Abstract
This study evaluated: I) the effect of photo-activation through ceramics on the degree of conversion (DC) and on the Knoop hardness (KHN) of light- and dual-cured resin cements; and II) two different protocols for obtaining the spectra of uncured materials, to determine the DC of a dual-cured resin cement. Thin films of cements were photo-activated through ceramics [feldspathic porcelain (FP); lithium disilicate glass-ceramics of low translucency (e.max-LT), medium opacity (e.max-MO) and high translucency (e.max-HT); glass-infiltrated alumina composite (IC) and polycrystalline zirconia (ZR)] with thicknesses of 1.5 and 2.0 mm. DC was analyzed by Fourier transform infrared (FTIR) spectroscopy. Two protocols were used to obtain the spectra of the uncured materials: I) base and catalyst pastes were mixed, and II) thin films of base and catalyst pastes were obtained separately, and an average was obtained. KHN assessment was performed with cylindrical specimens. The results were analyzed by ANOVA and Tukey's test (α= 0.05). The light-cured cement showed higher DC (61.9%) than the dual-cured cement (55.7%). The DC varied as follows: FP (65.4%), e.max-HT (65.1%), e.max-LT (61.8%), e.max-MO (60.9%), ZR (54.8%), and IC (44.9%). The light-cured cement showed lower KHN (22.0) than the dual-cured (25.6) cement. The cements cured under 1.5 mm spacers showed higher KHN (26.2) than when polymerized under 2.0 mm ceramics (21.3). Regarding the two protocols, there were significant differences only in three groups. Thus, both methods can be considered appropriate. The physical and mechanical properties of resin cements may be affected by the thickness and microstructure of the ceramic material interposed during photo-activation.
Highlights
All-ceramic restorations have become popular because of their excellent esthetics, high color stability, wear resistance, and biocompatibility.[1,2] Even though the mechanical and optical properties of the ceramic materials are important, many variables may contribute to the predictability and clinical longevity of all-ceramic restorations, including the adhesive and luting system used, the curing mechanism, the light-curing unit, and the microstructure and thickness of the ceramic.[3]Resin cements are necessary to bond porcelain and glass-ceramic restorations to ensure high strength,[4] better esthetics and longer clinical survival.[5]
The objectives of this study were: I. to evaluate the effect of photo-activation through different ceramic spacers of 1.5 and 2.0 mm thickness on the degree of conversion (DC) and Knoop hardness number (KHN) of light- and dual-cured resin cements, and II.to compare two different protocols for obtaining the initial spectra of the uncured materials, to determine the DC of a dual-cured resin cement
Significant differences for DC were observed for the luting cement (p < 0.001) and the ceramic sys
Summary
All-ceramic restorations have become popular because of their excellent esthetics, high color stability, wear resistance, and biocompatibility.[1,2] Even though the mechanical and optical properties of the ceramic materials are important, many variables may contribute to the predictability and clinical longevity of all-ceramic restorations, including the adhesive and luting system used, the curing mechanism, the light-curing unit, and the microstructure and thickness of the ceramic.[3]. Resin cements are necessary to bond porcelain and glass-ceramic restorations to ensure high strength,[4] better esthetics and longer clinical survival.[5] In some situations, lightcured resin cements have been indicated, because of their color stability and longer working time.[6] their maximum degree of conversion (DC) cannot be ensured in situations where light has been attenuated. Some studies have demonstrated that they depend on photo-activation to reach high DC and good mechanical properties.[8,9]
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