Objective <p>This study proposes a novel combined intraosseous-subperiosteal hybrid implant to rehabilitate severely atrophic edentulous mandibles. We aimed to elucidate its biomechanical behavior through finite element analysis.</p> Methods <p>Using CBCT data from an edentulous patient, we reconstructed a 3D mandibular model. We designed intraosseous fixtures tailored to the residual bone volume and fused them with superstructure abutments and a customized subperiosteal titanium mesh using 3-matic software. Four finite element models were assembled, varying in implant design and abutment count. These models were subjected to four loading conditions: anterior vertical, unilateral molar vertical, bilateral molar vertical, and unilateral molar lateral occlusions. Biomechanical performance was assessed by evaluating the maximum and minimum principal stresses in the peri-implant bone and the von Mises stresses in the prosthetic components.</p> Results <p>Under simulated masticatory loads, the novel combined intraosseous-subperiosteal hybrid implant exhibited stress levels well within the elastic range of the material, avoiding plastic deformation. Notably, the six-abutment configuration proved superior under posterior loading, reducing peak von Mises stress in screws by roughly 33% and in implants by 25.5% relative to ultra-short implants.</p> Conclusions <p>The proposed combined intraosseous-subperiosteal hybrid implant exhibits superior biomechanical stability for severe mandibular atrophy scenarios. By significantly mitigating stress concentrations, particularly in the six-abutment setup, this design presents a viable clinical alternative to overcome common prosthetic rehabilitation challenges.</p>