The effect of acidity level on ions released and corrosion of metal orthodontic appliances at different time intervals : an in vitro study

Abstract EN

Background : This study measured the effects of three parameters pH value, length of immersion and type of archwire on metal ions released from orthodontic appliances.

Materials and Methods : Ninety maxillary halves simulated fixed orthodontic appliances that were immersed in artificial saliva of different pH values (6.75, 5 and 3.5) during 28 day period.

Three types of archwires were used: stainless steel, nickel titanium and thermal activated nickel titanium.

The quantity of nickel and chromium ions was determined with the use of atomic force spectrophotometer while iron ions by spectrophotometer.

Each orthodontic set was weighted two times, before the ligation and immersion in the artificial saliva and after 28 days at the end of immersion period using analytic balance device.

Results : The release different metal ions was observed: nickel (Ni), chromium (Cr) and iron (Fe)).

Statistically analysis of variance (ANOVA) and t-test were used.

Results showed that (1) the appliances released measurable quantities ofall ions examined ; (2) the change in pH had a very strong effect on the release of ions ; (3) the release of ions was dependent on wire composition, but it was not proportionalto the content of metal in the wire and (4) orthodontic samples showed decreases in the weight at the end of the study.

Conclusion : Levels of released ions are sufficient to cause delayed allergic reactions.

This must be taken into account when type of archwire is selected, especially in patients with hypersensitivityor compromised oral hygiene