Is it worth to reuse nitinol arch wires?

Objective: Is to investigate the effect of different methods of sterilization (autoclave sterilization, cold chemical disinfection solution (CIDEX) and gas sterilization) on the bending properties of nickel titanium arch wires. The surface roughness and the elemental analysis measurements of the passive layer were also performed to verify if it is possible to reuse these sterilized nickel titanium arch wires. Material and Methods: Seventy nickel titanium arch wires were used: ten control specimens (unused and unsterilized group). Thirty specimens unused, of which each ten specimens were subjected to a different method of sterilization: a- Autoclave. b- Cold chemical disinfection solution using CIDEX. c- Gas sterilization. The last thirty specimens were clinically used and subjected to the three methods of sterilization previously mentioned. All specimens were tested under three point loading test using a universal testing machine with a cross head speed of 0.5 mm/mn. The atomic force microscopy (AFM) was used to analyze in three-dimension the surface topography and the surface roughness (Ra) of the alloy and energy dispersive X-ray analysis (EDX) was used to identify quantitatively and qualitatively the elements present on the surface of the nickel titanium arch wires. Results: Comparing the control group with the unused sterilized arch wires; it was found that there were insignificant differences in the maximum bending strength, maximum deflection property and the modulus of elasticity between the control group and the unused autoclave and gas sterilized arch wires. There was a significant drop in the modulus of elasticity of the unused sterilized arch wires disinfected with cold chemical solution (CIDEX). Comparing the control group with the clinically used sterilized arch wires as well as, the unused with the clinically used sterilized arch wires, it was found that a statistically significant high maximum bending strength of the clinically used autoclave and gas sterilized arch wires groups from the control group. The maximum deflection property and the modulus of elasticity showed insignificant results. The AFM image of nickel titanium surfaces indicates increase in roughness and change in surface topography of the passive layer after cold chemical disinfection solution. The EDX analysis results showed that the elements of the outermost surface of the passive film on all nickel titanium arch wires were all the same after different methods of sterilization. Conclusions: 1- It is worth to reuse the nickel-titanium arch wires due to its high cost. 2- Autoclave and gas sterilization did not affect the nickel titanium alloy. 3- Chemical sterilization may alter the topography of nickel titanium alloy and consequently affects its bending property. 4- Mechanical forces during the usage affect the maximum bending strength of arch wires.