A Comparison of the Compositional, Microstructural, and Mechanical Characteristics of Ni-Free and Conventional Stainless Steel Orthodontic Wires.

Daniela Brüngger,Theodore Eliades,Monika Hersberger-Zurfluh,Spiros Zinelis,Theodoros Koutsoukis,Youssef S Al Jabbari

doi:10.3390/ma12203424

Abstract

Ni-free orthodontic wires were introduced to mitigate concerns associated with the use of Ni-containing alloys in orthodontics. However, limited information is available on their properties and therefore, the aim of this study was to characterize the elemental composition, the microstructure, and the mechanical properties of Ni-free orthodontic wires and compare them with their stainless steel (SS) counterparts. Four Ni-free and four conventional SS wires were included in this study. All the wires were initially imaged with a Scanning Electron Microscopy (SEM) and their elemental compositions were determined by X-ray Energy Dispersive Spectroscopy (EDX). Then, their microstructure was assessed by X-ray Diffraction (XRD) and the indentation modulus, elastic index, Martens Hardness and Vickers Hardness by Instrumented Indentation Testing (IIT). All the wires demonstrated surface cracks and pores oriented parallel to their long axis. The elemental composition of Ni-free alloys showed an increased Mn and Cr content while both SS and Ni-free wires shared the same dominant austenite structure. In conclusion, despite the differences in elemental composition, Ni-free wires demonstrated a similar microstructure and comparable mechanical properties with their conventional SS counterparts and thus may be considered as a promising alternative for patients with Ni supersensitivity.

Highlights

Orthodontic wires and brackets made of Ni-containing stainless steel (SS) alloys are extensively used in modern orthodontic therapy, the possible adverse biological consequences ofNi are a well-documented and highly investigated topic in dental literature [1,2,3]
The change in the elemental composition of SS alloys resulting from the substitution of Ni by other elements may have an effect on microstructure, which may impact the stiffness, strength, resilience, formability, weldability, corrosion resistance, and other clinically important properties [12]
All the materials demonstrated the presence of cracks and pores parallel to the long axis of the wires

Summary

Introduction

Orthodontic wires and brackets made of Ni-containing stainless steel (SS) alloys are extensively used in modern orthodontic therapy, the possible adverse biological consequences ofNi are a well-documented and highly investigated topic in dental literature [1,2,3]. Orthodontic wires and brackets made of Ni-containing stainless steel (SS) alloys are extensively used in modern orthodontic therapy, the possible adverse biological consequences of. The austenite structure is preferable as it combines greater ductility and weldability and a greater degree of cold working and increased corrosion resistance [10,11]. Ni stabilizes the austenite structure at lower temperatures [3,12], providing ductility and other desirable mechanical properties and an increased corrosion resistance [10]. The change in the elemental composition of SS alloys resulting from the substitution of Ni by other elements may have an effect on microstructure, which may impact the stiffness, strength, resilience, formability, weldability, corrosion resistance, and other clinically important properties [12]

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