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Abstract
One common test of single-unit restorations involves applying loads to clinically
realistic specimens through spherical indenters, or equivalently, loading curved incisal
edges against flat compression platens. As knowledge has become available regarding
clinical failure mechanisms and the behavior of in vitro tests, it is possible to
constructively question the clinical validity of such failure testing and to move
toward developing more relevant test methods.
This article reviewed characteristics of the traditional load-to-failure test, contrasted
these with characteristics of clinical failure for all-ceramic restorations, and sought
to explain the discrepancies. Literature regarding intraoral conditions was reviewed
to develop an understanding of how laboratory testing could be revised. Variables
considered to be important in simulating clinical conditions were described, along
with their recent laboratory evaluation.
Traditional fracture tests of single unit all-ceramic prostheses are inappropriate,
because they do not create failure mechanisms seen in retrieved clinical specimens.
Validated tests are needed to elucidate the role(s) that cement systems, bonding,
occlusion, and even metal copings play in the success of fixed prostheses and to make
meaningful comparisons possible among novel ceramic and metal substructures. Research
over the past 6 years has shown that crack systems mimicking clinical failure can
be produced in all-ceramic restorations under appropriate conditions.