Purpose: Since natural dental arches usually form Monson or Spee occlusal curvatures among the posterior teeth, they tend to incline in mesial and lingual directions. The purpose of this study was to examine the biomechanical rationale for placing implants according to these curvatures in the mandibular posterior region. Materials and Methods: A 3-dimensional finite element model was created in which 2 implants were placed in the mandibular molar area. Stress distribution in the bone around the implants was analyzed under different distal implant inclinations. Results: Stress in the cervical area of the mesial and distal implants and the surrounding bone was higher when the implants were placed parallel to each other compared to when the distal implant was placed with a mesial or mesiolingual inclination. Discussion: The slightly smaller effect of a mesiolingual inclination compared to a mesial inclination can be explained by the large cantilever on the buccal side of the superstructure. Conclusion: Within the limitations of this study, it was suggested that there is a biomechanical rationale for placing implants in the posterior mandible area with a mesial inclination similar to that of natural teeth. It was also suggested that too much lingual inclination can put the implant at risk of overload.