Ni Ion Release Research Articles

Corrosion potential in artificial saliva and possible genotoxic and cytotoxic damage in buccal epithelial cells of patients who underwent Ni-Cr based porcelain-fused-to-metal fixed dental prostheses

Nickel–chromium(Ni–Cr) based alloys account for the majority of the porcelain-fused-to-metal fixed dental prostheses(PFM-FDPs) on account of their superior properties despite both nickel and chromium being known as human carcinogens. Understanding the genotoxicity and the cytotoxicity alongside the characteristics of corrosion behavior of the alloy is vital for understanding their biocompatibility. This study has evaluated whether the Ni-Cr based alloys corroded in artificial saliva by analyzing alloy decomposition at different pH levels and immersion durations(7, 14, 21, and 28 days) using inductively coupled plasma-optic emission spectrophotometry(ICP-OES). The principal aim of the study was to determine the possible genotoxicity and cytotoxicity using micronucleus(MN) and other nuclear anomaly frequencies [nuclear bud(NBUD), binucleated(BNC), condensed chromatin(CC), karyorrhectic(KhC), pyknotic(PC) and karyolytic(KC) cells] and various cytome parameters [basal cells(BC), differentiated cells(DF)] with the buccal epithelial cell(BEC) micronucleus cytome assay(BMCyt). This test was administered at 1 pre- and 3 post-treatment time points to 40 patients who underwent installation of PFM-FDPs made of Ni-Cr based alloy. Furthermore, at the final post-treatment time point, saliva cotinine levels were measured with salivary cotinine quantitative enzyme immunoassay(EIA) kit and information obtained by questionnaire prior to the first pre-treatment time point was confirmed. The highest greatest release of Ni and Cr ions were seen at pH 2.3. MN and micronucleated cell frequencies, and BNC cell frequencies were significantly elevated at post-treatment time points(p < 0.03). BC, CC, KhC, PC and KC cell frequencies however were not significantly different between pre-and post-treatment time points(p > 0.05). MN frequency was significantly lower in non-smokers than in current and former smokers(p < 0.001) at the pre-treatment time point. There was no significant correlation between the unit number of PFM-FDPs and MN frequencies. Our results revealed that Ni-Cr based alloys are prone to corrosion and that PFM-FDPs fabricated with Ni-Cr based alloys may induce genotoxic effects rather than cytotoxic effect.

On the Ni-Ion release rate from surfaces of binary NiTi shape memory alloys

Abstract The study is focused on Ni-ion release rates from NiTi surfaces exposed in the cell culture media and human vascular endothelial cell (HUVEC) culture environments. The NiTi surface layers situated in the depth of 70 μm below a NiTi oxide scale are affected by interactions between the NiTi alloys and the bio-environments. The finding was proved with use of inductively coupled plasma mass spectrometry and electron microscopy experiments. As the exclusive factor controlling the Ni-ion release rates was not only thicknesses of the oxide scale, but also the passivation depth, which was two-fold larger. Our experimental data strongly suggested that some other factors, in addition to the Ni concentration in the oxide scale, admittedly hydrogen soaking deep below the oxide scale, must be taken into account in order to rationalize the concentrations of Ni-ions released into the bio-environments. The suggested role of hydrogen as the surface passivation agent is also in line with the fact that the Ni-ion release rates considerably decrease in NiTi samples that were annealed in controlled hydrogen atmospheres prior to bio-environmental exposures.

Hybrid a-CNH+TiO2+TiN-type surface layers produced on NiTi shape memory alloy for cardiovascular applications.

The goal was to improve the properties of NiTi shape memory alloy to make it suitable for cardiac applications. For this purpose, a hybrid a-CNH+TiO2+TiN-type surface layer was produced on NiTi alloy and characterized. The NiTi alloy subjected to hybrid process combining low-temperature oxynitriding under glow discharge conditions and radio frequency chemical vapor deposition process was examined for microstructure, surface topography, corrosion resistance, wettability and surface-free energy, Ni ion release and platelets adhesion, aggregation and activation. The hybrid surface layers showed slightly increased surface roughness, better corrosion resistance, a more hydrophobic nature, decreased surface free energy, smaller release of nickel ions and reduced platelets activation. The produced layers could expand the range of NiTi medical applications.

