Effect of Ceramic Interposition and Post-activation Times on Knoop Hardness of Different Shades of Resin Cement

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.

Effect of lithium disilicate ceramic thickness, shade and translucency on transmitted irradiance and knoop microhardness of a light cured luting resin cement

“…Inadequate polymerization of the resin cement results in poor mechanical properties, higher solubility and decreased color stability [14,15]. Many studies have shown that ceramics attenuate light and may compromise the photoactivation of the resin cement [13,16,17]. The ceramic translucency, thickness, shade and crystalline structure are factors that impact the amount of attenuation [16][17][18][19][20][21][22][23].…”

“…Many studies have shown that ceramics attenuate light and may compromise the photoactivation of the resin cement [13,16,17]. The ceramic translucency, thickness, shade and crystalline structure are factors that impact the amount of attenuation [16][17][18][19][20][21][22][23]. Decreased light transmittance decreases the total energy that reaches the composite resin, resulting in inadequate polymerization [13].…”

Evaluation of Dual-Cure Resin Cement Polymerization under Different Types and Thicknesses of Monolithic Zirconia

“…The hardness of the resin was found to decrease as the shade of the cement gets darker in case of direct light exposure [14, 29, 30]. Moreno et al recently evaluated the cement shade effect on microhardness of dual-cure resin cement indirectly light-activated beneath different ceramics and in accordance with the previous study results, they have reported that a specific activation strategy is essential for each cement shade in order to maximize the material hardness [31]. Transparent resin cements enable higher depth of cure and microhardness values due to their capability of absorbing more light than the opaque cements [14, 30–32].…”

Microhardness of resin cements after light activation through various translucencies of monolithic zirconia

“… 31 46 So-called ‘transparent’ shades of resin cement exhibited more light absorption than opaque shades, being associated with increased curing depth and microhardness. 47 In the present study, the ‘transparent’ shades of Variolink N (VL and VD) and the ‘translucent’ shade of RelyX (RL and RD) were used to minimize the impact of shade on the VHN and focused on the effect of the translucency of the zirconia and the post-curing interval.…”