The degree of microleakage between a restoration and the cavity wall is difficult to quantify objectively. A silver-staining method is used and compared to the radioisotope method with results that indicate a superior definition and more accurate evaluation of microleakage. In addition to the accuracy, two advantages are presented: (1) scoring of the leakage can be refined and divided into more precise numbers, and (2) teeth can be observed directly in a microscope without resorting to the indirect interpretation of film or photograph.
Pin-and-disc wear and Knoop Hardness measurements were made on three commercial glass-ionomer cements having slightly different compositions. The specific objective was to determine whether these cements have potential for use in posterior teeth, and, if not, what modifications in composition and structure would be appropriate to enhance their performance. The specimens were pre-conditioned in air, water, or lactic acid at 37 degrees C for one week prior to being wear-tested. Although differences among the samples were noted, some common trends were observed. From changes in hardness, before and after storage, two opposing trends were observed. One trend involved continued cross-linking and possible dehydration, resulting in a substantial increase in hardness. The other trend involved softening from penetrant liquid absorption and a concomitant decrease in hardness. The wear resistances compared favorably with those for resin-based composites except for the lactic-acid-stored specimens, for which changes in microstructure were revealed by SEM. All specimens were very brittle, and catastrophic failure during wear was frequent. Although our conclusion is that glass-ionomer cements with composition similar to those evaluated here are not acceptable for posterior occlusal application, some compositional changes may enhance their performance in stress-bearing applications.
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