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Studies have reported the discoloration of dentin beneath amalgam restorations. The purpose of this study was to test the hypothesis that the bond strengths of adhesive resins to this discolored dentin are lower than those to normal dentin, and are related to the presence of metallic ions or corrosion products. Amalgam-filled extracted human teeth were used. After the removal of amalgam, the discolored dentin and surrounding normal dentin were bonded with Single Bond or Clearfil SE Bond and tested for microtensile bond strengths. The bond strengths of Single Bond and Clearfil SE Bond to normal dentin were greater than to discolored dentin. Clearfil SE Bond demonstrated higher bond strength to normal dentin than did Single Bond. However, no differences were found between the bond strengths to the discolored dentin of both adhesives. Elemental micro-analysis revealed various amounts of tin in all discolored dentin.

When amalgam was triturated with Hg-In liquid alloys instead of pure mercury, the resultant amalgams released a significantly smaller amount of mercury vapor during setting. To understand the mechanisms responsible for the drastic decrease in mercury evaporation from the In-containing amalgam, we used Auger Electron Spectroscopy to examine surface oxide films on amalgams made with Hg-10 wt% In or pure mercury. The surface of the In-containing amalgam was rapidly covered with both indium and tin oxide films. Greater amounts of oxygen were found on the gamma 1 Ag-Hg matrix in the In-containing amalgam than in the amalgam without indium. The rapid formation of the oxide film contributes to a reduction in the mercury release from the In-containing amalgam by forming an effective barrier to evaporation.

The fact that mercury is released from dental amalgam restorations after abrasion provides a source of continued controversy over the safe use of this material. Studies have shown that the amount and rate of mercury release vary for different amalgam products. The objective of this study was to determine how alloy composition affects mercury vaporization from experimental amalgams with similar alloy particle size and shape and percent residual mercury. An hypothesis to be tested was that mercury release is dependent upon the concentration of tin in the silver-mercury matrix phase of the amalgam. Seven spherical amalgam alloys (two low-copper and five high-copper) were made by a dental manufacturer (Tokuriki Honten, Japan). Trituration conditions were adjusted so that all set amalgams had the same residual Hg (47.3%). ADA-type amalgam cylinders were aged for 14 days at 37 degrees C, then lightly wet-abraded on #600 silicon carbide, dried, and placed into a tube through which air was blown at a rate of 750 mL/min. Mercury vaporization was monitored with a gold film analyzer (Jerome 411) for 30 min. Total Hg release was determined by integration. We analyzed polished specimens via electron microprobe to determine composition, volume fraction of silver-mercury matrix (gamma 1), and amount of tin in the gamma 1. The results showed a strong negative correlation (r2 = 0.941) between the log of total mercury released and the amount of tin in the gamma 1. The effect of alloy composition, specifically the presence or absence of zinc in the amalgam, could not be definitively determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Elemental analysis of two precious alloyceramic systems revealed the accumulation of Sn atoms within the interaction zone of couples subjected to a range of metal oxidation time; and varying total firing times. The source of Sn atoms which accumulated within the interaction zone was the opaque porcelain layer which contained an initially higher Sn concentration than the alloy. It is hypothesized that SnO2 provides continuity of electronic structure between alloy and ceramic structures and is a primary factor in controlling ceramic-metal adherence.

The metallurgical structure of a non-gamma-2 amalgam was investigated by using metallurgical microscopy, surface, point, and line analyses by an electron probe microanalyzer, and a microhardness test. Referring to these findings, their effects on clinical results were then discussed. Findings were as follows: The residual dispersant particle was less hard than the gamma 1 matrix, but the ring around it was much harder than the gamma 1 matrix or the residual gamma particle. The improved mechanical properties seem to be the result of the presence of this ring. The gamma 2 phase was absent in this amalgam. The absence of gamma 2 phase seems to improve chemical resistance, to prevent the deformation by mercuroscopic expansion of amalgam margins, and thus to decrease their fracture potential. The minute gamma 1 crystals found adjacent to the ring around the residual dispersant particle seem to indicate that they were late in crystallization, resulting in low early strength.

The oxidized surfaces of cross-sections of gold alloys containing a total of 1.5 mass % Fe and Sn, oxidized at 1000 degrees C for one hr, have been studied by various techniques, including secondary electron micro-analysis, X-ray micro-analysis, X-ray diffraction, and thermogravimetry. Over the composition range (0.30-1.50 mass % Fe), an external oxidation zone containing only Fe oxides was formed. The quantity of Fe2O3 was greater than that of SnO2 for 0.45-1.50 mass % Fe. With an Fe content below 0.45 mass %, the amount of SnO2 was greater than that of Fe2O3. Traces of Fe3O4 were formed in high Sn content alloys. Internal oxidation particles composed of Fe2O3 and SnO2 precipitated deep in the alloy matrix (0.90-1.50 mass % Fe), and these changed to an internal oxidation band composed mainly of SnO2 for 0.3 mass % Fe.

