Fluorimetric determination of tin and organotin compounds in hydroorganic and micellar media in the presence of 8-hydroxyquinoline-5-sulfonic acid

The fluorescence of tin(IV) complexed by 8-hydroxyquinoline-5-sulfonic acid (8-HQSA) has been studied in both aqueous and hydroorganic (acetate buffer and dimethylsulfoxide) media. Several experimental parameters such as pH, DMSO/water ratio and reactant concentration have been investigated to increase the fluorescence of the tin(IV)-8-HQSA complex. A linear relationship between tin(IV) concentration and fluorescence intensity was observed between 1.7 and 20 microM). Mechanistic and quantitative studies in the presence of surfactants have been performed. Judiciously selected micellar media permitted solubilisation and quantitation of tin(IV) as well as dibutyltin compounds. A linear relationship between concentration and fluorescence intensity was found for mono-, di- and tributyltin with detection limits of 0.1 microM, 0.7 microM and 1 microM, respectively.

Cyclic voltammetry of dental amalgams

OBJECTIVES

This study used cyclic voltammetry to examine the effect of the composition of dental amalgams on their electrochemical behavior, including reactions occurring outside of oral conditions.

METHODS

Amalgams (residual mercury 47.5%) were prepared using two low-copper (3 wt% Cu) powders and five high-copper powders (40-80 wt% Ag, 12-30 wt% Cu) with and without zinc (1.5 wt%). Cyclic voltammograms were obtained at 37 degrees C in 1.0% NaCl scanning at 2 mV/s in the potential range from -1.5 V to +0.8 V vs. Ag/AgCl.

RESULTS

During the anodic scans, AgCl and Hg2Cl2 films were formed on all amalgams except the one with only 40 wt% Ag. In all high-copper amalgams, a prominent Cu (oxidation) peak was found at -0.1 V, indicating the release of copper during corrosion. Zinc affected the oxidation process for both low- and high-copper amalgams. When zinc was absent, a peak for Sn2+ oxidation appeared at -0.4 V. When zinc was present, a Sn4+ oxidation peak was revealed at -0.6 V. In some amalgams, there was evidence of the selective corrosion (pitting corrosion) of tin and copper. In the lowest silver-content amalgam, no protective films were formed, which is indicative of its poor corrosion resistance. As expected, in all the low-copper amalgams, an extreme increase in current density was recorded immediately at 0 V, due to the release of tin from gamma 2.

SIGNIFICANCE

Cyclic voltammetry is useful for the rapid examination (less than an hour) of the electrochemical behavior of amalgams, specifically to obtain information on the formation of compounds and the sequences of electrochemical reactions.

Protein interactions with bivalent tin. 1. Hydrolysis and complexation of tin(II) ion with glycine

The complexation between tin(II) ion and glycine was studied in 0.15 mol/dm3 NaCl medium at 310 K using potentiometric glass electrode titrations. In the pH range 1.1-4.5 and concentration range of the tin(II) between 0.2 and 5.0 mmol/dm3, with variable glycine-to-tin molar ratio up to 10:1, the experimental data were explained by the formation of the following complexes and their overall stability constants: log(beta +/- sigma): Sn(HGly)+, (12.78 +/- 0.08); Sn(Gly)+, (10.02 +/- 0.07); Sn(OH)Gly, (7.34 +/- 0.03), as well as the pure hydrolytic complex Sn4(OH)2+(6), whose stability constant was determined in separate experiments and found to be -4.30 +/- 0.08, under the same experimental conditions as for complexation study. The precipitate formed in tin(II)-glycine system at pH ca. 5.0 was characterized by chemical and TG analysis, I. R. spectra, X-ray powder diffraction, and electron scanning microscopy measurements. It has been shown that the precipitate has the composition Sn(OH)Gly and crystallizes in a tetragonal system with unit cell dimensions a = b = 1.584 nm, c = 0.597 nm. The mechanism of the complex formation in solution is discussed.

