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PubMed1976

In vitro corrosion of dental amalgam phases.

The effects of corrosion on the major phases of dental amalgam microstructure have been studied in vitro on samples prepared by electroplating mercury on Ag3Sn. Tests were made in synthetic saliva, and samples were examined in a scanning electron microscope before and after the exposure. Simple immersion had little effect on the phases. Contact of amalgam with gold increased the probability of deterioation of the gamma2 phase. By anodic polarization beyond the breakdown potential, the gamma2 phase was selectively dissolved. Under conditions simulating a crevice, the gamma2 phase was dissolved and the gamma1 phase suffered morphological changes.

Corrosion↗
PubMed1982

Tissue reactions to implanted dental amalgam, including assessment by energy dispersive x-ray micro-analysis.

Dental amalgam, either in the form of a solid rod or as a fine powder was implanted subcutaneously into guinea-pigs and the tissue reactions were examined after varying time periods. The solid rods were enclosed by fibrous capsules within which only extremely limited breakdown occurred. This appears to result from electrolytic corrosion of the gamma 2 (SnHg) phase of the rod's surface. Powdered amalgam induced granulomata and most of the particles of amalgam were actively digested by macrophages and giant cells. This resulted in the progressive loss of mercury and tin from the lesion and the formation of minute particles containing silver and sulphur which became widely distributed throughout the lesion, being associated with basal lamina, collagen and elastic tissue and giving rise to the formation of a tattoo. In contrast, some particles of amalgam, too large to be interiorised, were encapsulated by collagen and persisted almost unchanged. Intracellular small amalgam particles and aggregates of fine particles, resulting from their degradation, were seen within lymph node macrophages. It is extremely likely that the sequence of events leadng to the formation of an amalgam tattoo of the oral mucosa in Man are the same.

Animals↗
PubMed1975

Flow and creep of dental amalgam.

The intention of the study was to assess the differences in results obtained from creep and flow measurements of dental amalgams. Flow registers deformation during setting. Creep denotes the deformation of the set amalgam. The present study did not demonstrate a correlation between flow and creep, and creep is considered a more desirable parameter to include in a standard.

Dental Amalgam↗
PubMed1996

Long-term use of nicotine chewing gum and mercury exposure from dental amalgam fillings.

In experimental studies, chewing gum has been shown to increase the release rate of mercury vapor from dental amalgam fillings. The aim of the present study was to investigate the influence of long-term frequent chewing on mercury levels in plasma and urine. Mercury levels in plasma (P-Hg) and urine (U-Hg), and urinary cotinine were examined in 18 subjects who regularly used nicotine chewing gum, and in 19 referents. Age and number of amalgam surfaces were similar in the two groups. Total mercury concentrations in plasma and urine were determined by means of cold vapor atomic absorption spectrometry. Urinary cotinine was determined by gas chromatography-mass spectrometry. The chewers had been using 10 (median) pieces of gum per day for the past 27 (median) months. P-Hg and U-Hg levels were significantly higher in the chewers (27 nmol/L and 6.5 nmol/mmol creatinine) than in the referents (4.9 nmol/L and 1.2 nmol/mmol creatinine). In both groups, significant correlations were found between P-Hg or U-Hg on the one hand and the number of amalgam surfaces on the other. In the chewers, no correlations were found between P-Hg or U-Hg and chewing time per day or cotinine in urine. Cotinine in urine increased with the number of pieces of chewing gum used. The impact of excessive chewing on mercury levels was considerable.

Adult↗
PubMed2001

Dental amalgam and selenium in blood.

It has been suggested that selenium (Se) exhibits protective effects against mercury (Hg) toxicity in humans due to formation of a Hg-Se complex bound to selenoprotein P in blood. The aim of the present study was to investigate Se concentrations in persons who had been examined with respect to general health problems associated with dental amalgam fillings. The Se concentrations were determined in whole-blood samples of 80 individuals by hydride generation atomic absorption spectrometry. The subjects comprised two main groups: 21 healthy controls with amalgam fillings and 20 patients who claimed symptoms from existing amalgam fillings. The median concentration of Se in blood (119.2 microg/L) was statistically significantly lower in subjects who claimed symptoms of mercury amalgam illness than in healthy subjects with amalgam (130.3 microg/L). The difference was more evident in individuals with more than 35 amalgam surfaces (P=0.003). Additional control groups without amalgam fillings comprised 19 healthy controls without amalgam experience and 20 subjects who have had amalgam fillings removed due to suspected symptoms associated with amalgam. The Se concentrations in these groups were not different from those with amalgam. It is indicated that persons with ill health self-related to dental amalgam might have a Se metabolism different from that of healthy people.

