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Summary In view of the ever increasing number of high copper alloys, it was the aim of this study to investigate the tensile strength property of some of the new alloy systems. The factors alloy system and heat treatment were investigated in relation to the tensile strength. The factors alloy system as well as the heat treatment turned out to be significant. The study suggests that the introduction of ‘dispersion’ alloys did not change the dental picture as to the property of the tensile strength. The selection of strength values in the range of 35–55 MN/m2 for the diametral tensile strength probably have no clinical relevancy as to the prevention of bulk fractures of amalgam restorations under oral conditions.

The marginal degradation and corrosion of restorations made of a high copper dispersed amalgam were studied as a function of time for up to 5-yr observation periods. The effect of minor defects present after finishing the restorations was included in the assessment of the initial marginal degradation. A slow progressive marginal degradation was noted and it was enhanced by initial defects. Subsurface corrosion including attacks of the phase and grain boundaries, corrosion within the bulk, and layers of corrosion products along the tooth/restoration interfaces were observed in restorations after some years in clinical service. The subsurface corrosion is considered to weaken the amalgam and it might enhance the marginal degradation, i.e. a stress corrosion type of degradation.

An in vitro dye leakage study was performed to compare the sealing ability of high-temperature thermoplasticized gutta-percha, high copper amalgam, and warm gutta-percha when used as retrofilling materials. Forty-five extracted anterior teeth were obturated with gutta-percha, the apical 3 mm of the roots were resected, and 2-mm-deep retrograde preparations were prepared. The roots were then randomly placed into three groups and retrofilled with one of the experimental materials. After 72 h in India ink, the teeth were cleared and evaluated for leakage using a stereomicroscope. No leakage was evident in the three teeth used as negative controls. Complete leakage was noted in the three positive control teeth. Statistical analysis of the results showed that high-temperature thermoplasticized gutta-percha had significantly less leakage than did high copper amalgam.

A survey carried out on the incidence of dental diseases and the distribution of fluoride in drinking water wells and also copper in such waters in Sri Lanka showed the influence of the natural environmental factors on the prevalence of certain geographical diseases. In the case of the geographical variation of dental fluorosis and dental caries it was found that in Sri Lanka, more than any artificially created causes, the natural environmental factors such as mineral occurrences containing the elements concerned, climate, topography, geology, structure, soil, etc. play a very significant role in the geographic variations of elements and hence incidence of diseases. The same was found to be true in the case of copper in potable waters. Two cities in the dry zone of Sri Lanka namely Anuradhapura and Polonnaruwa had a natural fluoride concentration ranging from 0.34 to 4.55 ppm. In some of these regions dental fluorosis was as high as 77.5%. Kandy, situated in the wet zone on the other hand, had in its well waters a low fluoride concentration of less than 0.2 ppm and hence only 13% dental fluorosis. Similarly copper in the well waters of Sri Lanka showed a range of concentrations depending on many natural environmental factors and in some areas far removed from any effects of industrialization still had high copper concentrations of the order of 1–3 ppm, due to the occurrence of copper bearing mineral deposits. It is the aim of this paper to illustrate the use of establishing natural geochemical data banks in monitoring the environment as they would provide useful background values. Any attempt at erecting national or international acceptable levels for the chemical elements must necessarily consider those which are natural to defined environments.

Herbarium specimens of the genus Haumaniastrum (mainly from Shaba Province Zaire) were analysed for copper and cobalt.H. homblei showed elevated copper levels and indicated its tolerance to mineralized ground.H. robertii (previously-known as a “copper flower”) showed the expected high copper concentrations, but contained abnormally high concentrations of cobalt (av. 4304 μg/g dry weight) far exceeding those of copper. This species has the highest cobalt content of any phanerogam and its distribution may be controlled by cobalt rather than by copper. re]19761220