Investigation of the Dissolution–Reformation Cycle of the Passive Oxide Layer on NiTi Orthodontic Archwires

Dissolution–reformation cycle of the passive oxide layer on the nickel–titanium (NiTi) orthodontic archwires was investigated, which has recently been recognized as one of the key parameters dictating the biocompatibility of archwires. Specifically, commercially available NiTi orthodontic archwires were immersed in artificial saliva solutions of different pH values (2.3, 3.3, and 4.3) for four different immersion periods: 1, 7, 14, and 30 days. Characterization of the virgin and tested samples revealed that the titanium oxide layer on the NiTi archwire surfaces exhibit a dissolution–reformation cycle within the first 14 days of the immersion period: the largest amount of Ni ion release occurred within the first week of immersion, while it significantly decreased during the reformation period from day 7 to day 14. Furthermore, the oxide layer reformation was catalyzed on the grooves within the peaks and valleys due to relatively larger surface energy of these regions, which eventually decreased the surface roughness significantly within the reformation period. Overall, the current results clearly demonstrate that the analyses of dissolution–reformation cycle of the oxide layer in orthodontic archwires, surface roughness, and ion release behavior constitute utmost importance in order to ensure both the highest degree of biocompatibility and an efficient medical treatment.

The influence of artificial salivary pH on nickel ion release and the surface morphology of stainless steel bracket-nickel-titanium archwire combinations

Background: In the oral cavity, orthodontic appliances come into contact with saliva which may cause corrosion capable of changing their surface morphology due to the release of metal ions. Surface roughness can influence the effectiveness of tooth movement. One of the ions possibly released when body fluid comes into contact with brackets and archwire is nickel ion (Ni). Ni, one of the most popular components of orthodontic appliances, is, however, a toxic element that could potentially increase the likelihood of health problems such as allergic responses during treatment. Purpose: The purpose of this study was to investigate the effect of different artificial salivary pH on the ions released and the surface morphology of stainless steel (SS) brackets-nickel-titanium (NiTi) and archwire combinations. Methods: Brackets and archwires were analyzed by an Energy Dispersive X-Ray Detector System (EDX) to determine their composition, while NiTi archwire compound was examined by means of X-ray Diffraction (XRD). The immersion test was performed at artificial salivary pH levels of 4.2; 6.5; and 7.6 at 37°C for 28 days. Ni ion release measurement was performed using an Atomic Absorption Spectroscopy (AAS). Surface morphology was analyzed by means of a Scanning Electron Microscopy (SEM). Results: The chemical composition of all orthodontic appliances contained Ni element. In addition, XRD was depicted phases not only NiTi but also Ni, Titanium, Silicon and Zinc Oleate. The immersion test showed that the highest release of Ni ions occured at a pH of 4.2, with no significant difference at various levels of pH (p=.092). There were surface morphology changes in the orthodontic appliances. It was revealed that at a pH of 4.2, the surfaces of orthodontic appliances become unhomogenous and rough compared to those at other pH concentrations. Conclusion: The reduction of pH in the artificial saliva increases the amount of released Ni ions, as well as causing changes to the surface morphology of brackets and archwires.

Preparation of Ca doping ZrO2 coating on NiTi shape memory alloy by cathodic plasma electrolytic deposition and its structure, in-vitro bioactivity and biocompatibility analysis

The Ca doping ZrO2 coatings were fabricated on NiTi alloys by cathodic plasma electrolytic deposition (CPED) technology. The CPED coatings exhibit a rough morphology filled with porous craters. The coating thickness is increased with the treatment time increasing. The X-ray diffraction (XRD) analysis shows that the coating is mainly composed of tetragonal phase ZrO2 (t-ZrO2). The X-ray photoelectron spectroscopy (XPS) indicates that the coating is composed by Zr, O, and Ca. The curves of potentiodynamic polarization suggest that the corrosion resistance of the NiTi alloy is significantly improved by the fabricated ZrO2 coating. Ni ions release test shows that CPED coating could mitigate the Ni ions release effectively. The SBF soaking test shows that the ZrO2 coatings exhibited excellent apatite-inducing ability, indicating the bioactivity of NiTi alloys is surely improved. The result of the osteoblast-like cells culture test shows that the adhesion, viability and proliferation of osteoblast-like cells on the ZrO2 coatings are enhanced. It indicated that the obtained ZrO2 coatings have good biocompatibility.

