Objective: To compare the mechanical properties of different phase transformation of nickel-titanium orthodontic archwires.
Methods: Nickel-titanium orthodontic archwires with same-sized (0.016") but different phase transformation were examined using a three-point bend test. Samples were tested at same conditions and oral temperature(37 degree), but in different utmost strain capacity, then the strain-stress chart was obtained, the phase transformation point (Af) was also examined.
Result: The wires of the highest phase transformation point had the least orthodontic force; on the contrast the least phase transformation point had the highest orthodontic force at 3.0 mm utmost strain capacity. The orthodontic forces were not different at the little strain capacity (P >0.05), but which was significantly different adove the 0.5 mm (P<0.05), which was same as 3.0 mm.
Conclusion: The nickel-titanium orthodontic archwires with high level of phase transformation have low orthodontic forces and more stability.