of different designs.
Figure 8. Equivalent stress in the cancellous bone in 3 different designs, from top to bottom (design I, II, and III, respectively). Figure 9. Equivalent stress in the compact bone in 3 different designs, from top to bottom (design I, II, and III, respectively). Figure 10. Equivalent stress in the implants in 3 different designs, from top to bottom (design I, II, and III, respectively).
Figure 11. Equivalent strain generated in cancellous bone in 3 different designs, from top to bottom (design I, II, and III, respectively). Figure 12. Equivalent strain generated in compact bone in 3 different designs, from top to bottom (design I, II, and III, respectively). Figure 13. Equivalent strain generated in implants in 3 different designs, from top to bottom (design I, II, and III, respectively).
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