Differences in Metal Ions Released from Orthodontic Appliances in an In Vitro and In Vivo Setting

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Abstract

The aim was to assess the composition of released metal ions from fixed orthodontic appliances both in an in vitro and in vivo setting and to compare their quantities to evaluate any possible health risks associated with them. For the in vitro setting, a set of 24 as-received sterile SS brackets, 2 SS sterile archwires, and 2 NiTi sterile archwires were aged for 90 days in artificial saliva, and released metal ion concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS), using matrix-matched standards for calibration. For the in vivo setting, 15 brackets, 15 SS, and 15 NiTi archwires were retrieved after 90 days of intraoral exposure in 15 subjects. Debris composition on each part of the orthodontic appliance was assessed using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). The present study evidenced a difference in the composition of released metal ions from fixed orthodontic appliances detected in an in vitro and in vivo setting. Generally, the relative content of metal ions was higher in the retrieved debris than that released in artificial saliva. The concentration of released metal ions from all tested alloys was below the upper recommended limit of daily intake; however, possible local effects in terms of hypersensitivity due to their accumulation in the debris cannot be excluded even with such concentrations.

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Most cited references 28

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Dietary reference intakes: vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc.

H. Poos, Christian Yates, P Trumbo … (2001)

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In vivo aging of orthodontic alloys: implications for corrosion potential, nickel release, and biocompatibility.

Theodore Eliades, Athanasios Athanasiou (2002)

Despite the large number of studies investigating nickel release from orthodontic stainless steel and nickel-titanium alloys, there is a lack of conclusive evidence with respect to the composition and kinetics of the corrosive products released. The objective of this review is to address the critical issues of corrosion potential and nickel leaching from alloys by investigating the effect of intraoral conditions on the surface reactivity of the materials. After an overview of fundamentals of metallurgical structure of orthodontic alloys, we provide an analysis of corrosion processes occurring in vivo. We present recent evidence suggesting the formation of a proteinaceous biofilm on retrieved orthodontic materials that later undergoes calcification. We illustrate the vastly irrelevant surface structure of in vivo- vs in vitro-aged alloys and discuss the potential implications of this pattern in the reactivity of the materials. Finally, we present a comprehensive review of the issue of nickel release, based on three perspectives: its biologic effects, the methods used for studying its release, and nickel-induced hypersensitivity in orthodontic patients.

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Biodegradation of orthodontic appliances. Part I. Biodegradation of nickel and chromium in vitro.

S N Bishara, Julia Barrett, Ronald J. Quinn (1992)

The purpose of this study is to compare in vitro the corrosion rate of a standard orthodontic appliance consisting of bands, brackets and either stainless steel or nickel-titanium arch wires. The corrosion products analyzed were nickel and chromium. Evaluation was conducted with the appliances immersed for 4 weeks in a prepared artificial saliva medium at 37 degrees C. Ten identical sets were used, each simulating a complete orthodontic appliance used on a maxillary arch with a full complement of teeth. Five sets were ligated to stainless steel arch wires, and the other five sets were ligated to nickel-titanium arch wires. Nickel and chromium release was quantified with the use of a flameless atomic absorption spectrophotometry. The analysis of variance was used to determine if differences existed between the nickel and chromium release according to arch wire type, as well as with time (days 1, 7, 14, 21, and 28). The results indicate that (1) orthodontic appliances release measurable amounts of nickel and chromium when placed in an artificial saliva medium. (2) The nickel release reaches a maximum after approximately 1 week, then the rate of release diminishes with time. On the other hand, chromium release increases during the first 2 weeks and levels off during the subsequent 2 weeks. (3) The release rates of nickel or chromium from stainless steel and nickel-titanium arch wires are not significantly different. (4) For both arch wire types, the release for nickel averaged 37 times greater than that for chromium. How much of these corrosive products are actually absorbed by patients still needs to be determined.