Long-term corrosion studies in vitro of gold, cobalt-chromium, and nickel-chromium alloys in contact

Specimens of various types of dental casting alloys were stored in phosphate-buffered 0.9% NaCl solution for 35 weeks. Every 7 weeks the solutions were changed and analyzed with regard to elements released from the alloys. The release of Cu from type III gold alloy increased in contact with gold alloys for metallo-ceramic use in a 1:2 area relation. However, when the area relation was reversed, no difference in the amounts of elements released was observed. Crevice corrosion was initiated with one of the Co-Cr alloys in contact with type III gold alloy. The crevice corrosion increased the amounts of Co and Cr released into the solutions. The release of Ni and Cr from the Ni-Cr alloys was prominent. These alloys were very susceptible to crevice corrosion. With one of the Ni-Cr alloys the release of elements increased in contact with type III gold alloy.     

Effects of chemical composition on the corrosion of dental alloys

The aim of this study was to determine the effect of the oral environment on the corrosion of dental alloys with different compositions, using electrochemical methods. The corrosion rates were obtained from the current-potential curves and electrochemical impedance spectroscopy (EIS). The effect of artificial saliva on the corrosion of dental alloys was dependent on alloy composition. Dissolution of the ions occurred in all tested dental alloys and the results were strongly dependent on the general alloy composition. Regarding the alloys containing nickel, the Ni-Cr and Ni-Cr-Ti alloys released 0.62 mg/L of Ni on average, while the Co-Cr dental alloy released ions between 0.01 and 0.03 mg/L of Co and Cr, respectively.The open-circuit potential stabilized at a higher level with lower deviation (standard deviation: Ni-Cr-6Ti = 32 mV/SCE and Co-Cr = 54 mV/SCE). The potenciodynamic curves of the dental alloys showed that the Ni-based dental alloy with >70 wt% of Ni had a similar curve and the Co-Cr dental alloy showed a low current density and hence a high resistance to corrosion compared with the Ni-based dental alloys. Some changes in microstructure were observed and this fact influenced the corrosion behavior for the alloys. The lower corrosion resistance also led to greater release of nickel ions to the medium. The quantity of Co ions released from the Co-Cr-Mo alloy was relatively small in the solutions. In addition, the quantity of Cr ions released into the artificial saliva from the Co-Cr alloy was lower than Cr release from the Ni-based dental alloys.     

Metallurgical, surface, and corrosion analysis of Ni-Cr dental casting alloys before and after porcelain firing.

OBJECTIVES: A porcelain veneer is often fired on nickel-chromium casting alloys used in dental restorations for aesthetic purposes. The porcelain-fused-to-metal (PFM) process brings the temperature to over 950 degrees C and may change the alloy's corrosion properties. In this study, the metallurgical, surface, and corrosion properties of two Ni-Cr alloys were examined, before and after PFM firing. METHODS: Two types of alloy were tested-a high Cr, Mo alloy without Be and a low Cr, Mo alloy with Be. Before the PFM firing, specimens from both alloys were examined for their microstructures, hardness, electrochemical corrosion properties, surface composition, and metal ion release. After the PFM firing, the same specimens were again examined for the same properties. RESULTS: Neither of the alloys showed any differences in their electrochemical corrosion properties after the PFM firing. However, both alloys exhibited new phases in their microstructure and significant changes in hardness after firing. In addition, there was a slight increase in CrO(x) on the surface of the Be-free alloy and increased Mo-Ni was observed on the surface of both alloys via X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). This might be one of the reasons why both alloys had increased Ni and Mo ion release after firing. SIGNIFICANCE: The PFM firing process changed the alloys' hardness, microstructure, and surface composition. No significant changes in the alloys' corrosion behavior were observed, however, the significant increase in metal ion release over a month may need to be further investigated for its clinical effects.     

