Static frictional force and surface roughness of nickel-titanium arch wires.

Surface roughness and static frictional force resistance of orthodontic arch wires were measured. Nine nickel-titanium alloy arch wires were studied. One beta-titanium alloy wire, one stainless steel alloy wire, and one cobalt-chromium alloy wire were included for comparison. Arithmetic average roughness in micrometers was measured with a profilometer. Frictional force resistance was quantified by pushing wire segments through the stainless steel self-ligating brackets of a four-tooth clinical model. The cobalt-chromium alloy and the nickel-titanium alloy wires, with the exception of Sentalloy and Orthonol, exhibited the lowest frictional resistance. The stainless steel alloy and the beta-titanium alloy wires showed the highest frictional resistance. The stainless steel alloy wire was the smoothest wire tested, whereas NiTi, Marsenol, and Orthonol were the roughest. No significant correlation was found between arithmetic average roughness and frictional force values.