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.

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.

Rationale: Orthodontic archwires undergo chemical and structural changes in the complex intraoral environment. The present work aims to investigate the safe duration for intraoral use (related to the nickel release hypothesis) of different types of nickel-containing wires. By analyzing how the nickel content (NC) varies over time, we aim to provide practical recommendations for the optimal use of said archwires. Materials and Methods: Our analysis focuses on the following nickel-containing archwires: stainless steel, Ni-Ti superelastic, heat-activated NiTi and CuNiTi, and multi-force archwires. The studied archwires of each type were divided into three groups: group 1, as received; group 2, retrieved after intraoral exposure for less than 6 weeks; group 3, used for more than 8 weeks. To assess NC, measurements using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and laser-induced breakdown spectroscopy (LIBS) were performed in multiple regions of each wire. Statistical analysis of the measured values using one-way ANOVA and multiple group comparisons showed significant differences in nickel content between groups. The dynamic behavior of the statistical results for NC was then modeled using logistic regression and fitted with cubic splines. Conclusions: The proposed behavior model, with further refinement, could enable orthodontists to make informed, patient-specific decisions regarding the safe and effective use of orthodontic floss. The overall conclusion of the study is that due to stability, SS-CrNi, HA-Ni-Ti with Cu, and TriTanium^TM are suitable for long-term use, and due to higher nickel release, Ni-Ti-Superelastic, HA-Ni-Ti without Cu, and Bio-Active^TM are better for short- to medium-term use.

The manufacturing of orthodontic archwires made from NiTi alloy has undergone numerous changes from the second half of the last century to modern times. Initially, superelastic-active austenitic NiTi alloys were predominant, followed by thermodynamic-active martensitic NiTi alloys, and, finally, the most recent development was graded thermodynamic alloys. These advancements have been the subject of extensive investigation in numerous studies, as they necessitated a deeper understanding of their properties. Furthermore, it is imperative that we validate the information provided by manufacturers regarding these archwires through independent studies. This review evaluates existing studies on the subject with a specific focus on the Bio-active multi-force NiTi archwire, by examining its mechanical, thermal, and physicochemical properties before and after clinical use. This archwire consists primarily of Ni and Ti, with traces of Fe and Cr, which release graduated, biologically tolerable forces which increase in a front-to-back direction and are affected by the temperature of the environment they are in. The review provides information to practicing orthodontists, facilitating informed decisions regarding the selection and use of Bio-active™ archwires for individual patient treatments.

Objectives: To evaluate the corrosion behavior and surface characteristics of four nickel-containing orthodontic archwires (stainless steel (SS), superelastic nickel–titanium (NiTi), copper–nickel–titanium (CuNiTi), and multiforce NiTi) under unused, in vitro artificial saliva-immersed, and clinically used (in vivo) conditions. Methods: Rectangular SS, NiTi, CuNiTi, and multiforce NiTi archwires were analyzed in the following three conditions: as received, after one week of immersion in artificial saliva (pH 6.4), and after clinical use for 6–8 weeks. Corrosion behavior was assessed using cyclic voltammetry (CV), open-circuit voltammetry (OCV), and electrochemical impedance spectroscopy (EIS). Surface morphology was examined by scanning electron microscopy (SEM). Results: Corrosion behavior was dependent on archwire type and exposure condition. SS archwires exhibited reduced impedance response after clinical use, indicating passive-film degradation. In the clinically used NiTi specimen, pronounced electrochemical instability was observed, characterized by a deep OCV transient, slow repassivation, and SEM evidence compatible with localized pitting corrosion. In the CuNiTi specimens, minimal differences were observed between the unused and clinically used conditions, which may be consistent with stable passive-film integrity in these specimens. In the multiforce specimen, clinical use was associated with a higher impedance response than the unused and saliva-immersed conditions of that same specimen. In the saliva-immersed specimens, possible passive-film formation and a higher impedance response were observed relative to the other conditions of the same specimens, but these did not reproduce the electrochemical and morphological changes observed after clinical use. Conclusions: In vitro artificial saliva immersion does not reliably replicate in vivo aging of nickel-containing orthodontic archwires. Corrosion behavior evolves during clinical service in an archwire-specific manner, with NiTi archwires showing susceptibility to clinically induced surface degradation.