Assessment of the hardness of different orthodontic wires and brackets produced by metal injection molding and conventional methods

Shiva Alavi, Marzie Kachuie

Abstract


Background: This study was conducted to assess the hardness of orthodontic brackets produced by
metal injection molding (MIM) and conventional methods and different orthodontic wires (stainless
steel, nickel‑titanium [Ni‑Ti], and beta‑titanium alloys) for better clinical results.
Materials and Methods: A total of 15 specimens from each brand of orthodontic brackets
and wires were examined. The brackets (Elite Opti‑Mim which is produced by MIM process and Ultratrimm which is produced by conventional brazing method) and the wires (stainless steel, Ni‑Ti, and beta‑titanium) were embedded in epoxy resin, followed by grinding, polishing, and coating. Then, X‑ray energy dispersive spectroscopy (EDS) microanalysis was applied to assess their elemental composition. The same specimen surfaces were repolished and used for Vickers microhardness assessment. Hardness was statistically analyzed with Kruskal–Wallis test, followed by Mann–Whitney
test at the 0.05 level of significance.
Results: The X‑ray EDS analysis revealed different ferrous or co‑based alloys in each bracket. The
maximum mean hardness values of the wires were achieved for stainless steel (SS) (529.85 Vickers
hardness [VHN]) versus the minimum values for beta‑titanium (334.65 VHN). Among the brackets, Elite Opti‑Mim exhibited significantly higher VHN values (262.66 VHN) compared to Ultratrimm (206.59 VHN). VHN values of wire alloys were significantly higher than those of the
brackets.
Conclusion: MIM orthodontic brackets exhibited hardness values much lower than those of SS
orthodontic archwires and were more compatible with NiTi and beta‑titanium archwires. A wide range of microhardness values has been reported for conventional orthodontic brackets and it
should be considered that the manufacturing method might be only one of the factors affecting the mechanical properties of orthodontic brackets including hardness.
Key Words: Casting technique, dental, hardness, metals, orthodontic brackets, orthodontic wires

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