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PubMed1978

Corrosion behavior of structural phases in high copper dental amalgam.

The effects of crevice corrosion on the major structural phases of a high copper dental amalgam were studied in vitro. Three kinds of samples were used: (1) amalgam prepared from a high copper, single composition alloy, (2) annealed ingots of the Ag3Sn and Cu3Sn phases, and (3) high copper, single composition alloy tablets electroplated with mercury. Specimens were examined in a scanning electron microscope before and after the exposure to a corrosion environment. The Ag3Sn and Cu3Sn phases were least affected by corrosion. The Ag-Hg-Sn phase (gamma1) slowly deteriorated, but the attack was nonuniform. The Cu6Sn5 phase exhibited good corrosion resistance, better than that of gamma1 phase. Particles of a tin rich phase of uncertain origin were observed on some of the samples after long exposures.

Copper↗
PubMed1998

Toxicological aspects on the release and systemic uptake of mercury from dental amalgam.

This paper summarizes some recent reports on mercury release from amalgam fillings and resulting concentrations in biological fluids, development of antibiotic resistance, and kidney function. In a series of studies of subjects with amalgam fillings, mercury (Hg) levels were followed in saliva, feces, blood, plasma, and urine before and until 60 d after removal of all of the fillings. The Hg concentrations in saliva remained elevated for at least 1 wk, suggesting that dissolved Hg vapor is not the major source of mercury in mixed saliva. An absorption phase of Hg was seen in plasma during 24 h after amalgam removal. After 60 d the plasma Hg concentration was reduced to 40%, of the baseline level. The decrease per amalgam surface was 0.11 nmol/l (range 0.02 0.40). The Hg level in feces increased two orders of magnitude two days after amalgam removal. At day 60, the median Hg concentration was still slightly higher than the median value of the amalgam free control group. The resistance patterns of the oral and intestinal microflora in these subjects were also studied. In the intestinal microflora, the relative amount of intestinal microorganisms resistant to 50 microM HgCl2 peaked 7 d after removal of the amalgam fillings, with a median value per sample of 6.1%, compared to 1.3% in samples collected prior to the Hg exposure. However, no statistical differences in the resistance pattern of the oral microflora were detected between the control and the experimental groups. A number of sensitive kidney function parameters were measured 1 wk before and 1, 2, and 60 d after amalgam removal. No effects on the various kidney parameters studied were recorded. According to the conclusions of independent evaluations from different state health agencies, the release of mercury from dental amalgam does not present any non-acceptable risk to the general population.

Absorption↗
PubMed1988

Effects of magnetic fields from underwater electrical cutting on in vitro corrosion of dental amalgam.

Metallic taste has been reported from divers working with underwater electric welding and cutting. An in vitro model was designed to simulate the intraoral situation of the divers with respect to the magnetic field. Potentiostatic analyses were performed on amalgam samples exposed to AC and DC magnetic fields. Morphologic changes were analyzed using differential interference light microscopy and scanning electron microscopy. Chemical changes on the surface of the amalgam samples were analyzed with secondary ion mass spectrometry. Results demonstrated that dental amalgams exposed to a specific AC magnetic field underwent morphologic and chemical changes in the superficial amalgam layers.

Corrosion↗
PubMed1986

Estimation of mercury body burden from dental amalgam: computer stimulation of a metabolic compartmental model.

Estimated release rates of Hg vapor from dental amalgams permitted calculation of the potential Hg body burden by employing a four-compartment model for inorganic and elemental Hg distribution. A computer program, compatible with most personal computers, simulated the cumulative and incremental distribution in each compartment and total body accumulation between 1 and 10,000 days for different daily Hg dosages. For a given Hg dose of 30 micrograms/day, metabolic compartments R1-R3 were close to equilibrium at 5, 100, and 300 days, respectively; whereas by 10,000 days, R4 closely approximated total body burden and had not yet attained equilibrium. Projected values obtained with the computer model were consistent with results obtained by another method using a standard tissue burden equation, which employed experimentally determined tissue half-lives for blood and CNS. The model predicted that continuous exposure to elemental Hg vapor, at 30 micrograms/day for 10 years, would result in a total Hg body burden of 5.9 mg, of which 4.8 mg could be contained in R4. Assuming that the Hg in R4 displayed uniform distribution throughout the body, then the brain concentration was estimated to be 68 ng/g wet weight. In contrast, if Hg in R4 reflected long-term preferential accumulation in brain and other neural tissue, then concentrations as high as 4.0 micrograms/g could be attained. However, predictions of Hg concentrations in blood and urine were well within established ranges, and were unlikely to be of utility in assessing effects of chronic low-dose Hg exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Burden↗
PubMed1992

Dental amalgam: the materials.

