Metal fatigue failure of the gold screw used to retain a fixed prosthesis to Branemark osseointegrated fixtures/abutments has been analyzed theoretically. Mechanical engineering principles show the importance of appropriate preload being applied through the gold screw to the gold cylinder and abutment. The significance of the screw design and necessity of applying the correct torque to achieve a long fatigue life for the screw are also described. The consequence of misalignment of a gold cylinder to an abutment is discussed. Keywords: Brånemark System, metal fatigue, osseointegrated implants, preload, stress, torque