Improving surface finish and wear resistance of additive manufactured nickel-titanium by ultrasonic nano-crystal surface modification

Nickel-titanium (NiTi) alloys have great potential to be used as biomedical implants or devices due to their unique functional properties (i.e., shape memory properties and superelastic behavior). The machining difficulty associated with NiTi alloys is impeding their wide application. Additive manufacturing (AM), however, provides an alternative method to manufacture NiTi structures. One major concern associated with NiTi devices fabricated in this route is the potential for the release of toxic Ni ions due to the poor surface finish as well as high surface porosity. In this study, NiTi samples were produced using selective laser melting, the most common AM techniques. Then, an innovative surface processing technique, ultrasonic nano-crystal surface modification (UNSM), was used to mitigate the potential for the Ni ions release. By simultaneous ultrasonic striking and burnishing, UNSM can significantly improve surface finish and decrease surface porosity. In addition, UNSM induces plastic strain which in turn hardens the surface layer. The synergistic effect of better surface finish, lower subsurface porosity, and a hardened surface layer resulted in higher wear and corrosion resistance. It is therefore expected that UNSM can be potentially used to treat biomedical devices.

Do Dietary Habits Influence Trace Elements Release from Fixed Orthodontic Appliances?

The objective was to investigate the effect of dietary habits on the release of Cr and Ni ions from orthodontic appliances by hair mineral analysis. Patients (N = 47) underwent electronic questionnaire survey to investigate the effect of dietary habits on Cr and Ni levels in hair. The research was carried out on hair sampled at the beginning and in the 4th, 8th, and 12th months of the treatment. The content of Cr and Ni in the collected samples was determined by ICP-OES. The study showed that consumption of acidic dietary products may have the effect on increasing the release of Cr and Ni ions from orthodontic appliances. The release of Cr from orthodontic appliances in patients who consumed fruit juice, coffee, yoghurt, and vinegar was higher. The coefficients enabling comparison of metal ions release pattern at a given sampling points were defined. The comparison of the coefficients yielded the information on the possible magnification of metal ions released as the result of the additional factor consumption of acidic food or drink that intensifies metal ions release. The following magnification pattern was found for chromium: coffee (7.57 times) > yoghurt (2.53) > juice (1.86) > vinegar (1.08), and for nickel: vinegar (2.2) > coffee (1.22) > juice (1.05). Yoghurt did not intensify the release of nickel. Concluding, orthodontic patients should avoid drinking/eating coffee, yoghurt, fruit juices, and vinegar.

Antibacterial effect of nickel-titanium alloy owing to nickel ion release

This paper demonstrates that a NiTi shape memory alloy demonstrates antibacterial effect owing to the release of Ni ions from the alloy itself. Moreover, non-cytotoxic NiTi alloy with antibacterial properties can be prepared by simple post-heat treatment. We demonstrated that applying Escherichia coli to a NiTi surface resulted in 40% reduction in the number of cells following a 4h incubation in an ambient atmosphere. When the alloy was heated at 450°C in air, the antibacterial effect was slightly reduced but the cytotoxicity was drastically reduced. This result indicates that the production of an antibacterial NiTi alloy (without cytotoxic effects) is feasible with an appropriate surface modification. We further revealed that the appropriate Ni ion concentration for both antibacterial effect and biosafety was in the range from 0.05mgL−1 to 3mgL−1. Our novel finding represents a new and unique strategy for improving the antibacterial performance of NiTi alloy.

Effects of tissue digestion solutions on surface properties of nitinol stents.

