The effect of pH on the corrosion of dental metal alloys

The aim of this study was to determine the effects of the oral environment's pH on the corrosion of dental metals and alloys that have different compositions, using electrochemical methods. The corrosion rates and the cathodic Tafel slopes were obtained from the current-potential curves. The effect of pH on the corrosion of dental metals and alloys was dependent on their composition. Dissolution of the ions occurred in all of the tested pH states. The dissolution was moderately low for samples containing titanium because its surface was covered with a protective layer, whereas the dissolution was maximal for the samples containing tin and copper. Addition of cobalt and molybdenum to the alloys improved their corrosion resistance; these cobalt and molybdenum alloys were not effected by changes in the pH. Dissolution of the precious metal alloys increased as the percentage of noble metals increased. The corrosion characteristics of dental metals and alloys are important because the corrosion tendencies of dental alloys in the mouth may cause health hazards, weakening and the aesthetic loss of dental restorations.     

The effect of abrasion on corrosion of dental Co-Cr alloys. An in vitro study

The effect of abrasion on corrosion of two dental Co-Cr alloys was investigated in vitro. The metals were abraded with a toothbrush and with a piece of tooth enamel. Changes in corrosion potentials and metal release due to the abrasion were measured. Abrasion by tooth enamel caused a persistent drop in corrosion potentials. The release of both chromium and, in particular, cobalt was higher than during brushing. The two alloys tested did not significantly differ with regard to mode and rate of corrosion. It was demonstrated that the corrosion behavior of electrochemically passive dental alloys was affected by abrasion of a magnitude normally encountered during clinical service.     

Galvanic series of some dental alloys.

Galvanic series for different metals in different electrolytes have been published, but never for dental alloys in artificial saline solution. The material classes studied are amalgam, gold alloy, nickel alloy, chromium cobalt casting alloy and temporary crown form. The electrogalvanic potentials were measured and determined in reference to a hydrogen electrode (H2/H+) arbitrarily defined as zero. A galvanic series of the tested materials was arranged in order of their potentials.     

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随着牙科合金在临床上使用日益广泛,其腐蚀引起的一些不良反应也日渐引起人们的重视。牙科合金的腐蚀主要为各种形式的电化学腐蚀,其主要影响因素包括合金的成分、pH值、介质的成分和异种金属等。关于提高牙科合金耐腐蚀性能的研究众多,主要为改变牙科合金的成分和表面改性。     

Use of domestic alloys of noble metals in prosthetic stomatology

The characteristics of the following domestic alloys of noble metals for fixed and removable dentures are given: alloys for metal-ceramic dentures--"Superpal", "Super KM"; alloys for clasp dental prostheses--"Super LB"; solders--"Becadent" and "Super VP"; alloy for castings and metal-composite constructions "Super TZ" and material for electrochemical gold cover "Super KEMZ". The above alloys open wide perspectives in the field of prosthetic treatment of main dental diseases due to their unique properties--high functional efficacy, longevity and biological inactivity.     

Galvanic series of some dental alloys

abstract – Galvanic series for different metals in different electrolytes have been published, but never for dental alloys in artificial saline solution. The material classes studied are amalgam, gold alloy, nickel alloy, chromium cobalt casting alloy and temporary crown form. The electrogalvanic potentials were measured and determined in reference to a hydrogen electrode (H₂/H⁺) arbitrarily defined as zero. A galvanic series of the tested materials was arranged in order of their potentials.     

Galvanic corrosion between dental precious alloys and magnetic stainless steels used for dental magnetic attachments

In this study, we examined the corrosion behavior of dental precious alloys and magnetic stainless steels, namely SUS 444, SUS XM27, and SUS 447J1, used for dental magnetic attachments. Their galvanic corrosion behavior was evaluated from the viewpoint of corrosion potentials when they were in contact with each other. Rest potentials of the precious alloys were constantly higher than those of magnetic stainless steels. Since most gold alloys raised the corrosion potential more significantly than silver alloys did, silver alloys seemed to be better suited than gold alloys for combination with magnetic stainless steels. However, all corrosion potential values were sufficiently lower than the breakdown potentials of the stainless steels and existed within their passive regions. Based on the findings of this study, SUS XM27 and SUS 447J1--which exhibited higher breakdown potentials than SUS 444--emerged as the preferred choices for combination with gold alloys.     

