Correlation between depth of cure and surface hardness of a light-activated resin

Microfilled test specimens were polymerized for 40 s with 10 different curing units. The specimens were stored for 7 days at 36 +/- 0.5 degrees C, and then the hardness of the surface was measured. The depth of cure of the 10 units was also measured, but no correlation was found between surface hardness and depth of cure. Even inferior curing units were able to polymerize the surface just as effectively as good light sources. The conclusion is that one cannot use the surface hardness of an irradiated resin to assess the quality of a curing unit.