The phase distributions of several dental amalgams have been determined by two methods: calculation from elemental analysis data obtained with the microprobe, and measurement of phase areas on backscattered electron photographs with the image analyzer. The results of these methods agree, in general, with the distributions predicted by the stoichiometric equations.

Microstructure of commercial dental alloys and their amalgams were studied primarily by x-ray diffraction, optical metallography, scanning electron microscopy, and x-ray energy dispersive spectroscopy. X-ray diffraction revealed more phases than normally reported in these materials. Presence of new phase was discussed and their formation mechanism understood. Some phases having interacting 2 theta degrees values with others were properly identified. Both new and conventional dental alloys and their amalgams, namely Tytin, Sybraloy, Dispersalloy, Kerr Spheraloy, Caulk Spherical, Shofu Spherical, and Caulk 20th Century Microcut were used to complete the investigation.

The chemistry of microstructures near the interfacial reaction zones of four non-precious alloys and two different brands of dental porcelain has been analyzed. It was found that most non-precious dental alloys contain second phases which can alter elemental concentration profiles. Recommendations for assessing interfacial reaction zone chemistry in dental non-precious alloys are offered.

Microstructures of high copper commercial amalgams containing varying amounts of mercury, ranging from 20% above to 25% below recommended values, were primarily investigated by x-ray diffraction. Mechanisms relating to the absence or presence of gamma 2 (Sn-Hg) phase in these amalgams were discussed in relation to the presence of copper and tin elements in their original alloys. The optimum mercury concentration in some amalgams was determined in order to keep them free of the gamma 2 (Sn-Hg) phase.

Gold alloys were given five different conditioning treatments prior to porcelain firing. The alloys were examined with a scanning electron microscope and energy dispersive X-ray analyzer. Only two of the alloys had tin and indium present; these were concentrated in particles partially fused to the alloy's surface.

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: All alloys consist essentially of Ag3Sn (gamma), Cu3Sn (epsilon), and, in some cases, Ag4Sn (beta). When the original alloy contains higher amounts of Cu, more Cu is found in solution in the Ag3Sn (gamma) and Ag4Sn (beta) phases. The reaction phases in amalgams made from these alloys consist essentially of Ag22Sn Hg27(gamma 1) and Cu6Sn5 (eta'), with no detectable Sn8Hg (gamma 2). When In is present, it is found principally in the Ag3Sn (gamma) and Ag22Sn Hg27(gamma 1) phases, and both the gamma and gamma 1 phases are of different composition than that for the other alloys. When Pd is present, it is found principally in the Cu3Sn (epsilon), Cu6Sn5 (eta'), and Ag22Sn Hg27(gamma 1) phases.

This study is the first to report on the use of x-ray photoelectron spectroscopy (XPS or ESCA) for studying the surface films (less than 10 nm thick) of aged amalgams. The concentrations and electron binding energies of the elements on the surfaces of four different amalgams aged for 20 min, one day, seven days, and 30 days were determined quantitatively. For comparison, the bulk compositions of the amalgams aged for seven days were also determined after removal of approximately 5 nm of material from the surface by argon-ion-sputtering. The XPS data revealed that the surface films of aged zinc-containing amalgams were not a simple oxide but were primarily composed of a (hydrated) tin and zinc oxy-hydroxide, whereas, in the zinc-free amalgams, the surface films were primarily a tin oxide. The concentration of mercury in this thin surface film after aging was depleted. This suggests that tin and/or zinc preferentially diffused to the surface and combined with oxygen, forming a surface film and diluting the mercury concentration in the surface. Another probable explanation for the depleted mercury is that a minimal amount of mercury in the surface film evaporated during the aging.

A new amalgam alloy consisting of spherical particles having a composition of 60% Ag, 27% Sn, and 13% Cu was investigated by microprobe and X-ray diffraction analysis. The alloy seemed to consist of minute dispersion of Cu3Sn, gamma(Ag3Sn), and beta(Ag-Sn). Amalgam made from this alloy exhibited a matrix of gamma1(Ag-Hg) with small reaction phase areas of Cu6Sn5. No gamma2(Sn-Hg) was observed.

For gold alloys containing only In as a base metal, an external In2O3 layer forms uniformly on the alloy surface. However, when the alloy contains Sn and In, no external oxide layer can be detected by electron probe micro-analysis, and oxide particles composed of In2O3 and SnO2 precipitate in the alloy. For alloys containing Ni, in addition to In and Sn, the external oxide is composed of NiO; there is little development of internal oxide. For alloys containing Fe and Sn, an oxide layer of only Fe2O3 forms on the alloy surface, and the internal oxidation zone shows a band-like structure containing SnO2 and a small amount of Fe2O3.

Spherical amalgam specimens were burnished, burnished-polished, polished (wet), or polished (dry). The amalgams were sectioned normal to the prepared surface, elemental analyses were made at a series of depths from the surface with the electron microprobe and the phase fractions were calculated. Significant variations in phase distributions exist within 100 micrometers of the surface.