3种牙科铸造金属模拟唾液浸泡后粗糙度的变化

目的：通过考察钴铬合金、镍铬合金以及纯钛在不同pH值人工唾液中浸泡后表面粗糙度的变化，研究3种常用牙科金属的耐腐蚀能力。方法：将3种金属的标准铸造试件逐级打磨抛光后。浸泡于pH值分别为7．0和5．6的人工唾液中。3个月后检测试件表面粗糙度，并用金相显微镜观察试件表面。采用SPSS11．0软件包对数据进行单因素方差分析及t检验。结果：pH=5．6的人工唾液浸泡后，3种材料表面粗糙度有显著差异，镍铬合金〉钴铬合金〉纯钛金属（P〈0．01）。pH=7．0的人工唾液浸泡后，镍铬合金表面粗糙度大于钴铬合金和纯钛（P〈0．01），但钴铬合金和纯钛之间无统计学差异（p〉0．05）。pH=5．6人工唾液浸泡组的镍铬合金和钴铬合金表面粗糙度大于pH=7．0组的同种材料（P〈0．01）。各试验组表面粗糙度大小与显微镜观察到的材料表面腐蚀程度一致。结论：纯钛在酸性和中性环境下均有较强的耐腐蚀性，钴铬合金、镍铬合金在酸性介质中的耐腐蚀性较差。3种金属的耐腐蚀性由大到小排列为：纯钛金属〉钴铬合金〉镍铬合金。     

Corrosion behaviour and surface analysis of a Co-Cr and two Ni-Cr dental alloys before and after simulated porcelain firing

This study evaluated the corrosion behaviour and surface properties of a commercial cobalt-chromium (Co-Cr) alloy and two nickel-chromium (Ni-Cr) alloys [beryllium (Be)-free and Be-containing] before and after a simulated porcelain-firing process. Before porcelain firing, the microstructure, surface composition and hardness, electrochemical corrosion properties, and metal-ion release of as-cast alloy specimens were examined. After firing, similar alloy specimens were examined for the same properties. In both as-cast and fired conditions, the Co-Cr alloy (Wirobond C) showed significantly more resistance to corrosion than the two Ni-Cr alloys. After firing, the corrosion rate of the Be-free Ni-Cr alloy (Stellite N9) increased significantly, which corresponded to a reduction in the levels of Cr, molybdenum (Mo), and Ni in the surface oxides and to a reduction in the thickness of the surface oxide film. The corrosion properties of the Co-Cr alloy and the Be-containing Ni-Cr alloy (ChangPing) were not significantly affected by the firing process. Porcelain firing also changed the microstructure and microhardness values of the alloys, and there were increases in the release of Co and Ni ions, especially for Ni from the Be-free Ni-Cr alloy. Thus, the corrosion rate of the Be-free Ni-Cr alloy increased significantly after porcelain firing, whereas the firing process had little effect on the corrosion susceptibility of the Co-Cr alloy and the Be-containing Ni-Cr alloy.     

Use of x-ray photoelectron spectroscopy and cyclic polarization to evaluate the corrosion behavior of six nickel-chromium alloys before and after porcelain-fused-to-metal firing

STATEMENT OF PROBLEM: Nickel-chromium casting alloys rely on a surface oxide layer for corrosion resistance to the oral environment. Porcelain-fused-to-metal (PFM) firing procedures may alter the surface oxides and corrosion properties of these alloys. Changes in alloy corrosion behavior affect metal ion release and therefore local and/or systemic tissue responses. PURPOSE: The aim of this study was to evaluate changes in alloy surface oxides and electrochemical corrosion properties after PFM firing. MATERIAL AND METHODS: The electrochemical corrosion behavior of 6 commercial nickel-chromium alloys was evaluated in the as-cast/polished and PFM fired/repolished states. Surface chemistries of the alloys were analyzed by x-ray photoelectron spectroscopy. RESULTS: Results indicated an increase in corrosion rates after PFM firing and repolishing for alloys containing 14% to 22% Cr and 9% to 17% Mo. This increase in corrosion rates was attributed to a decrease, caused by the PFM and repolishing process, in the Cr and Mo levels in the surface oxides of these alloys. The PFM firing and repolishing process did not alter the corrosion behavior of the alloys containing lower levels of Cr and Mo and/or Be additions in their bulk composition. These alloys exhibited low levels of Cr and Mo surface oxides in both test conditions. Si particles became embedded in the surfaces of the fired alloys during repolishing and may have contributed to the changes in surface oxides and the corrosion behavior of some alloys. CONCLUSION: The effects of PFM firing and repolishing on Ni-Cr dental casting alloy surface oxides and corrosion properties appear to be alloy dependent.     