Adult↗
PubMed1989

A mechanistic study of the electrochemical corrosion of the gamma 2 phase in dental amalgams. II. Introduction of a model.

Electrochemical impedance measurements on conventional dental amalgams at an anodic polarization potential of -250 mV vs. SCE were performed. An initial evaluation was given in part I of this study; in the second part the results are interpreted in terms of a model. The latter, characterized by an equivalent circuit, is a parallel combination of a flat surface and a pore. The selection of appropriate values for the elements of the equivalent circuit leads to a better insight into the corrosion process. Although no simple relationship exists between the circuit elements and the impedance curves, an explanation was found for some typical features of these curves. As an application, the influence of the anodic polarization potential on the impedance curves was studied. Evaluation by means of the model demonstrated the importance of the characteristics of the corrosion products.

Corrosion↗
PubMed2004

Factors affecting mercury release from dental amalgam exposed to carbamide peroxide bleaching agent.

PURPOSE: To assess, in vitro, the effects of aging and surface polishing on mercury release from dental amalgams exposed to 10% carbamide peroxide at two pH levels. METHODS: Samples of fresh and aged amalgam, polished and unpolished, were treated with 10% carbamide peroxide at pH 4.5 and at pH 6.5 for periods of 1, 4, 7, 10 and 13 days. At each time period, mercury concentrations in solution were measured using a cold-vapor atomic absorption mercury analyzer system and compared to control samples treated with phosphate buffer. RESULTS: Amalgam samples exposed to 10% carbamide peroxide released significantly more mercury in solution than samples exposed to phosphate buffer controls. Mercury release was time-dependent and significantly higher in aged amalgam than in fresh amalgam (P < 0.001). Mercury release was also pH-dependent and higher in unpolished amalgam.

Analysis of Variance↗
PubMed1989

Mercury vapor from dental amalgams, an in vitro study.

The aim of this investigation was to examine in vitro the rate of mercury vapor from different types of dental amalgams. Amalgam surfaces of three different states were used, polished, oxidized and corroded. The influence of temperature, tooth brushing and water on the specimens was also examined. The results showed great differences between the polished amalgams stored in air and amalgams corroded in artificial saliva. Single composition types released more mercury than conventional and dispersed ones. Higher temperature raised and water lowered the vapor rates. When the surfaces of the amalgams were brushed with a tooth paste, an instant increase of mercury vapor occurred.

Dental Amalgam↗
PubMed1985

Dimensional and phase changes of dental amalgams.

The relationship of long-term expansion to phase changes of dental amalgams was examined. Using multiple regression analysis, a predictive equation was found which showed that the linear dimensional change was dependent on the alterations in the content of gamma 2 and beta 1.

Chemical Phenomena↗
PubMed2006

Time-dependent corrosion potential of newly-placed admixed dental amalgam restorations.

OBJECTIVE: It was the objective of this study to measure the corrosion potential over time of newly-placed admixed dental amalgam restorations as a possible indicator of corrosion activity. METHODS: The corrosion potentials of 271 amalgam restorations, 4-min to 24-month old were measured in a convenience sample of 81 subjects. The selected restorations had no occlusal or interproximal contact with other metallic restorations. Eighty-one percent of the restorations aged 4 min to 7 months were made from zinc-containing admixed high-copper amalgam. The remaining amalgams were an unknown mixture of admixed high-copper and single-composition-alloy amalgams. RESULTS: The data were fit to a mixed-effects model with random patient effects to allow for the correlation, using the maximum likelihood method. The early data best fit a quadratic model with an initially rapidly rising corrosion potential that leveled off to a constant mean value of -146 (60)mV (versus Ag/AgCl, 3M KCl at 35 degrees C) by approximately 7 months. Most of the ennoblement occurred within the first 4 months after restoration placement. SIGNIFICANCE: This in vivo study observed a slower rate of corrosion potential ennoblement for admixed amalgam restorations than would be predicted from in vitro studies. The slower rate is believed due to the combination of mechanical, chemical and biological forces in the mouth that are generally absent using simulated conditions. The slower rate of ennoblement suggests a slower rate of achieving maximum corrosion resistance than would be predicted using in vitro studies.

