Microhardness of nanofilled composite resin light-cured by LED or QTH units with different times

Aim: To evaluate the influence of light-curing units and light-curing time on the microhardness of a nanofilled composite resin. Methods: Forty-five composite resin (Z350 - 3M) specimens were randomly prepared using Teflon ring molds (4.0 mm internal diameter and 2 mm depth) and divided into nine experimental groups (n=5): three polymerization units (conventional - 450 mW/ cm2; 2nd generation LED - 1100 mW/cm2; and 3rd generation LED - 700 mW/cm2) and three lightcuring times (20 s, 40 s, and 60 s). All specimens were polymerized with the light-curing tip positioned 8 mm far from the top surface of the specimen. After 24 h, Knoop microhardness measurements were made on the top and bottom surfaces of the specimen, with a load of 10 g for 10 s. Five indentations were made on each surface. All results were analyzed statistically by subdivided parcel ANOVA (Split-Plot) and Tukey&apos;s tests (p<0.05). Results: There were no statistically significant differences for the polymerization unit and light-curing time factors in either top or bottom surface. For all experimental conditions, the top surfaces showed greater hardness than the bottom surfaces (p