GC EUROPE Kalore - Manual (Page 9)

9 GC Kalore technical manual
5.1 The Importance of Low Polymerization Shrinkage (Stress)
Low shrinkage and low shrinkage stress are important for several reasons. Shrinkage stress occurs
when the resin matrix in composite resins shrinks in volume during polymerization, while the
particles retain their pre-polymerization volume. The resulting stress at the filler and resin matrix
interface remains within the cured composite resin and can lead to early replacement of restorations,
as particles will be lost from the matrix. If shrinkage stress is high and exceeds the initial bond
strength of the restoration, de-bonding may occur at the cavity wall resin interface. this can result
in post-operative sensitivity and marginal leakage. long-term, marginal leakage will often lead to
replacement of the composite restoration. it has also been reported that if both the shrinkage
stress and bond strength are high, tooth deformation and cuspal deflection can occur, and cracks
can form in the tooth structure. We will first review the principles of polymerization shrinkage and
technology used to reduce these.
Figure 3a. Dimethacrylate
resin monomer molecules in
the resin matrix.
Figure 3b. the carbon-
carbon double bond is
broken by the catalyst.
Figure 2. Dimethacrylate resin.
Figure 3c. Dimethacrylate
monomers polymerize,
resulting in polymerization
shrinkage.
5.2 Basic Principles of Shrinkage
Dental resin materials typically use dimethacrylate resin, which has
a methacrylate group at each end of the monomer chain.
methacrylates contain two carbon-carbon double bonds and can
easily form polymers as the double bonds are very reactive (Fig. 2).
During polymerization, the carbon-carbon double bond is broken
by the catalyst, the monomers react with each other to form
polymers, and the distance between the reacting monomers
lessens. While the particles retain their pre-polymerization
volume, the reduced distance between the reacting monomers
results in volume loss due to shrinkage (Fig. 3).