GC EUROPE Kalore - Manual (Page 11)

11 GC Kalore technical manual
5.4 Reducing Polymerization Shrinkage Stress
Polymerization shrinkage stress is the force generated at polymerization. During polymerization,
the bonded composite resin will pull towards the cavity walls as shrinkage occurs. this force is
shrinkage stress. at a given level of shrinkage, the most rigid materials result in the highest stress.
The modulus of elasticity (Young’s modulus) measures the rigidity of a material (its ability to resist
deformation). the higher the modulus of elasticity, the greater the stress. there are several ways to
reduce shrinkage stress, including the following:
Reduce Volumetric Shrinkage
Shrinkage stress can be decreased by reducing volumetric shrinkage, since the greater the
volumetric shrinkage, the greater the force to pull the preparation wall.
Decrease the Modulus of Elasticity
materials with a high modulus of elasticity result in stress build-up at the composite/tooth
interface during polymerization shrinkage. in addition, brittle materials with a high modulus of
elasticity are inefficient buffers for masticatory pressure. in contrast, materials with a low modulus
of elasticity will deform and expand and, consequently, reduce stress at the composite/tooth
interface (Fig. 7).
Increase the Initial Flow of the Material
if the composite resin is flowable, shrinkage will occur at the free surface and lead to a reduction
in shrinkage stress at the composite/tooth interface (Fig. 7).
Figure 7a. Flowable and low modulus composites deform during polymerization.
Shrinkage stress occurs at the free surface; consequently, less shrinkage stress occurs at the cavity walls.
Figure 7b. composites with a high modulus of elasticity.
These can only deform slightly during polymerization. Shrinkage stress will occur at the free surface
and at the composite/tooth interface.