Amalgam made with Brewster Alloy (62% Ag, 33% Sn, 5% Cu, and 0.2% Zn) had little or no dimensional change during 24 h at 23 degrees C. Brewster amalgam stored for five yr in air expanded 186, 68, and 14 microns/cm at 60, 37, and 23 degrees C, respectively. Nearly "stable" conditions were approached at about 50 mo.

The tin and fluoride concentrations in surface layers of intact enamel specimens were analytically determined after treatment with 8% SnF2 solutions at temperatures of 25, 45, 65, and 85 C. Significant increases in fluoride uptake and particularly tin uptake in enamel correlated directly with the temperature of the SnF2 treatment.

A quantitative microprobe analysis was conducted on three commercial amalgams to determine the nature of the phases present. The presence of tin in the Ag-Hg phase (gamma1) was confirmed and Cu-3Sn was found in the original alloy particles. In the dispersant amalgam studied, little Sn-Hg phase (gamma-2) was found and the reaction phase Cu-6Sn-5 was identified.

The growth of bacteria on stainless steel wires was used as a model to investigate which properties of SnF2 produced anti-bacterial effects against S. mutans. Wire-adherent bacteria were exposed for one min, twice a day, to various fluoride or control compounds having similar ions, pH, valence, or atomic weights. After two days, the thickness of adherent bacteria was scored visually, and the decrease in pH of the growth medium was determined. Bacteria from each wire were then dried, weighed, and analyzed for metal content. Electron microscopy and electron microprobe were used to identify the location of heavy metal deposits in the bacteria. Only SnF2 dramatically altered S. mutans growth and metabolism, and this anti-bacterial effect was associated with a large uptake of tin into the bacterial cells. The fluoride salts of sodium, lead, zinc, and copper had little influence on S. mutans growth in this test system. The pH of the various fluoride salts or controls generally had no effect on the activity of the test compounds, except for the noted inactivation of SnF2 at elevated pH's. Since SnF4 did not alter the growth or metabolism of S. mutans, a unique property of SnF2--possibly the reactivity in an aqueous environment--may be responsible for its anti-bacterial properties.

Several types of amalgams were prepared with carved, burnished, or polished surfaces. Elemental analyses were made of these surfaces with the electron microprobe and the phase fractions were calculated from these data. The phase distributions were found to vary with the technique of finishing.

Changes in the morphology of the oxidation zone and the quantities of oxide for gold alloys containing two base metals (In and Sn) were investigated by exposing alloys at 1000 degrees C for one h in air. The contents of In and Sn were varied in the range of from 0-1.5 wt%. In the range of from 1.5-0.35 wt% In (from 0-1.15 wt% Sn), In 2O3 was formed predominantly at the alloy surface. The electron probe x-ray micro-analyzer detected no uniform external oxidation zone. A mixture composed of In2O3 and SnO2 precipitated internally in the alloy matrix. An external oxidation zone composed of SnO2 was formed on the alloys containing over 1.2 wt% Sn, and no internal oxidation zone was observed.

ESCA has been combined with argon-ion etching to obtain depth profiles for SnF2-treated enamel. Three zones of products from the topical treatment are detected: a layer of tin oxide on the surface; fluoroapatite + hydroxyapatite at depths below about 0.2 micron; an intermediate layer CaF2, Sn(OH)2, Sn2PO4OH, and fluoroapatite between the two. Sn3F3PO4 was not detected.

In a recent study, Sarkar and Eyer (1986) studied an amalgam which was formed using a unique procedure. Based on their results, they concluded that the solubility of Sn in the Ag-Hg (gamma 1) phase of dental amalgam was virtually nil (less than 0.25 wt%). This finding is contrary to the published results of other investigations. The purpose of the present study was to clarify these disparate findings. A low-copper dental amalgam was examined by electron probe microanalysis. This amalgam was selected because it exhibits unusually large gamma 1 grains (10 microns). Because the influence of the electron-analyzing beam can be completely contained within these large grains, grain boundaries or peripheral phases would not be excited, and a valid analysis of the gamma 1 grains themselves could be made. The analyses showed significant Sn contents of 2.0-3.0 wt%. Analyses of areas which contained grain boundaries showed slight or no differences in Sn content compared with that for the grains alone. Furthermore, secondary electron scans of this dental amalgam failed to reveal the intergranular precipitates of Sn-Hg observed by Sarkar and Eyer (1986) in their amalgam. These different results can be explained by the fact that the unique amalgam investigated by Sarkar and Eyer does not exhibit the same diffusional patterns as does dental amalgam, and that the composition of the gamma 1 in the two amalgams is not the same. The final conclusion is that the Ag-Hg (gamma 1) phase in dental amalgam does indeed contain a significant amount of Sn.

Nickel-chromium alloy-ceramic couples used in this study exhibited Cr, Ni-Cr, and Ti-Cr interactions with bonding agent-ceramic complexes. Bonding agents may broaden or suppress the width of interaction zones. Metal oxides such as NiO, Cr2O3, or more complex forms such as TiO-Cr2O3 and NiCr2O4 may play a prominent role in controlling ceramic-metal adherence.