Evaluation of Stress Distribution on Mandibular Implant-Supported Overdentures With Different Bone Heights and Attachment Types: A 3D Finite Element Analysis
The biomechanical behavior of the edentulous mandible with bone irregularities that has been rehabilitated with implant-supported overdentures has become an important factor for treatment planning. Restorative options, including dental implants with various attachments, affect the stress distribution. The purpose of this study was to evaluate the stress distribution of cortical bone around the implant neck and implant structures in overdentures with two different attachment types at the edentulous mandible and with different bone heights using three-dimensional finite element analysis. Five three-dimensional models of an edentulous mandible were designed and implemented. Ten models were constructed with ball and locator attachments. Static bilateral and unilateral vertical and oblique occlusal loads with magnitudes of 100 N were applied to the overdentures. The principal stresses were higher in the presence of oblique loads compared to vertical loads in all the analyzed models. Maximum principal stresses were observed around the mesial side of the contralateral implant, and the minimum principal stresses were noted around the distal side of ipsilateral implant during unilateral vertical loading. These patterns were reversed during oblique loadings. The ball attachment models yielded lower von Mises stress values than the locator models at all the loading conditions, while the stress distributions were similar in the models with the same and different bone levels. Correspondingly, bone corrections due to irregularities may not be necessary in terms of biomechanics. The results of this study may provide clinicians a better understanding for the mandibular overdenture design in the cases at which different bone heights exist.
All the constructed three-dimensional (3D) models and overdentures. (a) Control model (1–1 mm); (b) Model 2 (1–2 mm); (c) Model 3 (1–4 mm); (d) Model 4 (2–2 mm); (e) Model 5 (4–4 mm); (f) simulated overdenture on model.
Boundary conditions and constraints are represented as red areas at the posterior of the mandible, and the loading area is illustrated with blue arrows.
Graphical illustration of tensile and compressive stresses according to the models under vertical loading. Ball attachment (Ball) and locator (Locator) models. R indicates loading from right; L, loading from the left sides of the overdenture.
Figure 4. Maximum principal stresses occuring on the symmetrical mandibular bone height models (Models 1, 4, and 5). Right and bilateral vertical loadings are presented. The left loading is not shown owing to the same stress pattern and value as the right loading. Figure 5. Maximum principal stresses occuring on the asymmetrical mandibular bone height models (Models 2 and 3). All vertical loading conditions are presented. Figure 6. Minimum principal stresses occuring on symmetrical mandibular bone height models (Models 1, 4, and 5). Right and bilateral vertical loadings are presented. The left loading is not shown owing to the same stress pattern and value as the right loading. Figure 7. Minimum principal stresses occuring on asymmetrical mandibular bone height models (Models 2 and 3). All vertical loading conditions are presented.
Graphical illustration of tensile and compressive stresses according to the models that were exposed to oblique loadings. Ball attachment (Ball) and locator (Locator) models. R indicates loading from the right side; L, loading from left side of the overdenture.
Figure 9. Maximum principal stresses occuring in all the models in the presence of oblique loading. Models 2 and 3 loaded from both right and left side due to the different bone heights. Figure 10. Minimum principal stresses in all the models in the presence of oblique loading. Models 2 and 3 loaded from both right and left side due to the different bone heights.
Graphical illustration of von Mises stresses on the attachments for vertical and oblique loadings for constructed models.
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