Three single-composition, high-copper amalgams were analyzed for the composition of their before- and after-reaction phases. The method used was electron probe microanalysis. The results may be summarized as follows: (1) All alloys consist essentially of Ag3Sn (γ), Cu3Sn (∈), and, in some cases, Ag4Sn (β). (2) When the original alloy contains higher amounts of Cu, more Cu is found in solution in the Ag3Sn (γ) and Ag4Sn (β) phases. (3) The reaction phases in amalgams made from these alloys consist essentially of Ag22Sn Hg27(γ1) and Cu6Sn5 (η'), with no detectable Sn 8Hg (γ2). alloys. (4) When In is present, it is found principally in the Ag3Sn (γ) and Ag22Sn Hg 27(γ1) phases, and both the γ and γ1 phases are of different composition than that for the other (5) When Pd is present, it is found principally in the Cu3Sn (e), Cu6Sn 5 (η'), and Ag22Sn Hg27(γ1) phases.

The first flash smelting in Japan began at Ashio Smelter in 1956. Since then many improvements have been made. In 1962, productivity increased three times from the first stage of development. Flash smelting offers great advantages in the use of reaction heat and recovery rate of sulfur, while reducing air pollution. The operating ratio of this smelting process at the early stage of development was not high enough because of problems of high copper loss in the slag, boiler troubles, and damages to refractories. Engineers of Furukawa Company in Ashio Smelter solved these problems one by one, and advised the building of the smelters listed below: The productivity of one flash furnace was previously thought to be 5,000 tons per month; now some furnaces produce more than 10,000 tons per month. Such increased productivity is largely due to the refractory structure developed in Ashio.

Palladium additions to a dispersed phase high-copper amalgam have been shown recently to suppress markedly the eta' (Cu6Sn5) concentration and decrease creep. A detailed study of the dental and 24 h creep for Pd containing high-copper amalgams and six commercial controls as a function of applied temperature and stress was performed. One part of Ag-Cu or Ag-Cu-Pd dispersants with substitutions of up to 20wt/o Pd for either Ag or Cu was blended with two parts of traditional amalgam alloy. Various temperatures from 25 to 60 degrees C and stresses from 36 to 72 MPa were applied to the samples during the test. For commercial controls and experimental amalgams with no Pd, creep is a strong function of temperature and stress. The experimental amalgam containing up to 10wt/o Pd, Pd substituted for Ag, demonstrated essentially constant creep over the temperature and stress range applied.

Nine Class II restorations with high-copper content amalgams were evaluated for microleakage for periods o f up to six months. Microleakage of the margins of Class II restorations of nine high-copper-content amalgams was evaluated after 24 hours and 1, 3, and 6 months. The restored teeth were stored in artificial saliva. Contact autoradiographs were made after incubation of the restored teeth in a calcium chloride solution. The adaptation of the cavosurface margins of the restorations was measured microscopically before the determinations of microleakage.

Morphological, histochemical, and chemical study of three necropsy specimens of liver in the terminal stage of Indian Childhood Cirrhosis revealed a strikingly high copper content. It is proposed that excess accumulation of copper in the cytoplasm of hepatocytes disturbs the microtubular system, causing hydropic swelling and the formation of Mallory's hyalin. Copper and copper-binding protein showed topographical association with Mallory's hyalin. Diffuse cytoplasmic staining and the lysosomal copper distribution also suggested that copper had a cytotoxic effect. The pattern of copper distribution in Indian Childhood Cirrhosis differs from that in Wilson's disease and in prolonged cholestasis with excessive hepatic copper deposition, indicating a different mechanism of the copper accumulation.

The effect of surface roughness of the trituration pestle and mortar on dimensional change was studied. For amalgams prepared from conventional lathe-cut silver-tin alloys, increase of surface roughness was shown to lower setting expansion. This effect was not observed in the case of amalgams prepared from spherical alloys, either of conventional or high copper composition.

Laser-induced-fluorescence measurements are extended to higher densities in excess of 1*1011 cm-3 by evaluating the spatial dependence of the fluorescence light. The technique is applied to measure high copper vapour densities after extinction of diffuse vacuum arcs.

