Background Orthodontic tooth movement relies on sliding mechanics usually achieved by sliding the archwire through brackets. Sliding causes friction which is a force resisting the relative motion of two contacting objects. Frictional resistance is undesirable in orthodontic tooth movement because the archwire might bind with the bracket and prevent tooth movement. In addition, friction causes bending of the archwire leading to unwanted tooth movement or space loss through anchorage interference, prolonging the treatment time and root resorption. This study was performed to compare the frictional resistance produced by different types of ceramic brackets and stainless steel brackets with Teflon-coated stainless steel and stainless steel archwires. The surface texture of the wire before and after friction test was also evaluated using a scanning electron microscope (SEM). Methodology A total of 48 samples were tested. In total, 12 premolar brackets each of stainless steel (Ortho technology, Carlsbad, CA, USA), monocrystalline ceramic (Ortho technology, Carlsbad, CA, USA), polycrystalline ceramic (Ortho technology, Carlsbad, CA, USA), and ceramic bracket with a metal slot (Ortho technology, Carlsbad, CA, USA) having an 0.022-inch slot were coupled with 0.019 × 0.025-inch stainless steel and Teflon-coated stainless steel wires. Each bracket-wire assembly was vertically mounted and clamped to the jaws of the universal testing machine. The wire was pulled across the bracket with a cross head speed of 10 mm per minute. The readings obtained were recorded. To evaluate the surface roughness, wires were examined using an SEM (in four magnifications 250×, 500×, 1,000×, and 5,000×) before and after testing. Results Under the testing conditions, the stainless steel bracket-stainless steel wire combination produced the least frictional resistance, and the polycrystalline ceramic bracket-stainless steel wire combination produced the highest frictional resistance. Ceramic brackets with a metal slot generated lesser friction than other types of ceramic brackets but more friction than stainless steel brackets. Moreover, for all bracket-archwire combinations, Teflon-coated wires generated reduced frictional resistance compared to stainless steel wires. The surface examination of Teflon-coated stainless steel wire and conventional uncoated stainless steel wire revealed that Teflon-coated wire had a smoother surface compared to uncoated stainless steel wire. Conclusions Within the limitations of this study, it was concluded that the stainless steel bracket produced the lowest frictional resistance and the polycrystalline ceramic bracket produced the highest frictional resistance. Ceramic brackets with a metal slot showed a coefficient of friction that was more than but comparable to that of stainless steel brackets. Monocrystalline ceramic brackets generated lesser friction compared to polycrystalline ceramic brackets. Further, Teflon coating of stainless steel archwires can reduce frictional resistance compared to conventional uncoated stainless steel archwires. The surface of Teflon-coated stainless steel wires was found to be smoother than uncoated stainless steel wires.
Keywords: ceramic bracket; ceramic bracket with metal slot; esthetic brackets; friction; scanning electron microscope; stainless steel; surface roughness; teflon-coated stainless steel; universal testing machine.
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