Objective: To evaluate the effects of sliding velocity on friction, particularly at extremely low sliding velocity approximating orthodontic tooth movement. Materials and Methods: Stainless-steel (SS) 0.022-inch preadjusted brackets and 0.016- and 0.016 × 0.022-inch SS wires and superelastic nickel-titanium 0.016 × 0.022-inch wires were used for this test. The wire was secured in a SS preadjusted bracket with an elastomeric module. One end of the wire was pulled upward 1.5 mm at a speed of 5.0 × 10-7, 1.0 × 10-5, 1.0 × 10-4, 1.0 × 10 -3, 1.0 × 10-2, and 1.0 × 10-1 mm/s by the micrometer. The measurements were conducted 10 times and averaged. Tukey-Kramer tests were used to compare the mean differences of each testing measurement among the different sliding velocities. Results: The frictional forces tended to increase as the sliding velocity decreased. The mean frictional force for 5.0 ×10-7 mm/s sliding velocity (approximating orthodontic tooth movement) was 106.8 cN in 0.016× 0.022-inch SS wires, almost double the 1.0 ×10-1 mm/s sliding velocity. Conclusion: The effects of sliding velocity cannot be ignored when we estimate frictional forces in clinical orthodontics.
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