Does the transition temperature of Cu-NiTi archwires affect the amount of tooth movement during alignment?

OBJECTIVES: To examine whether the transition temperature of Cu-NiTi archwires has an effect on the tooth movement during the alignment phase of orthodontic treatment.
DESIGN: 'Split mouth' design in randomly selected patients. SETTING AND SAMPLE POPULATION: The Department of Orthodontics, School of Dentistry, University of Aarhus. Fifteen randomly selected patients with identical level of irregularity in the alignment phase of their treatment. Experiment Variable - Specially manufactured Cu-NiTi archwires for the upper arch were inserted. These consisted of two separate halves, each with its own transition temperature, respectively 27 degrees and 40 degrees C, and clamped together in the middle. OUTCOME MEASURE: The tooth movement, expressed as two translations and a rotation, in the occlusal plane was measured from the patients' intraoral photographs taken upon insertion of the archwires and again after 1 month.
RESULTS: Tooth movements tended to be larger on the 40 degrees C-side, however only in case of the total translation of the premolars was this difference significant. In general, patients had not noticed any difference between the two sides of the archwire, although one patient stated the 27 degrees C-side to be more comfortable as the 40 degrees C-side had bothered her when drinking hot beverages.
CONCLUSION: The transition temperature of Cu-NiTi archwires has indeed an effect on the amount of tooth movement during alignment. However, the differences are so small though that it is the question whether they can be noticed clinically. The study corroborates the trend towards the use of lower forces within orthodontics.