Mercury

The present investigation was performed to elucidate possible etiological factors behind the complaints reported by 62 patients referred because of presumed oral galvanism. Twenty-nine patients, matched with a subsample of the test group regarding age and sex, comprised a control group. The patients were examined regarding oral medical and stomatognathic health. Their psychological and social health and symptoms were evaluated by means of a standardised interview and 5 self-rating questionnaires. A complex symptomatology including symptoms from both the oral regions and other parts of the body constituated the most distinctive feature of the patients in the test group. The clinical examination as well as patient-perceived symptoms revealed high prevalences of parafunction and dysfunction in the muscles of the stomatognathic system. Furthermore, general complaints were mainly related to muscles of the extremities, and diseases of the joints and muscles were the most commonly reported disorder. The findings at the oral medical examination revealed no differences between the groups, except for signs of parafunction. Patients in the test group gave evidence of being more exposed to negative social events and the results clearly indicate a psychogenic component behind the reported complaints.

In an autopsy study in two men and an experimental study performed on three female beagles the mercury burden of nerve tissues was determined. Nerve tissues from the head and face region and from three peripheral nerves were analyzed for mercury content with the aid of atomic absorption spectroscopy. In the dogs dental amalgam restorations were placed so as to investigate the possible influence from the amalgam on the mercury content of the tissues under study. The mercury content in man and dogs differed widely from one nerve to another, with no apparent relation to the number, type, or location of tooth restorations.

The galvanic current densities between gold, amalgam and cobalt-chromium, three different classes of dental alloys, were determined in vitro in artificial saliva kept at 35 degrees C. The maximum current density of 200 microA/dm2 was obtained between the conventional amalgam and a type III gold alloy. Galvanic currents of lesser magnitude could also be measured between amalgams high in copper and the other alloys. No measurable current densities were obtained between gold alloys and between gold and cobalt-chromium alloy with the exception of a casting and a solder gold alloy commonly used in combination.

These values surprised us, as we had assisted in some observations, made by a Specialist Inspector of Health and Safety Executive, of mercury levels in the breathing zone of dentists following a number of procedures, including the removal of amalgam with high speed drills. These unpublished observations indicate that high levels of mercury vapour can be released during the cutting of cavities in teeth previously filled with amalgam, when minimal aspiration and cooling water are used.  This paper describes some experiments performed to clarify the position and if possible measure and qunatify any exposure to mercury vapour during the preparation and restoration of cavities.

The release rate of mercury from a conventional, a dispersed phase or a spherical high copper content amalgam under static conditions in stimulated or artificial saliva has been measured and found to decrease approximately exponentially with time. A higher initial release rate was observed for mercury in stimulated saliva than in artificial saliva during the in vitro experiments. In a pilot study corrosion current was recorded from an amalgam specimen immersed in saliva, and was found to decrease approximately exponentially with time. After brushing the surface of the amalgam during two subsequent periods, in a manner similar to toothbrushing, an increase in corrosion current was measured indicating the removal of loosely bound corrosion products. A model describing the periodical mercury release from an amalgam surface has been proposed.

Fourteen dental casting alloys were analyzed for release of nickel and beryllium into acidic salivary solutions in vitro. Corrosion rates of varying pH levels and time in solution were calculated through the 120-day level, and the possible significance of these rates to allergic reactions or other health hazards were postulated.

Not available.

“Intra-oral air was analyzed for mercury (Hg) vapor concentration in 46 subjects, 35 of whom had dental amalgam restorations. Measurements were made with a Jerome Hg detector both before and ten min after chewing stimulation. Subjects with dental amalgams had unstimulated Hg vapor concentrations that were nine times greater than basal levels in control subjects with no amalgams. Chewing stimulation in subjects with amalgams increased their Hg concentration six-fold over unstimulated Hg levels, or a 54-fold increase over levels observed in control subjects. Concentrations of Hg measured in intra-oral air larger than those reported in expired air were attributed to the rate and direction of air passage across amalgam surfaces. There were significant correlations between Hg vapor released into intra-oral air after chewing stimulation and the numbers and types of amalgam restorations. It is concluded that intraoral air is a reliable physiological indicator of Hg released from dental amalgam that may reflect a major source of chronic Hg exposure.”

“Serial measurements of Hg concentration in intra-oral air were made during and after chewing stimulation in 35 subjects with occlusal amalgam restorations. Hg concentrations remained elevated during 30 min of continuous chewing and declined slowly over 90 min after cessation of chewing. By curve-fitting and integration analysis of data during these time periods (including corrections for respiratory volume, retention rate of inspired Hg, oral-to-nasal breathing ratios, and consumption of three meals and three snacks per day), we calculated that all subjects received an average daily Hg dose of approximately 20 micrograms. Subjects with 12 or more occlusal amalgam surfaces were estimated to receive a daily Hg dose of 29 micrograms, whereas in subjects with four or fewer occlusal amalgam surfaces, the dose was 8 micrograms. These Hg dosages from dental amalgam were as much as 18-fold the allowable daily limits established by some countries for Hg exposure from all sources in the environment. The results demonstrate that the amount of elemental Hg released from dental amalgam exceeds or comprises a major percentage of internationally accepted threshold limit values for environmental Hg exposure. It is concluded that dental amalgam Hg makes a major contribution to total daily dose.”

“The release of mercury from an amalgam surface in natural saliva during cyclic loading, as well as under static conditions, simulating the clinical conditions of chewing and rest, has been studied using a nuclear tracer technique. Cyclic loading strongly promoted degradation of the amalgam surface in the saliva environment. Corrosion products were found to be loosely bound on the amalgam surface and could be removed by brushing similar to toothbrushing. Most of the mercury released from the surface was present in amalgam particles, produced during the cyclic loading procedure. The daily release of ionic mercury was estimated to be approximately 3 micrograms/cm2, according to the model experiment. Extrapolating the present findings to clinical conditions, man’s ionic mercury intake from dental restorations may be at the same level as the total mercury intake from food and drink.”