Long-term corrosion studies in vitro of amalgams and casting alloys in contact

Evaluation of Ion Release from Two Base-Metal Alloys at Various pH Levels

We examined the influence of salivary pH on the corrosion of two base-metal alloys. Cobalt — chromium (Co — Cr) and nickel — chromium (Ni — Cr) alloy samples were created and submerged in artificial saliva of different pH values (pH 4, pH 5 and pH 7). The amount of each ion present in solution 1 month later was measured by flame atomic absorption spectrophotometry. Statistical analysis showed that pH significantly affected total and Co ion release, but not Ni or Cr ion release. The alloy type did not affect total ion release, but was significant for Cr ion release. Alloy — pH interaction significantly affected Cr and total ion release. To prevent metal particle release, the alloys used for dental restoration should, whenever possible, be made from noble metals and corrosion-resistant alloys.

Intraoral galvanic corrosion: literature review and case report

This article reviewed the dental history of a patient with symptomatic electro-chemical reactions after the occlusal relationship of an existing complete gold crown and silver amalgam restoration was changed. A literature review of oral galvanism is presented with diagnostic techniques and treatment options.

Evaluation of the interactions between amalgam, cement and gold castings

The purpose of this study was to determine the interactive effects between a dental amalgam, cements and a gold alloy and therefore evaluate cements as barriers to corrosion. There were 48 castings cemented to either simulated amalgam cores or teeth using zinc phosphate (ZnPO4) or glass polyalkenoate (ionomer) cement. An additional 12 castings were placed in direct contact with the amalgam restoration. Half of the specimens were thermocycled between 5 degrees and 50 degrees C for 12 weeks. The other half were stored at 37 degrees C for the same period of time. The specimens were then encased in epoxy resin and sectioned. The sectioned specimens were examined for cement loss, as well as evidence and extent of corrosion. Significantly more cement loss occurred with the ZnPO4 compared with the glass polyalkenoate (ionomer) cement when the castings were cemented to amalgam cores. Evidence of corrosion was apparent in all specimens; thermocycling produced significantly more corrosion than the 37 degrees C environment. The direct-contact group produced significantly more corrosion compared with the specimens where castings were cemented with ZnPO4.

Release of corrosion products from amalgam in phosphate containing solutions

The effect of phosphate concentration on corrosion was compared for two types of amalgam: a conventional alloy (ANA 68) and a high-Cu admixed alloy (Dispersalloy). The test specimens were stored for 4 months in electrolytes containing 85 mM NaCl and 85 mM NaCl with 2.5, 10, or 100 mM phosphate buffer respectively. The solutions were renewed each month and analyzed for Cu, Zn, Sn, Hg, and Ag in an atomic absorption spectrophotometer. The surfaces and cross-sections of the specimens were studied in a scanning electron microscope (SEM) with an energy dispersive detector (EDAX). The corrosion products, mainly Sn-compounds, at the surface of the amalgams were less in the solutions containing high concentrations of phosphate. In cross-section subsurface corrosion of the high-Cu amalgam was observed especially in specimens immersed in the NaCl solution without phosphate. The conventional amalgam showed surface corrosion only. The decrease in release of elements with time from the conventional amalgam in all the experimental solutions might indicate passivation. For the high-Cu amalgam the release of elements increased with time, except for Cu and Sn in the solution with 100 mM phosphate, indicating that phosphate inhibits corrosion of the Cu-Sn-phases. Release of corrosion products from the high-Cu amalgam was more dependent on the presence of phosphate than the conventional amalgam.

Area ratio effects on metal ion release from amalgam in contact with gold

The effect of area ratio, chloride concentration and brushing on amalgam in contact with gold was studied by measuring the amounts of elements released in the electrolyte. A type III gold alloy was stored for 4 months in contact with a conventional amalgam, area relations 6/1 and 6/3, in an electrolyte containing 85 mM NaCl with 10 mM phosphate buffer. A specimen with area relation 6/1 was also stored in a 10 mM NaCl solution with 10 mM phosphate buffer. The solutions were renewed each month and analyzed for Cu, Zn, Sn, Hg, and Ag in an atomic absorption spectrophotometer. Cross-sections of the amalgams were studied in a scanning electron microscope. The tendency for Sn and Cu to be released from the amalgam was greater than for the other elements. The Sn-release probably mainly originated from surface corrosion and Cu-release from subsurface corrosion. A stronger galvanic influence enhanced only the release of Cu, and to a less extent Zn. The subsurface corrosion of the amalgam and increasing release of Cu was, in contrast to the other elements, largely dependent on a high chloride concentration in the electrolyte. Light brushing of the specimens had no effect on the amounts of elements released.

