Purpose: The purpose of the three-dimensional (3D) finite element analysis study was to compare the use of titaniumzirconium (Ti-Zr) narrow-diameter implants as an alternative to titanium (Ti) or Ti-Zr standard-diameter implants in the posterior jaw regions. Materials and Methods: Ti-Zr and Ti standard-diameter implants (4.1 mm) and Ti-Zr narrow-diameter implants (3.3 mm) in cylindrical (parallel) macrodesign were simulated in the mandibular and maxillary first premolar area. Forces of 100 N were applied to the crowns in a vertical and oblique (45-degree angle to the long axis) direction. The von Mises stresses and fatigue strength values of the implants and principal stresses in the bone structures were evaluated. Results: In vertical and oblique force application, stress data in cortical and trabecular bone structures were found to be higher in 3.3-mm Ti-Zr narrow-diameter implant models than 4.1-mm Ti-Zr and Ti standard-diameter implant models. Also, the von Mises stress data of the 3.3-mm Ti-Zr narrow-diameter implants were higher than the 4.1-mm Ti-Zr and Ti standard-diameter implants. The shortest cycle of fatigue failure and estimated duration of clinical success (years) results were found in the mandibular 3.3-mm Ti-Zr implant model under oblique force, and these results remained below the identified 30-year critical threshold. Conclusion: Considering all implant models, Ti-Zr narrow-diameter implants exhibited higher stress values than Ti-Zr and Ti standard-diameter implants. In the premolar region, care should be taken biomechanically when using Ti-Zr narrow-diameter implants as an alternative to standard-diameter implants. Further comparative and in vivo studies are needed to examine the long-term success of Ti-Zr narrow-diameter implants as an alternative to standard-diameter implants. Keywords: failure analysis, finite element analysis, narrow-diameter implant, standard-diameter implant