Factors influencing the microhardness of a microhybrid composite

This study investigated how different photocuring units, exposure times, and ethanol storage affected the depth of cure in a microhybrid composite. Forty composite specimens (each with a depth of 4 mm) were prepared and divided randomly into four groups (n = 10) to receive treatment from a quartz-tungstenhalogen (QTH) curing unit (400 mW/cm2) or a light-emitting-diode (LED) curing unit (180 mW/cm2). The specimens were photocured for either 20 or 40 seconds and stored in the dark for 24 hours at room temperature. Knoop hardness was measured by making three indentations at each depth interval of 1 mm (up to 4 mm) with a 50 g load for 30 seconds. The specimens were stored in ethanol for 24 hours; at that time, hardness was measured again. Data were submitted to three-way ANOVA, Tukey's test, and Student's t-test (p < 0.05). Statistical analysis revealed that hardness was significantly affected by depth, exposure time, and storage in ethanol (p < 0.001). No differences were observed between the curing units tested.