2020 Volume 39 Issue 2 Pages 168-174
The degradation of mechanical properties of Ni-Ti superelastic orthodontic alloy wire induced by fluoride in the oral cavity is reviewed here from the viewpoint of hydrogen absorption accompanied by corrosion. The alloy is subjected to general corrosion and absorbs a large amount of hydrogen in acid fluoride solutions in a short time, thereby causing the degradation of mechanical properties, i.e., hydrogen embrittlement. In neutral fluoride solutions, active path corrosion occurs before hydrogen embrittlement. The degradation markedly depends on environmental factors, such as the fluoride content and pH, and material factors, such as hydrogen states and martensite. Hydrogen embrittlement of the alloy is essentially dominated by the formation and accumulation of damage induced by dynamic interactions between stress-induced martensite transformation and hydrogen. One of the countermeasures to inhibit hydrogen absorption in fluoride solutions is to shift the noble direction of the corrosion potential by adding a small amount of hydrogen peroxide.