Effect of placement of amalgam restorations on urinary mercury concentration

Dental amalgam emits mercury, especially during setting. In addition, the preparation of the amalgam and its compaction into the cavity involve unbound metallic mercury or create a waste product with free metallic mercury. The present study was performed to explore whether emission of mercury in these situations would measurably influence the individual urinary mercury concentration of dental patients as a result of a single-session treatment with dental amalgam restorations. Informed consent was obtained from the patients of nine children about to be treated with amalgam restorations as part of their regular dental care. The children delivered a total of five morning urine samples before, during, and after the treatment period. No effect on the urine mercury concentration was found during the treatment period. Conclusively, one single session of amalgam treatment did not per se represent a mercury exposure of sufficient quantity to be detectable in a longitudinal, individual study.

Corrosion of dental amalgam and mercury vapor emission in vitro

Amalgam specimens were immersed for 30 days in 1) water, 2) 0.9% NaCl in water, 3) 0.9% NaCl and 10 mM phosphate buffer in water, and 4) 0.9% NaCl, 7.7 mM phosphate, and 6.1 mM citric acid in water. The solutions were stored in stoppered glass tubes. Hg-drops were immersed in solutions 1, 2, and 3. The concentration of mercury vapor in the air above the solutions was measured once a day. After 30 days the amounts of Cu, Zn, Hg, and Ag in the solutions were analyzed by atomic absorption spectrophotometry. The results showed that 0.9% NaCl alone or in combination with the additives increased the amounts of elements released into the solutions. The concentration of Hg0 in the glass tubes increased with the amount of Hg in the solutions, with the exception of solution No. 3, from which significantly less Hg0 evaporated. The results indicate that the composition of the saliva, oral hygiene and dietary factors may be determinants of Hg0 emission from amalgams in the oral cavity.

Research on dental amalgam: 1982-1986

This paper is a five-year review of selected research papers on dental amalgam which were published during the years 1982 through 1986. Papers presented at scientific dental meetings are also included. During the past five years, clarification of amalgam metallurgy has been made, and a few innovative modifications have been recommended. The addition of palladium, indium, and selenium to dental amalgam has been suggested, but commercial applications have yet to be made. The mechanical property of creep has been studied more extensively, while the applicability of fracture toughness tests has been examined. More work has been done on the microleakage of amalgam restorations, with certain alloy factors showing an influence on this problem. Most in vitro investigations on the use of cavity varnish or resin films beneath amalgam restorations show reduced microleakage. Additionally, many electrochemical investigations were conducted. A most significant finding was that amalgam does not appear to break down in vivo as much as in vitro tests would indicate, the buffering action of saliva being protective in this regard. The marginal fracture evaluation of clinical amalgam restorations is still being used as a major clinical performance criterion, and measuring techniques for this failure mode have been improved. Measurements of metallic ion loss from amalgam were made with instruments of high sensitivity, but no evidence has been found to associate this loss with any disease entity. The rare presence of an allergy to mercury appears to be the only contra-indication for the use of amalgam as a dental restoration. Further research on dental amalgam can lead to improved clinical performance of this most useful restorative material.

Electrochemical properties of corroded amalgams

Three types of amalgam, one conventional, ANA 68, and two with high copper content, Dispersalloy (dispersed type) and ANA 2000 (single composition type), were investigated. The amalgams were immersed for periods of 7 wk at a time, up to 35 wk, in 23 ml (37 degrees C) of 0.9% NaCl aqueous solutions and in 0.9% NaCl solution buffered with NaH2PO4 (8.8 mM) and Na2HPO4 (1.2 mM). The amalgam specimens were embedded in epoxy resin. The surface area of amalgam exposed to the solutions was 0.2 cm2 for each specimen. Every 7 wk the corrosion potential was measured, the amalgam specimens lightly brushed with a soft toothbrush, and the solutions renewed. After 14-21 wk and 35 wk the currents during anodic polarization sweeps over the amalgams were recorded. The corrosion potential for the high-Cu amalgams was somewhat more positive (noble) in the phosphate buffered solution than in the non-buffered solution during the 35 wk of corrosion. The phosphate buffer reduced the reactivity of the amalgams during anodic polarization. Corrosion made the amalgams more passive during the anodic polarization. However, all the elements leached from the amalgams into the solutions throughout the entire experiment.

Correlation between amalgam restorations and mercury concentrations in urine

The creatinine-adjusted urinary concentration of mercury in 73 schoolchildren with a mean age of 12 years was determined. In addition, the number of amalgam restorations and their size, prevalence of allergy, and days absent from school due to illness were recorded for each individual. A significant positive correlation (r = 0.55) was found between urine Hg and extent of amalgam restorations, but no correlation existed between urine Hg and allergy or between urine Hg and absence from school due to illness. Neither could any correlation be found between extent of amalgam restorations and either allergy or absence from school.

