Resulting Stresses of Using Angle-Neck Implant in the All on Four Treatment

This study aims to evaluate the biomechanical effect of using angled-neck implants in the All-on-Four treatment concept on resulting stresses, using Finite Element Analysis (FEA). The All-on-Four concept is a widely used solution for the rehabilitation of completely edentulous patients with advanced alveolar resorption, allowing the placement of four strategically positioned implants without the need for systematic bone augmentation procedures. In this protocol, the anterior implants are placed axially, while the posterior implants are angled to increase the anteroposterior distance and reduce the length of the prosthetic cantilever. In this research, three-dimensional models of the atrophied maxilla and mandible were obtained from computed tomography (CT) scan data and digitally reconstructed. Two main configurations were compared: a model with posterior implants with a straight neck and a model with implants with a 30° angled neck. The implant structures, multi-unit abutments, prosthetic superstructure, and cortical and trabecular bone tissues were modeled using computer-aided design software and then analyzed by a finite element solver. An oblique load of 218 N, applied at 30° to the longitudinal axis of the tooth at the first molar, was simulated to reproduce functional occlusal conditions. The maximum and minimum principal stresses in the cortical bone, as well as the Von Mises stresses in the implants, were evaluated. The results showed that modifying the implant neck geometry significantly influences the stress distribution, particularly in the posterior peri-implant cortical bone. Angled-neck implants allowed for a more homogeneous redistribution of compressive stresses, with a reduction in localized stress peaks in certain critical areas, particularly in osseointegrated models. Thus, finite element analysis confirmed that the design of the implant neck is a determining factor in the biomechanical behavior of the All-on-Four implant system, influencing primary stability, load transmission, and potentially the clinical longevity of the rehabilitation.