Corrosion of dental amalgam

Effects of bleaching on mercury ion release from dental amalgam

The chemical reactions that take place at the amalgam surface when exposed to bleaching agents are not well-understood. It is known, however, that mercury ions are released from dental amalgam when bleached. We hypothesized that increasing concentrations of hydrogen peroxide are more effective than water at increasing mercury ion release from dental amalgam. We prepared dental amalgam discs (n = 65) by packing amalgam into cylindrical plastic molds and divided them into 13 equal groups of 5 discs each. The discs in each group were individually immersed in either 0%, 3.6%, 6%, or 30% (w/v) hydrogen peroxide at exposure periods of 1, 8, 48, and 168 hrs. Samples were taken for mercury ion release determination by inductively coupled plasma mass spectrometry. There were significant increases in mercury release between control and all other hydrogen peroxide concentrations at all exposure times (p < 0.05).

Morphological findings and energy dispersive X-ray microanalysis of oral amalgam tattoos

Oral amalgam tattoos (AT) are distinct pigmentations of the oral mucosa resulting from accidental incorporation of dental amalgam in the oral soft tissues. Dental amalgams and in particular mercury, one of the constituents of dental amalgams, have for long been considered toxic. Oral ATs are easily accessible to study soft tissue reaction to amalgam and its degradation products. In this study, 17 oral ATs were examined by transmission electron microscopy and energy dispersive X-ray microanalysis. Ultrastructurally, in the ATs, three kinds of electron-dense particles were observed. The largest particles ranged in size from 0.5 up to several 100 microm. Smaller electron-dense inclusions (0.5-0.1 microm) were seen extracellularly associated with meshworks of elastic fibers and collagen bundles. The third and smallest type of particles (5-30 nm in diameter) was found with basement membranes of small vessels and pericytes and particularly decorating collagen bundles. Element analysis regularly revealed the presence of silver, sulphur, copper and lead in the AT decay products. Mercury was found in only one instance. Tissue reactions due to ATs seem to be minimal. No acute inflammatory changes were seen. Larger inclusions occasionally were surrounded by macrophages and multinucleated cells. TEM and element analysis may in specific cases be helpful in the differential diagnosis of pigmented lesions of the oral mucosa.

The amalgam controversy. An evidence-based analysis

BACKGROUND

There are a number of patients and health care professionals who believe dental amalgam restorations are a factor in a host of diseases and conditions. They have been influenced by anecdotal case reports in the medical and dental literature, research published in the refereed literature and media stories concerning the alleged dangers of amalgam restorations.

METHODS

The author uses an evidence-based approach in analyzing the data both supporting and condemning the continued use of amalgam restorations. He reviewed the articles from both peer-reviewed and non-peer-reviewed sources and evaluated their relevance, research design and statistical analysis, as well as whether the conclusions follow from the data.

CONCLUSIONS

There are numerous logical and methodological errors in the anti-amalgam literature. The author concludes that the evidence supporting the safety of amalgam restorations is compelling.

CLINICAL IMPLICATIONS

Amalgam restorations remain safe and effective. Dentists should educate patients and other health care professionals who may be mistakenly concerned about amalgam safety.

Corrosion of orthodontic devices

A brief overview of the theory of corrosion and the formation of galvanic couples is presented, followed by a discussion of the metals and alloys used in the fabrication of orthodontic appliances and devices. Attention is paid to the factors that contribute to establishment of corrosion cells in the mouth. Although oral corrosion generally does not cause significant destruction of metal, it can elicit in patients adverse physiological responses such as local irritation and metal hypersensitivity. There are indications that orthodontic treatment may lower the incidence of nickel hypersensitivity. Destructive attack on orthodontic appliances does occur, however, when certain types of denture cleanser are used to clean appliances that contain soldered joints.