The bending creep of six different dental amalgams was continuously measured up to 30 days under different static loads. All six amalgams induced creep rupture within 30 days under 9 kgf of static load and some of them did under the lower static load. The high copper amalgams resisted for a longer period of time compared to the low copper amalgams. The admixed high copper amalgam had the highest creep value at rupture under the same load, which indicates that this amalgam is more flexible under continuous loading than the other amalgams. The rupture time was approximately proportional to the reciprocal of the creep rates and the rupture time drastically increased as the creep rate decreased. This result basically explains and supports the previously reported correlation between the compressive creep during a specific period of time and the marginal fracture of amalgam restorations.

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.

湿気汚染が, 新しい加銅アマルガムの膨縮変化に及ぼす影響を検討し, 従来型のアマルガムのそれと比較するため, 各種合金から正常に練和したものと, 2%食塩水にて汚染練和したアマルガムの円柱形試片をADA規格に従って作製してその膨縮変化を測定し, 次のような知見を得た。(1) 亜鉛を含むアマルガムの中で, 湿気汚染により遅発膨張が観察されたのは従来型の削片型アマルガムのみで, 分散強化型アマルガムと, 従来型の球状アマルガムには見られなかった。(2) 亜鉛を含まない従来型の球状アマルガムと新しい加銅アマルガムには湿気汚染によって遅発膨張は観察されなかった。(3) 亜鉛を含有するアマルガムの硬化膨縮変化は湿気汚染により若干の影響を受けたが, 亜鉛を含まないアマルガムはほとんど影響を受けなかった。

Cattle fed ad libitum a mixture of salt containing 0.5% copper as copper sulfate had an average increase in Cu concentration from 111 to 328 ppm on a dry weight basis in liver biopsy samples over a 333-day test period. The alfalfa hay ration contained an average of 8.2 ppm Cu and a relatively high copper to molybdenum ratio of 3.9:1. Copper supplementation from a variety of sources was given orally or by injection in an 87-day test. Chelated Cu was compared with Cu in copper sulfate, both mixed with salt, and with Cu injected as Cu calcium edetate. The ration of mixed alfalfa and grass contained 6.9 ppm Cu with sufficient sodium molybdate added to produce a Cu/Mo ratio of unity against which the various Cu sources were tested. There was no significant (P

Summary A clinical study was conducted in which two operators made 180 class I or II amalgam restorations in a group of fifty-seven adult patients. The restorations were made in a series of six per patient. Each restoration was made of a different alloy (five conventional composition alloys and one high copper alloy). During a period of 5 years the marginal fracture formation of all restorations was yearly quantified with a 6-point photo rating scale. The quantifications were analysed as to their variance for the factors alloy, patient and operator. The relative importance of significant factors was calculated. The results show that for a period of 5 years the alloy, patient and operator all had a significant influence on the marginal fracture formation. The operator influence was stable in time. This factor was relatively small because the operator sample was highly selected. After 1 year the influence of the patient on marginal fracture was equal to that of the alloy. The patient influence in time was stable. However, the alloy influence increased considerably. The longer the service time of the amalgam restoration the more important becomes the influence of the alloy on the marginal fracture formation.

Clinical and laboratory research has had difficulty keeping pace with the rapid introduction of new amalgam alloys. These laboratory profiles identify the alloy system and reflect the performance of the alloy during various laboratory tests.

The microstructures of an Ag-Sn amalgam and an admixed high-copper amalgam have been observed during compressive creep tests. Sliding of γ1 grains has been observed. The sliding rate is much lower in the γ2-free high-copper amalgam than in the γ2-containing Ag-Sn amalgam.

Chalcopyrite oxidation by CuCl2 in NaCl solutions has been studied as a function of leaching time, temperature, grain size, Cu(II)/Cu(I) ratio, and Cl− activity. The experiments have been performed under conditions where the solution potential remains almost constant in each test. Leaching rates are high above 85 °C, and high copper recovery can be obtained provided that high Cu(II)/Cu(I) ratios are maintained. Elemental sulfur is obtained with no sulfate formation. It was observed that the combined influence of Cu(II)/Cu(I) ratio and Cl− activity on the leaching rate is related to the solution potential, explaining the action of the concentration of chloride ion in chalcopyrite leaching.

