This investigation was designed to determine the effects of wire size, bracket width and the number of bracket on bracket-wire dynamic frictional resistance during simulating arch wire-guided tooth movement in vitro. For simulation of an arch wire-guided tooth movement, we simulated tooth, periodontal ligament and cancellous bone. Maxillary premolar and 1st molar were simulated as real sized resin teeth, the simulated resin teeth which its root was coated by polyether impression material which its elastic modulus is similar to periodontal ligament were embedded in steel housing with inlay wax which its elastic modulus is similar to cancellous bone. Stainless steel wires in four wire size (0.016, 0.018, 0.016 X 0.022, 0.019 X 0.025 inch) were examined with respect to three (stainless steel) bracket widths (2.4, 3.0, 4.3nun) and the number of medium bracket(one, two, three) included in the experimental assembly under dry condition. The wires were ligated into the brackets with elastomeric module.
The results were as follows
1. In all the brackets, frictional resistance increased with increase in wire size. But, statistically similar levels of frictional resistance were observed between 0.018 inch and 0.016 X 0.022 inch wires in narrow bracket and also between 0.016
inch and 0.018 inch wire in wide backer.
2. The frictional forces produced by 0.016 inch wire were statistically similar levels in all the brackets. In 0.018 inch round wire, wide bracket was associated with lower amounts of friction than both narrow and medium brackets. In 0.01€ X 0.022, 0.019 X 0.0"25 inch rectangular wire, wide bracket produced larger friction than both narrow and medium brackets. In all the wires, narrow and medium bracket demonstrated no statistical difference in levels of frictional resistance.
3. Frictional resistance increased with increase in number of medium bracket. 0.016 inch round wire demonstrated the greatest increment in frictional resistance, followed by 0.019 X 0.025, 0.016 X 0.022 inch rectangular wire which were similar level in increment of frictional resistance, 0.018 inch wire demonstrated the least increment. The increments of frictional resistance were not constantly direct proportion to number of bracket.
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