The resistance and retention of a fixed partial denture are influenced by the number and distribution of the abutment teeth that support it, the path of insertion, the shape of the arch to which it must conform, and the occlusal relationship it will have with the opposing teeth. If the prosthesis is to be designed properly, it is necessary to understand how each of these factors influences the stability of the prosthesis and its ability to resist dislodgment. If the conditions that contribute to the instability of the prosthesis are misunderstood, overlooked, or ignored, it is impossible to design a prosthesis that will be predictably successfull.