Cobalt–chromium alloys fabricated with four different techniques: Ion release,toxicity of released elements and surface roughness

ObjectiveTo investigate the metal ion release, surface roughness and cytoxicity for Co–Cr alloys produced by different manufacturing techniques before and after heat treatment. In addition, to evaluate if the combination of materials affects the ion release.MethodsFive Co–Cr alloys were included, based on four manufacturing techniques. Commercially pure titanium, CpTi grade 4 and a titanium alloy were included for comparison. The ion release tests involved both Inductive Coupled Plasma Optical Emission Spectrometry and Inductive Coupled Plasma Mass Spectrometry analyses. The surface analysis was conducted with optical interferometry. Cells were indirectly exposed to the materials and cell viability was evaluated with the MTT (3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide) method.ResultsAll alloys showed a decrease of the total ion release when CpTi grade 4 was present. The total ion release decreased over time for all specimens and the highest ion release was observed from the cast and milled Co–Cr alloy in acidic conditions.The cast and laser-melted Co–Cr alloy and the titanium alloy became rougher after heat treatment. All materials were within the limits of cell viability according to standards.SignificanceThe ion release from Co–Cr alloys is influenced by the combination of materials, pH and time. Surface roughness is influenced by heat treatment. Furthermore, both ion release and surface roughness are influenced by the manufacturing technique and the alloy type. The clinical implication needs to be further investigated.     

Potentiodynamic polarization study of the in vitro corrosion behavior of 3 high-palladium alloys and a gold-palladium alloy in 5 media.

STATEMENT OF PROBLEM: Corrosion of cast alloy restorations may lead to their failure or adversely affect their biocompatibility. Although some documentation of the corrosion behavior of the high-palladium dental alloys exists, questions remain about their corrosion resistance and mechanisms. PURPOSE: This study compared the in vitro corrosion characteristics of 3 high-palladium alloys and 1 gold-palladium alloy in simulated body fluid and oral environments. MATERIAL AND METHODS: Two Pd-Cu-Ga alloys and 1 Pd-Ga alloy were selected; an Au-Pd alloy served as the control. The corrosion behavior for the as-cast and simulated porcelain-firing (heat-treated) conditions of each alloy (N = 5) was evaluated in 0.9% NaCl, 0.09% NaCl, and Fusayama solutions. Heat-treated specimens of each alloy (N = 5) were also tested in N(2)-deaerated 0.09% NaCl and Fusayama solutions (pH 4). After immersion in the electrolyte for 24 hours, the open-circuit potential (OCP) was measured, and linear polarization was performed from -20 mV to +20 mV (vs. OCP) at a scanning rate of 0.125 mV/s. Cyclic polarization was performed from -300 mV to +1000 mV and back to -300 mV (vs. OCP) at a scanning rate of 1 mV/s. Data were evaluated with analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range test (alpha=.05). RESULTS: The OCP of each alloy varied with the condition (as-cast or heat-treated) and electrolyte used. Corrosion resistance was similar for the 4 alloys tested. For cyclic polarization, all alloys showed active-passive or spontaneous passive behavior in nearly all electrolytes. During some reverse scans, the 3 high-palladium alloys displayed 3 or 5 anodic peaks. No positive hysteresis was observed for any of the alloy/electrolyte combinations evaluated. CONCLUSION: The corrosion resistances of the 3 high-palladium alloys in simulated body fluid and oral environments were comparable to that of the gold-palladium alloy. The similar corrosion resistance for the 3 high-palladium alloys was attributed to their high noble metal content and theorized stable structure at the submicron level. Selective corrosion of different phases and elements, surface enrichment of palladium, and adsorption of species are possible corrosion mechanisms. The cyclic polarization results suggest that none of the 4 alloys would be prone to pitting or crevice corrosion under in vivo conditions, but crevice conditions should nonetheless be avoided for these alloys in the oral environment.     

