Effect of preliminary irradiation on depth of cure and hardness of a veneering composite.

This study evaluated the effect of preliminary irradiation on the depth of cure and Knoop hardness of a veneering composite. The composite was filled into a mold, and irradiated with different irradiation duration or irradiance. After removing the mold, the depth of cure was measured, and the Knoop hardness number at each depth was determined and statistically analyzed using Mann-Whitney U test. Depth of cure of the composite polymerized by the Sublite S unit with a distance of 15 cm for 30 or 60 s was less than 2.0 mm. The Knoop hardness number of the group polymerized by the Hyper LII unit without preliminary irradiation and the group polymerized by the Sublite S unit with a distance of 3 cm was higher than that of the group polymerized by the Sublite S unit for 90 s or the group polymerized by the Solidilite unit, respectively, even though the depth of cure for these four groups was higher than 2 mm. Preliminary irradiation with long duration and low irradiance caused a low degree of polymerization, which is probably effective in enhancing the bond strength between veneering composite and cast framework.