# Transformation Temperatures and Mechanical Properties in Bending of a Multizone Rhodium-Coated NiTi Archwire: A Retrieval Analysis Study

## TL;DR

This study analyzed how the mechanical and thermal properties of a rhodium-coated NiTi archwire change after use in dental applications.

## Contribution

The study provides new insights into the performance degradation of multizone NiTi archwires after clinical use.

## Key findings

- Posterior segments of new wires produce 0.50–0.80 N higher forces than anterior or retrieved wires.
- Anterior segments have higher austenite start and finish temperatures than posterior segments.
- Retrieved wires show reduced force output and surface cracking, affecting their long-term effectiveness.

## Abstract

This study compared the mechanical and thermal properties of new and retrieved multizone rhodium-coated superelastic nickel-titanium (NiTi) archwires across anterior and posterior segments. Using three-point bending tests, Scanning Electron Microscopy with Energy-Dispersive Spectroscopy analysis, and multiple linear regression, it was found that the posterior segments of new wires generated forces 0.50–0.80 N higher than those of anterior or retrieved specimens. While anterior segments exhibited higher austenite start and finish temperatures (by 6.15 °C and 5.21 °C, respectively) compared to posterior segments, these temperatures remained below average intraoral levels, and clinical retrieval did not significantly alter transformation temperatures. However, retrieved wires produced lower overall forces, likely due to surface cracking identified through microscopy. Ultimately, while posterior segments consistently generate higher forces than anterior segments, the observed reduction in force over time and the risk of surface degradation led to the conclusion that these archwires are not recommended for tooth movements exceeding 2 mm.