Solenne Fleutot

Influence of recasting on the quality of dental alloys: A systematic review.

STATEMENT OF PROBLEMnDental alloy manufacturers advise against the reuse of previously melted alloy. However, for economic reasons, dental laboratories often reuse the casting surplus (sprue and metal remaining in the crucible former). Such reuse remains a controversial topic in dental practice.nnnPURPOSEnThe purpose of this systematic review was to assess the effects of remelting dental alloys by evaluating the following parameters: reasons for recasting and associated processes, feasible number of recastings, treatment of alloys before recasting and its effects on cytotoxicity, color of opaque porcelain, castability of alloys, marginal accuracy, mechanical properties, porcelain-metal interfaces, and corrosion.nnnMATERIAL AND METHODSnThe systematic review included all studies on dental alloy recasting. MEDLINE, Dentistry and Oral Science Source, Science Direct, and ISI Web of Science were searched (up to July 2014). Data were extracted and the quality of studies was assessed.nnnRESULTSnThirty-four studies published between 1983 and 2014 were included. The number of recastings ranged from 1 to 10. The percentage of new alloy ranged from 0 to 100 wt%, although the mean value was 50 wt%.nnnCONCLUSIONSnEvidence for the feasibility of adding 50% new metal at each recasting is limited. The number of recastings should be limited to a maximum of 4. No general test protocol can be deduced from these studies, which limits the comparison and exploitation of data. Furthermore, no consensus protocol exists for the evaluation of recasting. Future studies should work toward establishing a standard protocol.

Multiscale characterization of the hierarchical structure of Dynastes hercules elytra

Beetle elytra are thickened forewings, they are lightweight and tough to protect the hindwings without hindering flight capacities. Dynastes hercules elytra are known for their hygrochromic properties. However, the whole structure of the elytron remains to be characterized. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and to our knowledge for the first time X-Ray tomography were undertaken on adult male Dynastes hercules to characterize their multi-scale structure. Trabeculae present a periodic arrangement over a short distance. Two inferred models describe the heights of plies in endocuticles of dorsal and ventral cuticles. We hypothesize that this study could provide inspiration for biomimetic materials.

Synthesis and Characterization of Nanofunctionalized Gelatin Methacrylate Hydrogels

Given the importance of the extracellular medium during tissue formation, it was wise to develop an artificial structure that mimics the extracellular matrix while having improved physico-chemical properties. That is why the choice was focused on gelatin methacryloyl (GelMA), an inexpensive biocompatible hydrogel. Physicochemical and mechanical properties were improved by the incorporation of nanoparticles developed from two innovative fabrication processes: High shear fluid and low frequencies/high frequencies ultrasounds. Both rapeseed nanoliposomes and nanodroplets were successfully incorporated in the GelMA networks during the photo polymerization process. The impact on polymer microstructure was investigated by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and enzymatic degradation investigations. Mechanical stability and viscoelastic tests were conducted to demonstrate the beneficial effect of the functionalization on GelMA hydrogels. Adding nanoparticles to GelMA improved the surface properties (porosity), tuned swelling, and degradability properties. In addition, we observed that nanoemulsion didn’t change significantly the mechanical properties to shear and compression solicitations, whereas nanoliposome addition decreased Young’s modulus under compression solicitations. Thus, these ways of functionalization allow controlling the design of the material by choosing the type of nanoparticle (nanoliposome or nanoemulsion) in function of the application.

Elaboration of hydroxyapatite nanoparticles and chitosan/hydroxyapatite composites: a present status

Novel formulations of nano-hydroxyapatite (nano-HAp) and nano-HAp/chitosan composites have attracted much attention in these last years. The use of natural chitosan is found to be potential for fabrication of modified nano-HAp with many biomedical applications such as orthopedic, osteoconductive, dental and drug delivery applications. This review summarizes the different techniques employed for the elaboration of HAp nanoparticles and the effect of the incorporation of HAp with chitosan on the fabrication of nano-HAp composite and on their physical properties. We discuss the effects of the reaction conditions such as reaction time, temperature, pH, solvent nature, surfactants, and concentration of reactants on crystallinity, particle size, morphology and properties of nano-HAp composite. The nano-HAp progress and the present status of HAp (either experimental or theoretical results) have been reviewed.

