Journal of Dental Research, Vol 67, 1086-1091, Copyright © 1988 by International & American Associations for Dental Research Online Journals
Delayed crack development in porcelain due to incompatibility stress
K. J. Anusavice, P. H. Dehoff, A. Gray and R. B. Lee
Department of Dental Biomaterials, College of Dentistry, University of Florida, Gainesville 32610.
Delayed failure of metal-ceramic restorations due to static fatigue can
occur when residual tensile stress is present in porcelain, even in the
absence of intra-oral forces. Fixed-partial-denture (FPD) specimens and
semicircular arch specimens with gapped cross-arch segments were employed
to characterize the potential of two incompatible metal-ceramic systems for
producing delayed crack development and to determine the relative
sensitivity of these test designs as monitors of incompatibility stresses
which resulted from thermal contraction differences between a
nickel-chromium alloy and three experimental porcelains. The arch specimens
were judged to be more suitable for analysis of residual stresses because
of the larger magnitude of gap changes at each procedural change. However,
the FPD specimens exhibited earlier evidence of delayed crack growth in
porcelain when the thermal contraction coefficient of the metal exceeded
that of the porcelain by either 1.7 X 10(-6)/degrees C or 2.2 X
10(-6)/degrees C. For these two states of incompatibility, the agreement
between experimental gap values for the arch specimens and the gap values
predicted from composite strip equations was excellent.
