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Effect of lithium disilicate veneers of different thickness on the degree of conversion and microhardness of a light-curing and a dual-curing cement
Full text linkPurpose: Various materials and systems for bonding lithium disilicate to the tooth substrate are available to clinicians, who can adapt the materials to each clinical situation to maximize the performance of indirect esthetic restorations. This study aimed to evaluate the degree of conversion (DC) and the microhardness (MH) of a dual-curing and a light-curing cement under lithium disilicate discs of different thicknesses. Materials and Methods: A total of 48 lithium disilicate (IPS e.max CAD, Ivoclar Vivadent) samples were prepared and divided into three groups (n = 16) according to the thickness (group A was 0.6 mm; group B was 1.0 mm; group C was 1.5 mm). Each group was further divided into two subgroups (n = 8) according to the resin cement employed, NX3 (Kerr) or Choice 2 (Bisco). A standardized quantity of cement was placed on the sample, and DC was evaluated with an attenuated total reflectance Fourier transformed infrared spectrophotometer (Nicolet IS10, Thermo Scientific). Twenty-four hours after DC was established, Vickers test was performed on the cement with a microindentometer (Leica Microsystems). Results were statistically analyzed with analysis of variance test and significance set at P < .05. Results: Statistical analysis showed cement type had a significant influence (P = .005) on DC. MH results were influenced by thicknesses only between 0.6 and 1.5 mm when light-cured cement was employed. Conclusion: The light-curing and the dualcuring cements reached comparable DCs between 0.6 and 1.5 mm. However, the light-curing resin showed a higher DC and MH
NMR Reinvestigation of the Caffeine–Chlorogenate Complex in Aqueous Solution and in Coffee Brews
No full textCaffeine complexation by chlorogenic acid (3-caffeoylquinic acid, CAS Number [327-97-9]) in aqueous solution as well as caffeine-chlorogenate complex in freshly prepared coffee brews have been investigated by high-resolution 1 H-NMR. Caffeine and chlorogenic acid self-associations have also been studied and self-association constants have been determined resorting to both classical isodesmic model and a recently introduced method of data analysis able to provide also the critical aggregation concentration (cac). Furthermore, caffeine-chlorogenate association constant was measured. For the caffeine, the average value of the self-association constant determined by isodesmic model ( K i = 7.6 ± 0.5 M −1 ) is in good agreement with the average value ( K a = 10 ± 1.8 M −1 ) determined with the method which permits the determination of the cac (8.43 ± 0.05 mM). Chlorogenic acid shows a slight decreased tendency to aggregation with a lower average value of association constants ( K i = 2.8 ± 0.6 M −1 ; K a = 3.4 ± 0.6 M −1 ) and a critical concentration equal to 24 ± 1 mM. The value of the association constant of the caffeine-chlorogenate complex (30 ± 4 M −1 ) is compatible with previous studies and within the typical range of reported association constants for other caffeine-polyphenol complexes. Structural features of the complex have also been investigated, and the complex conformation has been rediscussed. Caffeine chemical shifts comparison (monomeric, complexed, coffee brews) clearly indicates a significant amount of caffeine is complexed in beverage real system, being chlorogenate ions the main complexing agents
Interactions in iodinated contrast media solutions Part 1. A thermodynamic study
No full textContrast media are synthetic molecules often characterized by the presence of heavy atoms, such as iodine, widely used in diagnostic studies. In the framework of a study on the physico-chemical of non-ionic contrast media (NICM), this study reports the calorimetric data for a characterization of the thermodynamic behavior of the aqueous solutions of three NICMs, namely, iopamidol, iomeprol, and iopromide, characterized by the presence of three iodine atoms in the benzene ring. Hydrophilicity is provided by three side arms with polar groups. Here, the results of a calorimetric investigation on the heat of dilution of iopamidol, iomeprol, and iopromide and on iomeprol–iopamidol mixture are illustrated. Despite the very similar chemical structures, the dilution process of iopamidol and iopromide was found exothermic, while an endothermic dilution is shown by iomeprol. The results are discussed in terms of the few other literature data and on the basis of structural and conformational properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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