Effect of bracket bevel design and oral environmental factors on frictional resistance

Abstract

Objective: To investigate the effects of bracket bevel design and oral environmental factors (saliva, temperature) on frictional resistance.

Materials and methods: Five types of brackets, namely a conventional bracket (Omni-arch), an active self-ligating bracket (Clippy), and three passive self-ligating brackets (Carriere, Damon, and Tenbrook T1) coupled with a 0.014-inch austenitic nickel-titanium archwire were tested. In the experimental model, which used a group of five identical brackets, the center bracket was displaced 3 mm to mimic the binding effects. The friction experiments were performed at three temperatures (20°C, 37°C, 55°C) in a dry or a wet (artificial saliva) state. Finally, the surfaces of the bracket slots were observed using scanning electron microscopy (SEM) before and after the friction tests.

Results: The sliding frictional force was significantly influenced by the bracket slot bevel and saliva whether in the active or passive configuration (P < .05). The frictional force significantly increased as the temperature increased in the active configuration (P < .01). Based on the SEM observations, a correlation was found among the level of frictional force, the bevel angle, and the depth of scratches on bracket bevels.

Conclusion: Frictional force can be reduced by increasing the bevel angle and by lowering the oral temperature, whereas the presence of saliva increases frictional resistance.

Figure 1.

Customized experiment model. (A) 0-mm position of center bracket (passive configuration). (B) 3-mm displacement of center bracket (active configuration).

Figure 2.

Experiment setup. (A) Temperature-controlled chamber. (B) Temperature controller. (C) Peristaltic pump.

Figure 3.

Force-displacement plots. Each combination was tested three times (T1, T2, T3). The kinetic frictional force was determined by averaging the readings on the Y-axis at intervals of constant drawing force.

Figure 4.

Top view, SEM images of five types of bracket, at 20× (left column) and 100× (right column). (A) (F), Omni-arch (conventional bracket). (B) (G), Clippy (ASLB). (C) (H), Carriere (PSLB). (D) (I), Damon (PSLB). (E) (J), Tenbrook T1 (PSLB).

Figure 5.

SEM images (100×) of Omni-arch (conventional) bracket slot under six oral conditions taken after friction test in the active configuration. Scratches are indicated by arrows. (A) 20°C dry state. (B) 37°C dry state. (C) 55°C dry state. (D) 20°C wet state. (E) 37°C wet state. (F) 55°C wet state.

Figure 6.

SEM images (100×) of Clippy (ASLB, left column) and Carriere (PSLB, right column) bracket slots under various oral conditions taken after friction test in the active configuration. Scratches are indicated by arrows. (A) (E), 37°C dry state. (B) (F), 37°C wet state. (C) (G), 55°C dry state. (D) (H), 55°C wet state.

Figure 7.

SEM images (100×) of Damon (left column) and Tenbrook T1 (right column) bracket slots under two different oral conditions taken after friction test in the active configuration. Scratches are indicated by arrow. (A) (C), 37°C wet state. (B) (D), 55°C wet state.