Semiprecious alloys for cast restorations: A preliminary report

A previous clinical evaluation indicated that semiprecious metals had a definite place in the construction of dowels and cores in endodontically treated teeth. 2 The results from the present in vitro study suggest that those alloys do have a place in the fabrication of single castings as type III and IV gold alloy substitutes. Although when compared with a type III gold alloy the behavior of the semiprecious alloys tested was less like that of a noble alloy, the semiprecious alloys appeared less active than the base-metal alloy. This suggests that the semiprecious alloys should be acceptably resistant to corrosion in the oral environment.     

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.     

Corrosion behavior of Pd-Cu and Pd-Co alloys in synthetic saliva

Pd-based alloys are major alternatives to gold-based alloys for PFM applications. In electrolytes simulating oral fluids, these alloys exhibit electrode behavior similar to passivity of active metals, i.e., a potential region of almost constant current density up to a critical potential, above which the current increases. The objective of this study was to correlate the electrode behavior with the results of solution analyses and changes in the surface composition of the alloys. Binary alloys Pd-15 wt% Cu and Pd-19 wt% Co, as well as the pure components, were examined. Corrosion potentials vs. time, potentiodynamic anodic polarization curves, polarization resistances vs. time, and potentiostatic anodic charges were measured with synthetic saliva used as the electrolyte. The concentrations of Pd, Cu, and Co in the solution after various exposures were determined by atomic absorption. The surfaces of the alloys were examined by x-ray photoelectron spectroscopy before and after the exposures. The results show that selective dissolution of the less-noble components occurred on the surfaces of both alloys for all the exposures, leaving the surfaces highly enriched in Pd. This enrichment contributed to the potential changes and the passive-type behavior. Copper dissolved more than cobalt at longer exposures and higher potentials, in spite of its higher nobility. Dissolution of cobalt seemed to be limited by the formation of a surface film, which may be related to the transition character of this element.     

The influence of the pure metal components of four different casting alloys on the electrochemical properties of the alloys

ObjectivesThe aim of this study was to investigate the influence of the pure metal components of the four different casting alloys on the corrosion behaviors of these alloys tested.MethodsPotentiodynamic polarization tests were carried out on four different types of casting alloys and their pure metals at 37 °C in an artificial saliva solution. The ions released from the alloys into the solutions during the polarization test were also determined quantitatively using inductively coupled plasma-mass spectrometry (ICP-MS).ResultsNi–Cr (M1) and Co–Cr (M2) alloys had a more homogenous structure than palladium based (M3) and gold based (M4) alloys in terms of the pitting potentials of the casting alloys and those of the pure metals composing the alloys. The total ion concentration released from M3 and M4 was less than from M1 and M2. This may be because M3 and M4 alloys contained noble metals. It was also found that the noble metals in the M3 and M4 samples decreased the current density in the anodic branch of the potentiodynamic polarization curves. In other words, noble metals contributed positively to dental materials.SignificanceCorrosion resistance of the casting alloys can be affected by the pure metals they are composed of. Au and Pd based noble alloys dissolved less than Ni–Cr and Co–Cr based alloys.     

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.     

Corrosion by galvanic coupling between carbon fiber posts and different alloys.

OBJECTIVES: The corrosion of metal type (NiCr, copper, etc.) posts in post and core restorations has been a well known fact over the last few years. A new generation of carbon fiber posts is now playing an extensive role in dental prosthetics, but these posts may, in some cases come in contact with alloys used for restoration purposes. The objective of this paper is to study the electrochemical behaviour of these posts in an artificial SAGF medium (Artificial Saliva Gal Fovet) for comparison with that observed for different alloys (gold, NiCr and amalgams) in the same medium, and to assess the coupling that might occur between these posts and alloys. METHODS: Posts of different diameters (1-2.1 mm) were molded in resin, thus forming 10 x 3 mm pads that were mounted on a rotating electrode. Pads of identical dimensions were also made for each alloy. Voltammograms (current-tension curves) were plotted for every material in the SAGF medium at 25 degrees C with normal aeration and low aeration (bubbling purified argon) using a potentiometer with three electrodes to determine the position of the zero current potentials. Evans graphs were then plotted once the anode part of the alloy curves and the cathode part of the post curves had been processed with computer software. The potentials and the maximum coupling current densities were estimated. RESULTS: Posts may be involved in galvanic coupling in the presence of oxygen. Galvanic activity in an aerated solution is highly probable upon contact with amalgams, but may also occur if the material in contact is NiCr alloy. Coupling between precious alloys and posts is improbable and can only induce very low currents in the presence of oxygen. SIGNIFICANCE: This study devoted to coupling of carbon fiber posts and metals in the mouth, attracts attention to the fact that a corrosion reaction can be set-up in the infiltration conditions relevant to the prosthetic restoration.     

