THERMAL BEHAVIOUR OF AS RECEIVED BIO-ACTIVE® ORTHODONTIC ARCHWIRES STUDIED BY DSC METHOD

BIO-ACTIVE is a new generation Ni-Ti archwires, which exert progressive forces, from the midline to the posterior sectors. Each Ni-Ti alloy has a specific temperature range (TTR) in which the phase transition from martensite to austenite and vice versa takes place. The differences between the Af in the three regions, may lead to some changes in modulus of elasticity of each sector, resulting in a variable force release along archwire' s length without changing the cross-section size (lowest in the frontal area, increasing at the premolar and highest at the molar).
The aim of our research is to determine Austenite finish temperature at each segment (frontal, premolar and molar) of as received Bio-active® archwire. As received upper Bio-active® orthodontic archwires with dimensions 0.016 x 0.022 inches, were investigated by DSC method. Each of the wire segments was prepared as follows: one side of the archwire was divided into three 30 mm long segments representing incisor, premolar, and molar sections. From one investigated archwire are formed six samples.
Upon cooling each segment has presented an R phase. Incisor, premolar and molar segments have different Af temperatures and they decrease from anterior to posterior, so that the posterior segment has the lowest Af and peak temperatures. Af temperature is close to the room temperature, so the Bio-active® is in austenite phase. The dual peaks in each segment can be interpreted as a two-step transformation from martensite to an intermediate R phase and then to austenite.


Keywords: Bio-active, DSC-method, thermal behavior

Mirela Georgieva

DDS, Postgraduate student and PhD candidate, Orthodontics Department, Faculty of Dental Medicine, Medical University – Sofia, Bulgaria