that NiTi is highly compatible with living tissues but adverse
effects caused by this material are also often reported. In
particular, severe cell death arising from the poor corrosion
resistance and toxic constituents such as Ni in NiTi alloys
has been observed [61]. Though this alloy exhibits high
corrosion resistance to pitting tested at passive conditions
and also potentiodynamic test at normal ranges of pH and
temperatures corresponding to human body, there are reports
which show the inferior corrosion behavior of this alloy
when compared to Ti-6Al-4V and also stainless steel based
materials when measured using potentiostatic scratch test
method. This clearly indicates that the passive layer formed
on NiTi is less protective than that on Ti-6Al-4V. Oxide
films present on different metal surfaces are characterized by
electrochemical impedance spectroscopy (EIS). Titanium
and its alloys have been analyzed extensively by EIS in
different media such as in Hank’s solution [62], Ringer
solution [15], 0.9% NaCl [63], 10% KCl and 30% KCl
solutions [64], phosphate buffer solution (PBS) and artificial
saliva [65]. However, research work carried out on the
interactions between the materials and biological systems in
in vivo are relatively new and not yet advanced. Hence a
systematic study based on physical chemistry and life
science is required to understand the formation of the oxide
film and repassivated layer obtained under different
environments.