Objectives
To investigate the role of different levels of pH of artificial saliva under simulated oral environment on the corrosion behavior of commercially pure titanium (cp‐Ti) and Ti‐6Al‐4V alloy. Special attention is given to understand the changes in corrosion kinetics and surface characterization of Ti by using electrochemical impedance spectroscopy (EIS).
Materials and methods
Fifty‐four Ti disks (15‐mm diameter, 2‐mm thickness) were divided into six groups (n = 9) as a function of saliva pH (3, 6.5, and 9) and Ti type. Samples were mechanically polished using standard metallographic procedures. Standard electrochemical tests, such as open circuit potential, EIS, and potentiodynamic tests were conducted in a controlled environment. Data were evaluated by two‐way ANOVA, Tukey multiple comparison test, and independent t‐test (α = 0.05). Ti surfaces were examined using white‐light‐interferometry microscopy and scanning electron microscopy (SEM).
Results
Saliva pH level significantly affected the corrosion behavior of both Ti types. At low pH, acceleration of ions exchange between Ti and saliva, and reduction of resistance of Ti surface against corrosion were observed (P < 0.05). Corrosion rate was also significantly increased in acidic medium (P < 0.05). Similar corrosion behavior was observed for both Ti types. The white‐light‐interferometry images of Ti surfaces show higher surface changes at low pH level. SEM images do not show detectable changes. No pitting corrosion was observed for any group.
Conclusions
The pH level of artificial saliva influences the corrosion behavior of cp‐Ti and Ti‐6Al‐4V alloy in that lower pH accelerates the corrosion rate and kinetics. The corrosion products may mitigate the survival rate of dental implants.
Biofilm-associated
diseases are one of the main causes of implant failure. Currently,
the development of implant surface treatment goes beyond the osseointegration
process and focuses on the creation of surfaces with antimicrobial
action and with the possibility to be re-activated (i.e., light source
activation). Titanium dioxide (TiO2), an excellent photocatalyst
used for photocatalytic antibacterial applications, could be a great
alternative, but its efficiency is limited to the ultraviolet (UV)
range of the electromagnetic spectrum. Since UV radiation has carcinogenic
potential, we created a functional TiO2 coating codoped
with nitrogen and bismuth via the plasma electrolytic oxidation (PEO)
of titanium to achieve an antibacterial effect under visible light
with re-activation potential. A complex surface topography was demonstrated
by scanning electron microscopy and three-dimensional confocal laser
scanning microscopy. Additionally, PEO-treated surfaces showed greater
hydrophilicity and albumin adsorption compared to control, untreated
titanium. Bismuth incorporation shifted the band gap of TiO2 to the visible region and facilitated higher degradation of methyl
orange (MO) in the dark, with a greater reduction in the concentration
of MO after visible-light irradiation even after 72 h of aging. These
results were consistent with the in vitro antibacterial effect, where
samples with nitrogen and bismuth in their composition showed the
greatest bacterial reduction after 24 h of dual-species biofilm formation
(Streptococcus sanguinis and Actinomyces naeslundii) in darkness with a superior
effect at 30 min of visible-light irradiation. In addition, such a
coating presents reusable photocatalytic potential and good biocompatibility
by presenting a noncytotoxicity effect on human gingival fibroblast
cells. Therefore, nitrogen and bismuth incorporation into TiO2 via PEO can be considered a promising alternative for dental
implant application with antibacterial properties in darkness, with
a stronger effect after visible-light application.
Even with implant treatment presenting higher patient satisfaction and improvement of quality of life, it was not possible to establish a direct comparison between the studies due to differences in adopted methodologies.
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