Susceptibility to localized corrosion of stainless steel and NiTi endodontic instruments in irrigating solutions

AIM: To evaluate the pitting and crevice corrosion characteristics of stainless steel (SS) and NiTi endodontic files in R-EDTA and NaOCl irrigating solutions. METHODOLOGY: The corrosion behaviour of two H-files produced from different SS alloys (Mani, AISI 303 SS, Dentsply Maillefer, AISI 304 SS) and one file produced from NiTi alloy (Maillefer) was determined in R-EDTA and NaOCl irrigating solutions by the cyclic potentiodynamic polarization method. The cutting flutes of 12 files of each material were embedded in an epoxy resin, polished, exposed to the irrigating solutions and used as an electrode. An Ag/AgCl electrode was used as a reference, a platinum plate was used as a counter electrode and polarization curves were obtained for all files in R-EDTA and NaOCl irrigating solutions in 37 degrees C with a potential scan rate of 5 mV min(-1). Corrosion potential (Ecorr), Corrosion current density (Icorr) and Pitting potential (Epit) were calculated from each curve. The results were statistically analysed with two-way anova and Student-Newman-Keuls (SNK) multiple comparison test with materials and irrigating solutions serving as discriminating variables (a = 0.05). RESULTS: Cyclic polarization curves presented negative hysteresis implying that pitting or crevice corrosion are not likely to occur for all the materials examined in both irrigating solutions. In NaOCl all materials showed significantly higher Ecorr (P = 0.011) as well as lower Icorr compared with R-EDTA reagent. Moreover, all materials demonstrated equal Epit in NaOCl, which was to be found significantly lower (P = 0.009) than the value of Epit in R-EDTA. CONCLUSIONS: None of the tested materials is susceptible to pitting or crevice corrosion in R-EDTA and NaOCl solutions and from this standpoint are appropriate for the production of endodontic files.     

表没食子儿茶素没食子酸酯对镍铬合金电化学腐蚀后表面结构和性能的影响

目的:研究表没食子儿茶素没食子酸酯(epigallocatechin gallate, EGCG)对镍铬合金电化学腐蚀后表面结构和性能的影响。方法:采用体视显微镜和扫描电镜,观察经0 g/L和1.0 g/L EGCG人工唾液电化学腐蚀后镍铬合金的表面形貌,并运用光电子能谱仪分析经0 g/L和1.0 g/L EGCG人工唾液电化学腐蚀后镍铬合金的表面腐蚀产物。结果:经0 g/L和1.0 g/L EGCG人工唾液电化学腐蚀后,镍铬合金表面均有不同程度的腐蚀,在0 g/L EGCG人工唾液中,出现的点蚀坑直径较小,基本未影响合金表面的枝晶结构;而在1.0 g/L EGCG人工唾液中,镍铬合金表面发生了较为严重的腐蚀,点蚀坑直径较大,枝晶区间开始融合、变得模糊不清。此外,经0 g/L EGCG和1.0 g/L EGCG人工唾液电化学腐蚀后,镍铬合金表面溅射120 s后均检测到了O、Ni、Cr、Be、C及Mo元素,表面氧化物均主要为NiO和Cr2O3。与0 g/L EGCG人工唾液相比,镍铬合金在1.0 g/L EGCG人工唾液电化学腐蚀后表面O元素、NiO和Cr2O3的含量较低。结论:经EGCG人工唾液电化学腐蚀后,镍铬合金表面形貌和表面腐蚀产物结果一致,提示1.0 g/L EGCG促使镍铬合金表面耐腐蚀性能变差,表面腐蚀产物中氧化物含量也降低。     

Elucidating the corrosion-related degradation mechanisms of a Ti-6Al-4V dental implant