Analysis of explanted medical implants can provide a wealth of knowledge about device safety and performance. However, the quality of information may be compromised if the methods used to clean tissue from the device disturb the retrieved condition. Common solutions used to digest tissue may adversely affect the surface of the device and its severity can be material and processing dependent. In this study, two groups of stents made from the same material (Nitinol) were shape set in a salt pot (SP) or further processed by mechanical polishing (MP) and then immersed in one of three tissue digestion solutions (TDS): nitric acid (HNO3 ), sodium hydroxide (NaOH), or papain enzyme (papain). Nickel (Ni) ion concentrations were measured for each stent-TDS combination and post-immersion stent surface constituents, morphology and oxide depths were compared to baseline samples. Exposure to the HNO3 TDS resulted in relatively high Ni ion release and surface damage for both stent types. Papain TDS induced a greater Ni ion release than NaOH TDS, however, both were significantly lower than HNO3 . The NaOH TDS increased the oxide layer thickness on MP stents. In contrast, all other stent immersions resulted in thinner oxide layers. For the Nitinol finishes used in this study, HNO3 is not recommended while papain and NaOH solutions may be appropriate depending on the post-retrieval analysis performed. This study elucidates the importance of preliminary testing for TDS selection and how the surface finish can affect the sensitivity of a material to a TDS. 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 331-339, 2018.

Ion Release and Galvanic Corrosion of Different Orthodontic Brackets and Wires in Artificial Saliva

To investigate the galvanic corrosion of brackets manufactured by four different companies coupled with stainless steel (SS) or nickel-titanium (NiTi) wires in an artificial saliva solution. A total of 24 mandibular central incisor Roth brackets of four different manufacturers (American Orthodontics, Dentaurum, Shinye, ORJ) were used in this experimental study. These brackets were immersed in artificial saliva along with SS or NiTi orthodontic wires (0.016'', round) for 28 days. The electric potential difference of each bracket/ wire coupled with a saturated calomel reference electrode was measured via a voltmeter and recorded constantly. Corrosion rate (CR) was calculated, and release of ions was measured with an atomic absorption spectrometer. Stereomicroscope was used to evaluate all samples. Then, samples with corrosion were further assessed by scanning electron microscope and energy-dispersive X-ray spectroscopy. Two-way analysis of variance was used to analyze data. Among ions evaluated, release of nickel ions from Shinye brackets was significantly higher than that of other brackets. The mean potential difference was significantly lower in specimens containing a couple of Shinye brackets and SS wire compared with other specimens. No significant difference was observed in the mean CR of various groups (p > 0.05). Microscopic evaluation showed corrosion in two samples only: Shinye bracket coupled with SS wire and American Orthodontics bracket coupled with NiTi wire. Shinye brackets coupled with SS wire showed more susceptibility to galvanic corrosion. There were no significant differences among specimens in terms of the CR or released ions except the release of Ni ions, which was higher in Shinye brackets.

First-principles study on the adsorption of oxygen at NiTi (110) surface

NiTi alloys with equiatomic compositions have been widely used as structural materials in aerospace, aviation and other fields due to their shape memory effects and good mechanical performances. At the same time, they are considered as excellent biomedical materials for their biocompatibilities and high fatigue resistances. As structural materials, the oxidation resistance of NiTi alloy should be improved. However, as biomedical materials, the formation of dense TiO2 layers on the surface of NiTi alloy is required to suppress the release of Ni ions in body liquid. As a result, it is of great significance to study the oxidation mechanism of NiTi alloy. In this work, while the total number of Ti is kept the same as that of Ni atoms in the whole system, a series of defected c(22)-NiTi (110) surfaces with antisite of Ti are constructed to further understand the oxidation mechanism of NiTi alloy. The adsorption of oxygen atom at the NiTi (110) surface is investigated by the first-principles calculations. The calculated results show that the stability of the oxygen adsorption is strongly related to the enrichment of Ti atoms on the surface. The higher the enrichment of Ti atoms on the surface, the stronger the adsorption of oxygen atoms is. When the coverage of oxygen is high enough, the adsorption of oxygen atoms on the surface could cause the antisite of Ti atoms on the surface by the exchange of Ni atoms in the first layer with Ti atoms in other layers. Under the O-rich conditions (O -9.35 eV), it is the most stable that the oxygen atoms adsorbed on Ti antisite surface, with the whole Ni atoms in the first surface layer exchanged with the whole Ti atoms in the third surface layer. With the increase of the adsorbed oxygen atoms on the surface, the heights of Ti atoms in the surface layers are raised by the adsorption of oxygen. The TiO2 layer is formed by the expansive growth, while Ni atoms are enriched beneath the TiO2. As a result, the reason why the TiO2 layer is formed on the NiTi alloy surface in the experimental conditions is well explained.