Adult↗
PubMed1975

[Studies on the effects of dental amalgam upon the fertilization and early development of sea urchin eggs (Hemicentrotus pulcherrimus) (author's transl)].

Silver-tin amalgam that has been used as a filling material in routine dental clinic contains a large amount of mercury and the cytotoxity of metal mercury may hazard to patients. There have been a number of papers reporting that the dental amalgam has not any toxic action to living cells in animal experiments in vivo. However, the mechanism of cytotoxic action and effects of these metals for tissues and cells were not reported so far. In the present experiments, the analysis of the cytotoxic action of silver-tin alloys and their amalgam in vitro cytological experiments with fertilized eggs and developing embryos of sea urchin, Hemicentrotus pulcherrimus, were examined. When the silver-tin alloy powder was incubated in normal sea water medium there are non or weak cytotoxic reaction upon fertilized eggs and early embryos of sea urchin. Metal mercury in the medium effects remarkable cytotoxic action upon the development of early embryos; the cleavage and early development were delayed and all of the embryos show deformity. Immediately after the alloy powder was triturated with mercury, it shows strong cytotoxic action as the metal mercury was incubated, however, the cytotoxic action decreased and almost disappeared in 5 hours after trituration. The mechanism of cytotoxic action and the adequacy of clinical application of the amalgam were discussed.

Animals↗
PubMed1993

Clinical evaluation of four dental amalgams over a three year period.

The aim of this study was to compare the clinical durability of four dental amalgams. In each of eighty-two patients one class 2 cavity was restored with Dispersalloy (Johnson and Johnson) which served as the control and all the other class 2 cavities were randomly restored with one of the following amalgams: Amalgaphase, Amalga 43 (Amalgam Alloys-South Africa) or Permite C (Southern Dental Industries). Matrix bands were placed and Kalzinol bases and Polyvar varnishes applied in all cavities. The amalgams were mixed according to the manufacturers' instructions, the cavities overpacked with amalgam, condensed by hand, carved and then burnished with a ball burnisher. Twenty-four hours later all restorations were polished and colour photographs taken. The restorations were evaluated using the Ryge and Snyder (1973) evaluation system, as well as comparison of the colour photographs. The Fisher's Exact Test was used for the statistical analysis. The two South African manufactured amalgams compared well with the two imported amalgams. However, at the end of the third year the score for the marginal integrity of Amalgaphase, one of the local products, was significantly different (p < 0.083) and inferior to that of the control, Dispersalloy. Evidence is produced to suggest that over a three year period Amalgaphase performed better than Dispersalloy, Amalga 43 and Permite C.

Dental Alloys↗
PubMed2003

Mercury release from dental amalgams into continuously replenished liquids.

OBJECTIVE: Studies have been performed using high- and low-copper amalgams to measure the amounts of mercury dissolution from dental amalgam in liquids such as artificial saliva; however, in most cases, mercury dissolution has been measured under static conditions and as such, may be self-limiting. This study measured the mercury release from low- and high-copper amalgams into flowing aqueous solutions to determine whether the total amounts of dissolution vary under these conditions when tested at neutral and acidic pH. METHODS: High- and low-copper amalgam specimens were prepared and kept for 3 days. They were then longitudinally suspended in dissolution cells with an outlet at the bottom. Deionized water or acidic solution (pH1) was pumped through the cell. Test solutions were collected at several time periods up to 6 days or 1 month and then analyzed with a cold vapor atomic absorption spectrophotometer. After dissolution testing, the specimens were examined using SEM/XEDA for any selective degradation of the phases in the amalgam. RESULTS: Except for the high-copper amalgam in the pH1 solution, the dissolution rates were found to decrease exponentially with time. The rate for the high-copper amalgam in pH1 solution slowly increased for 1 month. The total amounts (microgram/cm(2)) of mercury released over 6 days or 1 month from both types of amalgam in deionized water were not significantly different (p>/=0.05). The high-copper amalgam released significantly more mercury than the low-copper amalgam in the pH1 solution at both time periods. For both amalgams, the dissolution in pH1 was significantly higher than in deionized water. SIGNIFICANCE: Mercury dissolution from amalgam under dynamic conditions is enhanced in an acidic media, and most prominently for a high-copper formulation.

