Metal ions release influenced by acidity from arch wire when placed in artificial saliva of different pH.

Abstract

Background: Orthodontic archwires are continuously exposed to the dynamic oral environment, where variations in salivary pH can influence their corrosion behavior and subsequent metal ion release. Acidic conditions resulting from dietary habits, plaque metabolism, and carbonated beverage consumption may compromise the protective oxide layer of metallic orthodontic materials, potentially affecting their biocompatibility and clinical performance.

Aim: This study aimed to evaluate the influence of salivary acidity on the release of metal ions from orthodontic archwires immersed in artificial saliva of varying pH levels.

Materials and Methods: An in vitro experimental study was conducted using 0.016-inch nickel–titanium (NiTi) and stainless steel (SS) orthodontic archwires. Forty standardized archwire specimens were immersed in artificial saliva adjusted to four pH levels (7.0, 6.0, 5.0, and 3.5) and incubated at 37 ± 1°C for 28 days. Metal ion release was evaluated at Days 1, 7, 14, and 28 using Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES). Surface alterations were assessed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Statistical analysis was performed using two-way repeated-measures ANOVA and Tukey’s post hoc test, with significance set at p < 0.05.

Results: Metal ion release increased significantly with decreasing pH and prolonged immersion duration (p < 0.001). The highest concentrations of nickel, chromium, iron, and titanium ions were observed in the highly acidic environment (pH 3.5). Nickel concentrations increased from 26.8 ± 2.1 µg/L on Day 1 to 68.3 ± 5.2 µg/L on Day 28, while iron exhibited the highest overall release, reaching 101.8 ± 6.6 µg/L at Day 28. SEM analysis demonstrated progressive surface deterioration characterized by pitting corrosion, microcracks, and surface roughening under acidic conditions. EDS findings confirmed elemental depletion of metallic constituents and increased surface oxidation following immersion.

Conclusion: Salivary acidity significantly influences the corrosion behavior and metal ion release of orthodontic archwires. Acidic environments accelerate degradation of the protective oxide layer, resulting in increased metal dissolution and surface deterioration. Although the detected ion concentrations remained within biologically acceptable limits, prolonged exposure to acidic conditions may have clinical implications, particularly in patients with metal hypersensitivity. Maintenance of a neutral oral environment may help reduce corrosion and improve the long-term biocompatibility of orthodontic appliances...