EVALUATION OF SOME PROPERTIES OF AN OPAQUE PORCELAIN FIRED SIMULTANEOUSLY WITH THE BODY PORCELAIN

Recently, a porcelain-fused-to-metal opaque porcelain was introduced t hat does not require a separate firing before application of the body porcelain. The objective of this study was to determine the properties of this new opaque porcelain and its ability to bond to metal. The pr operties studied included flexural strength, linear firing shrinkage, coefficient of thermal expansion, powder particle size, and ability to bond to body porcelain and dental alloys. Sintering of this opaque po rcelain was complete when fired at 1760 degrees F (960 degrees C) with a linear firing shrinkage of 13.1% +/- 0.2%. No boundary between the opaque and body porcelains could be found with a scanning electron mic roscope after firing at 1760 degrees F (960 degrees C). The mean flexu ral strengths were 99 +/- 7 and 101 +/- 8 MPa respectively, for this o paque porcelain and a conventional opaque porcelain, and were not sign ificantly different as assessed with Student's t-test (p = 0.548). The coefficient of thermal expansion for this opaque porcelain was 13.3 /- 0.2 X 10(-6)/degrees C. Particle size analysis showed a 63% increas e in the particles below 5 mu m for this opaque porcelain and bonding to two alloys was adequate as indicated by its cohesive failure. Simul taneous firing of this special opaque porcelain and body porcelain pro duced satisfactory sintering, strength, and bonding to metal.