Acids↗
PubMed2003

An in vitro study into the corrosion of intra-oral magnets in the presence of dental amalgam.

The aim of this investigation was to study the corrosion behaviour and products of uncoated neodymium-iron-boron magnets in the presence of dental amalgam. Microcosm plaques were grown on discs of neodymium-iron-boron magnets or amalgam in a constant depth film fermentor. The biofilms were supplied with artificial saliva and growth was determined by viable counting. The results showed that the neodymium-iron-boron magnets corroded with an average daily weight loss of 0.115 +/- 0.032 per cent. However, when the magnets were in close proximity to the amalgam the amount of corrosion was reduced to a daily loss of 0.066 +/- 0.023 per cent. The highest loss of constituent elements from the corrosion products of the magnets was observed for iron. The composition of the microcosm plaques altered markedly between the two materials with less streptococci and more Veillonella spp. present in the biofilms grown on magnets in the presence of amalgam. The corrosion of neodymium-iron-boron magnets is limited and in the presence of amalgam is reduced further. This suggests that amalgam present in the mouth will not cause an increased clinical risk in terms of biocompatibility with neodymium-iron-boron magnets.

Actinomyces↗
PubMed1993

Updates in dental materials--Part 3: Dental amalgams.

Recent years have seen a number of innovations and developments with respect to dental materials and their applications in clinical dentistry. This series of short articles considers the more important aspects of these developments under the general term 'Updates in Dental Materials'. Dental composite systems and bonding to tooth material are discussed in Part 1. Resin cements are treated in Part 2. Part 3 presents dental amalgams and Part 4 advances in ceramic materials.

Copper↗
PubMed1983

Relationship between creep, gamma 2, and marginal fracture of dental amalgams.

The effect of gamma 1 and gamma 2 on the creep deformation of dental amalgams has been investigated. It has been shown that the creep of a conventional amalgam is not dependent on gamma 1 as was previously reported. Rather it is strongly influenced by gamma 2 and its volume fraction. It has been speculated that Sn-rich grain boundaries also enhance creep by facilitating grain boundary sliding. The reported correlation between creep and marginal fracture has been explained in terms of this dependence of creep on corrosion-prone Sn-rich microstructural constituents of amalgams.

Chemical Phenomena↗
PubMed1975

Electrochemical behavior of some commercial dental amalgams in artificial saliva.

Cathodic, linear anodic, and anodic polarization studies conducted on three commercial dental amalgams, Caulk Fine Cut Alloy, Spheralloy, and Dispersalloy, showed that all amalgams were in a passive state at the corrosion potential in synthetic saliva solution. The corrosion currents at the corrosion potential were therefore small for all the amalgams, in the range 0.08 to 0.30 muA/cm2. However, the Caulk Fine Cut Alloy and Spheralloy amalgams exhibited a breakdown of passivity and high anodic currents at potentials only approximately equal to 100 mV more noble than the corrosion potential whereas Dispersalloy amalgams maintained passivity at potentials up to 700 mV more noble than the corrosion potential. The breakdown of passivity in Caulk Alloy and Spheralloy amalgams is attributed to the presence of the gamma2 phase (Sn7-8Hg) whereas the passive behavior of Dispersalloy amalgam is attributed to the absence of the phase. It is concluded that none of the amalgams will exhibit severe general corrosion in use, but that both Caulk Alloy and Spheralloy amalgams will exhibit pitting corrosion whereas this type of corrosion should be minimal in Dispersalloy amalgams.

Carbon Dioxide↗