Curing depths of a universal hybrid and a flowable resin composite cured with quartz tungsten halogen and light-emitting diode units.

• This in vitro study evaluated curing depths of a universal hybrid resin composite with two viscosities (Tetric Ceram and Tetric Flow) after curing with 6 different quartz tungsten halogen and light-emitting diode curing units. Irradiance (light intensity) of the curing units varied between 200 and 700 mW/cm2. The curing units were used for standard, soft-start, or pulse curing. Curing times were 20 and 40 s for standard curing, 3 + 10 s and 3 + 30 s for pulse curing, and 40 s for soft-start. Resin composite specimens, 5 in each group, with a diameter of 4 mm and a height of 6 mm, were made in brass molds and cured from one side at a distance of 6 mm. After 2 weeks, the specimens were ground longitudinally half through the specimen. Curing depth was then determined by measurement of Wallace hardness for each half millimeter starting at 0.5 mm from the top surface. For all curing units and for both resin composites an increased curing time led to statistically significantly higher depth of cure (P < 0.0005). Tetric Flow showed a statistically significantly higher depth of cure than Tetric Ceram (P < 0.0005). All curing units cured more than 2.0 mm of both composites from a distance of 6 mm at 20 s curing time. The value for 40 s was 3.0 mm. The composite closer to the surface than the depth of cure value was equally well cured with all curing units investigated. There was a significant linear correlation between the determined irradiance of the curing units and the depths of cure obtained (20s: r = 0.89, P < 0.025; 40 s: r = 0.91, P < 0.01).

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