Comparative assessment of frictional forces between differently designed esthetic brackets during simulated canine retraction.

Abstract

Objectives: To evaluate force loss due to friction (FR) with an emphasis on esthetic brackets and their design differences during simulated canine retraction.

Materials and methods: The tested brackets were round and sharp-cornered conventional-ligating brackets and round-cornered self-ligating brackets. The tested archwires were stainless steel (0.018 × 0.025″ and 0.019 × 0.025″, and 0.018″) archwires. A total of 90 bracket-archwire combinations in 9 equally-sized groups (n = 10) were analyzed. Canine retraction was experimentally simulated in a biomechanical set-up utilizing the custom-made orthodontic measurement and simulation system (OMSS) using a NiTi coil spring that delivered a constant force of 1 N. The simulated retraction path was up to 4 mm. FR was compared among groups using the Welch t‑test. Significance level (α) was set to 0.05.

Results: The round-cornered conventional-ligating bracket exhibited the least FR (28.6 ± 5.4%), while there were no significant differences in FR between the round-cornered conventional-ligating bracket and the round-cornered self-ligating bracket with 0.018″ stainless steel wires. However, the round-cornered self-ligating bracket exhibited the least FR (34.9 ± 5.1% and 39.3 ± 4.6%) with 0.018 × 0.025″ and 0.019 × 0.025″ stainless steel archwires, respectively. The sharp-cornered conventional-ligating bracket showed the highest FR of 72.4 ± 3.0% among the bracket systems tested in this study.

Conclusions: The round-cornered conventional-ligating bracket showed less FR when compared to sharp-cornered conventional-ligating bracket. Conversely, the round-cornered conventional-ligating bracket exhibited greater FR when compared to the round-cornered self-ligating bracket, with an exception with respect to the 0.018″ wire. In general, FR increased with increased wire dimension.