Hardness of composite resin polymerized with different light-curing units

Introduction: the degree of polymerization depends on the type of light-curing unit. the aim of this study was to compare the hardness of composite resin cured by led and halogen light curing units.methods: in this experimental study, 20 cylindrical samples of tetric ceram composite were prepared. half of them were cured with ultralume 2 led and the other half with astralis 7 halogen light curing unit. in the depths of 0,1,2 and 3 mm from surface, one point in peripheral and one point in central portion were marked ,then the hardness of these points was measured by vickers test . the data was analyzed by a pvalue less than 0.05 considered as significant.results: the mean hardness of samples cured by led was more than halogen group in different depths and this difference was statistically significant in peripheral points (p=.048) but this was not significant in central points (p=0.644). the mean hardness in both groups had a decreasing trend from surface to the deep parts in central and peripheral parts and this was more in the central parts.conclusions: composites cured by led light curing unit showed more hardness in similar depths, besides the hardness of composites in central parts is more than the peripheral ones in both groups.