Enamel Remineralization and Crystallization after Fluoride Iontophoresis.

Early caries lesions consist of noncavitated subsurface demineralization caused by the dissolution of hydroxyapatite from the surface to the subsurface area of the enamel. Such lesions cannot be remineralized effectively by the conventional treatment. Thus, there is a need for a noninvasive technique capable of delivering the remineralizing agent to subsurface sites. For this purpose, fluoride iontophoresis (IP) using weak currents has been investigated with some conflicting results and no information on the crystal structure and composition. Because enamel remineralization involves the role of fluid from dentin, the presence of enamel fluid is necessary to determine the repair associated with the physiological condition. This study aimed to investigate structural and compositional characteristics, including the remineralizing effect of 5% sodium fluoride (NaF) IP with different polarities, cathodal iontophoresis (CIP), and anodal iontophoresis (AIP) for the treatment of natural enamel caries under simulated pulpal pressure. A bulk measurement of the crystal structure inside the lesion was first determined using calcium (Ca) K-edge X-ray absorption spectroscopy. IP with both polarities significantly promoted subsurface remineralization. The CIP generated a significant increase in the Ca/phosphorus ratio, and fluoride at the surface lesion significantly correlated with higher mineral density (MD) and more strengthening crystal structure of the lesion volume, while the lesion's MD and other impurities at the lesion surface, mostly the carbonate ions, affected the significant increase in MD with the unchanged structure of the lesion volume after AIP. The CIP of NaF is an ideal method for rapid enamel remineralization and recrystallization of fluoroapatite/fluorohydroxyapatite.

The influence of CeF3 on radiation hardness and luminescence properties of Gd2O3-B2O3 glass scintillator.

The effect of CeF3 concentration and γ-irradiation on the physical, optical and luminescence properties of Gd2O3-B2O3-CeF3 glasses were studied in this work. Before irradiation, the addition of CeF3 in glass degraded the network connectivity observed from FTIR and possibly created the non-bridging oxygen (NBO) in glass structure. This NBO caused the reduction of Ce3+/Ce4+ ratio in XANES, the red-shift in transmission spectra and the raise of refractive index with addition of CeF3 content. Such red-shift also was influenced by 4f-5d transition of Ce3+ dopant. This ion generated the strongest photoluminescence (PL) and radioluminescence (RL) in 0.3 mol% CeF3-doped glass with nanoseconds decay time. The irradiation with γ-rays damaged the glass structure, broke the chemical bonds, and created color center in the glass network. The non-bridging oxygen hole center (NBOHC), that absorbed photons in the visible light region, caused the darkening, color change and increment of refractive index. These irradiation effects on glass were mitigated by the addition of CeF3 that the electron donation of Ce3+ decreased the number of NBOHC. The Ce3+/Ce4+ ratio in most glasses after irradiation then reduced compared to them before irradiation, resulting to the decrease in PL and RL intensity. Our results confirm that CeF3 can enhance the radiation hardness of glass and the 0.3 mol% CeF3-doped glass is a promising glass scintillator.

Photocatalysis of S-metolachlor in aqueous suspension of magnetic cerium-doped mTiO2 core-shell under simulated solar light.

Magnetic cerium-doped mesoporous titanium dioxide was synthesized by combining sol-gel method and calcination using tetrabutanate and ammonium cerium nitrate as precursors and Pluronic P123 as a template coating on iron oxide covered with carbon in ethanol. The magnetic Ce-doped catalyst showed only anatase structure with a slight increase in lattice parameters compared to the undoped catalyst. The Ce LIII-edge X-ray absorption near-edge spectroscopy (XANES) spectra showed Ce3+, and the cerium substitution doping into titanium dioxide was proposed. Degradation of S-metolachlor in aqueous magnetic photocatalyst suspension followed (pseudo) first-order kinetics in the presence of 0.5 g L-1 of γ-Fe2O3@C@0.16 mol% Ce-mTiO2 with a half-life of 55.18 ± 1.63 min. Fifteen degradation products were identified, and their transformation routes of the photocatalytic degradation were then proposed. Complementary toxicity assessment of the treated S-metolachlor solution was undertaken with Environment Canada's algal microplate assay measuring growth inhibition (72-h IC50) in the freshwater chlorophyte Pseudokirchneriella subcapitata. This test method revealed a significant decrease in toxicity (1.7-fold reduction after 180 min of irradiation treatment), thereby confirming that the by-products formed following photocatalysis would be less harmful from an environmental point of view. Photocatalytic degradation of S-metolachlor thus appears to hold promise as a cost-effective treatment technology to diminish the presence of this herbicide in aquatic systems.