Effects of sliding velocity on friction: an in vitro study at extremely low sliding velocity approximating orthodontic tooth movement.

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 x 0.022-inch SS wires and superelastic nickel-titanium 0.016 x 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 x 10(-7), 1.0 x 10(-5), 1.0 x 10(-4), 1.0 x 10(-3), 1.0 x 10(-2), and 1.0 x 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 x 10(-7) mm/s sliding velocity (approximating orthodontic tooth movement) was 106.8 cN in 0.016 x 0.022-inch SS wires, almost double the 1.0 x 10(-1) mm/s sliding velocity. Conclusion: The effects of sliding velocity cannot be ignored when we estimate frictional forces in clinical orthodontics.