Biocompatibility of mercury derivatives

In vitro evaluation of the effect of freshly mixed amalgam and gallium-based alloy on the viability of primary periosteal and osteoblast cell cultures

The effect of freshly mixed specimens of a gallium-based alloy Galloy and a high copper spherical amalgam Tytin on the viability of primary periosteal and osteoblast cells was investigated. The cells were grown from the parietal bones of 2-3 day old Albino Wistar rats and were seeded in multi-well plates and exposed to the test materials for 1 or 6 days. The number of viable cells in each test group was determined using the Trypan blue dye exclusion test and compared with the controls. The area of cell death around the test specimens was also measured. Statistical analysis (ANOVA, Tukey's pairwise comparisons) showed a significant effect of the test materials on cell viability (P < 0.01). The viability of cultures containing Tytin was significantly lower than cultures with Galloy and the controls (P < 0.05). The viability of cultures containing Galloy was significantly lower (P < 0.05) than controls except for periosteal cells after 1 day. The culture media was analysed using atomic absorption spectrophotometry (AAS) for metal ion content. The results suggested that mercury (Hg) was the main element released from the dental amalgam followed by copper (Cu) and silver (Ag) whilst gallium (Ga) was the main element released from the gallium-based alloy followed by indium (In), Ag and Cu.

Mercury release from dental amalgams: an in vitro study under controlled chewing and brushing in an artificial mouth

The release of mercury vapor from class I amalgam restorations prepared in human molar teeth was studied during chewing simulations in an artificial mouth of a bi-axial servo-hydraulic mechanical test system. So that the total mercury released from the restoration over a fixed time could be determined, a closed chamber surrounded the envelope of chewing motion. In addition, the influence of sampling frequency on mercury release was corrected by the use of different sampling frequencies over a fixed time interval of mercury release measurement and extrapolation to zero sampling time. Thus, a combination of a closed environment and an extrapolation method to determine the mercury release under continuous sampling was used to determine the mercury released under normal breathing conditions. The measured mercury release rate data were used to calculate the potential daily mercury dose in a patient due to a single amalgam restoration, following the method previously outlined by Berglund. The mercury release from both a conventional and a high-copper amalgam was evaluated at different age intervals after the restoration was placed in the teeth. The results show that while the age of the amalgam and the amalgam type influence the extent of mercury release during the initial non-steady-state conditions, the steady-state value of mercury daily dose due to a single amalgam filling is 0.03 micrograms/day, which is well below the calculated threshold-limiting value (TLV) of 82.29 micrograms/day considered dangerous for occupational exposure in the United States.

The mechanism of Hg2+ toxicity in cultured human oral fibroblasts: the involvement of cellular thiols

To study amalgam-related toxicity in a primary target cell type, human oral fibroblasts were grown in a low-serum medium containing 1.25% fetal bovine serum and exposed to Hg2+, a corrosion product of amalgam. A 1-h exposure to various concentrations of Hg2+ resulted in a dose-dependent loss of colony forming efficiency. Removal of the low-molecular-weight thiol cysteine from the medium increased the toxicity of Hg2+ almost 50-fold in comparison with complete medium or medium without fetal bovine serum. Accordingly, fetal bovine serum was not found to contain detectable levels of low-molecular-weight thiols. The levels of cellular free protein thiols were shown to be depleted Hg2+ at significantly lower concentrations of the metal ion than those required to decrease the levels of the major cellular low-molecular weight thiol glutathione. These decreases were dependent on the exposure conditions, i.e. the presence of serum and thiols, in a manner similar to the effect on colony forming efficiency. Other functions commonly related to cell viability, including the accumulation of the vital dye neutral red, the cytosolic retention of deoxyglucose and the mitochondrial reduction of tetrazolium were also inhibited by Hg2+, albeit at higher concentrations. Finally, the depletion of cellular glutathione, by pre-exposure of the cells to the glutathione synthesis inhibitor buthionine sulfoximine, somewhat increased the toxicity of Hg2+ and potentiated the depletion of protein thiols. Taken together, the toxicity of Hg2+ in human oral fibroblasts was demonstrated in several assays of which colony forming efficiency was the most sensitive, cell killing by this agent was related to its high affinity for protein thiols, whereas glutathione showed a significant, but limited, ability to protect the cells from Hg2+ toxicity.

Development of low- and high-serum culture conditions for use of human oral fibroblasts in toxicity testing of dental materials

With the aim of establishing conditions applicable to the testing of dental materials in human target cells, fibroblastic cell lines have been derived and grown from explants of human oral mucosa. Both a high-serum medium (termed "HSM") (CMRL 1066 supplemented with 10% fetal bovine serum) and a low-serum medium (termed "LSM") (a 1:1 mixture of M 199:MCDB 153 supplemented with 1.25% serum) supported radial outgrowths of cells from oral explants, as well as the subsequent transfer and growth of the cells in mass culture and at clonal density. Cells were typically fibroblastic in that they expressed vimentin uniformly, but did not express immunocytochemical markers of epithelial or endothelial cells. Cells derived in either LSM or HSM showed significantly higher colony-forming efficiency and clonal growth rate when transferred in LSM, as compared with HSM. Because cell migration occurred to a lesser extent in LSM, microscopic scoring of colony formation was also markedly facilitated. In both LSM and HSM, cellular low-molecular-weight thiols constituted about 30% of the total amount of sulfhydryls. Glutathione was present in about six- to seven-fold-higher amounts than cysteine--glutathione primarily in its reduced form and cysteine primarily in its oxidized form. A corrosion product of dental amalgam, i.e., Hg2+, decreased cell survival measured as colony-forming efficiency in a dose-dependent manner following either an acute (one h) exposure or continuous exposure (seven days). These studies demonstrated that human oral fibroblasts could be cultured at about one-tenth of the serum content that is commonly used.(ABSTRACT TRUNCATED AT 250 WORDS)

Amalgam: reactor response

Although the number of research reports on dental composites far outnumbers those on amalgams in recent years, amalgam remains the popular clinical choice for posterior restorations. Recent research on corrosion phenomena, mechanical properties, and new compositions indicates that the useful properties of amalgam may still be improved. Given the current position of amalgam within the dental armamentarium, focused research on the physical chemistry and metallurgy of current and new amalgams may continue to pay dividends.