A. Gebhardt, R. Strietzel*, (Free University Berlin, Germany)
Through bending of wires from manufacturing of orthodontic apparatures the wire materials are stressed mechanical. Different solutions can reveal differing amounts of released ions as shown for amalgams and titanium. The aim of this study is to show the influence of mechanical and chemical stress on the ion release of orthodontic wires made of steel. Therefore orthodontic wires (Dentaurum: Remanium, Scheu-Dental: Menzanium; 8 = 0,7 mm and 1,0 mm; each hard and spring hard; for every series 1,5 m) were cut in 5 cm long pieces. A part of those were bend in an 90 angel and rebend. After that all test specimens were stored in several corrosion solutions (NaCl, NaSCN or NaF and lactic acid, each 0,1 mol/l) for 4 weeks. Every week the solutions were exchanged and analysed with atomic absorption spectroscopy. The exhibited ion releases depend on several parameters (decreasing order):
1. Composition of the corrosion solution - 2. Lot -
3. mechanical stress (bending) - 4. Diameter - 5. hard/ spring hard
The lowest release of iron, chromium an nickel ions was in chloride containing solutions. Thiocyanate solutions revealed at the beginning the highest releases. Over the whole investigation period fluoride solutions showed the highest amount of chromium and nickel ions. The results are significant (p = 0,05, T-test). Specific affinities of the wire to chloride, thiocyanat and fluoride and the increase of internal energy through bending are responsible for the different ion releases.
The uptake from iron, chromium and nickel through nutrition are higher than the measured ion release of orthodontic wires. By proven nickel allergy other wire materials should be used.