Mercury

Galvanism is seldom mentioned to the dental student, yet nearly every dentist alters a patient’s galvanic current every time he treats him. Galvanism is electrical current produced by placing dissimilar metals inan electrolyte. Saliva is the electrolyte. The dental dissimilar metal list is seemingly inexhaustive. We place copper, tin, zinc, mercury, silver, gold, platinum, irridium, indium, paladium, cobalt, chromium, nickle and baryllium into this electrolyte. A battery is produced. Electrical current is generated. Electricity doesn’t just exist. It is the simultaneous biproduct of a chemical reaction between the various phases of metallic interaction in the mouth. As electrical current is generated, various ions of these metals are emitted into the saliva. Many of these metals, or their corrosion products, are known toxins. Among them is mercury.

Galvanic corrosion of amalgam, induced by contact with a type IV dental casting gold alloy, was determined under simulated oral conditions in an electrochemical cell. The effect of a pellicle layer formed by 1 h exposure to saliva in the oral cavity was determined. Pellicle on the amalgam had no effect on the maximum corrosion rate or the 2 h corrosion charge, whereas pellicle on the gold alloy substantially reduced both these parameters of the conventional low-copper amalgam; the corrosion of the high-copper amalgam was less and was not influenced by pellicle formation.

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“Dental amalgam used by the dentist as a restorative material should meet the following criteria: (1) a reduced risk of marginal failure with a minimal risk of recurrent caries, (2) resistance to creep and corrosion, and (3) the characteristics for mixing, inserting, and polishing that are optimally duplicated. To achieve these criteria, the optimal amalgam technique includes the use of the following: Rubber dam whenever possible Conservative cavity preparations to offset the amalgam’s inherent weak physical properties A high copper alloy combined with the appropriate amount of mercury for optimal plasticity and to reduce susceptibility to creep and corrosion Trituration, precondensation, and condensation methods that are consistently practiced by the dental assistant and dentist A burnishing scheme combined with a subsequent polishing method to complete the final amalgam restoration.”

“Consumers spent $10 billion on restorative dental treatment in 1979. Little information is available regarding the life expectancy of these restorations or what proportion of these restorations replaces previous ones. A critical literature review was presented, covering all available longevity data of posterior restorations. Necessary methodologic standards for evaluation of the studies were outlined and used in the review. The lack of these critical variables–patient selection, missing follow-up data, and judgment criteria for determining need for replacement or failure (or both)–minimized the usefulness of the results. Study results are generalizable only to similar patient populations and not all patients. Much more controlled research needs to be done.”

Base metal alloys which contain nickel are not new to dentistry. For the past 25 years, these alloys with nickel content as high as 73.5 percent, have been used to fabricate denture bases and removable partial dentures.

“Patients with histologically verified oral lichen planus (OLP) were studied regarding allergic reactions to substances in dental materials, presence of clinical corrosion orally and factors influencing corrosion, such as mixed gold and amalgam therapy, non-precious pin-constructions or complete dentures. The material consisted of 48 OLP patients (33 female, 15 male) and the results were compared with those of a control group (40 patients) and/or general population samples. When patch tested, 39% of the OLP patients reacted to one or more components in dental materials. Reaction to mercury was most common, being noted in 26%. Clinical signs of corrosion were significantly more frequent in the OLP group (72%) than in the control cases (28%). Patients with atrophic-erosive OLP exhibited a significantly higher frequency of corrosion (83%) than those with reticular type (46%). Mixed gold and amalgam therapy and screwposts were equally present in both the OLP and control group and the frequency of complete dentures corresponded to that reported for general populations. A change of dental materials in 8 patients with positive patch tests led to marked oral improvement in 6 cases, 2 of which became completely cured. The frequencies recorded for allergic reactions and corrosion as well as the result of treatment indicate that substances in dental materials may be of significance in cases of OLP.”

“This investigation was conducted to test the hypothesis that exposure of pregnant women to chemicals increases the risk of spontaneous abortion. The chemical risk factors under study to which dental assistants, factory workers, painters, and gardening workers were exposed were nitrous oxide, inorganic mercury, organic solvents, and pesticides. The study was carried out within the Danish county of Funen. It included all dental assistants employed in private or public dentistry. A comparable reference group was made up by employees less exposed to chemicals. Further study groups included all women painters within the county, women factory workers from selected factories, and about 50% of the women gardening workers within the county. Shop assistants and packers formed their control group. Information was obtained through a postal questionnaire study in May 1980 and from hospital records. Only among factory workers and painters was the odds ratio of spontaneous abortion found to be significantly increased. Neither among these women nor among dental assistants and gardening workers, however, was the reported exposure to any single chemical during pregnancy associated with a significantly increased odds ratio of spontaneous abortion.”

“The risk for inducing toxic reactions in patients as a result of amalgam treatment is negligibly low. For hyper­ sensitive patients, there is always a potential risk for allergic reactions to many materials. The tissue changes resulting from amalgam sensitivity reactions are relatively mild and will, in most cases, be resolved without  any therapeutic treatment.
To reduce the exposure of the patient to mercury, the use of a rubber dam is recommended during insertion, as well as during removal of old amalgam restorations. Effective water-spray and high-vacuum suction procedures should also be  employed. Storage of mercury liquid and amalgam scrap should be handled in accordance with procedures recommended by the American Dental Association.”

“Hand tremor due to industrial exposure to metallic mercury vapour was recorded in 26 exposed and 25 non-exposed male workers by an accelerometer attached to the dorsum of the hand. The subjects were instructed to hold the hand and the forearm in the same position first without and then with a load of 1250 g supported by the hand. Analysis of the records showed that the highest peak frequencies (HPF) (the frequency corresponding to the highest acceleration) were higher in the exposed men than in the controls and were related to the duration of exposure to mercury and to age. The changes in HPF between rest and load were again higher in the exposed men than in the controls and again related to the duration of exposure and to age. The second moment (M2) (an index taking into account the whole recorded spectrum) was similar in the exposed men and controls at rest. The changes in M2 between rest and load were higher in the exposed men than in the controls but were related to duration of exposure and to the biological measurements (loge of mercury in urine or blood) and not to age. These neurophysiological impairments might result from the tendency of metallic mercury to accumulate in the cerebellum and the basal ganglia. These results are consistent with the hypothesis that metallic mercury, even at concentrations probably below the current TLV-TWA of 0.05 mg/m3, can lead to neurological disorders.”