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Abstract
The aim of this study was to evaluate the free (unrestricted)
polymerization shrinkage of three composite materials using a water
dilatometer. The inward intercuspal deflection of MOD cavities in upper
maxillary premolars was examined under the microscope with a micrometer
scale after 15 minutes and after one month storage in distilled water. The
microleakage of the cuspal deflection specimens after one month storage in
distilled water was assessed by dye penetration.
The results of this study showed that conventional hybrid composite
exhibited the highest significant volumetric polymerization shrinkage % and
intercuspal deflection after 15 minutes. No significant difference was
observed in reduced shrinkage hybrid composite and nanofilled hybrid
composite in volumetric polymerization shrinkage and intercuspal deflection
after 15 minutes.
The inward cuspal deflection after one month storage in distilled
water didn’t show any significant differences in the mean cuspal deflection of
any of the three materials under investigation, although there is a slight
reduction in intercuspal deflection.
The leakage results showed that there was no difference between the
three materials.
There was a direct correlation between leakage scores and cuspal
deflection in the three materials after one month storage in distilled waterfrom the results of this study the following conclusions could be drawn:
1) The formulation of composite resin as well as the co-monomer ratio
in its matrix dramatically control the polymerization shrinkage,
intercuspal deflection and marginal leakage.
2) Filler loading, particle size and size distribution in nanohybrid
composites enhance its marginal seal.
3) The incorporation of prepolymers decisively shares in the reduction
of intercuspal deflection of reduced shrinkage composite.