Mercury

“Estimated release rates of Hg vapor from dental amalgams permitted calculation of the potential Hg body burden by employing a four-compartment model for inorganic and elemental Hg distribution. A computer program, compatible with most personal computers, simulated the cumulative and incremental distribution in each compartment and total body accumulation between 1 and 10,000 days for different daily Hg dosages. For a given Hg dose of 30 micrograms/day, metabolic compartments R1-R3 were close to equilibrium at 5, 100, and 300 days, respectively; whereas by 10,000 days, R4 closely approximated total body burden and had not yet attained equilibrium. Projected values obtained with the computer model were consistent with results obtained by another method using a standard tissue burden equation, which employed experimentally determined tissue half-lives for blood and CNS. The model predicted that continuous exposure to elemental Hg vapor, at 30 micrograms/day for 10 years, would result in a total Hg body burden of 5.9 mg, of which 4.8 mg could be contained in R4. Assuming that the Hg in R4 displayed uniform distribution throughout the body, then the brain concentration was estimated to be 68 ng/g wet weight. In contrast, if Hg in R4 reflected long-term preferential accumulation in brain and other neural tissue, then concentrations as high as 4.0 micrograms/g could be attained. However, predictions of Hg concentrations in blood and urine were well within established ranges, and were unlikely to be of utility in assessing effects of chronic low-dose Hg exposure.”(ABSTRACT TRUNCATED AT 250 WORDS)

“Their observations and astute comment prompt me to submit this report of my own recent exacerbation, associated with a poorly defined and easily overlooked dental trigger, an altogether different process from the initial attack 40 years ago and my own recollection of it.”

“To measure the effects of chronic low-level exposure to inorganic mercury, the neuropsychological performances of 13 female dental auxiliary workers with elevated head mercury levels (as measured by an X-ray fluorescence technique) were compared with 13 workers with no measurable mercury levels. Workers with elevated mercury levels scored significantly less well on the Recurrent Figures, and SCL-90-R, but not on the WAIS, Rey’s AVL, PASAT, BGT, Grooved Pegboard, and Finger Tapping tests. Chronic subtoxic levels of inorganic mercury appear to produce mild changes in short-term nonverbal recall and heightened distress generally, and particularly in categories of obsessive compulsion, anxiety and psychoticism, without alterations in general intellectual functioning, attention, verbal recall, and motor skills.”

“Samples from the central nervous system (occipital lobe cortex, cerebellar cortex and ganglia semilunare) and kidney cortex were collected from autopsies and analysed for total mercury content using neutron activation analyses. Results from 34 individuals showed a statistically significant regression between the number of tooth surfaces containing amalgam and concentration of mercury in the occipital lobe cortex (mean 10.9, range 2.4-28.7 ng Hg/g wet weight). The regression equation y = 7.2 + 0.24x has a 95% confidence interval for the regression coefficient of 0.11-0.37. In 9 cases with suspected alcohol abuse mercury levels in the occipital lobe were, in most cases, somewhat lower than expected based on the regression line. The observations may be explained by an inhibition of oxidation of mercury vapour. The regression between amalgams and mercury levels remained after exclusion of these cases. The kidney cortex from 7 amalgam carriers (mean 433, range 48-810 ng Hg/g wet weight) showed on average a significantly higher mercury level than those of 5 amalgam-free individuals (mean 49, range 21-105 ng Hg/g wet weight). In 6 cases analysis of both inorganic and total mercury was carried out. A high proportion (mean 77% SD 17%) of inorganic mercury was found. It is concluded that the cause of the association between amalgam load and accumulation of mercury in tissues is the release of mercury vapour from amalgam fillings.”