The goal of this presentation is to describe the material as it is used clinically, explain why small quantities of Hg can be released, and suggest ideas for amalgams that do not release mercury. A set amalgam is a dynamic material that undergoes many microstructural changes during clinical use, related to both the elevated temperature and corrosion-prone environment in the mouth and mechanical forces applied to the restoration. Amalgams can be divided roughly into two groups by their copper content: low Cu (traditional) and high Cu. High-Cu amalgams generally perform better clinically, but all amalgams corrode to some extent in the mouth. Some corrosion is deemed to be a positive factor, because corrosion product deposition reduces leakage at the margins of restorations; that is, the restorations are partly self-sealing. One of the reasons cited for the improved clinical performance of high-Cu amalgams over low-Cu amalgams is that the corrosion-prone phase, gamma 2, is nearly eliminated in high-Cu amalgams. Future research should involve improvements in the clinical performance of dental amalgams, studies of the mercury release from various types of amalgams and the toxic potential of this exposure, and the development of new amalgam systems that reduce the mercury exposure. Although the longevity of modern amalgams is impressive, it is important for their stability to be increased both clinically and microstructurally. An amalgam should be developed with a stable microstructure that, once set, would not change during clinical use. Microstructural changes lead to clinical deterioration. A stable system would not corrode, and the matrix transformation gamma 1 to beta 1 would be prohibited.(ABSTRACT TRUNCATED AT 250 WORDS)

Copper↗
PubMed1997

The future of dental amalgam: a review of the literature. Part 5: Mercury in the urine, blood and body organs from amalgam fillings.

This is the fifth article in a series of seven on the future of dental amalgam. This covers the studies of mercury distribution to the blood, body organs and the fetus and its excretion in the urine and faeces of humans and experimental animals. It firstly describes the clinical studies comparing the blood and urine mercury levels in patients with and without amalgam fillings and goes on to consider attempts which have been made to calculate tolerable mercury thresholds for the urine. It secondly describes the studies on the body distribution of mercury from amalgam restorations in experimental animals and human cadavers. It finally describes the studies of mercury distribution to the fetus during pregnancy and includes both studies of experimental animals and human clinical studies. The factors affecting the accuracy of these calculations and the relevance of these results is also extensively discussed.

Animals↗
PubMed1986

Corrosion of dental amalgams in solutions of sodium chloride, sodium sulfide and ammonia.

Specimens were prepared from three different dental amalgams and were immersed in 0.5% aqueous solutions of sodium sulfide, ammonia and sodium chloride. Every month and over a 6-month experimental period the solutions were replaced with fresh electrolyte and were analyzed in an atomic absorption spectrophotometer with respect to their content in silver, mercury, copper, tin and zinc. In sulfide solutions large amounts of tin and mercury were released from the amalgams while none of the other elements could be detected. Copper, tin and mercury were mostly dissolved in ammonia solutions. An increased silver dissolution could also be observed. Zinc was the first element to be released in sodium chloride solutions. After a 4-month immersion, considerable amounts of copper and mercury could also be found in the same solutions.

Ammonia↗
PubMed1998

Surface chemistry of a high-copper dental amalgam.

In amalgam, mercury is intended to take the form of stable intermetallic compounds. Any mercury leakage must therefore come from free mercury not involved in such compounds. Thus, a knowledge of the exact surface chemistry of dental amalgam is necessary if this phenomenon is to be understood. From XPS and EDS analyses, a model of the surface chemistry of amalgam is proposed which fully characterizes all the phases that are present. The data show the surface to have a composition different from that of the bulk, being comprised of a hydrocarbon deposit and adsorbed water covering the intermetallic phase gamma2 (Sn(6-8)Hg), tin (iv) oxide, and mercury in a free state. After amalgamation, the amount of mercury at the surface decreases with time and eventually attains a constant concentration, where it is all involved in the gamma2 phase, leaving no free mercury. A model is proposed for the surface of amalgam and the changes in this model with time.