ObjectiveThe Ti-6Al-4V (TAV) alloy is commercially used as a dental implant material. This work seeks to elucidates the origins of degradation of Ti-6Al-4V (TAV) implant alloys that result in peri-implant bone loss. Methods: In this work, a combination of microstructure, surface, and solution analyses was utilized to study the corrosion mechanism of the TAV alloy in oral environments. The corrosion of TAV alloys in the F^--enriched environment of a crevice was evaluated through nanoscale surface analysis. And, the findings were further rationalized via electrochemical means. ResultsOur results suggest the bone loss was caused by crevice corrosion and the consequential release of by-products, and the crevice corrosion was potentially induced by the buildup of corrosive species such as fluorides, which are common additives in dental products. In turn, the corrosion properties of the TAV alloy were evaluated in fluoride enriched environments. Nanoscale analysis of corroded surfaces, carried out using vertical scanning interferometry (VSI) showed that the corrosion susceptibility of the constituent phases dictates the corrosion product species. In specific, the aluminum-rich α phase preferentially dissolves under potential-free conditions and promotes the formation of insoluble Al-Ti oxides. Notably, under conditions of applied potential, oxidative dissolution of the vanadium-rich β phase is favored, and the vanadium release is promoted. SignificanceThese findings elucidate the origins of degradation of TAV-implants that result in the release of corrosion by-products into the local biological environment. More important, they offer guidelines for materials design and improvement to prevent this nature of degradation of dental implants.     

Influence of alloying elements on cellular response and in-vitro corrosion behavior of titanium-molybdenum-chromium alloys for implant materials

PurposeNot all elements with β-stabilizing properties in titanium alloys are suitable for biomaterial applications, because corrosion and wear processes release the alloying elements to the surrounding tissue. Chromium and molybdenum were selected as the alloying element in this work as to find balance between the strength and modulus of elasticity of β-titanium alloys. This study aimed to investigate the effect of Titanium-10Molybdenum-10Chromium (Ti-10Mo-10Cr), Titanium-10Chromium (Ti-10Cr) and Titanium-10Molybdenum (Ti-10Mo) on the elemental leachability in tissue culture environment and their effect on the viability of human gingival fibroblasts (HGFs).MethodsEach alloy was immersed in growth medium for 0–21 days, and the elution was analyzed to detect the released metals. The elution was further used as the treatment medium and exposed to seeded HGFs overnight. The HGFs were also cultured directly to the titanium alloy for 1, 3 and 7 days. Cell viability was then determined.ResultsSix metal elements were detected in the immersion of titanium alloys. Among these elements, molybdenum released from Ti-10Mo-10Cr had the highest concentration throughout the immersion period. Significant difference in the viability of fibroblast cells treated with growth medium containing metals and with direct exposure technique was not observed. The duration of immersion did not significantly affect cell viability. Nevertheless, cell viability was significantly affected after 1 and 7 days of exposure, when the cells were grown directly onto the alloy surfaces.ConclusionsWithin the limitation of this study, the newly developed β-titanium alloys are non-cytotoxic to human gingival fibroblasts.     

不同质量分数氯离子对铬合金钝化膜性能的影响

目的 在不同质量分数氯化钠溶液中研究3种铬合金表面钝化膜的性能改变,分析其抗腐蚀性能,以期为铬合金的临床应用提供参考.． 分别配制氯化钠质量分数为1%、2%、3%的人工唾液,分别以钴铬合金、镍铬合金和含钛镍铬合金(各5个)为工作电极,施加0.1 V钝化电位600 s形成钝化膜.分析3种铬合金的电压-电容关系曲线和时间-电流对数曲线,分析不同氯离子质量分数对3种铬合金表面钝化膜的半导体特性及致密性的影响.结果 3种铬合金钝化膜均呈n型半导体特性;随着氯化钠质最分数的增大,3种铬合金钝化膜的载流子密度均增大,当氯化钠质量分数为3%时镍铬合金、钴铬合金和含钛镍铬合金的载流子密度分别增至3.71×10～8、2.34×10～9和7.66×10～9/cm～3,时间-电流对数曲线斜率随之减小,钝化膜稳定性和致密性降低.结论 在高氯离子环境中3种铬合金的抗腐蚀性能均降低,严重影响修复体的使用寿命.     

