Background:
NiTi (nickel-titanium) alloy wires are widely used in orthodontics due to
their unique properties, such as shape memory and superelasticity. However, these wires can be susceptible
to corrosion in the oral environment, which can compromise their mechanical performance
and longevity. Zinc tetraphenyl porphyrin (ZnTPP) is a corrosion inhibitor that forms a protective
layer on the aluminum oxide (Al2O3) surface, acting as a barrier against corrosive agents.
Objective:
The electrodeposition of a sacrificial layer of Al2O3 with ZnTPP was carried out onto Ni-
Ti orthodontic wire to enhance the corrosion resistance.
Methods:
10 mM aluminum nitrate was dissolved in 10 mL of 0.1 M phosphate buffer solution
(PBS), which was used as an electrolyte. Firstly, electrodeposition of Al2O3 on NiTi wire was carried
out by using cyclic voltammetry by potential scanning between 0 and -2.0 V at a scan rate of 50
mV/s for 50 cycles. Secondly, 10 mL of 1 mM ZnTPP: 0.1 M PBS mixture (1:1) was prepared and
used as an electrolyte. Electrodeposition of ZnTPP onto Al2O3/NiTi wire was achieved by cyclic
voltammetry through the potential window of 0 to -2.0 V at a scan rate of 50 mV/s for 50 cycles.
Results:
The ZnTPP/Al2O3/NiTi wire displayed a potentiodynamic polarization resistance of 412931
Ω, with high stability compared to the bare NiTi wire (396421 Ω). Additionally, the corrosion rate
for the ZnTPP/Al2O3/NiTi wire was measured as 0.254 mm/year, which was notably lower than that
of the bare NiTi wire (0.540 mm/year). This decrease in corrosion rate can be attributed to the presence
of the ZnTPP/Al2O3 film, which renders the NiTi wire electrically insulative and significantly
increases its impedance compared to the bare NiTi wire.
Conclusion:
The bilayer coating of Al2O3 and ZnTPP has proven to significantly improve the corrosion
resistance and stability of the wires. Thus, these materials can be considered for coating orthodontic
archwires with improved corrosion stability