Effect of different photoactivation methods on the polymerization depth of a light-activated composite.

This study verified the polymerization depth of the composite Z100 (3M Dental Products) by Knoop Hardness test using four photoactivation methods. Twenty cylindrical specimens (5 mm in diameter by 5 mm in height) were prepared in a metallic mold and photoactivated by one of the four methods: continuous light (520 mW/cm2 for 40 seconds); stepped light (150 mW/cm2 for 10 seconds followed by 520 mW/cm2 for 30 seconds); intermittent light (cycle of 1 second, 1/2 second with the light on and 1/2 second with the light off for 60 seconds at 520 mW/cm2) and Xenon plasma are (1370 mW/cm2 for 3 seconds). Knoop hardness measurements were obtained on the surface, at the depths of 1.5 mm, 2.5 mm, 4.0 mm and at the bottom area by the HMV-2000 microhardness, with a load of 50 grams for 30 seconds. Twenty-five indentations were performed in each sample, and a total of five samples were prepared for each photoactivation method. The obtained values were submitted to ANOVA and Tukey's test at the 5% significance level. The results indicated that (1) for the continuous light method, the values of hardness were statistically superior in the surface area when compared to other areas. For the other methods, there were no statistical differences between the surface area and 1.5 mm; (2) the continuous and stepped light methods showed the highest mean Knoop Hardness Number in all areas; (3) the Xenon plasma are method was not statistically different from continuous and stepped light ones on the surface at 1.5 mm and 2.5 mm of depth. However, a great decrease in hardness was observed in the deeper areas; (4) the intermittent light method showed intermediate results.