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dc.contributor.authorAli Mohammed Alhelalen_US
dc.description.abstractAmalgam restorations continues to be the most versatile restorations clinically and economically. However, even modern dental amalgam types can corrode when placed in the oral cavity. This research investigated the amount of mercury mass loss due to exposure to three acidic conditions (pH 1.1 , pH 2.5 and pH 3.5 HCl solutions), often encountered equivalent pH values in the oral cavity using atomic force microscopy (AFM) and 3D optical profilometry (OPI). Amalgam samples were prepared and condensed in cylindrical brass moulds, afterwhich they were polished with 600, 800 and 1000 grit size silicon carbide paper, followed by 6, 3 and 1 μm diamond suspensions and colloidal silica. Samples were then etched with pH 1.1, pH 2.5 and pH 3.5 HCl solutions for 3, 24 and 24 hours, respectively, then viewed under an optical microscope and a scanning electron microscope (SEM), to observe microstructual changes occurred due to corrosion and note any solubility differences between the different phases. SEM with Energy Dispersive Spectroscopy (EDS) was also used to identify the different phases constitiuting this type of amalgam with their elemental composition. An AFM and optical profilometer were used to further observe these changes and calculate mercury mass loss from a typical 28mm2 MOD amalgam filling using the surface areas and volume of scanned areas. EDS results, revealed the presence of four amalgam phases (γ, ε, η and γ1) with varying weight percentages of four major elements: silver, tin, copper and mercury. No γ2 phase, the exceptionally susceptible phase to corrosion, was recorded. Eutectic η phase of amalgam, 13 – 21 μm in diameter spherical like particles (with mercury globules) were observed on most etched and polished samples. Other phases (ε, η and γ1) were identified on a backscattered electron SEM image of untreated amalgam sample. No major solubility differences were observed between the different phases in the pH 1.1, pH 2.5 and pH 3.5 HCl etched samples and when compared to standard sample. Small one μm and large surface pits six to ten μm were also identified. AFM revealed a general roghening of the surface with the HCl etched amalgam samples, and the presence of a surface layer covering surface pits on unetched and etched amalgam surfaces. Calculated mercury loss (gm) for 50 x 50 scanned areas,were 14.9 μg (AFM) and 1.8 μg (OPI), 3.3 μg (AFM) and 0.71 μg (OPI) and 2.0 μg (AFM) and 0.23 μg (OPI) for the pH.1.1, pH 2.5 and pH 3.5 HCl etched amalgam samples, respectively with both imaging systems. Within the limitation of the current study the calculated mercury release was found to reach toxic levels only if more than 800 molar teeth were restored with Class II MOD amalgam fillings.en_US
dc.publisher Kuwait university - college of graduate studiesen_US
dc.subjectAtomic Force Microscopyen_US
dc.titleDental Amalgam Corrosion Evaluation using Atomic Force Microscopy and Optical Topographyen_US
dc.contributor.supervisorProf. Michael Vincent Swainen_US
dc.description.conclusionsThis study aimed to quantify the release rate of individual ions of mercury that resulted from the corrosion of a typical 28mm2 MOD amalgam filling due to its exposure to different acidic conditions normally encountered in the oral cavity, and study the effect of these conditions on the microstructure of an amalgam alloy. Optical microscope and SEM which were used to observe the general microstructure and post-corrosion changes that occurred on the amalgam surface, revealed typical microstructure of amalgam similar to what has been reported by others in the literature, in addition to better differentiation of the different phases and surface pits after etching. However, no major differences were observed between the pH 1.1, pH 2.5 and pH 3.5 HCl etched samples with both imaging systems, hence it was difficult to note solubility differences between the different phases upon etching. η phases of amalgam, 13 to 21 μm in diameter spherical like particles, were observed on all etched and polished sample surface with both optical and scanning electron microscopes, in addition to γ1 phase (amalgam matrix). However, the other phases were difficult to discern with optical microscopy but could be identified on the SEM image of standard untreated amalgam sample taken in backscattered electron mode (Figure 3.9). Small and large surface pits that ranged from one μm to six-ten μm, respectively were also observed on both optical and scanning electron microscope images. Mercury globules in eutectic γ phases were also discerened on pH 1.1 and pH 3.5 HCl etched amalgam SEM images, however, no globules were identified on pH 2.5 HCl etched amalgam scanning electron images.en_US
Appears in Programs:1210 Dental Materials Science
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