Phase In Dental Amalgam Research Articles

Hg Emission from Dental Amalgam as Related to the Amount of Sn in the Ag-Hg (γ1) 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.

The effect of the electrode potential on the release of mercury from dental amalgam.

The effect of the electrode potential on the rate of mercury dissolution from the matrix phase (gamma 1) of dental amalgam was investigated. Specimens of the Ag-Hg phase, with and without dissolved tin, were exposed to synthetic saliva and maintained at various potentials by means of a potentiostat. The amount of dissolved mercury was determined after 24 h by cold-vapor Atomic Absorption Spectrophotometry. Anodic polarization curves for the gamma 1 specimens and pure silver and mercury were also recorded. The results for the Ag-Hg phase showed a potential-independent dissolution rate between -0.6 and -0.1 V (SCE), followed by a sharp increase. Mercury dissolution from the Ag-Hg-Sn phase was much slower than from the tin-free gamma 1 phase, and potential-independent to +0.05 V (SCE); a sharp increase in mercury dissolution was observed at +0.1 V (SCE). The anodic polarization curves for the Ag-Hg-Sn phase indicated passivity between -0.67 V and +0.1 V (SCE), but no clear passivation for the Ag-Hg specimen, silver, or mercury. The results show that in the potential-independent region, mercury dissolved in the atomic form from both the tin-free and tin-containing gamma 1 phase. The increase in dissolution in the upper range of potentials was tentatively attributed to selective anodic dissolution of silver and an onset of electrochemical dissolution. The results indicate that the rate of mercury release from the gamma 1 phase of dental amalgam was not affected by potential changes due to alloying or galvanic contacts unless the potential exceeded some critical value.

The Effect of Tin on the Corrosion Behavior of the Ag-Hg Phase of Dental Amalgam and Dissolution of Mercury

The anodic polarization behavior of the Ag-Hg matrix phase of dental amalgam (gamma 1) and the rate of mercury dissolution were examined as a function of the tin content. The objectives were to determine the effect of tin on the electrochemical behavior and dissolution of mercury and to provide evidence on whether tin dissolves in the gamma 1 phase or precipitates as a tin-rich phase. Anodic polarization curves were recorded for specimens of the gamma 1 phase containing 0-1.5% Sn and for the gamma 2 phase and a gamma 2-containing dental amalgam, in synthetic saliva. Mercury dissolved in synthetic saliva in 24 h was determined for the gamma 1 phase containing 0-1.0% Sn, with cold-vapor Atomic Absorption Spectrophotometry used for mercury analysis. Tin induced passive behavior of the gamma 1 phase and suppressed mercury dissolution. The passive gamma 1 phase did not exhibit a breakdown of passivity occurring at the gamma 2 phase. The results were consistent with the tin presence in gamma 1 in a solid solution, rather than in tin-rich precipitates, and indicated that at least 1.5% Sn can be dissolved in gamma 1 at 37 degrees C.

Sn in the Ag-Hg phase of dental amalgam.

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.

Corrosion of the eta'(Cu-Sn) phase in dental amalgam.

Previous studies have shown preferential corrosion of the eta'(Cu-Sn) phase in high-copper dental amalgam both in vitro and in vivo, while samples of pure eta' have shown high corrosion resistance. To clarify this contradiction, samples of pure eta' crystals mixed with other phases were prepared and tested. Evaluation of the corrosion resistance was based on the results of coulometry at constant potential and potentiodynamic polarization. The corrosion susceptibility of eta' in the matrix of gamma 1(Ag-Hg) was considerably higher than the susceptibility of isolated eta'. The susceptibility of pure eta' also could be increased by plating it will small amounts of Hg. It was concluded that in dental amalgam, the presence of mercury in the phases surrounding eta' reduces its resistance to corrosion. Although eta' is more resistant to corrosion than gamma 2(Sn-Hg) which appears in low-copper amalgams, it is the least corrosion resistant major phase in high-copper amalgams and can suffer deterioration.

Quantitation of colorimetric reaction for determination of gamma 2 phase in dental amalgam

A simple, convenient means of establishing a standard for gamma 2 phase analysis has been outlined which may be summarized as follows: (1) preparation of synthetic gamma 2 sample, (2) use of a standard die, and (3) preparation of a standard curve from any source of soluble stannous ions. This allows for the comparison of color intensity of test specimens to that of a 100% gamma 2 standard and allows for relating color directly to milligrams of tin.

Colorimetric determination of gamma 2 phase in dental amalgam

A new quantitative colorimetric test for the gamma 2 phase of dental amalgam, developed by Kropp, 5 has been used to examine a number of the newer “low gamma 2” dental amalgam alloys. The original method has been modified in that the wavelength at which the color was read was changed from 578 nm to 700 nm. Of the dental amalgams tested. Tytin and Caulk Ease had the lowest gamma 2 phase content after 24 hours. Kropp's colorimetric method for gamma 2 phase determination is simple, quick, and convenient and requires relatively simple equipment, namely, a colorimeter. However, for general use, a more convenient quantitative reference standard needs to be developed.

Corrosion behavior of the tin-containing silver-mercury phase of dental amalgam.

Through the use of anodic polarization studies in Ringer's solution, the electrochemical behavior of γ 1 phase of dental amalgam (Ag2Hg3) and γ 1 containing dissolved tin is compared with that for the γ 2 phase in dental amalgam (Sn7-8Hg). The results indicate that when tin is dissolved in γ1 it does not affect the electrochemical behavior of that phase.

Pressure-induced disappearance of the gamma 2 (HgSn7-8) phase in dental amalgam.

Examination of the crystalline structure of dental amalgam during an investigation that involved high pressures led to the detection of the disappearance of the γ2 phase after high pressure treatment. This phase disappearance was detected during periodic X-ray diffraction measurements made several months to a year after the samples had been subjected to pressures of up to 50 kilobars (750,000 psi) by use of a solid medium pressure apparatus. No new phases were detected during the process.

Confirmation of the presence of beta(Ag-Hg) in dental amalgam.

AbstractThe presence of the β1 phase in dental amalgam after 60°C heating has been confirmed by x‐ray diffraction, metallography, microhardness tests, and electron beam analysis. It appeared that the γ1 → β1 transformation began at preferred sites, believed to be possibly areas deficient in Hg, and grew outward from these sites. Even after heating for nearly a year, however, some γ1 still remained in the sample.

Strength of the mercury-tin phase in dental amalgam.

Strength of the mercury-tin phase in dental amalgam.