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

Background and aim: minimizing the polymerization shrinkage of compositeresins is a critical goal in composite restorations. many factors affectpolymerization shrinkage. this study aimed to evaluate the effect of compositeresin shade on its polymerization shrinkage.materials and methods: in this in vitro study, 14 composite discs measuring 1.5×8mm were fabricated from the a2 and wb shades of g-aenial composite resin.composite resin discs were placed in a brass ring bonded to a glass slide. anotherglass slide was placed over it. the samples were light-cured at 750 mw/cm2 lightintensity for 20 seconds. polymerization shrinkage and its strain rate weremeasured for up to 600 seconds after the onset of irradiation by the bonded disctechnique and a linear variable differential transformer machine. data wereanalyzed by independent-sample t-test (p≤0.05).results: the polymerization shrinkage strain at 20 and 600 seconds was notsignificantly different between the wb and a2 shades of g-aenial composite resin.the differences in polymerization shrinkage in each group at 20 and 600 secondswere significant (p<0.000). the difference in the shrinkage rate between the twogroups up to 20 seconds was not significant (p=0.505).conclusion: the polymerization shrinkage of g-aenial composite resin was notaffected by shade. however, in both shades, polymerization shrinkage showed asignificant difference immediately after irradiation and 600 seconds after that.