Biomechanical evaluation of three full-arch immediate loading protocols in the mandible via finite element analysis: All-on-4, Trefoil, and Five-implant design

Background: Edentulism in the mandible poses major functional and biomechanical challenges, as conventional dentures often fail to provide stability due to progressive bone resorption. Immediate loading full-arch implant protocols such as All-on-4, Trefoil, and Five-Implant designs have been developed to improve masticatory efficiency and long-term outcomes. Finite element analysis (FEA) enables the biomechanical assessment of these approaches by simulating stress, strain, and deformation under functional loads. This study aimed to biomechanically compare three immediate loading full-arch rehabilitation protocols—Trefoil, All-on-4, and 5-Implant designs—in the edentulous mandible using three-dimensional finite element analysis (FEA), focusing on stress distribution, strain accumulation, and deformation patterns under functional loading. Materials and Methods: A digital edentulous mandible model was constructed, incorporating cortical and cancellous bone layers, and standardized prosthetic designs for each configuration. Three implant-supported protocols were simulated: Trefoil (three axial implants with a prefabricated bar), All-on-4 (two axial anterior and two posterior tilted implants), and a Five-Implant design (implants at midline, canine, and second premolar positions). The implant–bone interface, simulating immediate loading without full osseointegration, was assigned a coefficient of 0.30. A 100 N axial and oblique load was applied to the first molar's central fossa. Stress distribution, equivalent strain, and deformation across these three treatment modalities were analyzed using FEA software. Results: The Five-Implant model exhibited the most favorable biomechanical outcomes, demonstrating the lowest stress and strain values across prosthesis, implant components, and cortical bone. The Trefoil system showed the highest prosthetic stress (156.48 MPa axial; 119.32 MPa oblique) and abutment screw deformation, attributed to its reduced implant support and increased cantilever length. The All-on-4 configuration generated elevated cortical bone strain under oblique loading (4180 με), surpassing the pathological overload threshold (>4000 με). In contrast, the Five-Implant model maintained cortical strain within the physiological remodeling range across all loading scenarios. Conclusion: Implant number and distribution significantly affect biomechanical behavior in full-arch immediate loading protocols. While the Five-Implant design offers biomechanical superiority in stress mitigation and bone preservation, Trefoil and All-on-4 configurations present design-dependent biomechanical challenges. Individualized treatment planning considering anatomical limitations and functional loading conditions is essential to optimize clinical outcomes.