Effect of Curing Time on Polymerization Rate of Bulk-Fill Composite Resins

The aim of this study was to compare polymerization depth of two bulk-fill and one conventional composite cured for different times.
This in vitro experimental study was conducted on 54 composite samples (2×4×10mm) fabricated of Tetric N-Ceram bulk-fill, x-tra fil bulk-fill, and Grandio conventional composite cured for 20, 30, and 40 seconds. The microhardness of samples was measured at 0.1, 2, 2.5, 3, 3.5, 4, and 4.5mm depths using a Vickers hardness tester. The results were analyzed using ANOVA, t-test, and Tukey’s test.
The x-tra fil, Tetric N-Ceram and Grandio had maximum microhardness at 0.1mm depth after curing for 40 seconds. The microhardness decreased as the depth of composite increased. Microhardness of x-tra fil was higher than that of Tetric N Ceram. By increasing the curing time, the microhardness value of x-tra fil significantly increased up to 2mm depth. In Tetric N-Ceram, by increasing the curing time from 20 to 30 seconds microhardness increased significantly (P The maximum microhardness was obtained for x-tra fil at 0.1mm depth following 40 seconds of curing. Microhardness in deep areas (>2mm depth) depends on the type of composite, curing time and depth. Overall, 20 seconds of curing for x-tra fil and 30 seconds for Tetric N-Ceram seem appropriate