Stress analysis of mandibular implant overdentures retained with one, two, or four ball attachments: A finite element study

Background: The aim of this study is to compare stress patterns induced by ball attachments when used to retain mandibular overdentures supported by one, two, or four dental implants. Materials and Methods: In this finite element study, three 3D models were prepared to simulate mandibular implant overdentures retained by one or two or four ball attachments of 3.5 mm diameter with collar height 1.6 mm. The geometric solid models were created by commercial engineering computer‑aided design package then transferred to ANSYS as set of standard ACIS text files. Vertical load of 100 N was applied on the central fossa of the right molar. Stresses were evaluated at the areas of implant and attachment components, mucosa underlying overdentures, and cortical and cancellous bone adjacent to implants. Results: The results of this study showed that the Von Mises stresses generated by the application of vertical loading varied according to the number of implants used to support the overdenture. Maximum Von Mises stress on cortical bone ranged between 1.15 and 1.77 MPa in all‑studied cases. Mucosa was squeezed under the one implant model. Flexibility of the overdenture material played a significant role in distributing the load stress and deformation of all underlying structure.Caps deformation was the highest when using two implants. Conclusion: With increasing the number of implants, stresses and deformations of overdenture are reduced, but implants receive greater stresses and deformations. Using two implants in the canine region showed the best results when compared with using one or four implants, except for the caps.