Metallurgical characterization, galvanic corrosion, and ionic release of orthodontic brackets coupled with Ni‐Ti archwires

Abstract

In orthodontics, a combination of metallic alloys is placed into the oral cavity during medical treatment and thus the corrosion resistance and ionic release of these appliances is of vital importance. The aim of this study is to investigate the elemental composition, microstructure, hardness, corrosion properties, and ionic release of commercially available orthodontic brackets and Copper Ni-Ti archwires. Following the assessment of the elemental composition of the orthodontic wire (Copper Ni-Ti) and the six different brackets (Micro Loc, Equilibrium, OptiMESH(XRT), Gemini, Orthos2, and Rematitan), cyclic polarization curves were obtained for each material to estimate the susceptibility of each alloy to pitting corrosion in 1M lactic acid. Galvanic corrosion between the orthodontic wire and each bracket took place in 1M lactic acid for 28 days at 37 degrees C and then the ionic concentration of Nickel and Chromium was studied. The orthodontic wire is made up from a Ni-Ti alloy with copper additions, while the orthodontic brackets are manufactured by different stainless steel grades or titanium alloys. All tested wires and brackets with the exception of Gemini are not susceptible to pitting corrosion. In galvanic corrosion, following exposure for 28 days, the lowest potential difference (approximately 250 mV) appears for the orthodontic wire Copper Ni-Ti and the bracket made up from pure titanium (Rematitan) or from the stainless steel AISI 316 grade (Micro Loc). Following completion of the galvanic corrosion experiments, measurable quantities of chromium and nickel ions were found in the residual lactic acid solution.

Metallic ion content and damage to the DNA in oral mucosa cells of children with fixed orthodontic appliances

“…These are associated with the corrosion products of the apparatus used that would be related to the cytotoxicity of these materials. In this way, biocompatibility is closely related to corrosion resistance and ion release, properties that consequently are important factors in the choice of materials used for biomedical applications (Darabara et al 2007).…”

Release of Metal Ions from Orthodontic Appliances by In Vitro Studies: A Systematic Literature Review

“…Hwang et al [14] and Park and Shearer [16] slightly exceeded the number of bands (two instead of one). Two papers did not include bands in the test [11,12]. In all the works, the studied material consisted of brackets and bands made of SS by various manufacturers, in one case, Ti brackets were used.…”

“…No additional search in other databases was performed. From 40 identified studies, eight met the selection criteria [10][11][12][13][14][15][16][17]. One additional paper [18] was found by reading abstracts of related papers.…”

Non-martensitic Needle-like Structures on Ni-Ti Alloys - Occurrence and Origin

“…Surprisingly these needle-like structures even occurred after chemical etching on NiTi that was stated as pseudo elastic (arch wire) and thus should be in an austenitic condition [5]. Upon closer examination there are several features that contradict an interpretation of the needle-like structures as martensite, particularly rounded edges, changes in orientation that have no connection with the crystallography of the underlying grains, and the absence of grain boundaries.…”

“…In recent years various authors presented micrographs of NiTi microstructures showing needle-like structures that are interpreted as martensite [2][3][4][5][6]. Surprisingly these needle-like structures even occurred after chemical etching on NiTi that was stated as pseudo elastic (arch wire) and thus should be in an austenitic condition [5].…”