Nitinol wires are now widely used in the orthodontic field because of their unique shape memory effect and superelasticity. But sometimes Nitinol wires are deformed in clinical use. Fatigue load is possible cause of Nitinol deformation. To determine the effect of fatigue load to the mechanical properties of Nitinol, various fatigue cycle(1X104, 2X104, 3X104, 4X104, 5X104, 1X105) were applied to 0.017 X 0.025 inch Nitinol. The results obtained were as follows; 1. Applied load increased as fatigue cycle increased in three point bending test. 2. Maximum tensile strength and elongation decreased as fatigue cycle increased. 3. In SEM, brittle fracture pattern was increased when fatigue cycle increased.
