RESUMO
Objective:To examine the polymerization shrinkage stress of three universal hybrid composite resins by photo-elastic analysis.Method:Epoxide resin disks (d=80 mm,h=4 mm) with a cylindrical cavity (d=4 mm) in the middle were prepared.Composite resins of Charisma,TPH Spectrum and Esthet-X were respectively filled in the cavities for the formation of specimens.Eight specimens were made for each resin.The resin specimens were light cured for 40 s by Dentsply QHL75 Curing lite. Polymerization contraction stress was calculated based on the diameter of the isochromatic rings of first order obtained from the diameter of epoxide resin specimen at 1,2,3,4,5,10,20 and 30 min,1,24 and 48 h after curing. The statistical analysis was carried out with the Wilcoxon test.Results:Polymerization contraction stress rised rapidly in the first 10 min after curing. 1 and 24 h after curing the shrinkage stress(MPa) of Charisma were 2.893 6?0.1 and 4.190 4?0.1,while that of Esthet-X were 2.291 7? 0.1 and 3.143 9? 0.3 ,respectively.The shrinkage stress values of TPH spectrum was between those of Charisma and Esthet-X 24 h after curing. 79% specimens showed shrinkage stress releasing during 24 and 48 h after curing.Conclusion:The rates of the shrinkage stress of the three studied resin composites are different.