Surface chemistry of a high-copper dental amalgam

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.

Surface analysis of dental amalgams by X-ray photoelectron spectroscopy and X-ray diffraction

OBJECTIVES

It is important to characterize the surface of dental amalgam in order to understand the process of mercury release from amalgam restorations in the oral cavity. The mercury evaporation occurs not only from the newly made restoration but also from the set material.

METHODS

The surfaces of four different types of amalgams, which had been well set, were analyzed with X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and the relationship between surface compositions and mercury release was studied. Fresh amalgam surfaces as well as aged surfaces, which were stored for 30 days in air, were investigated using XPS and the chemical states of amalgam components and oxygen were studied. The aged surfaces were also characterized with XRD and grazing angle XRD.

RESULTS

With increased oxidation, the surface contents of tin and oxygen were increased in all amalgams. In contrast, the surface contents of copper and mercury were decreased. An increase of zinc or indium content were observed in zinc or indium containing amalgams, respectively. A surface layer enriched with indium and oxygen was clearly detected by XPS but not with grazing angle XRD.

SIGNIFICANCE

The thickness of the enriched surface layer is estimated to be in the order of few nanometer, which is approximately equal to the analysis depth of XPS. In addition, the presence of metallic elements, like tin and zinc, that readily form a stable oxide layer at the surface suppress the release of mercury.

Corrosion by galvanic coupling between carbon fiber posts and different alloys

OBJECTIVES

The corrosion of metal type (NiCr, copper, etc.) posts in post and core restorations has been a well known fact over the last few years. A new generation of carbon fiber posts is now playing an extensive role in dental prosthetics, but these posts may, in some cases come in contact with alloys used for restoration purposes. The objective of this paper is to study the electrochemical behaviour of these posts in an artificial SAGF medium (Artificial Saliva Gal Fovet) for comparison with that observed for different alloys (gold, NiCr and amalgams) in the same medium, and to assess the coupling that might occur between these posts and alloys.

METHODS

Posts of different diameters (1-2.1 mm) were molded in resin, thus forming 10 x 3 mm pads that were mounted on a rotating electrode. Pads of identical dimensions were also made for each alloy. Voltammograms (current-tension curves) were plotted for every material in the SAGF medium at 25 degrees C with normal aeration and low aeration (bubbling purified argon) using a potentiometer with three electrodes to determine the position of the zero current potentials. Evans graphs were then plotted once the anode part of the alloy curves and the cathode part of the post curves had been processed with computer software. The potentials and the maximum coupling current densities were estimated.

RESULTS

Posts may be involved in galvanic coupling in the presence of oxygen. Galvanic activity in an aerated solution is highly probable upon contact with amalgams, but may also occur if the material in contact is NiCr alloy. Coupling between precious alloys and posts is improbable and can only induce very low currents in the presence of oxygen.

SIGNIFICANCE

This study devoted to coupling of carbon fiber posts and metals in the mouth, attracts attention to the fact that a corrosion reaction can be set-up in the infiltration conditions relevant to the prosthetic restoration.