Setting reactions in dental amalgam. Part 2. The kinetics of amalgamation

The literature on the setting mechanisms of dental amalgams made from powders of silver-rich alloys of tin and/or copper has been critically reviewed. Part 2 is a review of the kinetics of the reactions that convert the mixture of alloy powder and liquid mercury to hardened amalgam containing the phases and microstructures described in Part 1. It is emphasized that amalgamation is a non-equilbrium process in which hardened microstructures are determined as much by kinetics as by chemistry. The setting reaction begins with dissolution of silver and tin into liquid mercury; most of the product phases precipitate in the liquid mercury. The processes that produce supersaturation in the liquid mercury and the subsequent nucleation and growth of solid phases are considered. Mass balance relationships that provide insight into the factors that control the volume fraction of the undesirable gamma 2 Sn-Hg phase are described. The nucleation and growth of eta' Cu-Sn crystals are also discussed; it is found that these crystals nucleate on copper-rich phases and grow into the liquid mercury. Finally, aspects of the setting reaction that are controlled by intergranular and interphase diffusion in the solid are discussed. These aspects include: the supersaturation of silver and tin within the liquid mercury, nucleation and growth of the beta 1 Ag-Hg phase in the surfaces of alloy particles, and the decomposition of initially formed gamma 2 Sn-Hg.

Setting reactions in dental amalgam. Part 1. Phases and microstructures between one hour and one week

The literature on the setting mechanisms of dental amalgams made from powders of silver-rich alloys of tin and/or copper has been critically reviewed. In Part 1 of the review, the microstructure and phase content of recently set amalgams are described. The composition, morphology, and location of product phases are emphasized, since these features are clues to the setting reaction. Thus, Part 1 provides the background needed to understand the kinetics of the setting reactions, which is the topic of Part 2 of the review.

Effect of mercury on corrosion of eta' Cu-Sn phase in dental amalgams

OBJECTIVES

The eta' Cu-Sn phase is the most corrosion-susceptible major component of the microstructure in high-copper dental amalgams, even though metallurgically prepared specimens of the phase are corrosion-resistant. The purpose of this study was to determine if mercury is the cause of the degradation.

METHODS

Specimens of metallurgically prepared eta' Cu-Sn phase were tested in synthetic saliva using electrochemical methods. Mercury was adsorbed on the surface by exposure to mercury vapor, and the changes in the corrosion potential and anodic polarization characteristics were determined. Galvanic currents between eta' specimens and a high-copper dental amalgam were measured for both Hg-free and Hg-contaminated eta' electrodes.

RESULTS

The Hg-free eta' phase showed a wide region of passivity. Exposure to mercury made the eta' phase electrochemically more active, and current peaks appeared on the polarization curves. The Hg-free eta' electrode was a cathode to a high-copper dental amalgam. The Hg-contaminated eta' electrode started also as a cathode, but became anode after a period of exposure.

SIGNIFICANCE

It was concluded that mercury destabilizes the protective passive film on the eta' phase, making the phase more susceptible to corrosion in the oral environment. The results of the galvanic current measurements seem to indicate that the galvanic interaction between eta' and the other phases facilitates the mercury-related degradation.

The effect of matrix phase morphology on the structure of Ag-Cu-Pd dispersed phase dental amalgam

The effect of an Ag-Cu-Pd dispersant alloy on the structure of amalgams fabricated with two different particle types of low-copper amalgam matrices was investigated. In amalgams L and L (0), a low-copper lathe-cut amalgam Aristalloy was used as the matrix. In amalgams S and S(0), the matrix used was Spheralloy, a low-copper spherical amalgam. X-ray diffraction was used to analyse the relative content of the phases in the amalgams. The presence of Pd in the dispersant of amalgams L and S resulted in a decrease in the amount of eta' (Cu6Sn5) and an increase in the amount of unreacted particles when compared to the controls L(0) and S(0). Amalgams fabricated with a spherical alloy matrix (S and S(0)) showed a greater effect than amalgams fabricated with a lathe-cut matrix alloy (L and L(0)).