The effects of a mine effluent containing high copper levels on the structure of the phytoplankton communities in a chain of low alkalinity and hardness oligotrophic reservoirs situated north of Portugal were studied monthly, during 1981–1982. In the reservoirs under mine influence, a shift in the dominant species have occurred. In contrast with the uncontaminated areas, more than 50% of the algal species developed lower populations. At the most polluted zone, phytoplankton density, biomass and species number were strongly reduced. The mine input stress on the algal communities was well assessed by species number and percentage similarity index.

The magnetomechanical damping peak height Δm, in a series of nickel-copper alloys, decreased both with increasing temperature and with increasing copper content. This behaviour was correlated with a corresponding decrease in the anisotropy constant K1. The reduction in Δm can therefore be explained either by a reduction in domain number or by an increase in domain boundary thickness. A possible interpretation of the more rapid reduction in Δm at high copper concentrations was offered in terms of short-range ordering effects.

The abnormally high copper content of cotton duck which has been impregnated with the solution of a copper salt is due to the adsorption of ionic copper by the cotton. This adsorption may be prevented completely by scouring the fabric and then applying the copper in the form of a water-soluble molecular complex. Citric acid and glycine form such complexes with copper and are effective in preventing its adsorption.

The participation of copper in plant and animal metabolism is well known (11), but its physiological role has not been defined in terms of distinct reactions. The role of copper in plant metabolism is complicated by the different copper requirements of plant species (5, 7). Data reported here are confined to observations made on Thatcher spring wheat, a plant with a comparatively high copper requirement. In earlier work, Brown and Harmer (3) observed an almost immediate build-up of reducing sugars during stem elongation of copper-sufficient Thatcher wheat. This rapid increase of reducing sugars, not found in copper-deficient plants, seemed to indicate a marked change in metabolism as affected by copper. In view of this observation, attention in this study was given to the Chromatographie determination of organic acids, sugars, and amino acids. The purpose was to determine relationships between sugar levels and the status of other metabolites in copper-sufficient and copper-deficient wheat. It was reasoned that the change in sugars could be related to head development in that copper-sufficient wheat produces heads whereas copper-deficient wheat does not. To eliminate heading as a variable, copper-sufficient wheat grown on long nights was included in the study. Such plants do not produce heads.

I t is very probable that an effect of certain metals upon the flavor of milk was observed from the very beginning of the extensive use of metals for equipment at the close of the last century. Both tin and oak were recommended for dairy equipment from 1850 to 1875. Commencing about 1920 the effect of metals on flavor of milk has been subjected to numerous studies probably due to the development of new alloys and to marked improvement in the quality of milk products. Hunziker, Cordes, and Nissen (1) in their extensive investigations of metals in dairy equipment reported that copper and iron produced metallic flavors in sweet milk. Kende (2) was probably the first to establish that this flavor (metallic, cappy, cardboard, stale, or oxidized) might develop in milk not subjected to exposure to either iron or copper. The development of the oxidized flavor was accelerated by increased copper content of the milk, by pasteurization at 63 ° C. for 30 minutes, by very low bacterial counts, and by elimination of green feeds in the rations of the cows. Davis (3) found that the contamination of milk with copper was greatest in the first milk through the equipment and that such milk became oxidized in flavor. Tracy, Ramsey, and Ruehe (4) gave special attention to the oxidative nature of the change which produced the off-flavor and to the deleterious effect produced on the first milk through the equipment. In 1932 it was noticed in our dairy operations that chlorine sterilization of equipment greatly accelerated the development of oxidized flavor when compared with hot water sterilization. I t was believed that this effect was due to high copper contamination and experiments were planned to establish this relationship.

The case history is given of a child who presented at 14 months with ascites and was found to have severe micronodular cirrhosis with biochemical evidence of Wilson9s disease, but in view of the severity of the pathology and early age of presentation, the possibility of chronic copper poisoning was investigated. It was found that the child9s drinking water was obtained from a bore via new copper pipes. The bore water had a p H of 4·4 and after passage through copper pipes had a very high copper level of 675 μg/100 ml. He subsequently died from liver failure and at necropsy very high copper levels were found in his liver. The final diagnosis remains uncertain.

