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“Gram-negative fecal bacterial from three longitudinal Hg exposure experiments and from two independent survey collections were examined for their carriage of the mercury resistance (mer) locus. The occurrence of antibiotic resistance was also assessed in both mercury-resistant (Hgr) and mercury-susceptible (Hgs) isolates from the same collections. The longitudinal studies involved exposure of the intestinal flora to Hg released from amalgam “silver” dental restorations in six monkeys. Hgr strains were recovered before the installation of amalgams, and frequently these became the dominant strains while amalgams were installed. Such persistent Hgr strains always carried the same mer locus throughout the experiments. In both the longitudinal and survey collections, certain mer loci were preferentially associated with one genus, whereas other mer loci were recovered from many genera. In general, strains with any mer locus were more likely to be multi resistant than were strains without mer loci; this clustering tendency was also seen for antibiotic resistance genes. However, the association of antibiotic multi resistance with mer loci was not random; regardless of source, certain mer loci occurred in highly multi resistant strains (with as many as seven antibiotic resistances), whereas other mer loci were found in strains without any antibiotic resistance. The majority of highly mult iresistant Hgr strains also carried genes characteristic of an integron, a novel genetic element which enables the formation of tandem arrays of antibiotic resistance genes. Hgr strains lacking antibiotic resistance showed no evidence of integron components.”

“For many years, the amalgamation of silver with mercury to produce a condensable mixture which could be used to restore carious defects in teeth followed a tortuous path of negative results. However, at the turn of the century, amalgam alloys having acceptable characteristics for successful clinical use emerged. From that point on, silver amalgam was widely accepted as the material of choice for low-cost, easily placed, and durable restorations. About 60 years later, a major discovery occurred that resulted in a most significant improvement in the clinical performance of this material. The key to this improvement was an increase in the Cu content of the amalgam alloy which previously had been considered to be inappropriate. This paper describes the history of this discovery, which produced what has come to be known as high-copper dental amalgam alloys.”

“Neonatal uptake of mercury (Hg) from milk was examined in a pregnant sheep model, where radioactive mercury (Hg203)/silver tooth fillings (amalgam) were newly placed. A crossover experimental design was used in which lactating ewes nursed foster lambs. In a parallel study, the relationship between dental history and breast milk concentration of Hg was also examined in 33 lactating women. Results from the animal studies showed that, during pregnancy, a primary fetal site of amalgam Hg concentration is the liver, and, after delivery, the neonatal lamb kidney receives additional amalgam Hg from mother’s milk. In lactating women with aged amalgam fillings, increased Hg excretion in breast milk and urine correlated with the number of fillings or Hg vapor concentration levels in mouth air. It was concluded that Hg originating from maternal amalgam tooth fillings transfers across the placenta to the fetus, across the mammary gland into milk ingested by the newborn, and ultimately into neonatal body tissues. Comparisons are made to the U. S. minimal risk level recently established for adult Hg exposure. These findings suggest that placement and removal of “silver” tooth fillings in pregnant and lactating humans will subject the fetus and neonate to unnecessary risk of Hg exposure.”

“The mercury (Hg) release from dental amalgam fillings increases by mechanical stimulation. The aim of this study was to investigate the possible impact of nocturnal bruxism on Hg exposure from dental amalgams and to evaluate the effect of an occlusal appliance. 88 female patients from an orofacial pain clinic with a complete maxillary and mandibular dentition, a normal frontal vertical overbite with cuspid guidance, and at least 4 occlusal amalgam fillings in contact with antagonists in intercuspidal position, were examined with the Bruxcore bruxism monitoring device to measure the level of on-going nocturnal bruxism. Based on the degree of abrasion recorded, the subjects were divided into a group defined as bruxists, (n = 29), another group defined as non-bruxists, (n = 32), serving as controls, the intermediate group being discarded. The Hg exposure was assessed from the Hg concentration in plasma and urine, corrected for the creatinine content. In a regression model with bruxism as the only explanatory variable, no significant effect of bruxism was found, but when the number of amalgam fillings, chewing gum use, and other background variables were taken into account, there was a limited impact of bruxism on Hg in plasma. The nocturnal use of an occlusal appliance did not, however, significantly change the Hg levels. This study indicates that mechanical wear on amalgams from nocturnal bruxism may increase the Hg uptake, but the magnitude of this effect seems to be less than from the use of chewing gum.”

“The interaction of inorganic mercury with human and bovine milk proteins was studied. Gel filtration chromatography of skimmed milk and whey incubated with mercury showed that, in human milk, mercury was mainly bound to caseins, while a low proportion was bound to albumin. In bovine milk, mercury was associated with two protein fractions, caseins and beta-lactoglobulin. Furthermore, it was shown by electrophoresis that mercury induced the formation of dimers of beta-lactoglobulin. Thus, in both human and bovine milk, mercury possessed greater ability to interact with milk proteins than to the low-molecular-weight substances. However, the pattern of mercury distribution was different between the milk of these two species.”

“The toxicological consequences of exposure to mercury (Hg) from dental amalgam fillings is a matter of debate in several countries. The purpose of this study was to obtain data on Hg concentrations in saliva and feces before and after removal of dental amalgam fillings. In addition Hg concentrations in urine, blood, and plasma were determined. Ten subjects had all amalgam fillings removed at one dental session. Before removal, the median Hg concentration in feces was more than 10 times higher than in samples from an amalgam free reference group consisting of 10 individuals (2.7 vs 0.23 mumol Hg/kg dry weight, p < 0.001). A considerable increase of the Hg concentration in feces 2 days after amalgam removal (median 280 mumol Hg/kg dry weight) was followed by a significant decrease. Sixty days after removal the median Hg concentration was still slightly higher than in samples from the reference group. In plasma, the median Hg concentration was 4 nmol/liter at baseline. Two days after removal the median Hg concentration in plasma was increased to 5 nmol/liter and declined subsequently to 1.3 nmol/liter by Day 60. In saliva, there was an exponential decline in the Hg concentration during the first 2 weeks after amalgam removal (t 1/2 = 1.8 days). It was concluded that amalgam fillings are a significant source of Hg in saliva and feces. Hg levels in all media decrease considerably after amalgam removal. The uptake of amalgam mercury in the GI tract in conjunction with removal of amalgam fillings seems to be low.”

“Hg2+ interacts with brain tubulin and disassembles microtubules that maintain neurite structure. Since it is well known that Hg vapor (Hg0) is continuously released from “silver” amalgam tooth fillings and is absorbed into brain, rats were exposed to Hg0 4h/day for 0, 2, 7, 14 and 28 d at 250 or 300 micrograms Hg/m3 air, concentrations present in mouth air of some humans with many amalgam fillings. Average rat brain Hg concentrations increased significantly (11-47 fold) with duration of Hg0 exposure. By 14 d Hg0 exposure, photoaffinity labelling on the beta-subunit of the tubulin dimer with [alpha 32P] 8N3 GTP in brain homogenates was decreased 41-74%, upon analysis of SDS-PAGE autoradiograms. The identical neurochemical lesion of similar or greater magnitude is evident in Alzheimer brain homogenates from approximately 80% of patients, when compared to human age-matched neurological controls. Total tubulin protein levels remained relatively unchanged between Hg0 exposed rat brains and controls, and between Alzheimer brains and controls. Since the rate of tubulin polymerization is dependent upon binding of GTP to tubulin dimers, we conclude that chronic inhalation of low-level Hg0 can inhibit polymerization of brain tubulin essential for formation of microtubules.”