The Effect of Radio Frequency Plasma Nitriding on Biocompatibility of Nickel-Titanium Shape Memory Alloys

Nickel-titanium (Ni-Ti) shape memory alloys (SMAs) are attractive materials for orthopedic and dental implants, due to its two intrinsic properties including shape memory effect (SME) and superelasticity (SE), which may not be found in other commonly- used surgical metals. Possible Ni ion release, however, hampers their medical applications, particularly in orthopedic implants where fretting is always expected at the articulating surface. Inductively coupled radio frequency plasma (ICRFP) was employed to alter the surface of equiatomic Ni-Ti discs in order to create a barrier to out-diffusion of Ni ions from the bulk material. The ICRFP experiments were carried out with nitrogen, which promoted the formation of a titanium nitride layer on the surface of the Ni-Ti samples. The present paper explores the biocompatibility and performance of the ICRFP treated and untreated Ni-Ti samples. The results confirm that nitrogen plasma modified Ni-Ti alloys are potentially suitable materials for orthopedics without inducing harmful biological effects.

The influence of the substrate on the adhesive strength of the micro-arc oxidation coating developed on TiNi shape memory alloy

TiNi shape memory alloys (SMAs), used as long-term implant materials, have a disadvantage. Ni-ion release from the alloys may trigger allergies in the human body. Micro-arc oxidation has been utilized to modify the surface of the TiNi SMA for improving its corrosion resistance and biocompatibility. However, there are very few reports investigating the essential adhesive strength between the micro-arc oxidized film and TiNi SMA. Two primary goals were attained by this study. First, Ti50Ni48.5Mo1.5 SMA having a phase transformation temperature (Af) less than body temperature and good shape recovery were prepared. Next, the Ti50Ni50 and Ti50Ni48.5Mo1.5 SMA surfaces were modified by micro-arc oxidation in phosphoric acid by applying relatively low voltages to maintain the adhesive strength. The results indicated that the pore size, film thickness, and P content increased with applied voltage. The micro-arc oxidized film, comprising Ti oxides, Ni oxide, and phosphate compounds, exhibited a glassy amorphous structure. The outmost surface of the micro-arc oxidized film contained a large amount of P (>12 at%) but only a trace of Ni (<5 at%). The adhesive strengths of all the micro-arc oxidized films exceeded the requirements of ISO 13779. Furthermore, Mo addition into TiNi SMAs was found to be favorable for improving the adhesive strength of the micro-arc oxidized film.

PEEK (polyether-ether-ketone)-coated nitinol wire: Film stability for biocompatibility applications

High quality biocompatible poly-ether-ether-ketone (PEEK) coatings were produced on NiTi shape memory alloy wires using dipping deposition from colloidal aqueous PEEK dispersions after substrate surface treatment. The surface morphology and microstructure were investigated by Scanning Electron Microscopy at every step of the process from the as-received Nitinol substrate to the ultimate PEEK-coated NiTi wire. Nanoscratch tests were carried out to access the adhesive behavior of the polymer coated film to the NiTi. The results indicate that the optimum process conditions in cleaning, chemical etching, and electropolishing the NiTi, were the most important and determining parameters to be achieved. Thus, high quality PEEK coatings were obtained on NiTi wires, straight or curved (even with a U-shape) with a homogeneous microstructure along the wire length and a uniform thickness of 12μm without any development of cracks or the presence of large voids. The biocompatibility of the PEEK coating film was checked in fibrobast cultured cells. The coating remains stable in biological environment with negligible Ni ion release, no cytotoxicity, and no delamination observed with time.

Differences in cytocompatibility, dynamics of the oxide layers' formation, and nickel release between superelastic and thermo-activated nickel-titanium archwires.

Superelastic (SE) and thermo-activated (TA) nickel-titanium (NiTi) archwires are used in everyday orthodontic practice, based on their acceptable biocompatibility and well-defined shape memory properties. However, the differences in their surface microstructure and cytotoxicity have not been clearly defined, and the standard cytotoxicity tests are too robust to detect small differences in the cytotoxicity of these alloys, all of which can lead to unexpected adverse reactions in some patients. Therefore, we tested the hypothesis that the differences in manufacture and microstructure of commercially available SE and TA archwires may influence their biocompatibility. The archwires were studied as-received and after conditioning for 24h or 35days in a cell culture medium under static conditions. All of the tested archwires, including their conditioned medium (CM), were non-cytotoxic for L929 cells, but Rematitan SE (both as received and conditioned) induced the apoptosis of rat thymocytes in a direct contact. In contrast, TruFlex SE and Equire TA increased the proliferation of thymocytes. The cytotoxic effect of Rematitan SE correlated with the higher release of Ni ions in CM, higher concentration of surface Ni and an increased oxygen layer thickness after the conditioning. In conclusion, the apoptosis assay on rat thymocytes, in contrast to the less sensitive standard assay on L929 cells, revealed that Rematitan SE was less cytocompatible compared to other archwires and the effect was most probably associated with a higher exposition of the cells to Ni on the surface of the archwire, due to the formation of unstable oxide layer.

