Project: Research project

Project Details


The overall goal of the proposed research is to determine the mechanisms
responsible for the thermally induced changes in coefficient of thermal
expansion that are experienced by dental porcelains and to use the
understanding thus gained to develop porcelains more resistant to such
changes. The development of such thermally stable porcelains would greatly
reduce the tendency for cracking and checking of the dental porcelains
during cooling of porcelain-fused-to-metal restorations, with consequent
reductions in cost, inconvenience, and re-treatment trauma to the dental
patient receiving this type of restoration. The first specific aim is to
measure the effects of multiple firings, isothermal heat treatments, and
different cooling rates on the coefficients of thermal expansion for a
variety of dental porcelains. These measurements will be accomplished in a
conventional differential dilatometer and in a laser dilatometer developed
in the Dental Materials Laboratory at the Medical College of Georgia. The
second specific aim is to determine the mechanisms responsible for
porcelain expansion changes during various heat treatments. The methods
which will be used to discriminate among the possible mechanisms are:
quantitative x-ray diffractometry, high-temperature x-ray diffractometry,
hot-stage scanning electron microscopy, and measurement of the mid-span
deflection of bimaterial porcelain-metal strips in a high rate infrared
bending beam viscometer developed at the Dental Materials Laboratory at the
Medical College of Georgia. Possible mechanisms for thermal instability of
dental porcelains involve the crystallization or dissolution of leucite,
the conversion of leucite to sanidine, the retention of metastable cubic
leucite upon cooling from high temperatures, the decoupling and recoupling
of leucite particles in the glass matrix via microcracking and sintering,
and trapping of various levels of excess volume in the glass matrix owing
to different cooling rates. The development of methods for improving the
thermal stability of porcelain frits is the third specific aim of the
proposed work. The strategies for developing improved porcelain frits
involve reduction or elimination of leucite coupling/decoupling,
stabilization of the leucite fraction, avoidance of metastable cubic
leucite retention upon cooling from the porcelain firing temperature, and
minimization of the effects to structural relaxation of the glass matrix.
StatusNot started


  • National Institutes of Health


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