A study of the regional load deflection rate of multiloop edgewise arch wire

To quantify the unique mechanical properties of multiloop edgewise arch wire (MEAW), its load deflection rate (LDR) and the LDR of various arch wires in the individual interbracket span were measured and compared. The MEAW arch wires were made out of .016 x .022-inch Permachrome stainless steel wire with L-loops of 4 different sizes. Five samples of each size were prepared for the comparison against wires of plain stainless steel, TMA, and nickel-titanium (NiTi) wires, all of the same dimensions. Five specimens for each of the various wires were used to eliminate the possibility of change in the physical properties of wires caused by the stress from repeated measurement. The LDR was measured by using the Instron model 4466 at a crosshead speed of 1 mm/min and maximum deflection of 1.0 mm. The regional wire stiffness of MEAW was calculated from the LDR in the interbracket spans that were measured by the Instron. The findings were as follows: (1) The LDR of the L-loop of MEAW at an individual interbracket span rate was 1:7.54 of the plain stainless steel wire, 1:1.76 of the NiTi, and 1:2.72 of TMA. (2) The L-loop at an individual interbracket span showed much lower wire stiffness than the entire arch wire, and the value of the stiffness differed according to the region.