Frictional resistances of different bracket-wire combinations.

BACKGROUND: It has been suggested that the frictional resistance of ceramic brackets can be reduced by either lining the slots with stainless steel or by contouring the base of the slot.

OBJECTIVES: The objectives of this investigation were to compare in vitro the static and kinetic frictional resistances of ceramic brackets with metal lined slots ("Clarity", CL), stainless steel brackets ("Miniature Twin", MT), and two ceramic brackets with different slot designs ("Contour", CO; "Transcend", TR).

METHOD: Two sizes (0.018 x 0.025 inch; 0.021 x 0.025 inch) of stainless steel (SS), nickel titanium (NiTi) and beta titanium (beta-Ti) wires were drawn through the brackets. All brackets had 0.022 inch slots, and the brackets and wires were used once. The brackets were of different widths: CL, 0.180 inch; CO, 0.114 inch; MT, 0.118 inch; TR, 0.138 inch. An Instron Universal Testing Machine was used in this study.

RESULTS: There were no significant static or kinetic frictional differences when the smaller 0.018 x 0.025 inch wires were drawn through the brackets. There were no statistically significant static or kinetic frictional differences between the CL-CO, CL-MT and CO-MT bracket pairs when the 0.021 x 0.025 inch wires (SS, NiTi, beta-Ti) were used. There were no significant kinetic frictional resistance differences between the CL-TR and MT-TR when the SS wires were used. In general the static and kinetic resistances of the 0.021 x 0.025 inch wires of NiTi wire < SS wire < beta-Ti wire. Regardless of wire type some of the lowest kinetic resistances were found with the narrow CO brackets with the rounded slot bases. The highest static and kinetic frictional resistances were found with the wide TR bracket, and with stainless steel and beta-Ti wires.

CONCLUSION: The high static and kinetic frictional resistances of ceramic brackets can be reduced either by lining the slots with stainless steel or by reducing the bracket width and rounding the slot base.