Influence of saliva contamination and abrasion on resin to tin-plated alloy bond strengths

This investigation studied the effects of abrasion and salivary contamination on the shear bond strength of a composite resin bonded to tin-plated gold alloy. Experimental groups (n = 15) consisted of: group 1, no surface treatment; group 2, enamel abraded; and group 3, saliva-contaminated. After surface stressing and bonding, groups were thermocycled before shear testing. Fractured interfaces were analyzed by use of light microscopy and SEM. Specimens in group 3 (12.2 +/- 2.5 MPa) had significantly lower bond strengths than group 1 (17.9 +/- 6.8 MPa). The shear bond strengths of resin bonded to tin-plated metal were significantly affected by salivary contamination but not by abrasion.

Amalgams made from liquid Hg-In

The addition of indium to amalgam appears to reduce the mercury vapour above fillings during setting. In the present work the structure and the physical properties of amalgams with In additions to the mercury up to 30 vol.% have been investigated. No new phase or undissolved in could be detected by X-ray diffraction and scanning electron microscopy studies. Energy dispersive spectroscopy measured 4 at.% In in the gamma 1-phase of an amalgam with 20 vol.% In added to the mercury. At the same time, the Ag/Hg ratio was substantially increased compared with amalgam having no In addition. The compression strength decreased with increasing In content, and for amalgam with as much as 30 vol.% In added to the mercury, it fell below the minimum requirement of ISO 1559 (Alloys for dental amalgam, International Organization for Standardization, Geneva, 1986). An abrupt drop of the load at the onset of failure and cracks running through the gamma 1-phase, as well as the eta-phase, indicates embrittlement of these phases with increasing In content.

A new technology for direct restorative alloys

OBJECTIVES

The purpose of this study was to develop a new technology for preparing mercury-free metallic dental restorative materials.

METHODS

The novel approach relies on the cold welding of surface treated silver particles. At ambient temperature, intermetallic compound formation takes place spontaneously at the silver-tin interface. The ability of a loose powder to consolidate at ambient temperature under moderate pressure and within a short time duration was investigated for various mixtures of elemental silver, tin, and pre-alloyed silver-coated powders. Surface treatment aimed at removing silver surface oxide layers is done with a dilute acid. The compressive and the transverse rupture strengths of several of the consolidated powder mixtures were determined.

RESULTS

Cold-welding of surface-treated powder particles takes place across the silver-silver interface and is promoted by exposure to a mild acid. Powder mixtures containing approximately 50% silver powder, 40% silver-coated silver-tin intermetallic compound particles, and a small silver-tin fraction deposited from an aqueous solution display very good condensability, depending on the amount of silver-silver interface area available. The attained rupture strength values (200 Mpa) were higher than those of amalgams; the compressive strengths (120 MPa) and hardness values (100 KHN), however, were lower than those found for amalgams.

SIGNIFICANCE

Mercury-free silver-tin powder mixtures can be processed for use as metallic composite dental restorative materials.

Lithiation-based silylation and stannylation of 6-chloro-9-(beta-D-ribofuranosyl)purine

Reaction of the lithiated species of 9-(2,3,5-tris-O-tert-butyldimethylsilyl-beta-D-ribofuranosyl)-6-chloropu rine with Me3SiCl or Bu3SnCl was found to furnish the corresponding C-2 substituted product, as a result of silyl or stannyl migration from C-8 to C-2 position.

