ABSTRACT
OBJECTIVE: The purpose of this study was to evaluate the influence of intraoral temperature changes on the orthodontic force level of a superelastic nickel-titanium alloy wire. METHODS: Nickel-titanium archwires of 0.016" x 0.022" thickness were tested with a three point bending test setup, and temperature changes were applied. The force level changes according to temperature changes were measured at a 1.5 mm deflection during the loading phase and a 1.5 mm deflection during the unloading phase from a deflection to 3.1 mm. Ten cycles of thermal cycling from baseline (37 degrees C) to cold (20 degrees C) or hot (50 degrees C) temperature were applied. RESULTS: After thermal cycling, the force level during the loading phase decreased and the force level during the unloading phase increased even after the temperature was changed to the initial 37 degrees C. CONCLUSIONS: The results suggest that the orthodontic force level can not return to the initial force level after temperature changes. When applying superelastic nickel-titanium archwires, we must consider that a lighter force than the loading force and a heavier force than the unloading force will be applied after intraoral temperature changes caused by eating and drinking.