Abstract
The aim of this study was to evaluate Knoop hardness of different shades of a resin cement light-cured directly or through ceramic discs, measured 15 min or 24 h after light exposure, and at different depths. Specimens of a commercial resin cement (Variolink Veneer) in seven shades, were fabricated in an elastomeric mold, covered with a mylar strip, a 0.7 mm thick ceramic disc (IPS e.max Press) was placed and the cement was light-activated for 20 s using a blue LED (Radii-Cal). The cured resin cement specimens were transversely wet-flattened to their middle portion and microhardness (Knoop) values were recorded at 15 min after light exposure and after deionized water storage at 37 ºC for 24 h. Five indentations were made in the cross-sectional area at 100 and 700 μm depths from the top surface. Ten specimens were made for each test conditions. Data were submitted to ANOVA split-plot design (shade, post-cure time, mode of activation and depth), followed by Tukey post hoc test (α=0.05). Significant differences for shade (p<0.0001), mode of activation (p<0.001), post-cure time (p<0.0001) and depth (p<0.0001) were detected. No significant interactions (p>0.05) were found, except for shade x post-cure time (p<0.0045) and mode of activation x post-cure time (p<0.0003). Resin cement shade has a significant effect on Knoop hardness. Indirect activation through a ceramic material reduced significantly Knoop hardness. Hardness Knoop significantly increased after 24 h in all cements shades compared to values obtained after 15 min. Resin cement depth significantly reduced Knoop hardness.
Highlights
Interest in dental ceramics has increased in restorative dentistry, mostly because of the excellent esthetic and mechanical properties of these type products
Previous investigators have reported that intervening restorative ceramics between the light curing unit (LCU) and resin cement might promote a significant attenuation of light reaching the photo-curable cement, and compromise the photo-activation of the luting material [7,8]
The mean Knoop hardness of MV0 was significantly greater than all other shades (p
Summary
Interest in dental ceramics has increased in restorative dentistry, mostly because of the excellent esthetic and mechanical properties of these type products. Previous investigators have reported that intervening restorative ceramics between the light curing unit (LCU) and resin cement might promote a significant attenuation of light reaching the photo-curable cement, and compromise the photo-activation of the luting material [7,8]. The level of this attenuation is dependent on characteristics of the restorative material (shade, crystalline structure, thickness and opacity), which may interfere with light transmittance and, as result, produce inadequate cement polymerization [9,10,11]
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