“…12,13 The absence of form lock and friction, as found in internal-taper designs, results in lack of protection against the bending forces in the system implicated in screw loosening. 14,15 Causes of screw loosen ing or fracture have been identifi ed as inadequate tightening, adverse occlusal forces, and fatigue character and yield ing strength of the screw material. 16,17 Additionally, the surface of a new metal screw has microscopic surface imperfec tions in the form of high spots, grooves, and irregularities, such that when initial torque is applied only the high spots in the system will be in contact.…”