This article reviews epidemiologic studies and basic researches concerning the mechanical risk factors that cause overload in implant occlusion. When natural teeth are adjacent to an implant, occlusal contact on the implant prosthesis requires a reduced initial mechanical load on the implant. This is called the implant-protected occlusion concept. However, few studies support this concept, and several researchers are concerned about the influence on the temporomandibular joint and the adjacent teeth when using this occlusal concept. It is thought that the same initial mechanical load on the implant and adjacent teeth does not result in an overload on the implant itself. The influence of a non-axial load, large cantilevers, and offset loading with a large occlusal table is greater than that of the axial load because of the bending moment. However, no epidemiologic study supports the biological influences of overloading. Meta-analysis of the connection of natural teeth and implants shows the biological and prosthetical risks.