Evaluation of Stress Distribution in "All-on-Four" Prostheses: A Three-Dimensional Finite Element Analysis

The growing demand for implant-supported rehabilitative prosthetic treatments has reinforced the need to optimize biomechanical performance, particularly regarding force distribution. This study aimed to evaluate the stress distribution generated by different configurations of full-arch implant-supported prostheses using three-dimensional finite element analysis. Two mandibular models were created using SolidWorks 2010 (SolidWorks Corp., Waltham, MA, USA) and Rhinoceros^® 3D 4.0 (NURBS Modeling for Windows, USA). Each model represented a mandible restored with a full-arch fixed prosthesis supported by external hex implants (4.0 × 13.0 mm; Master, Conexão Sistemas de Prótese, São Paulo, Brazil) placed in the interforaminal region, differing only in implant angulation. Model 1 included four implants positioned perpendicular to the alveolar ridge, whereas Model 2 represented the All-on-Four configuration with distal implants tilted at 30°. The prosthesis was modeled in acrylic resin with a NiCr metal framework. The geometries were exported to FEMAP 11.0 for mesh generation. Axial loading of 300 N was applied bilaterally (75 N per tooth), and oblique loading of 150 N was applied unilaterally (75 N per tooth) on the first premolars and first molars. Obtained using NEiNastran^® 9.2 showed that the tilted-implant model exhibited higher stress concentrations under both loading conditions. The All-on-Four configuration generated the highest stress levels, particularly around the distal implants. The null hypothesis of this study was that there would be no difference in stress distribution among full-arch implant-supported prostheses supported by straight implants and those rehabilitated according to the All-on-Four concept with tilted distal implants.