Study on the migration phenomena of selected metals in canned fruits during long storage

Experimental studies were conducted on the migration of Fe, Sn, Ca, and Mg in canned fruits: black currant, cherry and strawberry. Three-piece-cans had been protected with different coatings and technics. Cans of 31 capacity with fruits were stored in ambient temperature (ca 20 degrees C) during 60 weeks. There was stated increasing dependence of storage time on concentration of Fe and Sn in cans. Contents of Ca and Mg in this time systematically decreased in cans due to adsorption process of these metals on internal coatings. Migration rate of Fe and Sn, as well as migration trends of Ca and Mg (adsorption process) are shown on figures. There are great differences among migration of Fe, Sn and migration trends of Ca and Mg. Both these phenomena are disadvantageous for quality of canned fruits.

A comparative electrochemical study of corrosion susceptibility of some Pd-enriched amalgams

Cyclic polarization technique was used to determine the corrosion susceptibility of some Pd-enriched amalgams as compared with the conventional and high-copper ones. Different oxidation and reduction peaks and their corresponding current intensities were determined in each case. Corrosion indices I and II were also calculated. Pd-enriched amalgams have shown lower corrosion susceptibility than conventional or unicompositional high-copper amalgams. A role was attributed to the alloy composition and the relative cathodic (reduction) current available.

Hg emission from dental amalgam as related to the amount of Sn in the Ag-Hg (gamma 1) phase

Previous studies have shown that: (1) different dental amalgams emit different amounts of Hg vapor after surface films have been removed by abrasion (Boyer, 1988); (2) Sn oxide may be the predominant factor in these surface films that inhibit Hg vapor loss (Okabe et al., 1989); and (3) Sn in the Ag-Hg (gamma 1) phase may influence the vapor pressure of gamma 1 (Reynolds, 1974). The purpose of this study was to explore the relationship between Hg vapor emission and the Sn content of the Ag-Hg (gamma 1) phase in dental amalgam. Eleven commercial amalgams were selected whose gamma 1 phases contain different amounts of Sn. Amalgam specimens were ground on 600-grit carborundum paper and immediately placed into an apparatus designed around a gold film Hg vapor detector. Hg vapor loss in air over a 30-minute period was determined, and the log10 Hg loss/volume fraction gamma 1 was plotted vs. the Sn content of the gamma 1 phase for the 11 test amalgams. A linear regression of these data, showing that of the higher the Sn content in gamma 1, the lower the Hg vapor loss, produced a highly significant R2 = 0.94 (p < 0.001). To examine for differences in vapor pressure among alloys, we eliminated the oxidation effect by conducting these same tests in an argon atmosphere. Although the Hg loss was significantly greater in argon than in air, the same differences among alloys were observed. Thus, from the standpoint of both vapor pressure and oxidation, the amount of Sn in the gamma 1 phase of dental amalgam has a significant and specific influence on the potential for Hg vapor emission.

99mTc-labeling of lipid vesicles containing the lipophilic chelator PE-DTTA: effect of tin-to-chelate ratio, chelate content and surface polymer on labeling efficiency and biodistribution behavior

When injected intravenously, lipid vesicles labeled with 99mTc by means of a lipophilic chelator dipalmitoylphosphatidylethanolamine-diethylenetriaminetetraacetic acid (PE-DTTA) are rapidly accumulated by the mononuclear phagocytic system (MPS). By derivatizing the membrane surface with the lipid-polymer complex dipalmitoylphosphatidylethanolamine-monomethoxy polyethylene glycol 5000 (PE-MPEG), MPS uptake can be suppressed and loss of 99mTc label from the lipid surface reduced depending upon both PE-DTTA and PE-MPEG content. For vesicles containing 20% PE-DTTA, addition of PE-MPEG makes no difference to their rate of clearance from the circulation. However for vesicles containing 2% PE-DTTA, addition of more than 0.8% PE-MPEG increases circulation half-life, suppresses liver uptake and reduces renal clearance of the 99mTc label. The molar ratio of reducing agent (Sn) to chelator (PE-DTTA) is critical to efficient and reproducible labeling. For vesicles containing 2% PE-DTTA at a lipid concentration of 100 mM, a Sn/DTTA ratio of 0.35 gives close to optimal labeling. Variation in the Sn/DTTA ratio by a factor of two negatively impacts upon both labeling efficiency in vitro and circulation half-life in vivo. Potential uses for technetium-labeled lipid vesicles with extended circulation half-life are discussed.