Copper↗
PubMed1991

Conceptions of dental amalgam and oral health aspects during pregnancy in Finnish women.

All 277 pregnant women (mean age 28.4 yr, SD 4.6) living at the Lohja municipal health center area in Southern Finland participated in a survey during the first 6 months in 1990. The women's own opinions of the effect of pregnancy on their oral health were questioned during their first trimester of gestation. A special emphasis was put on the attitudes of dental restorative materials. The results showed that 57% of the subjects would have accepted the use of any restorative material during pregnancy while 43% were against one or more materials. 77 (65%) were opposing dental amalgam. 129 women (47%) were of the opinion that pregnancy as such is detrimental to their dental health. This opinion was significantly more frequent among women who were pregnant for third or more times than those having their first gestation. 70 (26%) thought dental treatment to have an effect on their gestation. Also 70 subjects (26%) thought that dental treatment may affect normal development of the fetus. The results showed that in spite of the long tradition in maternity counseling in Finland, the conceptions among pregnant women are often erroneous from the dental point of view.

Adolescent↗
PubMed1991

Dental amalgams subjected to sub-fracture stresses at 37 degrees C.

Amalgam beam specimens were subjected to sub-modulus of rupture loads at 37 degrees C. The specimens tested underwent varying degrees of deformation and ultimate fracture determined by the degree of specimen bend and time to fracture. The property most closely related to the sub-fracture loading behaviour was creep, particularly the 72-h determination of this property. Time and temperature of testing are also significant factors. The present study indicates the importance of the use of 37 degrees C testing in low-load stressing of dental amalgam. The study has confirmed the nature of failure of amalgam in relation to its rheological properties at the temperature at which amalgam functions clinically.

Dental Alloys↗
PubMed1989

Correlation of dental amalgam crevice corrosion with clinical ratings.

In vitro corrosion behavior of gamma 2-containing and gamma 2-free dental amalgams was examined under crevice conditions which simulated the amalgam-tooth interface. By means of potentiostatic testing, current-density/time behavior and integrated anodic current were measured for 16 hr. All of the amalgams demonstrated crevice corrosion susceptibility. Crevice corrosion propagation for gamma 2-free vs. gamma 2-containing amalgams was characterized by lower acceleration and maximum rates during the most dynamic period. Integrated anodic current results were correlated with marginal breakdown ratings reported in two clinical investigations. Strong and significant coefficients were found between integrated current and marginal breakdown ratings when gamma 2-containing and gamma 2-free amalgams were correlated as a single group, but not when correlated separately.

Corrosion↗
PubMed1977

A study of oxidation of dental amalgams with age.

A quantitative test for corrosion due to oxidation has been accomplished. The oxygen concentration of dental amalgams was measured by fast neutron activation which provides a means of detecting oxygen in as small a quantity as 10 to 20 micrograms. An increase in oxygen content with age of spherical blend amalgam implants was observed, comfirming the importance of oxidation processes in in vivo corrosion.

Adolescent↗
PubMed1992

Dental amalgam and mercury vapor release.

Dental diseases are among the most common ailments, and dentists in the United States spend over 50% of their time in dental practice rebuilding carious, malformed, and traumatically injured teeth. It is logical, therefore, that the majority of the dental school curriculum is devoted to the diagnosis, prevention, and treatment of teeth with anomalies. Dentists have several choices of materials they can use to accomplish the task of rebuilding teeth. Besides amalgam, they have ceramic materials, resin composites, base-metal and noble casting alloys, and glass-ionomer cements to use to restore the posterior dentition. Each of these restorative materials has advantages and disadvantages, and the clinical judgment as to when a particular material should be used is given a high priority in dental education. Amalgam is the most widely used of these restorative materials, with 92% of dentists listing it as the material of choice in the posterior of the mouth (Clinical Research Associates, 1990). Dentists have been placing amalgams for over 150 years in the US. They placed 150 million last year, which represents over 75 tons of amalgam alloy. The reasons that dentists use this restorative material so frequently are its durability, ease of manipulation, and low cost. Numerous clinical studies have been conducted on the serviceability of amalgam. Most of these have been on the old, low-copper alloys, and results indicate that they last from 8 to 15 years (Bailit et al., 1979; Osborne et al., 1980; Qvist et al., 1986). In the past 20 years, vast improvements have been made in amalgams with the development of the high-copper systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Amalgam↗