Abstract
This study investigated potential variations in polymerisation of light- and dual-cured (LC and DC) resin cements photoactivated through four CAD/CAM restorative materials as a function of substrate thickness. Four CAD/CAM materials [two resin composites CeraSmart (CS) and Grandio Blocs (GB); a polymer infiltrated ceramic Vita Enamic (VE) and a feldspathic ceramic Vita Mark II (VM)], with five thicknesses (0.5, 1, 1.5, 2, and 2.5mm) were prepared and their optical characteristics measured. 1mm discs of LC and DC resin cement (Variolink® Esthetic, Ivoclar AG) were photoactivated through each specimen thickness. After 1h post-cure, polymerisation efficiency was determined by degree of conversion (DC%) and Martens hardness (HM). Interactions between materials, thicknesses and properties were analysed by linear regressions, two-way ANOVA and one-way ANOVA followed by post hoc multiple comparisons (α=0.05). All substrates of 0.5- and 1.0-mm thickness transmitted sufficiently high peak irradiances at around 455nm: (It = 588-819mW/cm2) with translucency parameter TP =21.14 - 10.7; ranked: CS>GB =VM>VE. However, increasing the substrate thickness (1.5-2.5mm) reduced energy delivery to the luting cements (4 - 2.8J/cm2). Consequently, as their thicknesses increased beyond 1.5mm, HM of the cement discs differed significantly between the substrates. But there were only slight reduction of DC% in LC cements and DC cement discs were not affected. Photoactivating light-cured Ivocerin™ containing cement through feldspathic ceramics and polymer-infiltrated ceramics achieved greater early hardness results than dual-cured type, irrespective of substrate thickness (0.5 - 2.5mm). However, only 0.5 and 1mm-thick resin composites showed similar outcome (LC>DC). Therefore, for cases requiring early hardness development, appropriate cement selection for each substrate material is recommended.
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