Report of Committee on Scientific Investigation of the American Academy of Restorative Dentistry

A few personal points seem appropriate in summary. It is axiomatic that while research solves problems, it also creates them. As an example, it is an accepted fact that dentistry more than any other profession has made serious inroads into putting itself out of business through research. Each year this report takes note of the reduction in dental caries in children, which has thus triggered a change in the nature of general practice. Be this as it may, it is well to acknowledge that major dental diseases are not disappearing, but their patterns in the population are changing, accompanied by an expansion of other services. Despite the optimistic picture painted earlier in this report, it is grossly premature to acclaim the elimination of caries, and thereby a significant segment of restorative dentistry. Of course the younger age groups have been the major beneficiaries of caries reduction. As the child ages from 9 to 16 years, the percentage of mouths free of caries drops by one half. In addition, the disease pattern in the adult population is being altered because of a longer life span and loss of fewer teeth. Unquestionably what we will, and are already seeing, is not an elimination of restorative dentistry but a different target and changes in procedures because of new materials, therapy, and expanded scope of services. There is yet another subtle change in the trend of dental research and it deals with the reduction in the number of dental schools worldwide and smaller class sizes in those schools. Dental research thereby suffers because of the traditional link between education and research. Thus the potential pool of researchers becomes smaller and research monies for training programs for dental investigators, particularly in clinical research, decreases. This year a surprising number of articles are concerned with manpower as it relates to research priorities. So, it is indeed a time that both the profession and the scientific community find filled with controversy and frustration. Yet never has there been a time that offers more in challenges and rewards.

The significance of pH for the inhibiting effect of phosphate buffer on the corrosion processes

The influence of pH on the protective effect of phosphate buffer on the corrosion processes was studied by measuring the amounts of elements released from a dental amalgam. The analyses were conducted by means of atomic absorption spectrophotometry. The protective effect of phosphate buffer was reduced in solutions with low pH, and mercury could be detected in the solutions. Phosphate buffer maintained its aftereffect in the pH region 6.8-5.5. The flow rate of the solution did not influence the inhibiting effect of phosphate buffer.

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 cupric ions on isolated guinea-pig ileum

The possible biological significance of low concentrations of Cu2+ on the guinea-pig ileum has been investigated. Responses to nerve stimulation by single electrical shocks, acetylcholine (ACh), and histamine and the response to ACh of depolarized muscle were examined. In summary, Cu2+ has diverse and dose-dependent effects on the ileum. A stimulant effect dominates in intestine accommodated in physiological saline solution. The excitatory effect of the ion, in the concentration range 10 nM-1 microM, is probably due to stimulation of a depolarization-coupled initiation of the contraction. The inhibitory effect of Cu2+ (10 nm-1 microM) is presumably due to a decreased Ca2+ availability for the contractile process. In a higher concentration range (10 microM-100 microM) the stimulant action could also, in part, be related to a copper-induced release of Ca2+ from a storage site. No effect that certainly could be ascribed to a neuronal site of action could be observed. The possible effect of Cu2+, released during corrosion of dental alloys, on oral excitable tissue such as taste and pain receptors is discussed.

Long-term corrosion studies in vitro of amalgams in contact

Three types of amalgams, one conventional and two with a high copper content, were stored in phosphate-buffered 0.9% NaCl solution, at pH 6, for 35 weeks. Every 7 weeks the solutions were changed and analyzed with regard to Cu, Zn, Sn, Hg, and Ag. In one of the amalgam combinations, the conventional amalgam and one of the copper-rich amalgams in an area ratio of 2:1, contact between the amalgams clearly increased the amounts of Cu, Hg, and Ag released the first 14 weeks compared with when immersed in separate solutions. With the reversed area relation, Cu, Hg, and Ag decreased when they were in contact. The conventional amalgam in contact with the other copper-rich amalgam, in an area ratio of 2:1, reduced the amount of Cu but increased the Zn released. Polishing initially decreased the amounts of Cu and Zn released compared with the unpolished amalgams.

The microstructure of corroded amalgams

One conventional amalgam and two amalgams with a high copper content were stored in 0.9% NaCl solution buffered with phosphate to pH 6. In one experimental series the amalgams were placed in contact with a gold alloy. Every 7 weeks the solutions were changed and analyzed with regard to elements released from the amalgams. The microstructure of the specimens was studied in a scanning electron microscope before immersion and after 7 and 35 weeks in the solution. All the amalgams corroded along the grain boundaries in the gamma 1 phase. Corrosion was greatest in the gamma 2 phase of ANA 68, in the eta phase of ANA 2000 and in the reaction zone (eta + gamma 1) surrounding the Ag-Cu-eutectic particles of Dispersalloy. The microstructure of the corroded amalgams showed similarities to amalgams corroded in vivo. The change in microstructure observed in cross-sections of the corroded specimens was related to the amounts of corrosion products released into the saline solution.