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

Abstract

In the present work, a systematic literature review on release of metal ions from orthodontic appliances under in vitro conditions is described. Detailed and schematic analysis of used materials and applied methods (immersion media, incubation time, temperature, and analytical techniques) is provided. The PubMed search identified 40 studies, among which eight met the selection criteria. One additional study was included in the review. All the authors agreed that the doses of released metal ions were far below the toxic level and the dietary intake. Although the concentrations of metal ions in immersion media greatly differed, the general conclusions were coherent. It must be underlined that the main disadvantage of in vitro tests was that the experimental setup did not reflect in vivo conditions, e.g., the presence of biofilm, which grows on the surface of the materials in oral cavity. The presence and activity of microflora to a large extent is responsible for the process of corrosion, in particular, biodeterioration. The further scheme of in vitro research should incorporate changeable conditions of oral cavity environment (pH, dynamic conditions-saliva flow) and the presence of microbiological flora (microbiological attack) in the experimental design and, first of all, the real proportions of appliance elements.

Surface deterioration and elemental composition of retrieved orthodontic miniscrews

“…10 Corrosion can severely limit the fatigue life and ultimate strength of the material, leading to mechanical failure of the implants. 33,34 Corrosion can lead to roughening of the surface, weakening of the implant, liberation of elements from the metal or alloy, and toxic reactions.…”

“…[7][8][9] Even though titanium alloys are known to be exceptionally corrosion resistant because of the stability of the passive titanium oxide layer on the surface, MSIs have been reported to undergo corrosion after clinical applications. 10 Generally, corrosion is observed when the titanium oxide film breaks down locally, and rapid dissolution of the underlying metal occurs in the form of pits. 11 Crevice corrosion occurs between 2 close surfaces or in constricted places where oxygen exchange is not available.…”

Release of Metal Ions from Orthodontic Appliances: An In Vitro Study

“…In vitro and in vivo studies aimed to investigate whether a patient is exposed to toxic doses of metals from orthodontic appliances have not yet been published [11, 12]. The relationship between the potential dose of toxic elements released from orthodontic appliances and the response of an organism has not been evaluated.…”

Virulence modulation of Streptococcus mutans biofilms by metal ions released from orthodontic appliances

“…Notwithstanding that the significant impact of metal surface on oral biofilm formation has been demonstrated, 28 to our knowledge, 29 this is the first study that prospected the action of released metal ions over bacterial cariogenic potential. However, the compiled data obtained in our study, although interesting, must be considered with some reservation.…”