Evaluation of titanium brackets for orthodontic treatment: part I. The passive configuration

The static and kinetic frictional coefficients of commercially pure titanium brackets were evaluated in the passive configuration in the dry and wet states against stainless steel, nickel-titanium, and beta-titanium arch wires. For comparison, stainless steel brackets were evaluated under identical conditions. Titanium brackets were grayer in color and rougher in texture than the stainless steel brackets. Bracket slots were up to 0.002 inch greater than the nominally stated values. Remarkably, the static and kinetic frictional coefficients of the couples formed by titanium and stainless steel brackets were comparable. When evaluated against stainless steel and nickel-titanium arch wires in the dry state at 34 degrees C, the static coefficient averaged.12 and.20, respectively, independent of bracket alloy. When evaluated against stainless steel and nickel-titanium wires in the wet state at 34 degrees C using human saliva, the static coefficient averaged.15 and.20, respectively, independent of bracket alloy. Only the beta-titanium arch wires increased by about 15%, when tested in either the dry or the wet state against titanium versus stainless steel brackets. Noteworthy, too, was the decrease of both coefficients in the beta-titanium wire couples from their previously reported values. Analyses of electron spectroscopy for chemical analysis spectra and depth profiles show that these new brackets are titanium only in the bulk. Indeed the immediate surfaces are composed of, at least, 80 atomic percent (at.%) carbon and oxygen; whereas, the titanium that is present (>11 at.%) is mostly in the form of titanium dioxide. The presence of this quite thin passivating layer, which resides on top of an oxygen-hardened titanium substrate, reduces the galling and fretting that would normally be expected in such materials. Pending the outcome of future angulation tests, these frictional measurements show that titanium brackets are not only comparable to stainless steel brackets but also are more biocompatible with nickel having been eliminated from their constitution.