Corrosion and Mercury Release from Dental Amalgam 1 Jaro Pleva, Ph.D. Abstract been presented, amalgam is still by far the most Corrosion attacks on twenty-two dental extensively used material for dental restorations.2 amalgam restorations after in vivo service have Since the investigations and warnings of the been studied by Scanning Electron Microscopy outstanding German chemist Alfred Stock, 1920- together with the Energy Dispersive X-Ray 19453 4 5 little epidemiological studies of mercury Technique, and by optical microscopy. From the release and its effects have been made. One of the measured depth and type of corrosion attack, possible reasons may be the very interdisciplinary estimates of released mercury amounts are made. character of the problem. For correct answer, The amalgam fillings have been obtained from specialist competence in the following fields is members of a group of 250 individuals, who required: materials science, suspected their health troubles potentially to be corrosion/electrochemistry, toxicology, chronic mercury poisoning from amalgam and medicine/diagnostics, physical biology, analytical were to have all amalgam fillings removed. Three chemistry. typical patient cases are presented. The common type of dental amalgam is an Model calculations of released mercury, based alloy containing typically in weight-%; 50 Hg, 35 on previously published measurements of Ag, 10 Sn, Cu, Zn. corrosion currents with and without abrasion are Reported types of amalgam degradation are also given. crevice corrosion,2 6 7 8 selective corrosion,9 The investigations show, that the long-term galvanic corrosion in contact with dissimilar release of mercury from a few amalgam fillings alloys10 11 and mechanical wear.12 33 Besides will often reach or exceed the recommended selective attack, stress corrosion has been limits for daily intake of mercury. Hence, proposed to be responsible for the marginal mercury from corroding amalgam fillings breakdown of amalgam restorations.13 Further, represents a potential health hazard. Danger of cyclic loading, simulating chewing, strongly galvanic contact between amalgam and gold promotes corrosion of the amalgam surface.14 15 restorations is particularly emphasized. Published investigations of amalgam corrosion are mostly concerned about the mechanical 1. Introduction performance of dental fillings and neglect to The impact of corrosion on operation of make estimates of mercury amounts released by industrial appliances and personal security is well corrosion attack and wear. Nevertheless, the recognized and subject to a large number of unfounded and simplified argument that "dental investigations. Corrosion can also be a cause of amalgam releases very small amounts of environmental contamination, for instance by mercury" is often used, even in scientific and heavy metals in pharmaceutical or food industry. official reports. In some cases, the exposure for Hitherto, the possible danger from the internal released mercury has been confused with source of corrosion products, dental amalgam mercury in urine and blood of exposed patients. fillings, has been mostly overlooked. Presently, Laboratory experiments, described in the this problem is devoted special attention.1 odontologic literature, often neglect a number of Though a proof of amalgam biocompatibility has important factors, which will influence corrosion never of fillings in vivo. These are for instance wear, pressure fluctuations from biting contact, 1. P1 3079, S - 68300 Hagfors, Sweden. temperature 141 Journal of Orthomolecular Medicine Vol. 4, No. 3, 1989 increase, acidic and salt food, galvanic contacts in more detail. The dental restorations, whose with dissimilar metals. details are shown in Figures 1 to 11 belonged to The work of Mayer and Diehl16 provides an these three patients. example. In their experiments, the investigators Persons with possible occupational exposure eliminated any cathodic depolarizer, which is to mercury and those consuming fresh water fish most often oxygen from the air. The use of more than twice a week have been excluded from oxygen free double distilled water effectively the investigation. stopped possibility of any corrosion process and Control group: Ten persons have been found, implied a wrong conclusion about high corrosion age 30-60 years, who have never had any resistance of amalgam. amalgam restoration. No person in the control The aim of the present work was to investigate group complained about more than three a number of amalgam fillings, which have served symptoms given in Table 2, and none of the in vivo for several years. Estimates of mercury symptoms was classified as severe. amounts, corresponding to measured intensity of Inversely, none of the patients with the corrosion attack, are given. The amounts of syndrome was free of dental amalgam, and all mercury are compared to recommended limits for complained about at least 5 symptoms, mostly maximum daily exposure in food and in air. more than ten. Most severely ill, till invalidity, For a number of patient cases, the removal of were bearers of galvanic cells gold - amalgam. A the corroded fillings is linked to a distinct statistical evaluation of the patient material will alleviation of symptoms, typical for chronic be the subject of another paper. mercury poisoning. Three of the cases are described in more detail. 