Extrasinus Zygomatic Implant Placement in the Rehabilitation of the Atrophic Maxilla: Three-Dimensional Finite Element Stress Analysis
Placement of zygomatic implants lateral to the maxillary sinus, according to the extrasinus protocol, is one of the treatment options in the rehabilitation of severely atrophic maxilla or following maxillectomy surgery in patients with head and neck cancer. The aim of this study was to investigate the mechanical behavior of a full-arch fixed prosthesis supported by 4 zygomatic implants in the atrophic maxilla under occlusal loading. Results indicated that maximum von Mises stresses were significantly higher under lateral loading compared with vertical loading within the prosthesis and its supporting implants. Peak stresses were concentrated at the prosthesis-abutments interface under vertical loading and the internal line angles of the prosthesis under lateral loading. The zygomatic supporting bone suffered significantly lower stresses. However, the alveolar bone suffered a comparatively higher level of stresses, particularly under lateral loading. Prosthesis displacement under vertical loading was higher than under lateral loading. The zygomatic bone suffered lower stresses than the alveolar bone and prosthesis-implant complex under both vertical and lateral loading. Lateral loading caused a higher level of stresses than vertical loading.
Figure 1. Four 50-mm zygomatic implants placed by the exterasinus technique in the left and right zygoma bones. All implants are splinted by a solid cast cobalt-chrome bar. Figure 2. Three-dimensional finite element mesh generated on the whole model; 4 connected zygomatic implants were placed into the zygomatic bones. Figure 3. The boundary conditions in which all posterior and superior bone borders were constrained in all directions. Loading the prosthesis bar anteriorly and posteriorly by 150 N vertically. Figure 4. Flow chart of the work sequence carried out at this study, which included scanning, 3D reconstruction, segmentation, reconstruction, computer-aided design assembly, Boolean operations, 3D finite element meshing, and analyses.
Figure 5. Maximum von Mises stress distribution within the prosthesis and its supporting zygomatic implants (a) and the supporting bone (b) under 150 N anterior vertical occlusal loading. Figure 6. Maximum von Mises stress concentration along the prosthesis-zygomatic implants interface and the mid- and apical thirds of the implant body under 150 N vertical occlusal loading on the right side (a) and along the prosthesis-zygomatic implants interface under 150 N loading of the left side of the prosthesis (b). Figure 7. Maximum von Mises stress distribution within the skull under 150 N right (a) and left (b) posterior vertical occlusal loading.
Figure 8. Maximum von Mises stress distribution within the prosthesis and its supporting zygomatic implants under 150 N on the right (a) and left (b) posterior lateral occlusal loading. Figure 9. Maximum von Mises stress distribution within the skull under 150 N right (a) and left (b) posterior lateral occlusal loading. Figure 10. Prosthesis displacement under 150 N vertical anterior (a), right posterior (b), and left posterior (c) occlusal loading.
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