Effects of third-order torque on frictional force of self-ligating brackets

Abstract

Objective: To investigate the effects of third-order torque on frictional properties of self-ligating brackets (SLBs).

Materials and methods: Three SLBs (two passive and one active) and three archwires (0.016 × 0.022-inch nickel-titanium, and 0.017 × 0.025-inch and 0.019 × 0.025-inch stainless steel) were used. Static friction was measured by drawing archwires though bracket slots with four torque levels (0°, 10°, 20°, 30°), using a mechanical testing machine (n = 10). A conventional stainless-steel bracket was used for comparison. RESULTS were subjected to Kruskal-Wallis and Mann-Whitney U-tests. Contact between the bracket and wire was studied using a scanning electron microscope.

Results: In most bracket-wire combinations, increasing the torque produced a significant increase in static friction. Most SLB-wire combinations at all torques produced less friction than that from the conventional bracket. Active-type SLB-wire combinations showed higher friction than that from passive-type SLB-wire combinations in most conditions. When increasing the torque, more contact between the wall of a bracket slot and the edge of a wire was observed for all bracket types.

Conclusions: Increasing torque when using SLBs causes an increase in friction, since contact between the bracket slot wall and the wire edge becomes greater; the design of brackets influences static friction.

Keywords: Archwire; Friction; SEM; Self-ligating brackets.

Figure 1.

Photographs of three self-ligating brackets and the conventional bracket used in the present study. (a) Damon Q. (b) SmartClip. (c) In-Ovation R. (d) Mini Uni-Twin.

Figure 2.

Friction testing system (a, b) Custom-fabricated frictional testing device attached to universal testing machine. (c, d) Bracket-mounting device. (e) Stainless-steel plate that could apply third-order torque to the bracket. A, grip; B, bracket-wire combination specimen; C, stainless-steel plate; D, weight (150 g); E, angle measurement device.

Figure 3.

Static frictional forces measured at four different bracket torques for the three self-ligating brackets and the conventional bracket with the nickel-titanium wire and the stainless-steel wires.

Figure 4.

Static frictional forces for the three self-ligating brackets and the conventional bracket with the nickel-titanium wire and the stainless-steel wires. DQ indicates Damon Q; SC, SmartClip; IO, In-Ovation R; MU(L), Mini Uni-Twin ligated with ligature wire; MU(E), Mini Uni-Twin ligated with elastomeric module.

Figure 5.

Scanning electron microscope photographs of cross-sectioned Damon Q bracket and each wire combination. (a–d) 0.016 × 0.022-inch nickel-titanium wire. (e–h) 0.017 × 0.025-inch stainless-steel wire. (i–l) 0.019 × 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0°. (b, f, j) Wire torque at 10°. (c, g, k) Wire torque at 20°. (d, h, l) Wire torque at 30°.

Figure 6.

Scanning electron microscope photographs of cross-sectioned SmartClip bracket and each wire combination. (a–d) 0.016 × 0.022-inch nickel-titanium wire. (e–h) 0.017 × 0.025-inch stainless steel wire. (i–l) 0.019 × 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0°. (b, f, j) Wire torque at 10°. (c, g, k) Wire torque at 20°. (d, h, l) Wire torque at 30°.

Figure 7.

Scanning electron microscope photographs of cross-sectioned In-Ovation R bracket and each wire combination. (a–d) 0.016 × 0.022-inch nickel-titanium wire. (e–h) 0.017 × 0.025-inch stainless-steel wire. (i–l) 0.019 × 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0°. (b, f, j) Wire torque at 10°. (c, g, k) Wire torque at 20°. (d, h, l) Wire torque at 30°.

Figure 8.

Scanning electron microscope photographs of cross-sectioned Mini Uni-Twin bracket and each wire combination. (a–d) 0.016 × 0.022-inch nickel-titanium wire. (e–h) 0.017 × 0.025-inch stainless-steel wire. (i–l) 0.019 × 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0°. (b, f, j) Wire torque at 10°. (c, g, k) Wire torque at 20°. (d, h, l) Wire torque at 30°.