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KMID : 0362420000380050575
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Journal of Korean Academy of Prosthodontics
2000 Volume.38 No. 5 p.575 ~ p.582
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FLEXURE STRENGTH AND MICROSTRUCTURE OF IPS EMPRESS 2 GLASS-CERAMIC ON HEAT PRESSING AND HEAT TREATMENTS
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Oh Sang-Chun
Dong Jin-Keun
Luthy Heinz
Scharer Pater
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Abstract
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This investigation was designed to determine whether heat-pressing and/or simulated heat treatments affected the flexure strength and the microstructure of the lithium disilicate glassceramic in the IPS Empress 2 system. Four groups of the specimens were prepared as follows group 1 - as-received material ; group 2 - heat-pressed material ; group 3 - heat pressed and simulated initial heat-treated material ; group 4 - heat-pressed and the simulated heat-treated material with full firings for a final restoration. The three-point bending test and the scanning electron microscope (SEM) analysis was conducted for the purpose of this study. The flexure strength of group. 2 was significantly higher than that of group 1. However, there were no significant differences in strength among group 2, 3, and 4, and between group 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed the closely packed, multi-directionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals of the heat-pressed materials (group 2, 3, and.4) were a little denser and about two times bigger than those of the as-received material (group 1). This change of microstructure is more obviously exhibited particularly between group 1 and 2. However, there was no a marked difference among group 2, 3, and 4 after the heat pressing procedure. Although there were significant increase of the strength and some changes of the microstructure after the heat-pressing operation, the conr bination of the heat-pressing and the simulated subsequent heat treatments did not produce the increase of strength of IPS Empress 2 glass-ceramic.
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KEYWORD
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IPS Empress 2 system, Lithium disilicate glass-ceramic, Heat-pressing procedure, Simulated subsequent heat treatments, Flexure strength, Microstructure
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