Page 292 - 00. Complete Version - Progress Report IPEN 2014-2016

292 Materials and Nanotechnology | Progress Report

Determinants of corrosion resistance conditions (H2O2), high acidity (pH=3), pres-
of Ti-6Al-4V alloy dental implants in ence of protein and deaeration of the physio-
an in vitro model of peri-implant logical medium. Our results provide evidence
that titanium corrosion can be triggered by in-
Titanium (Ti) and its alloys are widely used for tense inflammatory conditions.
manufacturing dental implants and orthope-
dic prostheses owing to their high biocompat- Zirconia dental ceramics
ibility and corrosion resistance. These favor-
able properties for in vivo implantation are Yttria tetragonal zirconia polycrystals (Y-TZP)
due to Ti ability to form a passive oxide film, have been used in dentistry for metal free pros-
i.e. TiO2, immediately after contact with ox- thesis due to esthetics associated with a high
ygen. This passive layer is very stable and ad- mechanical performance. However, the pres-
herent to the Ti surface during function in the ence of humid environment can cause an ac-
oral cavity. However, up to 20% of individuals celerated tetragonal to monoclinic (t-m) phase
with dental implants develop peri-implantitis; transformation and consequent catastrophic
a chronic inflammatory disease causing loss of failure of this material. This process, known as
jawbone and eventually implant failure and low temperature degradation (LTD) or aging,
removal. The etiology of peri-implantitis has has been evaluated in vitro in our laboratory in
not been fully unraveled, but has been tradi- a hydrothermal pressurized reactor at 150°C in
tionally considered to be associated to micro- order to accelerate the crystallite phase trans-
bial infection. Recent results from our group, formation kinetics. The degradation studies
however, have found that Ti corrosion products have been performed in commercial and lab-
are vastly increased around diseased implants oratory synthesized dental ceramics.
as compared to healthy ones. This observation
indicates that the micro-environment to which The aim of commercial dental Y-TZP studies
the implant is exposed during peri-implant was the determination of speed of the front of
inflammation is highly aggressive leading to phase transformation zone growth during hy-
TiO2 passive layer attack. The aim of this work drothermal aging, and to correlate with the bi-
is to simulate peri-implant inflammatory con- axial flexural strength. The effect of the associ-
ditions in vitro to determine which factors af- ation of hydrothermal aging and fatigue with
fect corrosion susceptibility of Ti-6Al-4V dental biaxial flexural strength was also evaluated.
implants in phosphate solution. The effect of
hydrogen peroxide (surrogate for reactive oxy-
gen species, ROS, found during inflammation),
albumin (a protein typical of physiological flu-
ids), deaeration (to simulate reduced pO2 con-
ditions during inflammation), and pH (3, 4.5
and 7) were investigated. The corrosion resis-
tance of Ti-6Al-4V was performed by electro-
chemical techniques and surface characteri-
zation after exposure to corrosion immersion
test. The results showed that the most aggres-
sive conditions to the Al-6Al-4V alloy were
Figure 7: Comparison of t-m phase transformation
these typical of occluded cells, i.e. oxidizing data: XRD (sigmoidal curve) and SEM (linear fit).

Instituto de Pesquisas Energéticas e Nucleares