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

Abstract

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. 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 X-ray diffraction.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 X-ray diffraction.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 -3-

Chemical characterization of selected high copper dental amalgams using XPS and XRD techniques

“…The total amount of mercury estimated for ANA 2000 in the conducted study was significantly smaller than the data obtained during investigations of this material carried out by Uo et al [11]. The experiment described by Hanawa [8] showed that the mercury concentration within the surface film of a fresh specimen was similar to that in the bulk.…”

“…Furthermore, silver and copper enabled the second stage of the amalgamation reaction, eliminating the transient ␥ 2 phase [11]. Uo et al [11] revealed that the oxygen content on a fresh ANA 2000 amalgam surface was 33 at%, compared to significantly less, 6.38 at%, in our study. Furthermore, the atomic oxygen concentration obtained by McDermott et al [7] for fresh Sybralloy HCSS amalgam (45.4 at%) was similar to the results of the XPS analysis of Safargam (48.78 at%) and Megalloy (52.21 at%).…”

“…The decrease of the oxygen concentration with increasing amount of Cu and Ag may show that the enhanced amount of these two noble elements makes the amalgam more resistent to oxidation [11]. Furthermore, silver and copper enabled the second stage of the amalgamation reaction, eliminating the transient ␥ 2 phase [11]. Uo et al [11] revealed that the oxygen content on a fresh ANA 2000 amalgam surface was 33 at%, compared to significantly less, 6.38 at%, in our study.…”

“…On the freshly triturated amalgams, oxygen was detected on the fractured surfaces, indicating the immediate formation of oxides. The decrease of the oxygen concentration with increasing amount of Cu and Ag may show that the enhanced amount of these two noble elements makes the amalgam more resistent to oxidation [11]. Furthermore, silver and copper enabled the second stage of the amalgamation reaction, eliminating the transient ␥ 2 phase [11].…”

“…However, Uo et al suggested a strong influence of addition of zinc or indium on the composition of the surface layer and oxidation intensity [11]. The reaction of zinc with H 2 O releases H 2 gas, causing clinical problems with excessive delayed expansion and possible postoperative pain.…”