In vitro and in vivo corrosion evaluation of nickel-chromium- and copper-aluminum-based alloys

STATEMENT OF PROBLEM: The low resistance to corrosion is the major problem related to the use of copper-aluminum alloys. PURPOSE: This in vitro and in vivo study evaluated the corrosion of 2 copper-aluminum alloys (Cu-Al and Cu-Al-Zn) compared with a nickel-chromium alloy. MATERIAL AND METHODS: For the in vitro test, specimens were immersed in the following 3 corrosion solutions: artificial saliva, 0.9% sodium chloride, and 1.0% sodium sulfide. For the in vivo test, specimens were embedded in complete dentures, so that one surface was left exposed. The 3 testing sites were (1) close to the oral mucosa (partial self-cleaning site), (2) surface exposed to the oral cavity (self-cleaning site), and (3) specimen bottom surface exposed to the saliva by means of a tunnel-shaped perforation (non-self-cleaning site). RESULTS: Almost no corrosion occurred with the nickel-chromium alloy, for either the in vitro or in vivo test. On the other hand, the 2 copper-aluminum-based alloys exhibited high corrosion in the sulfide solution. These same alloys also underwent high corrosion in non-self-cleaning sites for the in vivo test, although minimal attack was observed in self-cleaning sites. CONCLUSION: The nickel-chromium alloy presented high resistance to corrosion. Both copper-aluminum alloys showed considerable corrosion in the sulfide solution and clinically in the non-self-cleaning site. However, in self-cleaning sites these 2 alloys did not show substantial corrosion.     

Elemental release from dental casting alloys into biological media with and without protein.

OBJECTIVE: The objective of this study was to determine the role of proteins in affecting elemental release from a variety of clinically available dental casting alloys. An important role for proteins was suspected based on previous reports about the corrosion of stainless steel and the cytotoxicity of alloys after exposure to a saline-protein solution. METHODS: Clinically available alloys with compositions ranging from 0 to 94at.% noble elements were exposed for 1 week to either saline, saline with 3% bovine serum albumin (BSA), or complete cell-culture medium with 3% serum. Atomic absorption spectrophotometry was used to measure the release of elements from the alloys. Elemental release was normalized for the exposed surface area of the alloys. RESULTS: In general, more elemental release occurred into the saline-BSA solution compared to saline alone for all released elements (Ag, Cu, Pd, and Zn) except for Ni. Ni release from the NiCr alloy was lower in the presence of BSA. Each element responded somewhat differently with Pd being the least predictable in its behavior. Elemental release was less in the cell-culture medium than in the saline-BSA solution for most elements. For alloys which released multiple elements, all elements responded similarly but not identically to the presence of protein. A high elemental release during exposure to the saline-BSA solution correlated with a low alloy cytotoxicity post-exposure to the saline-BSA. SIGNIFICANCE: This study demonstrates the importance of defining exactly the composition of biological solutions used to assess in vitro corrosion and biocompatibility of dental casting alloys. Other molecules in addition to proteins appeared to be critical to the corrosion of these alloys in vitro.     

Corrosion of some selected ceramic alloys used in fixed partial dentures and their postsolder joints in a synthetic neutral saliva

The electrochemical behavior of several alloys used in the frameworks of fixed partial dentures and their corresponding postsolders was studied in artificial saliva as a function of chemical composition. Open circuit potentials and polarization resistances were measured. The general electrochemical behaviors between the cathodic domain and the oxidation of solvent were characterized using cyclic polarization. The possible galvanic corrosion of coupled parent and postsolder alloys was also studied. The polarization resistances were high or very high. During immersion, the noblest alloys stayed in the immunity domains of their base elements, whereas Ni–Cr alloys were quickly passivated. The oxidation of the noble elements occurred only when the alloys were exposed to very high potentials solely achievable by artificial means. However, problems of galvanic corrosion may occur between an alloy and its postsolder joint if they are both exposed to saliva. Such corrosion may lead to a weakening of the framework. The parent alloy was often potentially affected by such corrosion but with low exchange currents.     