In der Zahnmedizin wird haufig beobachtet, das auch Edelmetall-Legierungen unter Ausbildung, dunkelbrauner bis schwarzer Deckschichten korrodieren. Uber die Entstehung und den Entstehungsverlauf derartiger Deckschichten ist bisher wenig bekannt. Da besonders in cyanidhaltigen Losungen schon nach kurzer Zeit sichtbare Verfarbungen auftreten, wird das Verhalten einiger Edelmetall-Legierungen in verdunnten, gepufferten Cyanidlosungen naher untersucht. An Hand von graphischen Darstellungen wird gezeigt, wie sich unterschiedliche Cyanidionenkonzentration, wechselndes pH der Korrosionslosung und zugesetzte Oxydationsmittel auf die Deckschichtbildung und Abtragung auswirken. Die Versuchsergebnisse lassen erkenne, das die Ausbildung von Verfarbungen und Deckschichten in erster Linie von der Zusammensetzung der Legierung bestimmt wird. An den kupfer- und silberreicheren Legierungen werden die intensivsten Verfarbungen beobachtet. Da die zunehmende Abdeckung der Metalloberflache die Angreifbarkeit dieser Legierungen einschrankt, ist bei ihnen die Abtragung am geringsten. Corrosion tests on noble metal alloys in diluted buffered KCN solutions with different pH values In dentistry, it is a often found that alloys even of noble metals show corrosion phenomena, forming dark-brown or black top layers. Little is known so far about the origin and development of such top layers. Since, especially in solution containing cyanide, disscoloration occur after a short time already, the behaviour of some noble metal alloys in dilated buffered cyanide solution has been investigated more closely. By means of graphs, it is shown how the formation of top layers and the diminution in size of the alloy are affected by different cyanide ion concentrations, by different pH values of the corroding solution, and by oxidants added to the latter. The results of the tests show that discoloration and the formation of top layers are primarily governed by the composition of the alloy. The most intensive discoloration were observed on alloys with high copper and silver contents. Since the thickening of the top layer on the metal surface has the effect of rendering these alloys less liable to be attacked, their diminution rate is lowest.

In calculating the acoustic characteristics of an electrically operated submarine sound-generator fitted with a spring-controlled diaphragm, it was found that the apparatus would not radiate efficiently at a given power input and frequency, unless the effective diameter was, within fairly narrow limits, of the correct size, and unless the fundamental pitch was very close to the frequency of the alternating current supplied. The calculations also showed that a non-periodic diaphragm ( i. e ., one in which there is no elastic restoring force) could not be set into vibration at frequencies in the neighbourhood of 500 cycles without incurring very high copper losses. A similar conclusion was reached with regard to the aperiodic diaphragm. It was concluded that the best efficiency could be secured by operating the sound-generator with alternating current of the same frequency as that of the diaphragm. Similarly, in most forms of sound-receiving apparatus, the response to submarine sound-waves is most marked when the size of the diaphragm is correctly chosen and when its fundamental pitch is in resonance with the frequency of the incident waves. In the field of submarine acoustic signalling it is evident that a great advantage is to be derived by utilising a means of continuously tuning the diaphragms of the sound-receivers or generators over a certain range of frequencies, thus realising selective transmission and reception. At the same time advantage is taken of the great increase in sensitivity characteristic of highly selective receivers, in which the damping may be reduced to a minimum in view of the possibility of being able to “tune in” to incoming waves as is now done in radiotelegraphy.

Summary The use of bryophytes in mineral exploration is reviewed. “Copper mosses”, mainly members of the genera Merceya and Mielichhoferia, grow preferentially over substrates with high copper concentrations. Examination of the collection locality in herbarium specimens and subsequent exploration of this locality by conventional methods of mineral exploration can sometimes lead to discoveries of mineralisation. In New Zealand, aquatic bryophytes have been used in the search for uranium since they concentrate this element from streams draining uraniferous areas.