Tissue reactions to the separate implantation of individual constituent phases of dental amalgam, including assessment by energy dispersive X-ray microanalysis

Soft tissue degradation of the 3 principal amalgam phases have been investigated in relation to their role in the formation of the amalgam tattoo. Each phase, finely powdered, was implanted subcutaneously into the submandibular region of guinea-pigs for periods ranging from 1 week to 1 year. The rates of breakdown were assessed radiographically and the final lesions were examined by light and electron microscopy and X-ray microanalysis. gamma 2 (Sn7Hg) phase degraded rapidly, mainly extracellularly, and did not produce a tattoo. Both mercury and tin disappeared from the lesion. gamma 1 (Ag2Hg3) phase degraded less rapidly, both extra and intracellularly, and produced a small tattoo. Mercury was lost from the lesion. gamma (Ag3Sn) phase degraded slowly, intracellularly, and produced a large tattoo. Tattoos always resulted from persistence of minute particles of silver and sulphur associated with basal lamina and connective tissue.

Tissue reactions to implanted dental amalgam, including assessment by energy dispersive x-ray micro-analysis

Dental amalgam, either in the form of a solid rod or as a fine powder was implanted subcutaneously into guinea-pigs and the tissue reactions were examined after varying time periods. The solid rods were enclosed by fibrous capsules within which only extremely limited breakdown occurred. This appears to result from electrolytic corrosion of the gamma 2 (SnHg) phase of the rod's surface. Powdered amalgam induced granulomata and most of the particles of amalgam were actively digested by macrophages and giant cells. This resulted in the progressive loss of mercury and tin from the lesion and the formation of minute particles containing silver and sulphur which became widely distributed throughout the lesion, being associated with basal lamina, collagen and elastic tissue and giving rise to the formation of a tattoo. In contrast, some particles of amalgam, too large to be interiorised, were encapsulated by collagen and persisted almost unchanged. Intracellular small amalgam particles and aggregates of fine particles, resulting from their degradation, were seen within lymph node macrophages. It is extremely likely that the sequence of events leadng to the formation of an amalgam tattoo of the oral mucosa in Man are the same.

The fate of amalgam implanted in soft tissues -- an experimental study

The soft tissue reaction to amalgam depended on whether it was finely ground or a solid mass. Finely ground amalgam was actively digested within macrophages and giant-cells with loss of mercury and the formation of the fine particles of silver and sulphur. Larger masses became surrounded by a fibrous capsule.

The in vitro measurement of amalgam corrosion rates by the polarization resistance technique

Measurement of the corrosion rates of three distinctive amalgam alloys (lathe-cut, spherical and dispersed-phase) when immersed in three different electrolytes, including saliva, is reported. The results indicate that the dispersed phase alloy amalgam exhibits a lower corrosion rate than a conventional lathe-cut alloy amalgam but is somewhat inferior to a spherical alloy amalgam.

Amalgam tattoos: light and electron microscopy and electron-probe micro-analysis

A common tattoo occurring in the mouth is caused by the insertion of amalgam filling material into the soft tissues. Fifteen amalgam tattoos were examined. Amalgam or its derivatives were found within macrophages, fibroblasts and multinuclear giant cells. Fine particles were found associated with: the basement-membranes of mucosal epithelium, of striped muscle fibres, and of muscle cells of blood vessels; collagen; elastic tissue; and the connective tissue of nerves. Amalgam consists mainly of mercury, silver and tin. The analytical results suggest that corrosion occurs and that mercury and some tin are lost from the tattoos, leaving silver and tin in macrophages and giant cells, and silver in fibroblasts and in the above-mentioned extracellular sites.

Analytical ultrastructural studies on implanted dental amalgam in guinea-pigs

Implantation of amalgam induced a cellular reaction, and a rapid loss of copper and zinc and a more gradual loss of tin and mercury occurred. The silver remaining was generally associated with sulphur and was present either as a diffuse fuzz around remaining masses or in a finely particulate form.

Electroetching of dental amalgam

Application of the potentiostatic polarization technique to the metallographic etching of set dental amalgam is described. Etching studies of amalgam prepared from a lathe-cut, a spherical, and a silver-copper dispersed-phase amalgam alloy are reported. The γ2 phase in set dental amalgam can be characterized by this electrochemical technique.