Corrosion Behavior of As‐Received and Previously Cast Type III Gold Alloy

Purpose: The rationale for using gold alloys is based largely upon their alleged ability to resist corrosion, but little information is available to determine the corrosion behavior of recast alloys. This study characterized the elemental composition of as‐received and recast type III gold alloy and examined the in vitro corrosion behavior in two media using a potentiodynamic polarization technique. Materials and Methods: Seventy‐eight disk‐shaped specimens were prepared from a type III gold alloy under three casting protocols according to the proportion of as‐received and recast gold alloy (n = 26). (1) Group as received (100% as‐received metal), (2) group 50% to 50% (50% wt. new metal, 50% wt. once recast metal), and (3) group recast (100% once recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy, and their elemental compositions were determined using X‐ray energy‐dispersive spectroscopy. Further, the potentiodynamic cyclic polarization between ?1000 and +1000 mV (SCE) were performed for six specimens from each casting protocol in 0.09% NaCl solution (n = 3) and Fusayama artificial saliva (n = 3) at 37°C. Zero‐current potential and corrosion current density were determined. The data were analyzed with 1‐way ANOVA and the Ryan–Einot–Gabriel–Welsch multiple‐range test t (α= 0.05). Results: Elemental composition was significantly different among the casting groups (p < 0.001). The mean weight percentage values were 72.4 to 75.7% Au, 4.5 to 7.0% Pd, 10.7 to 11.1% Ag, 7.8 to 8.4% Cu, and 1.0 to 1.4% Zn. The mean values for Zero‐current potential and corrosion current density for all casting protocols were not significant (p > 0.05); however, the difference between the electrolytes was significant (p < 0.001). Fusayama artificial saliva seemed to offer the most corrosive environment. Conclusions: Type III gold alloy in any casting protocol retained passivity under electrochemical conditions similar to the oral environment. Moreover, high‐gold type III alloys from reputable manufacturers and recasting protocol tested should produce acceptable corrosion‐resistant castings.     

Corrosion potential variation of aged dental amalgam restorations over time.

OBJECTIVE: The corrosion potential of a dental amalgam restoration is generally determined using a single measurement, even though environmental factors and abrasion can continuously alter the surface state and reactivity of this alloy. It was, therefore, the purpose of this study to determine the maximum variability of the corrosion potential of aged dental amalgam restorations, for 28 days. METHODS: The corrosion potentials of 148 aged dental amalgam restorations in 12 human subjects were measured at t = 0 and 4 h, and 4, 7, 14, 21 and 28 days. Measurements were made with a high impedance voltmeter and a Ag/AgCl micro-reference electrode. The subjects were instructed not to alter their usual eating and oral hygiene routines. RESULTS: Corrosion potential changes occurred throughout the 28 days. They were both positive and negative for the same restoration, and were sometimes very large. Only 4 h after the initial measurement, the absolute value of the corrosion potential changes ranged between 18 and 287 mV for 50% of the restorations. The largest maximum absolute corrosion potential change for each subject's restorations ranged between 85 and 329 mV. Statistical analysis showed that the overall mean maximum absolute corrosion potential change for the subjects' restorations was 74 mV. SIGNIFICANCE: It was shown that the corrosion potential of aged dental amalgam restorations varies substantially over time, and that a single measurement is not representative of short- or long-term electrochemical behavior. This finding has implications regarding the corrosion rate of dental amalgam restorations, particularly those that are part of a galvanic couple.     

Corrosion behaviour of high copper dental amalgams

This study evaluated the corrosion behaviour of two high copper dental amalgam alloys [Dispersalloy (Dentsply-Caulk) and Tytin (Kerr)] in different electrolytes. Amalgam specimens were prepared, coupled to a copper wire, cemented into glass tubes and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode as the reference and amalgam as the working electrode. The alloys were tested in the following mediums at 37 degrees C: (i) artificial saliva based on Fusayama's solution (FS), (ii) artificial saliva with citric acid adjusted to pH 4.0 (FC) and (iii) 1% sodium chloride solution (SC). Corrosion potentials (E(corr)) and corrosion rates (I(corr)) were determined using potentiostatic and impedance spectroscopy methods. Data was subjected to anova/Scheffe's post hoc test at 0.05 significance level. For both alloys, the corrosion potential in FS was significantly greater than in SC. Corrosion potential of Tytin in FS and SC was also significantly greater than in FC. The corrosion rate of Dispersalloy in FC was significantly greater than in FS and SC. For Tytin, corrosion rate in SC was significantly greater than in FS and FC. Although no significant difference in corrosion potential/rate was observed between the alloys when tested in FS, significant differences were observed when electrochemical testing was carried out in FC and SC. The corrosion behaviour of high copper amalgam alloys are both material and environment dependent. Certain food substances may increase the corrosion of high copper amalgams.     