Compositions of surface layers formed on amalgams in air, water, and saline

The surface layers formed on both a zinc-free and a zinc-containing dental amalgam after polishing and aging in air, water, or saline, were characterized using x-ray photoelectron spectroscopy (XPS) to determine the compositions of the surface layers which might govern the release of mercury from amalgam. The XPS data revealed that the formation of the surface layer on the zinc-containing amalgam was affected by the environment in which the amalgam was polished and aged, whereas that on the zinc-free amalgam was not affected. In addition, among the elements contained in amalgam, zinc was the most reactive with the environment, and was preferentially dissolved from amalgam into water or saline. Mercury atoms existed in the metallic state in the surface layer.

Dynamics of soldering reactions: microscopic observations

This paper provides a summary of some in situ, high-resolution studies of solder spreading reactions on microelectronic circuit metallizations. Experiments are described that focus on the use of the environmental scanning electron microscope, or ESEM. Those experiments have been complemented by studies using optical hot-stage microscopy and have been supplemented by additional analytical tools such as energy dispersive X-ray microanalysis, Auger and ESCA to evaluate chemical processes. Two general results from dynamic scanning electron microscope observations are that 1) molten solder alloys undergo a segregation process during spreading in which a "precursor" film spreads in advance of the bulk solder and 2) the spreading front, which may be enriched in Sn from Pb-Sn or Bi-Sn solders, or In from Pb-In solders, spreads along high-reactivity features of the metallization surface as a reacting "precursor" film. A third observation from these tests is that, in unconfined geometries, the reactive metallization, if not sufficiently thick, can be dissolved by the solder before wetting is complete, leading to dewetting of the solder. Both the kinetics and extent of spreading of these films and the relationship of these phenomena to the commonly measured contact angle and wetting forces are currently being examined by a range of complementary techniques. Information gathered in these studies shows that process temperature as well as composition, reactivity, and relative amounts of the solder and metallization species should all be factors of interest to the those responsible for control of soldering processes.

Application of ESEM to fluxless soldering

The ESEM is ideally suited to study soldering processes. We have used it to observe solder reflow and joining in ambient gases. It reproduces effects of atmospheric pressure reflow in a hot stage light microscope, but with much better clarity and depth of field. Compared to a regular SEM, the ESEM offers advantages of atmosphere control and ability to observe the solder samples without carbon or gold coating. These coatings could interfere with the oxidation/reduction reactions which occur at the solder/ambient gas interface. Very thin surface films, especially oxide layers, dramatically influence the flow of liquid solder and the ability of solder to wet or join to another surface. Fluxless processes in particular are ideally suited for study in the ESEM. We have used the ESEM to observe dynamic fluxless soldering and have recorded events on videotape for later stop-action still pictures and slow motion photography. Examples of these processes are shown to illustrate the ESEM capability. Included are solder deformation structure, balling reflow of eutectic solder in hydrogen, balling reflow of eutectic solder in nitrogen, joining of two solder disks in nitrogen, and dynamic melting and freezing of an off-eutectic dendritic alloy. All of these are observed in the absence of flux.

Copper/solder intermetallic growth studies

Copper samples, hot solder (eutectic) dipped and thermally aged, were cross-sectioned and placed in an environmental scanning electronic microscope (ESEM). While in the ESEM the samples were heated for approximately 2.5 h at 170 degrees C to stimulate the growth of additional Cu/Sn intermetallic compound. The intent of the study was to obtain a continuous real-time videotape record of the diffusion process and compare the observations to static SEM images reported to represent long-term, naturally aged intermetallic growth. The video obtained allows the observation of the diffusion process and relativistic growth phenomena at the Cu, Cu3Sn, Cu6Sn5, and solder interfaces as well as effects on the bulk Cu and solder. Effects contrary to earlier reports were observed; for example, growth rates of Cu3Sn were found to greatly exceed those of Cu6Sn5.

