Purpose: To analyze the impact of microthreads on the stresses generated in peri-implant bone surrounding reduced-diameter zirconia and titanium implants under loading. Materials and Methods: Two custommade zirconia implants, microthreaded or smooth neck, and two titanium replicas were made. Strains were recorded in the peri-implant region under 200-N vertical load. Two three-dimensional finite element models were created. Zirconia and titanium implants were tested under 200-N vertical load and 150-N oblique load at 30, 45, and 60 degrees. Results: The lowest peri-implant strain (40 ± 6 με) under vertical load was related to the microthreaded zirconia implant. Oblique load showed higher von Mises stress on bone in comparison with vertical load. The von Mises stress increased by increasing the load angle by approximately 2 MPa per degree. Under oblique load, implants showed more stress in peri-implant bone and the implant itself. On the other hand, total strains were within physiologic limits in all tested cases. Conclusion: Stresses within the peri-implant cortical bone around the reduced-diameter implant with microthreads appeared to be superior compared with the smooth-neck one. Reduced-diameter zirconia implants induced less stress on bone in comparison with the titanium implants, suggesting that zirconia is a feasible alternative for titanium. Keywords: finite element model, implant, reduced-diameter, single-piece, strain gauge