in vivo measurements of vertical forces and bending moments during biting and chewing were carried out on 10 three-unit prostheses in the posterior mandibles of five patients. Each patient had two prostheses, one supported by two implants and the other supported by one implant and one tooth. The results demonstrated no major difference in functional load magnitudes related to the support type. The distribution of load between the abutments was influenced more by the prosthesis geometry and implant placement than by the difference in load characteristics of tooth and implant. This conclusion, however, is limited to one implant connected to a tooth, because multiple implants form a considerably stiffer unit than do teeth. An increase in vertical load resulting from cantilever extensions on the prostheses was documented, both at bite fork measurements and during chewing. No substantial lateral bending was registered, probably because the flat occlusal surfaces and the presence of the opposing complete denture reduced lateral forces.