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
Introduction
Orthodontics studies the shape, position, functioning of teeth and dental arches and then modifies them to ensure their health, embellish their appearance and improve their functions.[1] The care of these anomalies due to dental position is made using an orthodontic appliance which can be fixed or removable. The fixed appliance includes several metals (bands, brackets, arcs), ceramics or plastics parts bonded on the teeth with glass ionomer cement or composite resins. Metal parts are made of stainless steel, nickel‑titanium or nickel‑chromium.[2]
Research has particularly focused on improving the physical properties of materials, which are very often used as commercial reasons. Fixed orthodontic appliance constituents degrade in contact with saliva, which particularly contributes to metal biodegradation.[3‑5] The variation in saliva pH combined with bacterial or enzymatic activity, the effects of chewing
Address for correspondence:
Dr. Youssouf Ouédraogo,
01 BP 5036 Ouaga 01, Burkina Faso.
E‑mail: ouedraogoy@yahoo.fr
Submitted: 23‑Jan‑2024 Revised: 20‑Aug‑2024 Accepted: 05‑Sep‑2024 Published: 25-Nov-2024
1Health Sciences Training and Research Unit, Joseph KI‑Zerbo University, Ouagadougou, Burkina Faso,
2Training and Research Unit in Exact and Applied Sciences, Joseph KI‑Zerbo University, Ouagadougou, Burkina Faso,
3Odontostomatology Training and Research Unit, Felix Houphouët Boigny University, Abidjan, Ivory Coast
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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

Artificial saliva, fixed orthodontic appliances, nickel ions, pH