LED and halogen lights: effect of ceramic thickness and shade on curing luting resin

The purpose of this study was to measure and compare the hardness of a light-cured luting resin cured under different shades and thicknesses of porcelain with a halogen and a light-emitting diode (LED) light. Square (11 mm x 11 mm) specimens of a commercially available porcelain with thicknesses of 1 mm and 2 mm were fabricated. Two shades of porcelain--A1 representing a high-value, low-chroma porcelain and C4 representing a low-value, high-chroma porcelain--were used to fabricate specimens. Composite luting resin, 0.5 mm in thickness, was placed under each porcelain specimen and light-cured for 30 or 60 seconds with LED or halogen light. The degree of polymerization of resin cement was determined by measuring the microhardness. The control group in this study was a 0.5-mm composite luting resin cured under clear Mylar matrix. No significant differences were recorded between surface hardness of control subgroups and LED subgroups cured for 30 or 60 seconds. A lower hardness value was recorded for 2-mm C4 porcelain cured for 30 and 60 seconds with the halogen light. Although a cumulative comparison of surface hardness revealed similar results for both lights, the LED light provided more consistent results than the halogen light.