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The main current-generating corrosion cells in the oral cavity are the bimetallic cell and the concentration cell, the latter mainly occurring due to differences in access to oxygen in the various parts of the metallic material. Corrosion resistance is not an intrinsic property of a metal or an alloy for it depends on an interaction with the environment. Thus, the contents of the oral cavity, have a decisive influence. This implies that corrosion tests in vitro are of limited value in predicting the clinical corrosion behaviour of a metallic material. Results from a series of clinical studies concerning a possible relationship between galvanic currents and certain oral and other symptoms in a group of patients who had been referred to the Faculty of Odontology, University of Umeå, are briefly presented. The possibility of local and systemic effects of intra-oral galvanic cells is discussed.

One hundred consecutive patients, 74 women and 26 men, aged between 18 and 83 years (mean = 54.8 years), referred with complaints related to oral galvanism were investigated and treated and the treatment results were evaluated after 2-3 years. Forty of the patients reported facial pain, pain from the teeth, temporomandibular joints (TMJ) and masticatory muscles and TMJ clicking and locking and 26 reported headache. Smarting in the oral mucosa, smarting of the tongue and xerostomia were reported by 26, 21 and 24 patients, respectively, and 30 patients reported an unpleasant taste, a metallic taste or a battery taste. The same patient often reported several symptoms. The patients also reported various general symptoms, above all joint symptoms, pain in the back, neck and shoulders and general muscular pain but also tiredness, weakness, difficulty in concentrating, depression and insomnia. After clinical and radiological examination, salivary tests, determination of the maximum galvanic current at metallic contacts and screening for contact allergy to dental materials, various oral diagnoses could be established. Most of the patients exhibited functional disturbances of the masticatory system, periodontitis, smarting of the oral mucosa, xerostomia, pulpitis and pulpal necrosis and mucosal lesions. The medical illnesses the patients reported themselves to be suffering from or had been treated for included cardiovascular disorders, high and low blood pressure, asthma, rheumatic disorders, diabetes, pernicious anaemia, gastritis and peptic ulcer. Seventy-six patients took drugs regularly. In most cases there were several oral, dental and medical explanations for the symptoms.

US. safety standards for mercury exposure, as established by the Occupational Safety and Health Act of 1970 (1972) is 0.1 mg/ M3 7- ten times this amount. Later, in 1972, the standard was lowered to 0.05 mg/M3 (ANSI, 1972) based on the studies of Smith et al. (1970). In the October issue of the ADA Journal, it recommends 0.02 mg/M3 (Kantor and Woqdcock, 1981). Russia established 0.01 mg as their maximum allowable count ration more than 30 years ago (Smelyanskiy and Nlanova, 1959). Trackh ten berg (1974) states, “Changes in immunological reactivity brought on by low mercury concentration generally fall into two periods, one of stimulated immunological reactivity, and the second in which it begins to decline.” Excerpts from his studies demonstrate these changes

Historically, hatters in England who used mercury in the felt hat industry got the shakes and became unstable – thus the term “Mad as Hatter.”

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.

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.

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.