The safety of dental amalgam use in patients needing dental fillings is well established, based on the relatively rapid decline in urinary mercury concentration following filling. Only a small number of studies, however, have attempted to describe the method of transfer of the mercury in the amalgam to the saliva. Atomic absorption spectrophotometry was utilized to study reduction and vaporization and showed excellent sensitivity in quantification. Using this method, the release of mercury from the amalgam to the saliva was studied. To begin with, in experiments in vitro, the release of mercury from the test amalgam to fresh saliva was shown to be approximately 10 times as great as the amount released to an inorganic test solution. The mercury concentration in the mixed sa liva sample obtained from 198 test subjects under ordinary conditions was then measured. The concentration of mercury in the mixed saliva obtained from 65 test subjects with either amalgam-filled teeth nor exposure to exogenous mercury was 1.48± 1.73 ppb using the a rithma tic mean, and 0.88?; 2.71 ppb using the geometric mean. These values were felt to represent the normal mercury concentration in mixed saliva. In test subj ects with amalgam-filled teeth, on the other hand, a significant correlation was noted between the mercury concentration in the mixed saliva and the number of teeth filled with amalgam, with a correlation coefficient of y=0.44. Measurement of the release of mercury from an amalgam·filled tooth to the saliva gave a mean of 12.3 ng/ml per filled tooth in the molar region as measured immediately after filling. Since the mercury concentration in the saliva showed a rapid decrease within 24 hours, it is not likely that this amount of mercury is ingested continuously. Test subjects with amalgam-filled teeth thus ingest an amount of mercury larger by approximately 2.1 p.g than those without such fillings, through the swallowing of saliva. Since this amount of mercury corresponds to less than 1/ 10 the amount contained in the food of a normal daily diet, the safety of the amalgam-filling of the teeth is thought to be confirmed.

“This paper discusses metal exposure in the male, the nonpregnant female, and the maternal-offspring unit. In the first two situations, the primary targets are the gonads. In the mother-offspring unit, consideration must be given to effects on the fertilized ovum, the growth of the embryo, and, finally, to the fetal and perinatal stages. The central nervous system may be especially vulnerable during development. The placenta also undergoes development, and either the placenta or the fetus may be the primary target. In humans, certain metals may cause abortion or other effects on the conceptus. Effects may also be produced by metal exposure both in utero and in the suckling infant. For example, methylmercury gives rise to a range of effects on the central nervous system at doses lower than those producing damage to the mature nervous system. Effects of lead and arsenic are associated mainly with postnatal exposures during infancy and early childhood, but there is reason to believe from animal experiments that some effects may occur from prenatal exposures to certain metal compounds.”

“A group of dentists had their offices monitored for mercury vapour and content.  Low values were found compared to other surveys, but a variety of locations of a reservoir of mercury-rich materials was identified.”

“Summary: The cases cited in the literature indicate that the potential for toxicity or poisoning with mercury exists as an occupational hazard to the dentist and dental personnel. The cause is the elemental form of mercury resulting from vaporization due to an accidental spill of mercury. Undetected or unreported spills produced chronic and low level exposures. When exposure to mercury affected the dental patient, it was during the placement of the amalgam restoration that an allergic reaction was precipitated. When allowed, the reaction was self-limiting, resolving by its own processes. For patients who are particularly allergic to mercury and not amenable to antihistamine therapy, removal of the newly placed amalgam restoration is recommended.”

“The maximum content of mercury forming intermetallic compounds has been determined in dental amalgams prepared from alloys with different copper contents. In amalgams made from alloys with silver contents less than about 42% there is a risk of occurrence of free mercury if an effective condensation technique has not been used.”

The potentials of 407 amalgam restorations have been determined in vivo. The measurements were performed with very high impedance equipment, and relative to a Ag/AgCl reference electrode. The readings varied from -23 mV to -595 mV, with 90% of the readings confined to within -127 mV to -431 mV and a mean value of -226.1 mV. Of the restorations, 394 were measured twice, and no significant difference could be found between the first and the second reading. During the study, eight new restorations were inserted. Their potentials varied from -180 mV to -565 mV, with a mean of -339.4 mV, which was significantly lower than that of the older restorations.