Determinants of corrosion resistance of Ti-6Al-4V alloy dental implants in an In Vitro model of peri-implant inflammation

Abstract

Background: Titanium (Ti) and its alloys possess high biocompatibility and corrosion resistance due to Ti ability to form a passive oxide film, i.e. TiO2, immediately after contact with oxygen. This passive layer is considered stable during function in the oral cavity, however, emerging information associate inflammatory peri-implantitis to vast increases in Ti corrosion products around diseased implants as compared to healthy ones. Thus, it is imperative to identify which factors in the peri-implant micro-environment may reduce Ti corrosion resistance.

Methods: The aim of this work is to simulate peri-implant inflammatory conditions in vitro to determine which factors affect corrosion susceptibility of Ti-6Al-4V dental implants. The effects of hydrogen peroxide (surrogate for reactive oxygen species, ROS, found during inflammation), albumin (a protein typical of physiological fluids), deaeration (to simulate reduced pO2 conditions during inflammation), in an acidic environment (pH 3), which is typical of inflammation condition, were investigated. Corrosion resistance of Ti-6Al-4V clinically-relevant acid etched surfaces was investigated by electrochemical techniques: Open Circuit Potential; Electrochemical Impedance Spectroscopy; and Anodic Polarization.

Results: Electrochemical tests confirmed that most aggressive conditions to the Ti-6Al-4V alloy were those typical of occluded cells, i.e. oxidizing conditions (H2O2), in the presence of protein and deaeration of the physiological medium.

Conclusions: Our results provide evidence that titanium's corrosion resistance can be reduced by intense inflammatory conditions. This observation indicates that the micro-environment to which the implant is exposed during peri-implant inflammation is highly aggressive and may lead to TiO2 passive layer attack. Further investigation of the effect of these aggressive conditions on titanium dissolution is warranted.

Fig 1. Schematic illustration of the three-electrode electrochemical cell used in this study.

Fig 2

Electrochemical results of Ti-6Al-4V alloy in PBS solution (pH 3) (A) Open circuit potential (E) variation with time of immersion and electrochemical impedance spectroscopy (EIS) as (B) Nyquist and (C) Bode phase angle diagrams in deaerated or naturally aerated solutions.

Fig 3

Electrochemical results of Ti-6Al-4V alloy in deaerated PBS solution (pH 3) (A) Open circuit potential (E) variation with time of immersion and electrochemical impedance spectroscopy (EIS) as (B) Nyquist and (C) Bode phase angle diagrams in solutions without 1 wt. % H₂O₂ or with 1 wt. % H₂O₂.

Fig 4

Electrochemical results of Ti-6Al-4V alloy in deaerated PBS solution (pH 3) (A) Open circuit potential (E) variation with time of immersion and electrochemical impedance spectroscopy (EIS) as (B) Nyquist and (C) Bode phase angle diagrams in solutions with 1wt. % H₂O₂ without BSA or with 1 wt. % H₂O₂ and 1 wt.% BSA.

Fig 5. Anodic polarization curves of Ti-6Al-4V alloy in aerated PBS solution (pH 3), deaerated PBS solution (pH 3), deaerated PBS solution with 1 wt. % of hydrogen peroxide and deaerated PBS solution with 1 wt.% of hydrogen peroxide and 1 wt.% BSA.

Fig 6

SEM images of Ti-6Al-4V sample as received and unexposed to the test solution (A), after polarization in PBS solution (pH 3) with 1 wt. % BSA and 1 wt. % of hydrogen peroxide, under naturally aerated condition (B) and same as (B) in deaerated condition (C).