2.2 Case Histories PATIENT A: Male, 41 years 2. Experimental Profession: corrosion engineer Oral status: 20 amalgam fillings, 1 gold bridge over 5 teeth (2 2.1 Material molars extracted) Root fillings: 3 From 15 persons, parts of 22 removed Investigated restorations: amalgam in the gold amalgam fillings have been gathered and bridge; 5 year old filling, intermittent contact to investigated. The material also included extracted gold; 20 year old large filling, no contact to teeth with amalgam fillings, and gold restorations dissimilar metal Number of symptoms: 25 After in direct metallic contact with amalgam. root filling, hole in the gold bridge has been The donators were selected from a group of filled with amalgam. A few months later the 250 persons, all of them having large amounts of patient suffered increasing symptoms of both amalgam, often in combination with gold physical, psychical and neurological kind, most restorations in direct or intermittent contact. With of them listed in Table 2. No dysfunction could a questionnaire, the following information has be found by common diagnostic methods on been gathered: heart muscle (ECG) or on gastrointestinal tract - age, sex, profession, anamnesis, (X-ray) or elsewhere. As a corrosion engineer, - history of dental treatments and oral status: the patient pointed at the black and rough number of amalgam fillings, other metals, amalgam filling in the galvanic cell gold - contact to gold, permanent or intermittent, amalgam, but no doctor took the idea of - root treated teeth, poisoning from corroding amalgam seriously. - all health complaints, symptoms classified as First a look into a toxicology handbook identified fair or severe. the symptoms as chronic mercury poisoning. Summary of the most frequent symptoms in the Removal of amalgam in the galvanic cell broke whole patient group is listed in Table 2. the trend and the strongest symptoms went Below, three patient cases are described 142 Corrosion and Mercury Release from Dental Amalgam partly back, but four years later many troublesome symptoms were still present, some 2.3 Method of them increasing in severity. First removal of The removed amalgam fillings have been all fillings resulted in alleviation and successive examined for corrosion attacks in both optical disappearance of all symptoms. All the recorded microscope and Scanning Electron Microscope symptoms are known to be comprehended in (SEM) type JEOL JSM 840, equipped with chronic mercury poisoning.38 39 40 4142 43 44 The EDAX or LINK systems for Energy Dispersive case history has been described in more detail X-ray Analysis (further EDX). Both morphology in.45Microscopic examination of removed of attack and chemical composition of amalgam amalgam fillings showed the following corrosion fillings at different locations have been types: investigated. - crevice corrosion, Fig. 1, - selective corrosion, Fig. 6, 3. Results - cracking and intergranular attack, Fig. 2, - galvanic corrosion. 3.1 Surface morphology and composition of Summary of the EDX-analysis of elements at corroded fillings various locations of a 5 and 20 years old fillings All obtained amalgam fillings showed is shown in Table 1, and some estimates of blackening of crevice surfaces, adjacent to tooth released mercury amounts in Table 3. cavity, and sometimes also of external surfaces. The grey-black surfaces (tin compounds) were Patient B: corroded by general attack, at some locations Female, 62 years cracks have been observed, Fig. 1, 2. The EDX- Profession: Office, administration analysis of the corrosion products consistently Oral status: showed decrease in contents of both mercury and 16 amalgams, silver, at some locations to zero contents (depth 1 gold bridge, of analysis some micrometers), Table 1. 3 gold crowns Two types of surface layers could be seen: Gold-amalgam contact: a) Deposits on the original amalgam surface, permanent and intermittent containing mainly hydrolyzed tin compounds Root fillings: 6 from preferential dissolution of tin containing Investigated restorations: phases, and chloride. Locally, the corrosion gold crown on amalgam, Fig. 3, 4, 7, 10. products were mixed with