Abstract
BACKGROUND: Immediate-loading full-arch concepts such as All-on-4, Trefoil, and Five-Implant protocols are widely used for mandibular rehabilitation, yet their comparative biomechanical behavior remains insufficiently defined. 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 (3D) 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 (midline, canine, and second premolar implants). The implant-bone interface, simulating immediate loading without full osseointegration, was assigned a coefficient of 0.30. Axial and 45° oblique loads of 100 N were applied to the first molar. Von Mises stress, principal stresses, equivalent strain, and total deformation were analyzed. 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. All-on-4 generated elevated cortical bone strain under oblique loading (4180 με), surpassing the pathological overload threshold (>4000 με), whereas, the Five-Implant model maintained cortical strain within the physiological remodeling range. CONCLUSION: Implant number and distribution significantly affect biomechanical behavior in immediate full-arch rehabilitation. The Five-Implant design offers biomechanical superiority in stress mitigation and bone-strain control, while Trefoil and All-on-4 configurations present design-dependent biomechanical challenges. Treatment planning considering anatomical limitations and functional loading conditions is essential to optimize clinical outcomes.