ABSTRACT
Esthetic orthodontic archwires [fiber reinforced composite archwires] are considered as the latest addition to orthodontic's world, and the load deflection rate is thought to be the most important mechanical property of archwires which has strong effect clinically, and this property is affected by the cross section diameter and the material's type, for these reasons this study aims to investigate the effect of the material's type and the cross section diameter of orthodontic archwires on the load deflection rate of fiber reinforced composite [FRC] archwires with a diameter of 0.014 inch and 0.016 inch which are suitable for the leveling and alignment stage, and to compare these new materials with Nickel titanium [NiTi] arch wires. This in vitro study used 60 wire specimens which were divided equally in to two major groups [FRC Group and NiTi Group], and each major group was divided equally into two subdivision groups according to arch wires diameter [0.014 inch group and 0.016inch group]. Three points bending test was used to execute this study and was modified by adding two brackets. The applied forces and the produced force were measured. Partial Eta square had been used to estimate the effect of material's type and cross section of the arch wire on the load deflection rate. [P<0.05] for all studied stages. Values of partial eta square for material's type and cross section of the arch wire respectively were 0.965, 0.96 in stage 1, 0.912, 0.908 in stage 2 and 0.837, 0.843 in stage 3. There is a large impact of the cross section and material's type on the load deflection rate of FRC and NiTi arch wires