An investigation on fatigue, fracture resistance, and color properties of aesthetic CAD/CAM monolithic ceramics

Objectives To evaluate and compare fracture resistance, translucency, and color reproducibility, as well as the effect of aging on the fracture load and color stability of novel monolithic CAD/CAM ceramics. Materials and methods One hundred crowns of uniform thickness were milled from five ceramic blocks (n = 20): partially crystallized lithium disilicate (PLD) and fully crystallized lithium disilicate (FLD), lithium metasilicate (LMS), 4Y-TZP (SMZ), and 5Y-TZP (UMZ) monolithic zirconia. PLD crowns were glazed, LMS was fired, and FLD was polished. SMZ and UMZ crowns were sintered and polished. Crowns were adhesively cemented to epoxy dies. Half of the crowns (n = 10) were subjected to 1.200.000 load cycles with thermal cycling. Color space values L, a, b defined by the Commission Internationale de l´Eclairage (CIELAB) were measured before and after aging, and (∆E) was calculated. Both aged and non-aged specimens were loaded until fracture in a universal testing machine and the fracture load was recorded. X-ray diffraction (XRD) and scanning electron microscope (SEM) fractographic analysis were carried out on fractured fragments of representative samples. For translucency and color reproducibility, 50 rectangular-shaped specimens were fabricated and processed as described previously. Color values were measured over black and white backgrounds, and the translucency parameter (TP) was computed. Using the shade verification mode, (∆E) to shade A3 was calculated. Data were statistically analyzed using one-way and two-way ANOVA, and t-test. Results Aging did not affect fracture resistance significantly (p > 0.05). The highest mean fracture load was obtained for the SMZ and UMZ. A significant color change was observed after aging in all groups. The highest TP was noted for FLD. SMZ and UMZ had the best shade match. Conclusions Zirconia showed higher fracture resistance and color stability than lithium silicate ceramics. Lithium silicate ceramics were more translucent. The experimental FLD demonstrated high translucency. Clinical relevance Tested ceramics showed sufficient stability to withstand masticatory forces. Characterization of final restorations might be mandatory for better color match

The electronic states of U⁴⁺ in U(PO₄)Cl: an example for angular overlap modeling of 5fⁿ systems

Detailed experimental data on UPO₄Cl comprising single-crystal UV/vis/NIR spectra and temperature-dependent magnetic susceptibilities form the basis for the investigation of the electronic structure of the U⁴⁺ cation in UPO₄Cl. For modeling of the observed physical properties the angular overlap model (AOM) was successfully employed. The computations were performed using the newly developed computer program BonnMag. The calculations show that all electronic transitions and the magnetic susceptibility as well as its temperature dependence are well-reproduced within the AOM framework. Using Judd–Ofelt theory BonnMag allows estimation of the relative absorption coefficients of the electronic transitions with reasonable accuracy. Ligand field splitting for states originating from f-electron configurations are determined. Slater–Condon–Shortley parameters and the spin–orbit coupling constant for U⁴⁺ were taken from literature. The good transferability of AOM parameters for U⁴⁺ is confirmed by calculations of the absorption spectra of UP₂O₇ and (U₂O)(PO₄)₂. The effect of variation of the fit parameters is investigated. AOM parameters for U⁴⁺ (5f) are compared to those of the rare-earth elements (4f) and transition metals (3d)

Synthesis, crystal structure and Raman spectrum of K2[(Pt2)(HPO4)4(H2O)2] containing (Pt2)6+ ions

In the crystal structure of the acid platinum phosphate dipotassium di-μ-hydrogenphosphato-bis­[aqua­platinum(III)](Pt—Pt), K2[Pt2(HPO4)4(H2O)2], the (Pt2)6+ dumbbells within the paddle-wheel complex show Pt—Pt distances of 2.4944 (5) and 2.4892 (5) Å. The pottassium ions are seven-fold coordinated by hydrogenphosphate groups. In the crystal, O—H⋯O hydrogen bonds help to establish the packing. The Raman spectrum was recorded

Ag2PdP2O7

Disilver(I) palladium(II) diphosphate, Ag2PdP2O7, is isotypic with Na2PdP2O7. It consists of infinite diphosphato-pallad­ate(II) [Pd(P2O7)2/2]2− ribbons with the PdII ion in an almost square-planar coordination ( symmetry) and the P2O7 group exhibiting 2 symmetry. The [Pd(P2O7)2/2]2− ribbons are linked by distorted [AgO6] octa­hedra. 31P-MAS NMR studies on Ag2PdP2O7 are in accordance with one independent site for phospho­rus; its isotropic chemical shift δiso = 21.5 p.p.m. is similar to that of Pd2P2O7

Sleep-wake sensitive mechanisms of adenosine release in the basal forebrain of rodents : an in vitro study

Adenosine acting in the basal forebrain is a key mediator of sleep homeostasis. Extracellular adenosine concentrations increase during wakefulness, especially during prolonged wakefulness and lead to increased sleep pressure and subsequent rebound sleep. The release of endogenous adenosine during the sleep-wake cycle has mainly been studied in vivo with microdialysis techniques. The biochemical changes that accompany sleep-wake status may be preserved in vitro. We have therefore used adenosine-sensitive biosensors in slices of the basal forebrain (BFB) to study both depolarization-evoked adenosine release and the steady state adenosine tone in rats, mice and hamsters. Adenosine release was evoked by high K+, AMPA, NMDA and mGlu receptor agonists, but not by other transmitters associated with wakefulness such as orexin, histamine or neurotensin. Evoked and basal adenosine release in the BFB in vitro exhibited three key features: the magnitude of each varied systematically with the diurnal time at which the animal was sacrificed; sleep deprivation prior to sacrifice greatly increased both evoked adenosine release and the basal tone; and the enhancement of evoked adenosine release and basal tone resulting from sleep deprivation was reversed by the inducible nitric oxide synthase (iNOS) inhibitor, 1400 W. These data indicate that characteristics of adenosine release recorded in the BFB in vitro reflect those that have been linked in vivo to the homeostatic control of sleep. Our results provide methodologically independent support for a key role for induction of iNOS as a trigger for enhanced adenosine release following sleep deprivation and suggest that this induction may constitute a biochemical memory of this state

Synthesis‐controlled polymorphism and optical properties of phyllosilicate‐analogous borosulfates M[B2(SO4)4] (M = Mg, Co)

Increased synthetic control in borosulfate chemistry leads to the access of various new compounds. Herein, the polymorphism of phyllosilicate-analogous borosulfates is unraveled by adjusting the oleum (65 % SO3) content. The new polymorphs beta-Mg[B-2(SO4)(4)] and alpha-Co[B-2(SO4)(4)] both consist of similar layers of alternating borate and sulfate tetrahedra, but differ in the position of octahedrally coordinated cations. The alpha-modification comprises cations between the layers, whereas in the beta-modification cations are embedded within the layers. With this new synthetic approach, phase-pure compounds of the respective polymorphs alpha-Mg[B-2(SO4)(4)] and beta-Co[B-2(SO4)(4)] were also achieved. Tanabe-Sugano analysis of the Co(2+)polymorphs reveal weak ligand field splitting and give insights into the coordination behavior of the two-dimensional borosulfate anions for the first time. DFT calculations confirmed previous in silico experiments and enabled an assignment of the polymorphs by comparing the total electronic energies. The compounds are characterized by single-crystal XRD, PXRD, FTIR, and UV/Vis/NIR spectroscopy, thermogravimetric analysis (TGA), and density functional theory (DFT) calculations