Thermal analysis of as-received and clinically retrieved copper-nickel-titanium orthodontic archwires.

OBJECTIVE To compare as-received copper-nickel-titanium (CuNiTi) archwires to those used in patients by means of differential scanning calorimetry (DSC). Also, the thermal or phase properties of 27 degrees C, 35 degrees C, and 40 degrees C CuNiTi archwires were studied to ascertain if their properties match those indicated by the manufacturer. MATERIALS AND METHODS Six wires of 27 degrees C, 35 degrees C, and 40 degrees C CuNiTi were tested as-received, and six each of the 27 degrees C and 35 degrees C wires were examined after use in patients for an average of approximately 9 and 7 weeks, respectively. Segments of archwire were investigated by DSC over the temperature range from -100 degrees C to 150 degrees C at 10 degrees C per minute. RESULTS There were no significant differences between as-received and clinically used 27 degrees C and 35 degrees C wires for all parameters (heating onset, endset, and enthalpy and cooling onset, endset, and enthalpy), except the 27 degrees C wires exhibited a significant decrease in the heating enthalpy associated with the martensite-to-austenite transition after clinical use. The heating endsets (austenite finish temperatures) of the 27 degrees C and 35 degrees C wires were within 2 degrees C of those claimed by the manufacturer, but the 40 degrees C wires were found to be nearer to 36 degrees C than 40 degrees C. CONCLUSIONS Clinical use of CuNiTi wires resulted in few differences when compared with as-received wires analyzed by DSC. Two temperature varieties of CuNiTi are reasonably within the parameters of those identified by the manufacturer.