Development of Biomimetic NiTi Alloy: Influence of Thermo-Chemical Treatment on the Physical, Mechanical and Biological Behavior.

A bioactive layer, free of nickel, has been performed for its greater acceptability and reliability in clinical applications for NiTi shape memory alloys. In the first step, a safe barrier against Ni release has been produced on the surface by means of a thicker rutile/anastase protective layer free of nickel. In the second step, a sodium alkaline titanate hydrogel, which has the ability to induce apatite formation, has been performed from oxidized surface. An improvement of host tissue–implant integration has been achieved in terms of Ni ions release and the bioactivity of the treated NiTi alloys has been corroborated with both in vitro and in vivo studies. The transformation temperatures (As, Af, Ms, and Mf), as well as the critical stresses (σβ⇔M), have been slightly changed due to this surface modification. Consequently, this fact must be taken into account in order to design new surface modification on NiTi implants.

Effects of lipopolysaccharides on the corrosion behavior of Ni-Cr and Co-Cr alloys

Statement of problemLipopolysaccharides (LPS) are constituents of gingival crevicular fluid and may affect the base metal alloys used in metal ceramic crowns. The role of LPS in base metal alloys is currently unknown. PurposeThe purpose of this in vitro study was to evaluate the effects of gram-negative bacterial LPS on the electrochemical behavior of Ni-Cr and Co-Cr alloys. Material and methodsAlloy specimens were divided into 4 groups according to Escherichia coli LPS concentration (0, 0.15, 15, and 150 μg/mL) in acidic saliva (pH 5). Open circuit potential (OCP) and potentiodynamic polarization behavior were examined using a computer-controlled potentiostat. Metal ions released from the 2 alloys were measured by immersion in LPS-free solution and 150 μg/mL LPS solution and analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Data were evaluated using 1-way ANOVA (α=.05). ResultsCompared with control groups, medium LPS concentration (15 μg/mL) accelerated Ni-Cr alloy corrosion (P<.05), whereas high LPS concentration (150 μg/mL) accelerated Co-Cr alloy corrosion (P<.05), as determined by OCP, corrosion current density, and polarization resistance parameters. After immersion in high LPS concentrations (150 μg/mL), a slight increase in Ni ion release (P >.05) was observed for the Ni-Cr alloy, while a more significant Co ion release (P<.05) was observed for the Co-Cr alloy. ConclusionsLPS negatively affected the electrochemical behavior of both the Ni-Cr and Co-Cr alloys.

Reciprocal interaction between dental alloy biocorrosion and Streptococcus mutans virulent gene expression.

Corrosion of dental alloys is a major concern in dental restorations. Streptococcus mutans reduces the pH in oral cavity and induces demineralization of the enamel as well as corrosion of restorative dental materials. The rough surfaces of dental alloys induced by corrosion enhance the subsequent accumulation of plaque. In this study, the corrosion process of nickel-chromium (Ni-Cr) and cobalt-chromium (Co-Cr) alloys in a nutrient-rich medium containing S. mutans was studied using inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS) and electrochemical corrosion test. Our results showed that the release of Ni and Co ions increased, particularly after incubation for 3 days. The electrochemical corrosion results showed a significant decrease in the corrosion resistance (Rp) value after the alloys were immersed in the media containing S. mutans for 3 days. Correspondingly, XPS revealed a reduction in the relative dominance of Ni, Co, and Cr in the surface oxides after the alloys were immersed in the S. mutans culture. After removal of the biofilm, the pre-corroded alloys were re-incubated in S. mutans medium, and the expressions of genes associated with the adhesion and acidogenesis of S. mutans, including gtfBCD, gbpB, fif and ldh, were evaluated by detecting the mRNA levels using real-time reverse transcription polymerase chain reaction (RT-PCR). We found that the gtfBCD, gbpB, ftf and Idh expression of S. mutans were noticeably increased after incubation with pre-corroded alloys for 24 h. This study demonstrated that S. mutans enhanced the corrosion behavior of the dental alloys, on the other hand, the presence of corroded alloy surfaces up-regulated the virulent gene expression in S. mutans. Compared with smooth surfaces, the rough corroded surfaces of dental alloys accelerated the bacteria-adhesion and corrosion process by changing the virulence gene expression of S. mutans.

