Paste opaque porcelains are used in metal-ceramic systems in order to laminate opaque porcelains in thin layers, interrupt the metal color effectively, and enhance workability. We manufactured the paste opaque porcelains using Propylene Glycol (PG) and Butylene Glycol (BG) as a solvent, and compared viscosity, the coefficient of thermal expansion, debonding/crack-initiation strength to metal, SEM observations of the interface between porcelain and metal, and color with those of the commercial products (Duceram Plus, Duceram GmbH; VMK 95, Vita Co.; Noritake EX-3, Noritake Co.) used in the clinical field. The viscosity of test materials was measured using viscometer at 25 o C. The coefficient of thermal expansion and debonding/crack-initiation strength to metal were measured by ISO 9693:1999, and the color was evaluated by a CIELab system. The rheological property of tested materials showed pseudo-plastic behavior. The coefficient of thermal expansion ( 10 -6 K -1 ) of the tested material ranged from 13.3 to 14.3 while debonding/crack-initiation strength (MPa) ranged from 35 to 41. ISO requires debonding/crack-initiation to be over 25 MPa. All test groups adhere effectively onto the metal surface in the SEM observations. And the colors of tested materials were distinguishable from each other despite of having similar shades (A3).
Alkali oxides were added to glass frit in order to lower the firing temperature of dental
porcelain, and the effects of Li2O and B2O3 on the thermal properties and chemical solubility of low-fusing dental porcelain were investigated.
The glass transition temperature(Tg) and softening temperature(Ts) of glass frits were decreased remarkably by adding Li2O, but the coefficient of thermal expansion(CTE) was increased with Li2O. In the case of adding B2O3, the thermal properties were unchanged. Tg of B0L4, B2L4 and B4L4 specimens were lower than 500°C and Ts were lower than 550°C. The chemical solubility of prepared low-fusing dental porcelain with these glass frits were 37.3,
43.9, and 49.2µg·cm-2 respectively. The chemical solubility was increased by adding Li2O and B2O3, but all the results were below 100µg·cm-2 and satisfactory to ISO Standards. Further, the chemical solubility of the commercial low-fusing dental porcelains were 52.6µg·cm-2 for Ceramco Finesse(Clear), 70.8µg·cm-2 for Duceram-LFC(TC) and that of conventional dental porcelain, CeraMax(T-C), was 34.8µg·cm-2.
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