Influence of water sorption on the shrinkage stresses of dental composites

Introduction. The elimination or reduction of
shrinkage stress generated during polymerisation
is one of the major problems in the development of
dental composites. Sorption of water by resin fillings
in the moist environment of the oral cavity and in
consequence its volume expansion should counteract
the observed shrinkage contraction. Aim of the study.
To evaluate the influence of water sorption in resinbased
materials on polymerization shrinkage stress
generated on the restoration-tooth interface. Material
and methods. The shrinkage stress was measured
immediately after curing. The samples stored in water
were evaluated after 24 h for 7 days and then once a
week up to 90 days. Photoelastic study was performed
on photosensitive epoxy resin plates in Transmission
Polariscope FL200. The study was based on the
analysis of dimension and arrangement of fringes.
Contraction stress was calculated on the basis of
photoelastic theory. In order to measure the water
sorption and its dynamics, the material samples were
weighed on analytical scale in the above mentioned
time intervals. Results. The tested materials during
polymerization generated shrinkage stresses ranging