COMPARISONS OF THE THERMODYNAMIC PROPERTIES OF 3 NICKEL-TITANIUM ORTHODONTIC ARCHWIRES

The unique memory property of thermodynamic wire is only partially und erstood. It is believed to result from the wire's inherent capability to markedly alter its atomic bonding forces as a function of temperatu re. This shape recovery phenomenon may be the result of a transition i n crystal structure that occurs by deformation and cooling. When the t ransition is reversed, by heating, the structure reverts to its origin al form and abrupt property changes occur. The purpose of th is study was to determine the transition temperature ranges (TTR) of three comm ercially available thermodynamic archwires and to determine the rate o f recovery of the wires when bent to a uniform shape. A jig was constr ucted to hold the wires and was suspended in a water bath within a ple xiglass box. The temperature of the water bath was gradually increased .:A program was written to acquire a single video frame from a running video tape and then allow the operator to graphically overlay the pos ition of each wire specimen. The results indicate that the TTRs for th e three commercially available thermodynamic wires are of similar magn itudes ( ($) over bar x = 6.7 degrees C, 6.2 degrees C and 6.7 degrees C). The greatest differences were in the standard deviations (1.3 deg rees C, 2.2 degrees C and 3.7 degrees C) which may be a function of ma nufacturing during alloying of the wire and/or its heat treatment.