Lactic acid jet test: in vitro erosion rates of glass ionomer dental cements containing radiopacifying elements

The lactic acid jet test erosion rates were measured for 13 radiopaque glass ionomer dental materials obtained from a number of manufacturing sources. The erosion rate was compared with that found for the non-radiopaque restorative from the same manufacturer to determine whether the addition of an extra element had affected the resistance to erosion. Six materials were not significantly affected, six showed a significant increase in erosion rate. Only one material showed a reduced erosion rate. Materials containing a high proportion of any additive could show an increased erosion rate. Glass ionomer cements with or without radiopacifying elements had low erosion rates compared with other dental materials.

Entrapment and release characteristics of 2-methoxynaphthalene from cylindrical microstructures formed from phospholipids

Many natural products that exhibit biocidal activity have poor solubility in water. In order to explore the prolonged delivery of these compounds from microtubules we have utilized 2-methoxynaphthalene as a model to elucidate release characteristics of hydrophobic compounds entrapped in microtubules by spectrophotometric absorbance at 255 nm. Entrapment of this compound in microcylinders was accomplished by addition of 2-methoxynaphthalene to a water-soluble epoxy, or entrapment of the neat compound. Variation of the release rate is possible for 2-methoxynaphthalene based on the mode of entrapment and by variations in the methods used to immobilize the compound within the microcylinders. Unlike conventional microencapsulation techniques which require inclusion of the active agent at the time of formation, the use of microcylinders allows for the inclusion of a variety of active agents and the tailoring of release characteristics after their formation. We report the results of in vitro release rates of 2-methoxynaphthalene from a static diffusion system designed to explore release of hydrophobic compounds into an aqueous environment.

Evaluation of tin plating systems for a high-noble alloy

The tensile bond strength of Panavia EX to a high-noble alloy prepared by abrasive spraying and tin plating was measured. Two different intraoperatory tin plating systems were compared. Disk-shaped specimens were cast in type III gold, abrasive sprayed with aluminum oxide, and divided into three groups of 30 specimens each. Specimens in one group were tin plated by using a Kura Ace Mini unit, those in the second group were tin plated by using a Micro Tin unit, and those in the third group were not tin plated and served as the control group. Disks within each group were luted to each other with Panavia EX. The specimens were thermocycled and tested in tension. There was no significant difference between the two tin plated groups; however, the luting bond of both experimental groups was significantly stronger than was that of the control (P < .05).

Comparison of the adhesive strength of a BIS-GMA cement to tin-plated and non-tin-plated alloys

This study compared the tensile bond strengths of two base metal alloys and two noble metal alloys, tin-plated and non-tin-plated, with an adhesive resinous cement. Two tin platers were compared for their effectiveness in enhancing the composite resin-to-metal bond. Cylinders of the alloys were bonded end to end with the adhesive cement, thermocycled for 24 hours, stored in distilled water for 27 days, and tested for tensile bond strength. The mean bond strengths and mode of failure were recorded, and scanning electron micrographs were recorded for subjective evaluation. Significant differences were demonstrated between the non-tin-plated and the tin-plated noble alloys and base metal alloys.

Effect of tinfoil substitute contamination on adhesion of resin denture tooth to its denture base

At least one manufacturer claims that contamination of denture teeth with tinfoil substitute during processing is not detrimental. The purpose of this study was to determine whether tinfoil substitute contamination has any significant effect on the bond strength between acrylic resin denture teeth and their processed acrylic resin base. Eighty acrylic resin maxillary central incisors were processed to denture base material. The experimental group had the denture tooth ridgelap area contaminated with tinfoil substitute. The control group was not contaminated. The bond strength of the two groups was tested. The results indicate that contamination with tinfoil substitute significantly reduces the bond strength of acrylic resin denture teeth bonded to their denture base.