Abstract
AIM: The aim of this study was to make a laboratory assessment of pH influence on the kinetics of
the release of nickel ions in artificial saliva.
METHODS AND MATERIAL: In this study, 15 basic orthodontic appliances are immersed in 15
polyethylene tubes each containing 40 ml of artificial saliva. Tubes were divided into three sub‑groups
of 5 tubes depending on the pH: pH 5, pH 7 and pH 8. The release of nickel ions was measured using
atomic absorption spectrometry in a sample of 5 ml of artificial saliva taken one hour, four hours and
one hundred and sixty‑eight hours after immersion in a water bath at 37°.
STATISTICAL ANALYSIS USED: Significance threshold P was set at 0.05. A Student T test and
the 2‑way Anova test (with a Bonferoni post‑test) were used respectively to compare the means.
RESULTS: The neutral pH causes a low release of nickel ions. The release kinetics of nickel ions is
minimal for neutral pH, it increases when pH varies. After one hour of immersion, the nickel released
did not reach the spectrometer quantification threshold as for neutral and acid pH. The alkaline
pH causes an average release of nickel ions from the beginning without kinetic variation. As time
passes (T3), the acidic pH causes more nickel ions release through a succession of oxidation‑reduction
reactions. After 168 hours, the average mass of nickel released is 0.30 µg for pH 7, 1.35 µg for pH 8
and up to 2.85 µg for pH 5.
CONCLUSIONS: Quantities released did not reach nickel toxicity threshold in humans. Orthodontists
must consider the potential risk of hypersensitivity due to nickel in fixed orthodontic appliances.

Keywords: Artificial saliva, fixed orthodontic appliances, nickel ions, pH