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

Background and Aim: 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. Materials and Methods: 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). Results: 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). Conclusion: 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.