A three-dimensional finite element stress analysis of two different implant distributions supporting and retaining mandibular overdentures

Statement of Problem: Hinging mandibular overdentures retained by anterior interforaminal implants results in denture rotation and posterior basal bone resorption. Wide spread implant distribution and posterior implant placement can improve overdenture support.
Aim of study: To evaluate the biomechanical aspects of novel implant distribution used to support mandibular overdentures and compare it with commonly used design. The novel design consists of mid-symphyseal and bilateral posterior implants in the first molar region as opposed to conventional design with anterior mid-symphyseal and bilateral implants in the canine region.
Materials and Methods: Two finite element models were created. In the two models a mid-symphyseal implant was simulated. In the first model (D1), 2 more implants were placed in the canine region bilaterally while for the second model (D2), the 2 additional implants were placed posteriorly in the first molar region. Unilateral vertical and oblique loads were applied on central fossa of right first molar and palatal aspect of central incisors in each model. Von Mises stress distribution was evaluated in the implants and peri-implant bone. Denture displacement was also calculated for each model.
Results: There was a slight increase in maximum Von-Mises stress values recorded in both implants and peri-implant bone under both vertical and oblique load in D2 when compared to D1. D1 showed higher denture displacement values when compared to D2.
Conclusions: Posterior implant placement resulted in improved denture support and minimal denture displacement on the expense of transferring extra load to the posterior implants. However, increased functional load on posterior implants is expected to have a positive effect on preservation of the residual alveolar ridge. D2 is an acceptable alternative prosthodontic design to D1 when anatomical factor permits.