Multiforce orthodontic archwires are thermodynamic wires made of nickel-titanium alloy (Ni-Ti). They release biologically tolerable forces along their length, progressively increasing from front to back. The frontal archwires’ segments distribute the weakest force: the premolar, the greater, and the molar, the greatest. The aim of the present study was to determine the influence of clinical use on the mechanical properties of two types of multi-force orthodontic archwires (TriTanium®, American orthodontics; Bio-Active®, GC) with dimensions of 0.016 × 0.022 inches for periods of up to 8 weeks and over 8 weeks of in-vivo use. A three-point bending test was used, and the data gained is statistically analyzed through a multi-variance comparison Mann-Whitney test. We found that after uses of up to 8 weeks and over 8 weeks, the shape memory effect and superelasticity are preserved, as well as the tendency for differential force release along the length of the archwires is kept.

This study aimed to characterize and compare the latest generation multi-force Bio-active™ orthodontic archwires to determine if there is a change in their physicochemical and mechanical properties during orthodontic treatment. The physicochemical characterization of the archwires was done by X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy and laser-induced breakdown spectroscopy. A modified dynamic nanoindentation method with depth control was used to determine the mechanical properties. Statistical analysis was done by one-way analysis of variance (ANOVA). The XRD analysis showed that all investigated archwires are made of Ni-Ti alloy with an austenite crystal structure. The surface roughness of the Bio-active™ wires decreases after clinical use. The elemental composition analysis showed that the weight percentage of nickel and titanium is approximately 55 wt.% and 45 wt.%, respectively, and traces of Fe and Cr were registered in some regions. The results from nanoindentation experiments showed that the indentation hardness in the bicuspid part of archwires used for six weeks decreases by about 154%, and the indentation modulus decreases by about 44% compared to as received archwires, probably due to the changes in the morphology. Statistically significant differences in the chemical content are found for the anterior and bicuspid regions, while in the mechanical properties, for the bicuspid and posterior regions of the investigated archwires. The obtained results give orthodontists important information about the physicochemical and mechanical properties of the Bio-active™ multi-force archwires during their clinical use.

Multiforce nickel–titanium (NiTi) orthodontic archwires release progressively increasing forces in a front-to-back direction along their length. The properties of NiTi orthodontic archwires depend on the correlation and characteristics of their microstructural phases (austenite, martensite and the intermediate R-phase). From a clinical and manufacturing point of view, the determination of the austenite finish (Af) temperature is of the greatest importance, as in the austenitic phase, the alloy is most stable and exhibits the final workable form. The main purpose of using multiforce orthodontic archwires is to decrease the intensity of the applied forces to the teeth with a small root surface area, such as the lower central incisors, and also provide forces high enough to move the molars. With the optimally dosed forces of multiforce orthodontic archwires in the frontal, premolar and molar segments, the feeling of pain can be reduced. This will contribute to the greater cooperation of the patient, which is of utmost importance to achieve optimal results. The aim of this research was to determine the Af temperature at each segment of as-received and retrieved Bio-Active® and TriTanium® archwires with dimensions of 0.016 × 0.022 inches, investigated by the differential scanning calorimetry (DSC) method. A classical Kruskal–Wallis one-way ANOVA test and multi-variance comparison based on the ANOVA test statistic using the Bonferroni corrected Mann–Whitney test for multiple comparisons were used. The incisor, premolar and molar segments have different Af temperatures, and they decrease from the anterior to posterior so that the posterior segment has the lowest Af. Bio-Active® and TriTanium® with dimensions of 0.016 × 0.022 inches can be used as first leveling archwires by additional cooling and are not recommended for use on patients with mouth breathing.