Influence of the interposition of ceramic spacers on the degree of conversion and the hardness of resin cements

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 photoactivated 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.

Degree of conversion of a flowable composite light-activated through ceramics of different shades and thicknesses

“…Although the resin composite evaluated in the present study is indicated for the cementation of ceramic restorations, other light-activated materials (i.e. the so called "veneer cements") have been indicated for the cementation of thin veneers 10 and also have shown good DC results when light-activated through ceramic materials [13][14] . As seen in Table 2, the similar results for DC in most groups indicate that the shade and thickness of the evaluated interposed ceramic veneers did not influence the polymerization of the flowable resin composite.…”

“…More opaque ceramics tend to absorb more light, which would decrease the DC of light-cured resin-based materials 20 . It has been reported that the DC of resin-based materials may change considerably as function of the type and opacity of the interposing ceramics [13][14] . Another aspect to be addressed is that one single shade of flowable resin composite was evaluated.…”

“…This clinical advantage, however, should not be the determinant factor for material choice in veneer cementation due to the possible attenuating effect provided by thickness, opacity and shades [11][12][13] . Additionally, the type and microstructure of the interposing ceramic material are significant factors in the properties of polymerized luting materials 14 . In general, the use of these light-activated cements should be limited to some clinical situations such as inlays, veneers and onlays, in which the thickness and shade of restoration do not affect the ability of light to reach and activate the cement 15 .…”

“…In general, the use of these light-activated cements should be limited to some clinical situations such as inlays, veneers and onlays, in which the thickness and shade of restoration do not affect the ability of light to reach and activate the cement 15 . Considering the light-activated resin cements for veneers and onlays cementation, the polymerization quality is related to several factors such as photo-activation light source, irradiance, irradiation time, material composition and light attenuation caused by ceramic 11,[13][14][16][17][18] . It was observed that the transmittance of light through ceramic decreases as function of the material interposed between the light source and the resin cement 19 .…”

Effects of layering technique on the shade of resin overlays and the microhardness of dual cure resin cement

“…2,3,4 The hardness of DCRCs was investigated, and it was reported that the thickness as well as the shade of the resin or ceramic inlays could affect the hardness of the resin cement. 5,6 Esthetics in the posterior region are not as critical as in the anterior region, and the shade guides of many direct resin composite systems recommend using a single dentin layer or dentin and enamel layers for posterior restorations. Some indirect resin composite systems are composed of dentin, enamel, and translucent layers, and manufacturers recommend Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript.…”