Methods: Three commercial composite resins (Admira,Voco ; Supreme,3M-ESPE ; Carisma, Heraeus Kulzer Gmbh & Co.KG) were used to prepare disk shaped specimens (10 mm x 2 mm) .The specimens were exposed in zero-distance with three different light curing unit (Led1 : Hilux, Ledmax 1 ; Led2: Freelight 2, 3M-ESPE ; QTH : Coltolux 75, Coltane) for 40 seconds. 18 groups and 8 specimens for 1 group of light-cure composite at A1 and A3 shade were used in this study. After curing process the samples are stored in % 100 humadity at 37 Cºfor 24 hours. Surface hardness was determined from top and bottom surfaces of each sample with Vickers hardness tester (Zwick) .
Results: Statistical analyses of the study was made by Kruskal Wallis test and Mann Whitney U test. For all composite samples the light curing units did not show significant difference at top surfaces except Carisma in A1 shade ; QTH shows significiantly better hardness values than others (p<0.05). At bottom surfaces for all composite samples , best Vickers hardness number obtained from botton surfaces when A1 shade Supreme was exposed with Led2 ( Mean 69.75 ± 6.48). Also in A3 shade Led2 show better hardness from other Light Curing Units , especially in Supreme(p <0.05). Led1 shows the worst bottom surfaces hardness value for all shades except Carisma in A3 shade. There is no difference in hardness values for Carisma in A3 shade in light curing units tested.
Conclusion: The type and the shade of the resin influences the depth of the cure for both QTH and LED curing devices.