The raw materials of brewing would appear to contain amounts of copper which vary from about 5 p.p.m. in barley up to some 85 p.p.m. in hops, the latter showing considerable fluctuation. The mean figure for brewery pitching yeast over a long period is 102 p.p.m., calculated on the dry material. Draught beers average 1·5 p.p.m. and bottled beers 0·9 p.p.m. The critical copper content at which fermentation is affected appears to be between 5 and 10 p.p.m. Yeasts are examined during their progress from the culture stage with virtually no copper content, through the culture room stainless-steel plant to the brewery, where successive generations are analysed after fermentations in copper vessels. A copper content is attained which appears unlikely to be exceeded in normal circumstances; in the experiments described this approached 175 p.p.m. Trace amounts of copper are recorded for the various stages of a complete brew. From this work it appears that spent grains and spent hops have comparatively high copper contents, whilst some copper is eliminated with the first yeast heads. The difficulties of obtaining truly representative samples from large bulks, and the contribution of variable amounts of copper from the plant involved, are apparent from the results.

Direct measurements of the temperature derivative of the electrical resistivity (d rho /dT) have been made on NiCu ferromagnetic alloys with high copper content. Near the critical temperature (Tc), the results can be fitted to 1/ rho (Tc).d rho /dT=constant-Aln mod epsilon mod where epsilon =(T/Tc)-1. An appropriate choice of Tc extends the validity of the logarithmic expression to the range 5.10-3

Summary 1.A modified Ritter Test for copper in butter has been described. 2.Three classes of readings for this copper test have been proposed to designate the extent of the copper contamination in the butter. 3.The test is influenced by a high pH of the butter serum, but may be corrected by the use of a small quantity of N/10H 2 SO 4 . 4.The copper contamination of Indiana butter was found to be 39.1 per cent negative, 39.6 per cent slight and 21.3 per cent positive according to the modified test. 5.The comparison of butter of high copper contamination from one creamery and that of another creamery with very little contamination was made. 6.This modified test although qualitative is fairly accurate in determining the extent of copper contamination in butter and is also a rapid, inexpensive test.

A preliminary investigation had been made into the evolution of copper tolerance in some Californian populations ofMimulus guttatusgrowing on abandoned copper mines. It has been shown that populations growing on soil with normally toxic levels of copper were tolerant to this heavy metal. There was also some indication of an increase in tolerance to zinc, lead and nickel in the copper tolerant populations, even when the soil was not particularly rich in these other metals. With one exception, populations on non-contaminated soils were non-tolerant as judged by root growth in aqueous solutions or soil containing copper. Furthermore, there was a marked difference in germination and seedling establishment on copper soil between stocks originating from mine and from non-mine environments. The superiority of the mine populations under such circumstances was less marked when established plants were potted up in mine soil. By testing theF1progeny of crosses involving tolerant and non-tolerant parents it was found that copper tolerance is dominant in effect at low copper concentrations, intermediate at intermediate concentrations, and recessive in effect at high copper concentrations. When the plants had been grown on normal soil there appeared to be a requirement for copper at low concentrations among the offspring of tolerant parents. It is suggested that this may result from the mechanism of tolerance by complexing the copper and thus making it unavailable to the plant. The genetic control of zinc and lead tolerance is not clear, but there is evidence that zinc tolerance may be dominant at concentrations of zinc in solution of 15 parts/106.

All types of dental amalgams contain mercury, which partly is emitted as mercury vapor. All types of dental amalgams corrode after being placed in the oral cavity. Modern high copper amalgams exhibit two new traits of increased instability. Firstly, when subjected to wear/polishing, droplets rich in mercury are formed on the surface, showing that mercury is not being strongly bonded to the base or alloy metals. Secondly, high copper amalgams emit substantially larger amounts of mercury vapor than the low copper amalgams used before the 1970s. High copper amalgams has been developed with focus on mechanical strength and corrosion resistance, but has been sub-optimized in other aspects, resulting in increased instability and higher emission of mercury vapor. This has not been presented to policy makers and scientists. Both low and high copper amalgams undergo a transformation process for several years after placement, resulting in a substantial reduction in mercury content, but there exist no limit for maximum allowed emission of mercury from dental amalgams. These modern high copper amalgams are nowadays totally dominating the European, US and other markets, resulting in significant emissions of mercury, not considered when judging their suitability for dental restoration.

