ANALYSIS OF POLYMERIZATION CONTRACTION IN COMPOSITES

There is mounting clinical and laboratory evidence that the flexure of
the dental crown following intracoronal composite shrinkage may be
related to a number of clinical and biological phenomena, including early
dentin bond failure, crack initiation and propagation, and possibly
post-operative symptoms. A major goal of this proposal is the
determination of the extent and possible clinical significance of these
effects in an in vitro experimental model with servohydraulic control and
direct strain read out from intact and restored human teeth. The
hypothesis to be tested is that polymerization contraction of composite
restorative materials results in decreased longevity of the restoration
due to internal stress development, early dentin bond failure,
alterations in occlusal contacts, and crack initiation and propagation of
the natural tooth structure. The biomechanics of composite
polymerization kinetics and its effects on tooth structure will be
investigated by: 1) strain gage characterization of polymerization
contraction strain and stress, 2) evaluation of the deformation of the
composite restored tooth through strain gage measurement, 3) evaluation
of the response of the composite restored tooth during simulated occlusal
loading in an artificial mouth and 4) validated finite element analysis
of the restored tooth complex. It is hoped that these studies will
increase the knowledge base of the biomechanical interactions internally,
at significant boundaries and on the surface of the restored tooth
complex. From this, new criteria in materials development can be
determined and a sounder basis for materials choice, treatment planning,
and fabrication of intracoronal restorations can be developed.