Fluorinated Agents Effects on Orthodontic Alloys: A Descriptive In Vitro Study

Abstract

Fluoride-based mouthwashes and gels are preventive measures in countering demineralization and caries but, modifying environmental acidity, can reduce the wet corrosion resistance of orthodontic alloys. To evaluate chemical stability, in vitro experiments were conducted on stainless steel and nickel–titanium wires, weighed before and after immersion in household fluorinated mouthwashes and gels, measuring weight variations and elution of metal ions from acid corrosion phenomena. Elution samples were analyzed by inductively coupled plasma mass spectrometry, detecting residual ion concentration, while surface changes were analyzed under scanning electron microscopy. Results showed stainless steel wires do not undergo significant erosion when exposed to most fluorinated mouthwashes but, at prolonged exposure, alloys elute gradually greater amounts of metals and Ni–Ti wires become more sensitive to some mouthwashes. Ions’ elution varies considerably, especially for Ni–Ti wires, if exposed to household fluorinated gels, for which significant negative values were obtained. Changes, affecting wires’ outer layer, negatively act on shiny appearance and luster, reducing corrosion resistance. Although examined orthodontic wires showed good chemical stability and low toxicity, surface corrosion from exposure to fluorinated agents was observed. Home use must be accompanied by clinician prescription and, for household dental gels, must follow manufacturers’ recommendations, ensuring prophylactic action without damaging alloys surfaces.

Effect of Fluoride Content of Mouthwashes on the Metallic Ion Release in Different Orthodontics Archwires

“…According to the European Council Directive for the quality of water for human consumption, the maximum admissible for nickel ions is 20 µg/L and the average chromium levels in drinking water are 0.43 µg/L. Daily amounts of chromium and nickel intake from foods are 5 to 100 µg and 300 to 500 µg, respectively [42,43].…”

“…Pits produced on the stainless steel surfaces by the fluorinated solution can be seen in the direction of the drawing, since this is where the greatest energy is stored, and these are the first corrosion points that cause the release of ions. This fact could be reduced if the wires, after being drawn, were subjected to an annealing heat treatment, which would cause the elimination of the internal energy that favors corrosion [42][43][44].…”

“…Because nicke most common element that causes metal ion-induced contact allergy leading to der in humans, the worst case scenario was NiTi treated at high fluoride concentrations mium is the second most common metal to cause allergic reactions, but the re stainless steel is low. There is scientific evidence that Ni ions are carcinogenic, mut and produce cytotoxicity in cells [42][43][44]. Even a small amount of release might p sensitivity when the orthodontic appliance is in place for 2 to 3 years.…”

“…Chromium is the second most common metal to cause allergic reactions, but the release in stainless steel is low. There is scientific evidence that Ni ions are carcinogenic, mutagenic, and produce cytotoxicity in cells [42][43][44]. Even a small amount of release might produce sensitivity when the orthodontic appliance is in place for 2 to 3 years.…”

“…Further research is needed to determine whether fluoride solutions on archwires cause dangerous effects in the oral cavity, possibly with long-term systemic consequences. It is known that nontoxic levels of metals like nickel can cause changes in DNA or inhibit DNA-restoring enzymes [42,45], which could have an adverse biological effect in the long term. A long-term evaluation should be conducted.…”