The release rate of mercury from a conventional, a dispersed phase or a spherical high copper content amalgam under static conditions in stimulated or artificial saliva has been measured and found to decrease approximately exponentially with time. A higher initial release rate was observed for mercury in stimulated saliva than in artificial saliva during the in vitro experiments. In a pilot study corrosion current was recorded from an amalgam specimen immersed in saliva, and was found to decrease approximately exponentially with time. After brushing the surface of the amalgam during two subsequent periods, in a manner similar to toothbrushing, an increase in corrosion current was measured indicating the removal of loosely bound corrosion products. A model describing the periodical mercury release from an amalgam surface has been proposed.

Effects of mixing time on the microstructure of several low and high copper amalgams were observed. An apparent relationship was found between the microstructure, especially enclosed porosities, and physical properties reported previously1). In regard to the mixing time, a greater influence was observed with either lathe-cut or high copper than spherical or low copper, with respect to the particle shape and copper content of the alloys. Sufficient mixing is required for lathe-cut high copper alloys.However, differences in the mixing characteristics were often observed even with alloys having similar particle shape or composition. This may be due to the dissimilar surface characteristics of alloy particles, causing the differences in affinity with mercury. Prolonged mixing to eliminate the porosities in the set amalgam may cause the poor results, such as remarkably shortened working time and increase in shrinkage during setting.The mixing time of an amalgam alloy should be estimated on both technological and practical bases.

A series of dental alloys were characterized with respect to chemical composition, microstructure and corrosion resistance in artificial saliva. The following types of amalgams were studied: conventional and high copper dispersed phase dental alloys. Anodic polarization curves were recorded on these samples and periodic polarization resistance measurements were performed during a test of immersion in artificial saliva. The results are in accordance with extensive clinical findings, which attribute a greater corrosion resistance to the dispersion phase alloys. Examination by scanning electron microscopy and electron probe microanalysis allowed the identification of the various phases present on the amalgams and of the main corrosion products.

In recent years alloys with a high copper content were developed to improve the corrosion resistance of dental amalgam by elimination of the γ 2 (Sn-Hg) phase. The purpose of the present investigation was to compare the electrochemical behaviour of high copper amalgams obtained from single composition amalgam alloys (Indiloy; Shofu, Dental Corp., Menlo Park, USA) with those that used the additive mode of copper alloying (Dispersalloy; Johnson & Johnson, East Windsor, USA).

– The phase content of a conventional zinc-free silver amalgam and a high copper silver amalgam has been determined by X-ray diffraction and by stoichiometric calculation. The γ2 content in the high copper amalgam is zero for low mercury contents and increases with rising mercury concentration. The γ2 content also rises with prolonged annealing of the alloy.

Clinically and electrophysiologically confirmed cases of primary retinitis pigmentosa have been investigated regarding their copper metabolic state. It is observed that these patients show a normal or near normal serum copper concentration, very low plasma caeruloplasmin concentration, and a very high copper urinary excretion. A similarity between this condition and hepatolenticular degeneration is drawn and it is suggested that retinitis pigmentosa may also be a condition caused by an inborn error of copper metabolism.

Isolated rat liver metallothionein was injected intraperitoneally into female rats to find whether or not the injected metallothionein was recovered from the kidneys with high copper content as in the case of rat kidney metallothionein induced by exposure to inorganic cadmium ion. The distribution patterns of cadmium and zinc among protein fractions in the kidney supernatants changed dramatically within one day after the injection. The changes were explained by the degradation and re-synthesis of the injected metallothionein in the kidneys. Copper was not found as a major metal in any metal-lothionein fractions obtained from the kidney supernatants. This is in marked contrast to cadmium ion-exposed rat kidney metallothionein. The relationships between the selective and profound toxicity of the injected metallothionein to the tubular lining cells and the changes of the chemical forms of cadmium were also discussed.

The in vitro surface tarnishing of selected commercially produced high-copper silver amalgams is investigated by exposure to H 2 S/acetic acid vapour using metallographic techniques and colour photomicrography. In most cases, coloured reaction products are observed which may yield a general indication of the major dispersion of copper-rich material within the set amalgam. The experimental approach may be suitable for development as a simple tarnish test for high-copper amalgams.