Noble alloys in dentistry.

Noble metals used for dental castings continue to consist of alloys of gold, palladium, and silver (not a noble metal), with smaller amounts of iridium, ruthenium, and platinum. The majority are used as a backing for ceramic baking, with the rest used as inlays, onlays, and unveneered crowns. Base metal alloys, principally made of nickel, chromium, and beryllium have gained widespread usage, especially in the United States, due to their lower cost and higher mechanical properties. The current literature, for the most part, cites the use of noble alloys as controls for trials of alternative materials. Direct gold (gold foil) still retains a following and a number of new patents were founded.     

Intraoral corrosion resulting from coupling dental implants and restorative metallic systems.

Materials used for the construction of dental restorations and implants include a wide range of metals and alloys, ceramics and carbons, and polymers. When metals and alloys are placed in direct contact in the oral cavity, a galvanic cell can be formed that may compromise the longevity of one or more of the materials in the couple. In vitro electrochemical corrosion analyses have proven to be a valuable tool for providing guidance on the selection of metallic materials. These analyses can provide basic data on electrochemical potentials, current rates, and the evaluation of galvanic corrosion conditions. This article seeks to provide the clinician with information that can be valuable in the selection of metallic materials that may be placed in direct contact with one another in the oral cavity.     

变形链球菌对牙科合金耐蚀性的影响

目的：探讨变形链球菌对镍铬合金、钴铬合金和金合金腐蚀性能的影响。方法：将3种牙科合金与变形链球菌在液体培养基中共同培养,以单纯培养基和空白组作为对照,8周后,进行电化学实验和扫描电镜观察。结果：电化学实验结果显示,镍铬、钴铬合金的自腐蚀电位绝对值及自腐蚀电流密度值均为培养基对照组低于变形链球菌组及空白对照组,且在变形链球菌组的合金表面不规则破裂孔明显增多。金合金各组自腐蚀电位和电流密度无统计学差异,金合金表面形貌无明显变化。结论：变形链球菌能增加口腔镍铬、钴铬合金的腐蚀倾向与腐蚀速率,但对金合金的影响不明显。     

Corrosion of three experimental AgMn-based casting alloys

OBJECTIVE: Alloys based on AgMn are being evaluated in our laboratory for their possible use as an alternative to Type III dental alloys. They respond to heat treatment and develop hardness values comparable to that of Type III alloys. The objective of the present research was to evaluate their corrosion characteristics. METHODS: The three experimental silver-based alloys of the following composition (at%): (1) 63Ag37Mn, (2) 60Ag35Mn5Au and (3) 60Ag35Mn5Pd, were tested in their peak-hardened condition. Following 0.5 h open-circuit potential (OCP) measurement of each alloy in a phosphated buffer saline (PBS) solution, its current-potential profile was generated by the cyclic voltammetry technique within -1300 and +200 mV (SCE) at 1 mV s-1. In a separate test, the OCP of each alloy was monitored over a 24 h period. RESULTS: Each of the three alloys showed ennoblement of their OCP over time due to dissolution of Mn and consequent enrichment with Ag (Au or Pd). At 24 h, the two ternary alloys were the most noble followed by the binary alloy. With respect to the cyclic voltammetry, oxidation of Ag was noted during forward scans at around 0 mV. The reverse scan was associated with a reduction current peak between -37 and -128 mV. The values for this peak, which is a measure of Ag oxidation, were highest (11.5 mA cm-2) for the binary alloy followed by the Au- (2.9 mA cm-2) and Pd-containing (0.04 mA cm-2) alloys, respectively. This indicates that, for equivalent concentration, Pd is more effective in reducing Ag corrosion than Au. SIGNIFICANCE: Alloys based on the AgMn system are as hard as Type III dental alloys. Information on the corrosion characteristics of the AgMn-based alloys presented here is of value in further development of this alloy system.