Mechanical Properties of Orthodontic Archwires by Traditional Vickers Hardness Testing

Objectives: The aim of this study was to evaluate the effects of intraoral aging on surface properties of orthodontic archwires, employing vickers hardness testing.
Methods: Segments were cut from ten diferents archwires. The first four are made of stainless steel (SS) 0.016”, 0.016”x 0.016”, 0.016”x 0.022”, 0.017”x 0.025” (American Orthodontics), and six are made of nickel-titanium alloys (NiTi Force I®), 0.012”, 0.014”, 0.016”, 0.016”x 0.016”, 0.016”x 0.022”, 0.017 x 0.025” (American Orthodontics), were considered for this study. For each type of wire four samples of 15-mm-length distal cuts, were analyzed as received and after one month of clinical use by the vickers hardness (Hv).
Results: Stainless steel wires showed the highest hardness followed by Ni-Ti alloys. SS wires depicted shallower indentation depth indicating higher hardness, steeper unloading compared to Ni-Ti wires. The representative indentations for Ni-Ti alloy showed curved sides, indicative of elastic recovery around the tip. However, the indentation of the SS wires didnt show this elastic recovery. We found an average of hardness in the SS wires of 523.6 Hv and in Ni-Ti wires was of 393.5 Hv. We observed that the SS wires tend to decrease their hardness after clinical use, while in most of the arches of nitinol tend to increase their hardness after one month of use.
Conclusions: The alloys of the archwires tested illustrated significant differences in their hardness properties.
The clinical use of orthodontic archwires modifies the hardness (Hv) of the nitinol and stainless steel archwires.