Review of nanomaterials in dentistry: interactions with the oral microenvironment, clinical applications, hazards, and benefits.

Interest in the use of engineered nanomaterials (ENMs) as either nanomedicines or dental materials/devices in clinical dentistry is growing. This review aims to detail the ultrafine structure, chemical composition, and reactivity of dental tissues in the context of interactions with ENMs, including the saliva, pellicle layer, and oral biofilm; then describes the applications of ENMs in dentistry in context with beneficial clinical outcomes versus potential risks. The flow rate and quality of saliva are likely to influence the behavior of ENMs in the oral cavity, but how the protein corona formed on the ENMs will alter bioavailability, or interact with the structure and proteins of the pellicle layer, as well as microbes in the biofilm, remains unclear. The tooth enamel is a dense crystalline structure that is likely to act as a barrier to ENM penetration, but underlying dentinal tubules are not. Consequently, ENMs may be used to strengthen dentine or regenerate pulp tissue. ENMs have dental applications as antibacterials for infection control, as nanofillers to improve the mechanical and bioactive properties of restoration materials, and as novel coatings on dental implants. Dentifrices and some related personal care products are already available for oral health applications. Overall, the clinical benefits generally outweigh the hazards of using ENMs in the oral cavity, and the latter should not prevent the responsible innovation of nanotechnology in dentistry. However, the clinical safety regulations for dental materials have not been specifically updated for ENMs, and some guidance on occupational health for practitioners is also needed. Knowledge gaps for future research include the formation of protein corona in the oral cavity, ENM diffusion through clinically relevant biofilms, and mechanistic investigations on how ENMs strengthen the tooth structure

Temporal origin of nitrogen in the grain of irrigated rice in the dry season: the outcome of uptake, cycling, senescence and competition studied using a \u3csup\u3e15\u3c/sup\u3eN-point placement technique

It is often suggested that nitrogen absorbed in the vegetative stage of growth acts as a “reservoir” to supply the shortfall in demand during grain filling. The main objective of the work described in this paper was to investigate how effectively nitrogen absorbed at different stages of the growing season was retained and used for grain growth. The total nitrogen in the grain is the integral of the product of the total nitrogen absorbed at any instant and the eventual allocation of a fraction of that nitrogen to the grain. A point-placement technique was used to deliver small amounts of 15N to the roots of the rice plant at different growth stages. The total nitrogen content of the crop was measured by growth analysis throughout its duration and the measurements used to calculate the rate of total nitrogen uptake. Using 15N as a tracer enabled the fate of nitrogen taken up at any time to be determined. In the short-term, the labeled nitrogen was distributed between the various plant organs depending on their demand for nitrogen during the period of absorption. In the long-term, transfers of 15N occurred between organs, in particular to the developing panicle (rice inflorescence). The rate of nitrogen absorption of the panicle exceeded the rate of absorption by the whole plant from 68 DAT onwards. Surprisingly, in the context of rice as an annual plant, the distribution patterns suggested that towards maturity, the perennial nature of the rice plant led to competition for nitrogen between the panicles and the next generation of developing tillers. The results showed that the total nitrogen absorption by the plant was high when the fractional allocation to the grain was low and vice-versa. About 30% of the total nitrogen in the grain was acquired before panicle initiation (45 days after transplanting, DAT) and the leaves acted as the main “reservoir” for nitrogen. Losses of labeled nitrogen acquired by the plants after 35 DAT were not significant, suggesting that there was no large loss of nitrogen through volatilization, once the nitrogen had been incorporated in the plant biomass

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Luminescence and Nonlinear Optical Properties in Copper(I) Halide Extended Networks

The syntheses, structures, and luminescence properties of a series of copper­(I) halide coordination polymers, prepared with mono- and bidentate N-heteroaromatic ligands, are reported. These metal–organic coordination networks form [Cu₂I₂L]_<i>n</i> for bidentate ligands (where L = pyrazine (<b>1</b>), quinazoline (<b>2</b>)) and [CuIL]_<i>n</i> for monodentate ligands (where L = 3-benzoylpyridine (<b>3</b>) and 4-benzoylpyridine­(<b>4</b>)). Both sets of compounds exhibit a double-stranded stairCu₂I₂polymer, or “ladder” structure with the ligand coordinating to the metal in a bidentate (bridging two stairs) or monodentate mode. The copper bromide analogues for the bidentate ligands were also targeted, [Cu₂Br₂L]_<i>n</i> for L = pyrazine (<b>5</b>) with the same stair structure, as well as compositions of [CuBr­(L)]_<i>n</i> for L = pyrazine (<b>6</b>) and quinazoline (<b>7</b>), which have a different structure type, where the −Cu–Br– forms a single-stranded “zigzag” chain. These copper halide polymers were found to be luminescent at room temperature, with emission peaks ranging from ∼550 to 680 nm with small shifts at low temperature. The structure (stair or chain), the halide (I or Br), as well as the ligand play an important role in determining the position and intensity of emission. Lifetime measurements at room and low temperatures confirm the presence of thermally activated delayed fluorescence, or singlet harvesting for compounds <b>1</b>, <b>2</b>, and <b>7</b>. We also investigated the nonlinear optical properties and found that, of this series, [CuBr­(quinazoline)]_<i>n</i> shows a very strong second harmonic generating response that is ∼150 times greater than that of α-SiO₂