Optimal depth of cure for nanohybrid resin composite using quartz tungsten halogen and new high intensity light-emitting diode curing units.

This study sought to evaluate the effects of quartz tungsten halogen (QTH) and light-emitting diode (LED) photocuring units on the degree of conversion (DC) and surface microhardness of a resin composite that had been cured for optimal depth of cure (DoC) assessment. Two hundred and forty cylindrical specimens (4.0 mm in diameter, 2.0-4.0 mm thick) of shade A2 resin composite were prepared and cured with either a QTH or an LED. The DC and top and bottom surface hardness were recorded, and data were analyzed using 2-way ANOVA, Tukey's test, t-test (α = 0.05) and linear regression analysis. The results showed that surface microhardness values and DC were affected by light intensity (P < 0.01), and resin composite thickness (2, 3, and 4 mm) (P < 0.01). Resin composite polymerized by the QTH had an optimal DoC of 3 mm, compared to 4 mm for the LED.