Abstract
The aim of this study was to evaluate the Knoop hardness after 15 min and 24 h of different shades of a dual-cured resin-based cement after indirect photoactivation (ceramic restoration) with 2 light-curing units (LCUs). The resin cement Variolink II (Ivoclar Vivadent) shade XL, A2, A3 and opaque were mixed with the catalyst paste and inserted into a black Teflon mold (5 mm diameter x 1 mm high). A transparent strip was placed over the mold and a ceramic disc (Duceram Plus, shade A3) was positioned over the resin cement. Light-activation was performed through the ceramic for 40 s using quartz-tungsten-halogen (QTH) (XL 2500; 3M ESPE) or light-emitting diode (LED) (Ultrablue Is, DMC) LCUs with power density of 615 and 610 mW/cm(2), respectively. The Koop hardness was measured using a microhardness tester HMV 2 (Shimadzu) after 15 min or 24 h. Four indentations were made in each specimen. Data were subjected to ANOVA and Tukey's test (alpha=0.05). The QTH LCU provided significantly higher (p<0.05) KHN values than the LED LCU. When the post-cure times were compared for the same shade, QTH and LED at 24 h provided significantly higher (p<0.05) KHN values than at 15 min. It may be concluded that the Knoop hardness was generally dependent on the LCU and post-cure time. The opaque shade of the resin cement showed lower Knoop hardness than the other shades for both LCUs and post-cure times.
Highlights
Resin-based luting cements have been recommended for the cementation of ceramic inlays [1]
The curing of the resin cement might be influenced by the light absorption and dispersion within the cement, shade, chemical composition, filler particle size the power density delivered by the curing unit and the irradiation time [3,4,5,6]
This study evaluated the Knoop hardness values after 15 min and 24 h of different shades of a dual-cured resin cement after indirect photoactivation with 2 light-curing units (LCUs)
Summary
Resin-based luting cements have been recommended for the cementation of ceramic inlays [1]. The light attenuation effect promoted by ceramics might reduce the amount of light reaching the bottom of the cavity, and compromise the photoactivation of the luting material [10]. The degree of this attenuation is dependent on the characteristics of the restorative material, shade, opacity and thickness, which interfere with light transmittance and, as a result, the polymerization process [4,6,8,10,11]. The combination of scattering, reflecting and absorbing properties at the outer surface of the intervening material may explain the reduction in the incident light [12]
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