Effect of Shade on Immediate and Post-Curing Polymerization Shrinkage of Composite Resin

Minimizing the polymerization shrinkage of composite resins is a critical goals in composite restorations. Many factors affect polymerization shrinkage. This study aimed to evaluate the effect of composite resin shade on polymerization shrinkage.

In this in vitro study, 14 composite discs measuring 1.5×8 mm were fabricated. The samples were prepared using the A2 and WB shades of G-aenial composite resin. Composite resin discs were placed in a brass ring bonded to a glass slide. Another glass slide was placed over it. The samples were light-cured at 750 mW/cm2 light intensity for 20 seconds. Polymerization shrinkage (shrinkage re-action) and its strain rate were measured for up to 600 seconds after the onset of irra-diation by the bonded disc technique and a linear variable differential transformer (LDTV) machine. Data were analyzed by independent-sample t-test (P≤0.05).

The polymerization shrinkage strain at 20 and 600 seconds was not significantly different between the WB and A2 shades of G-aenial composite resin. The differences in polymerization shrinkage in each group at 20 and 600 seconds were significant (P<0.000). The difference in the shrinkage rate between the two groups up to 20 seconds was not significant (P=0.505).

The polymerization shrinkage of G-aenial composite resin was not affected by shade. However, in both shades, polymerization shrinkage showed a sig-nificant difference immediately after irradiation and 600 seconds after that.