Journal of Dental Research, Vol 68, 1313-1315, Copyright © 1989 by International & American Associations for Dental Research Online Journals
The effect of thermal history on porcelain expansion behavior
C. W. Fairhurst, D. T. Hashinger and S. W. Twiggs
Department of Restorative Dentistry, School of Dentistry, Medical College of Georgia, Augusta 30912.
Porcelain-fused-to-metal restorations are fixed several hundred degrees
above the glass-transition temperature and cooled rapidly through the
glass-transition temperature range. Thermal expansion data from room
temperature to above the glass-transition temperature range are important
for the thermal expansion of the porcelain to be matched to the alloy. The
effect of heating rate during measurement of thermal expansion was
determined for NBS SRM 710 glass and four commercial opaque and body
porcelain products. Thermal expansion data were obtained at heating rates
of from 3 to 30 degrees C/min after the porcelain was cooled at the same
rate. By use of the Moynihan equation (where Tg systematically increases in
temperature with an increase in cooling/heating rate), the glass-transition
temperatures (Tg) derived from these data were shown to be related to the
heating rate.
