Evaluation of friction during sliding tooth movement in various bracket-arch wire combinations

Frictional forces during simulated sliding tooth movement were measured with a model that was representative of the clinical condition. The model allowed tipping of the tooth until contact was established between the arch wire and diagonally opposite corners of the bracket wings; it also allowed rotation until the wire contacted opposite corners of the ligature tie, or the buccal shield with self-ligating brackets, and the base of the slot. Conventional and self-ligating stainless steel brackets as well as conventional ceramic brackets, and ceramic brackets with a stainless steel slot, all with 0.022 inch bracket slot, were tested with 0.019 x 0.025 inch arch wires of stainless steel, nickel titanium, and beta titanium. Each of the 12 bracket-arch wire combinations was tested 10 times. No significant interaction was detected between brackets and arch wires (P = .89), but the bracket and arch wire effects were significant (P < .001). The pairwise differences between conventional and self-ligating stainless steel brackets and ceramic brackets with stainless steel slot were not significant. However, the conventional ceramic brackets generated significantly higher friction than the other brackets tested. Beta titanium arch wires produced higher frictional forces than nickel titanium arch wires, but no significant differences were found between each of the two and stainless steel arch wires. Attempts to identify differences in surface scratches of the arch wires produced by the different brackets were unsuccessful.