Objectives: To determine the polymerisation efficiency of three light curing units on two different thickness of different composites

Methods: Three commercial composite resins (Admira,Voco ; Supreme,3M-ESPE ; Carisma,Heraeus Kulzer) were used to prepare disk shaped specimens (10 mm x 2 mm and 10 mm x 3 mm ). All of specimens were light-polymerized for 40 seconds with three different light curing unit (Led1 : Hilux, Ledmax 1 ; Led2: Freelight 2, 3M-ESPE ; QTH : Coltolux 75, Coltane).18 groups and 8 specimens for 1 group of light-cure composite at A1 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. The light curing units did not show any significant difference at top surfaces for all groups. Led1 shows significantly lower hardness values than Led2 and QTH except for 3 mm samples of Carisma at bottom surface. There is no significant difference for all light curing units at 3 mm samples of Carisma. Led2 shows significantly better hardness values than QTH for all 2 mm samples except Ormocer. The best results obtained for bottom surfaces when 2 mm samples of Supreme exposed with Led2 (Mean= 64.40 ± 12.27). Significantly high number of samples exposed with L2 shows the percentage ratio for bottom:top hardness values exceeded % 80 (p<0.01).Also Halogen samples are significantly better than Led1. (p<0.05)

Conclusion: The second generation LED technology shows significantly better depth of cure from QTH lights without some drawbacks like heat transmission and limited effective lifetime .

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