Thermo-mechanical properties in bending of a multizone nickel-titanium archwire: A retrieval analysis

Abstract

Objective: This study aimed to compare the mechanical and thermal properties in the anterior and posterior segments of new and retrieved specimens of a commercially available multizone superelastic nickel-titanium (NiTi) archwire. Methods:The following groups of 0.016 × 0.022-inch Bioforce NiTi archwires were compared: a) anterior and b) posterior segments of new specimens and c) anterior and d) posterior segments of retrieved specimens. Six specimens were evaluated in each group, by three-point bending and bend and free recovery tests. Bending moduli (Eb) were calculated. Furthermore, the new specimens were evaluated with scanning electron microscopy/energy-dispersive X-ray spectrometry. A multiple linear regression model with a random intercept at the wire level was applied for data analysis. Results: The forces in the posterior segments or new specimens were higher than those recorded in the anterior segments or retrieved specimens, respectively. Accordingly, Eb also varied. Higher austenite start and austenite finish (Af) temperatures were recorded in the anterior segments. No statistically significant differences were found for these temperatures between retrieved and new wires. The mean elemental composition was (weight percentage): Ni, 52.6 ± 0.5; Ti, 47.4 ± 0.5. Conclusions:The existence of multiple force zones was confirmed in new and retrieved Bioforce archwires. The retrieved archwires demonstrated lower forces during the initial stages of deactivation in three-point bending tests, compared with new specimens. The Af temperature of these archwires may lie higher than the regular intraoral temperature. Even at 2 mm deflections, the forces recorded from these archwires may lie beyond biologically safe limits.

Thermal Behavior Changes of As-Received and Retrieved Bio-Active® (BA) and TriTanium® (TR) Multiforce Nickel–Titanium Orthodontic Archwires

“…A recent study detected statistically significant differences in the As and Af transformation temperatures between the anterior and posterior segments of BioForce archwires in new and retrieved specimens. However, aging did not significantly affect the transformation temperatures [ 29 ].…”

“…A recent study conducted by Roulias et al [ 29 ] aimed to compare the mechanical and thermal properties of the anterior and posterior segments of unused and retrieved commercially available multizone superelastic Bioforce NiTi archwires. The results showed that the Af temperature is higher than regular intraoral temperature, and, even at 2 mm deflections, the forces released are higher than biologically safe limits, which presents a concern.…”

Multi-Force Bio-Active™ Archwires and Various Contemporary NiTi Multi-Force Archwires: Properties and Characteristics—A Review

“…The archwire hardens, changes into austenite, and regains its shape when the temperature rises. Roulias et al [ 73 ] also studied the mechanical and thermal characteristics of the front and posterior segments of this archwire and found that the Af temperature is higher than the average intraoral temperature and that the forces released exceed the medically permissible limits, even at 2 mm deflections. Both studies were conducted on unused archwires and are important for their clinical use.…”