The effect of thermal treatment on the acid neutralizing capacity of newberyite: structural assessment and kinetics of the HCl neutralization reaction

The newberyite MgHPO4·3H2O antacid activity has never been investigated before. Crystalline and heated Newberyite, at 200xa0°C, was tested as a neutralizing of hydrogen chloride acid (HCl 0.1xa0M to simulate gastric juice). Results show that the substrate has a basic behavior and may be used as an active ingredient in the antacid formulation. HCl Neutralization 0.1xa0M depends of newberyite concentration and pH1 was reached when 0.5xa0M was used. The crystalline and heated newberyite antacid power was compared with that of some commercial antacids. The newberyite heated pushed pH to 4 after 4xa0min when the crystalline product was brought it to 3 after 15xa0min. The antacid neutralizing capacity (ANC) was evaluated using direct and reverse titration methods. ANC values increased when particle sizes decreased. The heated product at 200xa0°C increased strongly the ANC and the maximum value reached was 13xa0meq/g. The kinetic study of neutralization reaction was carried out by pHmetry. The rate constants are depending of newberyite quantity and the optimal neutralization of HCl 0.1xa0M was obtained for 0.5xa0g. The resulting structural transformations have been investigated. XRD showed that the product became amorphous after heating at 200xa0°C. FT-IR and Raman spectroscopy agree on departure of the three crystallization water molecules, when MgHPO4·3H2O was heated. Surface area measurement was determined by Brunauer, Emmett and Teller and indicates that the product hasn’t an important porosity. Scanning electron microscopy coupled with energy dispersive spectrometry elementary analysis was also carried out and confirmed FT-IR and Raman spectroscopy results.

Bioactive Films Containing Alginate-Pectin Composite Microbeads with Lactococcus lactis subsp. lactis: Physicochemical Characterization and Antilisterial Activity

Novel bioactive films were developed from the incorporation of Lactococcus lactis into polysaccharide films. Two different biopolymers were tested: cellulose derivative (hydroxylpropylmethylcellulose (HPMC)) and corn starch. Lactic acid bacteria (LAB) free or previously encapsulated in alginate-pectin composite hydrogel microbeads were added directly to the film forming solution and films were obtained by casting. In order to study the impact of the incorporation of the protective culture into the biopolymer matrix, the water vapour permeability, oxygen permeability, optical and mechanical properties of the dry films were evaluated. Furthermore, the antimicrobial effect of bioactive films against Listeria monocytogenes was studied in synthetic medium. Results showed that the addition of LAB or alginate-pectin microbeads modified slightly films optical properties. In comparison with HPMC films, starch matrix proves to be more sensitive to the addition of bacterial cells or beads. Indeed, mechanical resistance of corn starch films was lower but barrier properties were improved, certainly related to the possible establishment of interactions between alginate-pectin beads and starch. HPMC and starch films containing encapsulated bioactive culture showed a complete inhibition of listerial growth during the first five days of storage at 5 °C and a reduction of 5 logs after 12 days.

Crystal structure and DFT study of the zwitterionic form of 3-{(E)-1-[(4-ethoxyphenyl)iminiumyl]ethyl}-6-methyl-2-oxo-2H-pyran-4-olate

The title Schiff base compound crystallizes in the zwitterionic form. The resulting iminium and hydroxyl groups are linked by a charge-assisted intramolecular N+—H⋯O− hydrogen bond, and the conformation about the C=N bond is E.

(E)-4-Hy­droxy-6-methyl-3-[1-(2-phenyl­hydrazinyl­idene)eth­yl]-2H-pyran-2-one

The title compound, C14H14N2O3, crystallized with three crystallographically independent molxadecules (A, B and C) in the asymmetric unit. The three molxadecules each have an E conformation about the C=N bond but differ in the orientation of the phenyl and pyran rings. The dihedral angles between the phenyl and pyran ring planes are 14.30u2005(1), 28.38u2005(1) and 25.58u2005(1)° in molxadecules A, B and C, respectively. There is an intraxadmolecular O—H⋯N hydrogen bond in each molxadecule with an S(6) ring motif. In the crystal, molxadecules are linked by N—H⋯O and C—H⋯O hydrogen bonds, forming layers parallel to (001), enclosing R22(8) and R33(21) ring motifs. The layers are linked via C—H⋯π interxadactions, forming bilayers, which are joined by a further C—H⋯π interxadaction, forming a three-dimensional structure.

Crystal structure of (E)-4-hy-droxy-3-{1-[(4-hy-droxy-phen-yl)imino]-eth-yl}-6-methyl-2H-pyran-2-one.

In the title Schiff base, C14H13NO4, which adopts the phenol–imine tautomeric form, the dihedral angle between the planes of the benzene and heterocyclic (r.m.s. deviation = 0.037u2005Å) rings is 53.31u2005(11)°. An intramolecular O—H⋯N hydrogen bond closes an S(6) ring. In the crystal, molecules are linked by O—H⋯O hydrogen bonds to generate C(11) chains propagating in the [010] direction. A weak C—H⋯O link is also observed, leading to the formation of R 5 5(32) rings extending parallel to the (101) plane.