Corrosion resistance of cobalt-chromium and palladium-silver alloys used in fixed prosthetic restorations

The corrosion resistance of a cobalt-chromium (Co-Cr) alloy was assessed with a view to determining its potential use in the manufacture of fixed dental prostheses. The electrochemical behaviour of the alloy was compared with that of two palladium (Pd)-based alloys. Measurements of corrosion potential and anodic polarization were performed on the alloys, and the specimen surfaces were examined by using scanning electron microscopy. Although the corrosion potential of the Co-Cr alloy was lower than that of the Pd-based alloys, the corrosion currents and polarization resistance values were similar for all three alloys. All materials showed a very high resistance to corrosion. Given that the beneficial mechanical properties of Co-Cr alloys have already been established, this type of alloy may be a suitable alternative for use in the manufacture of fixed dental prostheses.     

人工唾液中氯化钠浓度对钴铬、镍铬、含钛镍铬合金腐蚀行为的影响

目的：在人工唾液中氯化钠浓度升高的条件下,用电化学阻抗谱研究3种牙科常用合金（钴铬、镍铬、含钛镍铬合金）腐蚀行为的变化。方法：测定在人工唾液中氯化钠浓度分别为0.9%、2%、3%的条件下,3种合金的电化学阻抗谱,将各体系中合金界面电容和电荷转移电阻拟合,分析其腐蚀机制和耐腐蚀性能的变化。结果：随着氯化钠浓度升高,3种合金的界面电荷转移电阻（Rt值）都分别减小,界面电容（Qdl）增大,腐蚀反应过程加剧,抗蚀能力降低。但钴铬合金的Rt值是最大的。结论：在高氯环境中,3种合金腐蚀反应加快,抗腐蚀能力均降低,但钴铬合金抗腐蚀能力相对较强,这将影响它们的使用寿命。     

Effect of chemical composition of Ni-Cr dental casting alloys on the bonding characterization between porcelain and metal

The purpose of this study was to investigate the influence of chemical composition of Ni-Cr dental casting alloys on the bonding behaviour between porcelain and metal. A three-point bending test was used to measure the fracture load of alloy after porcelain firing. A scanning electron microscope, accompanied by an energy dispersion spectrometer, was used to analyse the morphology and chemical composition of the fracture surface. An X-ray photoelectron spectrometer and glow discharge spectrometer were used to identify the structure and cross-sectional chemical composition, respectively, of oxide layers on Ni-Cr alloys after heat treatment at 990 degrees C for 5 min. Results showed that the oxide layers formed on all Ni-Cr alloys contained mainly Cr2O3, NiO, and trace MoO3. The Ni-Cr alloy with a higher Cr content had a thicker oxide layer, as well as a weaker bonding behaviour of porcelain/metal interface. The presence of Al (as Al2O3) and Be (as BeO) on the oxide layer suppressed the growth of the oxide layer, leading to a better porcelain/metal bonding behaviour. However, the presence of a small amount of Ti (as TiO2) on the oxide layer did not have any influence on the bonding behaviour. The fracture propagated along the interface between the opaque porcelain and metal, and exhibited an adhesive type of fracture morphology.     

Corrosion evaluation of gold-based dental alloys

Three commercial gold-based dental alloys and three constant-nobility ternary alloys (Au-Ag-Cu) were evaluated for corrosion using a quantitative test battery. Integration of the current density, in a de-aerated solution of 1% NaCl along the approximate potential range found in the mouth (-300 mV to +300 mV vs. SCE), yields a quantitative rank ordering of the test alloys. The results are combined with prior findings on other commercial alloys to demonstrate the interaction of nobility and microstructure. Nobility determines the overall corrosion resistance for gold-based alloys. However, because of mutual insolubility, alloying with copper induces silver segregation, resulting in a higher corrosion rate at a given nobility. Thus, microstructure has an influence on corrosion, but heat treatments are largely ineffective in altering the basic corrosion characteristics. The test techniques, in combination with tarnish evaluations, provide a quantitative battery for alloy evaluation. The results indicate the combinations of nobility, microstructure, and environment most likely to avoid corrosion difficulties.