Journal of Dental Research, Vol 70, 137-139, Copyright © 1991 by International & American Associations for Dental Research Online Journals
Effect of cooling rate on leucite volume fraction in dental porcelains
J. R. Mackert Jr and A. L. Evans
Division of Dental Materials, School of Dentistry, Medical College of Georgia, Augusta 30912-1264.
Prasad et al. (1988) have shown that slow cooling of dental porcelain
produces increases in thermal expansion sufficient to make a compatible
metal-porcelain system incompatible. The present study was undertaken to
determine whether the increase in porcelain thermal expansion might be
attributable to crystallization of additional leucite during slow cooling
of the porcelain. Eight x-ray diffraction specimens for each of six
commercial dental porcelains and for the Component No. 1 frit of the
Weinstein and Weinstein (1962) and Weinstein et al. (1962) patents were
fabricated and divided into two groups. Specimens in the first group
(termed fast-cooled) were cooled in the conventional manner by removing
them from the furnace at the maximum firing temperature immediately into
room air. Specimens in the second group (termed slow-cooled) were cooled
slowly by interrupting power to the furnace muffle and allowing them to
cool inside the closed furnace. Quantitative x-ray diffraction was
performed on the fast- and slow-cooled porcelain specimens with standards
containing leucite volume fractions of 0.111, 0.223, 0.334, and 0.445.
Unpaired, one-tailed t tests were performed on the fast- and slow-cool
data, and a significant increase (p less than 0.05) in the amount of
leucite (as a function of the slow cooling) was found for each of the
porcelains. The increases in the leucite volume fractions resulting from
the slow cooling ranged from a low of 8.5% to a high of 55.8%, with an
average increase of 26.9%.(ABSTRACT TRUNCATED AT 250 WORDS)