Galvanic corrosion between CuNiTi arch wires and other metallic alloys for orthodontic applications

Event Abstract Back to Event Galvanic corrosion between CuNiTi arch wires and other metallic alloys for orthodontic applications Elisa Kassab1, 2 and José P. Gomes1 1 Federal University of Rio de Janeiro, Department of Metallurgy and Materials Science, Brazil 2 Pontifical Catholic University of Rio de Janeiro, Department of Metallurgy and Materials Science, Brazil Introduction: NiTi based alloys are widely used in biomedical applications due to their special mechanical properties, corrosion behaviour and biocompatibility[1]. As orthodontic wires, they deliver light and relative constant force, resulting in a more physiological dental movement. Addition of copper (Cu) as a third element can improve some mechanical properties desirable to their application as orthodontic wires, such as narrowing of stress hysteresis and a more stable stress-strain plateau[2]. However, the better mechanical properties are not accompanied by an increase in the corrosion behaviour. A recent report revealed a lower corrosion resistance of CuNiTi in physiological medium[3]. Using different metals in oral environment, for example as orthodontic arch wires and brackets, may result in galvanic corrosion. The aim of this work is to assess the galvanic corrosion of CuNiTi with other alloys commonly used in dentistry, such as stainless steel (SS) and beta titanium. Materials: The materials used for this work were the following: CuNiTi, SS and beta titanium arch wires. CuNiTi was an 0.18-inch heat activated (35 oC) arch wire from Ormco Corp. (Orange, USA). SS and beta titanium wires were 0.16-inch arch wires ordered from GAC International Inc. (New York, USA). Methods: Electrochemical tests were performed in 0.9% NaCl electrolyte in order to simulate physiological solution. A conventional three electrode cell with a saturated calomel electrode as a reference electrode and platinum as a counter electrode was used. This cell was connected to a potentiostat (Metrohm Autolab). Potentiodynamic polarization was conducted at a scan rate of 20 mV/min starting from -600 mV to 800 mV. Cathodic curves of the materials with higher corrosion potentials (SS and beta titanium) were overlaid with the anodic curve of the CuNiTi. At this intersection point, the value corresponding to x axis was determined as the estimated potential of the galvanic couple (Ecouple) and y axis as the estimated current from the galvanic couple (icouple). Results: Initial results indicate an electrode potential gap between CuNiTi and SS and titanium alloys in 0.9 NaCl solution. This suggests that galvanic corrosion might occur in this environment. Mean Ecouple measured for the CuNiTi/SS couple was -0.1 mV. For CuNiTi/titanium was -0.8 mV. A typical polarization curve for CuNiTi and titanium is shown in Figure 1. Direct galvanic coupling and potentiostatic experiments will be performed for CuNiTi/SS and CuNiTi/titanium couples. Discussion: In dentistry, there are usually two or more different metals together in a potential corrosive environment. Therefore, galvanic corrosion must be investigated. Potentiodynamic curves revealed that for both couples, CuNiTi/SS and CuNiTi/titanium, CuNiTi would act as an anode, and therefore, would corrode faster than it would alone. As a result of corrosion, deterioration of the arch wire surface may occur and the mechanic properties of CuNiTi wires could be altered, delaying orthodontic treatment. Moreover, CuNiTi corrosion might affect the material biocompatibility due to release of potential allergic Ni ion. Conclusion: CuNiTi might be susceptible to galvanic corrosion in oral environment when coupled to more noble materials, such as SS and titanium. This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); and the Fundação Coordenação de Projetos, Pesquisas e Estudos Tecnológicos (Fundação COPPETEC).