Crack formation during post-treatment of nano- and microfibres prepared by sol-gel technique.

We report on the method of TiO2 nano- and microfibres preparation and their cracking during processing and post-treatment. Nano- and microfibres were fabricated by drawing from viscous alkoxide based oligomeric concentrate precursors with the following exposure into an atmosphere of 30-50% humidity. The fibres microstructure was analyzed with TEM, solid state NMR, X-ray diffraction tools, and AFM. Experiments on crack formation in TiO2 microfibres proved that fibres with diameter larger than 10 micron are fractured for chosen post-treatment regimes. In theoretical considerations sol-gel produced and thermally treated microfibres are modeled as core/shell structures. It is suggested that the formation of fibres starts via solidification of liquid jet through the appearance of a rigid solid shell, which reveals tensile mechanical stresses because of material shrinkage. The effect of post-treatment is taken into account by additional densification of the fibre surface layer. The stress intensity factor K(I) is calculated for the model core/shell structures and the dependence of K(I) on the fibre diameter is demonstrated. The results of modeling qualitatively confirm experimental data of microfibre cracking above a certain threshold diameter.

Pentagonal nanorods and nanoparticles with mismatched shell layers.

Nano-scale rods and particles having the axes of fivefold symmetry, i.e., pentagonal nanorods and nanoparticles, are theoretically and experimentally investigated. Such objects possess elastic strains and mechanical stresses. In the present research a new mechanism of stress relaxation in nanorods and nanoparticles is considered. The mechanism is implemented by a formation of a surface layer with crystal lattice mismatch. The elastic fields and energies for nanorods and nanoparticles with the mismatched layers are calculated in the framework of the disclination model. The optimal mismatch parameter giving the maximal energy release is determined. The threshold radius as the minimal radius of nanorods or nanoparticles for which the formation of the layer is energetically favorable, is found. The threshold radius is approximately 10 nm for nanoparticle and 100 nm for nanorod of typical FCC metal.

[Characteristics of leukocytic markers in patients with chronic generalized periodontitis during exacerbation]. / Kharakteristika leikotsitarnykh markerov u bol'nykh s khronicheskim generalizovannym parodontitom v faze obostreniia.

The immune status of patients with periodontitis was studied using monoclonal antibodies. Two variants of the immune status were distinguished: with high and low reactivity of T cellular system. The data on the presence of receptors and apoptosis markers on lymphocytes, neutrophils, and monocytes of patients with periodontitis are presented for the first time. The authors recommend to take the results of this study into consideration when treating patients with chronic periodontitis.

[A comparative evaluation of modern antibacterial preparations in the treatment of a severe degree of periodontitis at a stage of exacerbation]. / Sravnitel'naia otsenka sovremennykh antibakterial'nykh preparatov pri lechenii parodontita tiazheloi stepeni v stadii obostreniia.

Sensitivities of peptostreptococci, streptococci, Actinomyces, bacteroid, and fusobacterial strains pathogenic for the periodontium to wide-spectrum penicillines, cephalosporines, lincomycin, macrolides, metronidasole, and nitasole are compared. New macrolide antibiotics rulide. Macropene, gramicidin C, levomycetin, and rifampicin are highly effective. Some narrow-spectrum drugs, e.g. augmentin, cephalexin, and vancomycin (towards actinomycetes) were highly effective, too.

[The comparative characteristics of the antibacterial activity of new antiseptics and the prospects for their use in dental practice]. / Sravnitel'naia kharakteristika antibakterial'noi aktivnosti novykh antiseptikov i perspektivy ikh primeneniia v stomatologicheskoi praktike.

Antibacterial activities of modern antiseptics listerine, myramistine, cidipol, octenisept, tantum verde, matecide, and rautine drugs chlorhexidine and dioxidine are compared. The prospects of their use in dentistry for the treatment of inflammations associated with anaerobes are discussed. Metacide, listerine, chlorhexidine, and dioxidine are characterized by the widest spectrum of activity towards obligate anaerobic bacteria; moreover, these drugs inhibit bacterial growth when used in lower concentrations than other drugs.

[A trial of the use of rulid, sumamed and makropen in the combined treatment of generalized periodontitis at a stage of exacerbation]. / Opyt primeneniia rulida, sumameda i makropena v kompleksnom lechenii generalizovannogo parodontita v stadii obostreniia.

In vitro study of the antibacterial activity of macrolide antibiotics azitromycin (sumamed), midicamycin (macropen), roxitromycin (rulide), and erythromycin demonstrated their high activity towards clinical strains of bacteroids, fusobacteria, peptostreptococci, streptococci, and corynebacteria. These antibiotics were effective in the treatment of 62 adult patients with severe and moderate generalized periodontitis. Rulide and sumamed were the most effective, macropen and erythromycin were inferior to them.

[The choice of antibacterial preparations for the combined treatment of periodontitis in the exacerbation stage]. / Vybor antibakterial'nykh preparatov dlia kompleksnogo lecheniia parodontita v stadii obostreniia.

Antibiotic sensitivities of peptostreptococci, streptococci, Actinomyces, bacteroid, and fusobacterial strains pathogenic for the periodontium are analyzed. The sensitivities of these bacteria to broad-spectrum penicillins, cephalosporines, lincomycin, and macrolides, and to metronidasole and nitasole are assessed. New macrolide drugs macropen and rulide and gramicidine C, levomycetine, and rifampicin are highly active towards the above microflora. Microbiological indications for oral and local use of these antibiotics are validated. Some narrow-spectrum antibiotics, such as augmentine, cephalexin, and vancomicin are highly active, too; the latter drug is specifically active towards Actinomyces.

[Antibacterial therapy in the combined treatment of periodontitis]. / Antibakterial'naia terapiia v kompleksnom lechenii parodontita.

The sensitivities of clinical strains of obligate anaerobic bacteria, isolated from the periodontal pouches of patients with generalized periodontitis, to antibiotics, quinolone drugs, and metronidasole were studied. The minimal suppressing concentration (MSC90) of ciprofloxacin, norfloxacin, and antibiotics gramicidin C, eritromicin, lincomycin, levomicetin, and trichopol for sensitive strains of Porphyromonas, peptostreptococci, and fusobacteria ranged from 5 to 10 mg/ml. Among the bacteria and actinomyces studied the highest percentage of resistant strains was noted for abactal and tarivid, and the minimal for gramicidin C and eritromicin. Actinomyces were little sensitive to quinolone derivatives.

[The species composition of the dental plaque on the surface of fillings made from different materials]. / Vidovoi sostav zubnoi bliashki na poverkhnosti plomb iz razlichnykh materialov.

The present research was aimed at assessment of the quantitative and qualitative composition of oral microflora in cases with different filling material used. Forty-four patients were fitted with 6 types of filling, both traditional and rarely used cliofil (Japan). Soft dental deposit was collected from the surface of fillings for microbiologic investigation. The results permit a conclusion that composites are preferable in comparison with amalgams and cements, the contamination being 8-9 times lower when they are used. Moreover, macrocomposite fillings were associated with streptococcal contamination, in contrast to other materials, when actinomycetes were mainly isolated.