Introduction: In dental prosthetics, a combination of porcelain masses and stellite alloys can be used, which meets the functional and aesthetic requirements of dental substitutes. There are several types of porcelain masses known; the samples used in the practical part are made from leucite dental porcelain, which is the most commonly used porcelain mass in dentistry. The dental porcelain mass, which is in the form of a powder, is mixed with a porcelain mixing liquid into a homogenous mixture and applied with a brush to a construction, which has been previously prepared in accordance with the alloy manufacturer's instructions. The process of sintering is performed at temperatures between 700°C and 1000°C, thus merging into a solid form, appropriate for dental prosthetics. Due to the complexity of both the layering and the process of modeling the appropriate anatomical shape of the teeth, it is necessary to apply, sinter, and grind the porcelain mass several times. In this case, when heated to high temperatures and grinded with grinding tools, a number of microstructural changes can occur in the porcelain, and these changes decisively affect its mechanism. Purpose: The purpose of this diploma work was to observe the microstructure of the dental porcelain with an optical microscope, after repeated application, grinding and technological sintering process. Using a spectrophotometer, we also analyzed the effect of sintering on the color change of the dental porcelain. Methods: The practical part of the diploma work includes the modelling of the samples and the conducting of tests. The metal base was a square plate with the surface of 10 mm² and the thickness of 1 mm. It was made from an alloy used for the production of fixed prosthetic structures, which meets the requirements for biocompatibility of materials and compatibility of the materials with the dental porcelain, a result of which is a functional and aesthetic prosthetic replacement. We applied a layer of porcelain mass to every sample, sintered it in a muffle furnace and grinded it with grinding tools. We divided the samples into three groups – A, B and C – each of the groups consisted of four samples. In group A, we repeated the cycle three times, in group B seven times, and in group C twelve times. Using a spectrophotometer, we studied whether repeating the cycle multiple times affects the color change of the dental porcelain mass. We also examined the microstructure of the porcelain mass on two samples from each group. We calculated the percentage of porosity of three chosen points in the layer of the porcelain mass, and calculated an average applicable to each sample. Results: We used a spectrophotometer to measure the color of every sample. The results showed that the color of the samples in group C significantly deviates from the base color. Using an optical and an electron microscope, we also examined the microstructure of the samples. We analyzed the influence of sintering conditions on porosity levels. The analysis showed that the percentage of porosity of the samples was higher in group C than in group A. Discussion and conclusion: The aim of the analysis was to determine whether repeated application of the porcelain mass, sintering and grinding affect the microstructure and the color of the porcelain mass. Color B3 was measured in three of the four samples after three applications of the porcelain mass, sintering and grinding (group A). After twelve applications of the porcelain mass, sintering and grinding (group C), color B3 was measured in only one of the four samples. Analyzing the micro images of the samples, we discovered that the pore size of the samples in group A was larger than of those in group C. The percentages of porosity of the samples in group C were approximately 0.50 % higher than of those in group A. It can be concluded that repeated application of the porcelain mass, sintering and grinding all affect the porosity and the color of the dental porcelain mass.
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