Background <p>Implant-supported prostheses are widely used in posterior mandibular restorations, where biomechanical factors play a critical role in long-term performance. Abutment design may influence stress distribution within implant-supported systems, potentially affecting both prosthetic components and surrounding bone. This study aimed to evaluate stress distribution in three-unit implant-supported prostheses with different abutment designs using three-dimensional finite element analysis.</p> Methods <p>A three-dimensional finite element model of the posterior mandible with two implants (4.1&#xa0;mm diameter, 10&#xa0;mm length) placed in the first premolar and first molar regions was constructed. Three abutment designs (multi-unit, octa, and variobase) supporting monolithic zirconia restorations were analyzed. Vertical (150&#xa0;N) forces were applied perpendicular to the occlusal surfaces, and oblique (200&#xa0;N at 45°) forces were applied in the buccolingual direction. Stress distribution in implants, abutments, screws, restorations, and surrounding bone was evaluated.</p> Results <p>Stress distribution varied according to abutment design and loading condition. Variobase abutments showed higher stress concentrations in implants under both loading conditions, while octa abutments exhibited higher stress values in screws and restorations. Multi-unit abutments demonstrated relatively lower stress values in screws and restorations compared to other designs. Oblique loading produced higher stress levels than vertical loading across all components. Bone stress values increased under oblique loading conditions.</p> Conclusions <p>Within the limitations of this finite element analysis, abutment design influenced stress distribution in implant-supported prostheses, and loading direction affected stress magnitude. These findings provide biomechanical insight into the behavior of different abutment designs in posterior implant-supported restorations.</p>