Characterization of chemical reactions of silver diammine fluoride and hydroxyapatite under remineralization conditions.

Introduction: Silver Diammine Fluoride (SDF) is a clinically used topical agent to arrest dental caries. However, the kinetics of its chemical interactions with hydroxyapatite (HA), the principal inorganic component of dental enamel, are not known. The aim was to characterize the step-wise chemical interactions between SDF and HA powder during the clinically important process of remineralization. Methods: Two grams of HA powder were immersed in 10 ml acetic acid pH = 4.0 for 2 h to mimic carious demineralization. The powder was then washed and dried for 24 h and mixed with 1.5 ml SDF (Riva Star) for 1 min. The treated powder was then air-dried for 3 min, and 0.2 g was removed and stored in individual tubes each containing 10 ml remineralizing solution. Powder was taken from each tube at various times of exposure to remineralization solution (0 min, 10 min, 2 h, 4 h, 8 h, 24 h, and 10 days), and characterized using Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. Results and discussion: 19F MAS-NMR spectra showed that calcium fluoride (CaF2) started to form almost immediately after HA was in contact with SDF. After 24 h, the peak shifted to -104.5 ppm suggesting that fluoride substituted hydroxyapatite (FSHA) was formed with time at the expense of CaF2. The 31P MAS-NMR spectra showed a single peak at 2.7 ppm at all time points showing that the only phosphate species present was crystalline apatite. The 35Cl MAS-NMR spectra showed formation of silver chloride (AgCl) at 24 h. It was observed that after the scan, the whitish HA powder changed to black color. In conclusion, this time sequence study showed that under remineralization conditions, SDF initially reacted with HA to form CaF2 which is then transformed to FSHA over time. In the presence of chloride, AgCl is formed which is subsequently photo-reduced to black metallic silver.

Bioactive glass composite for orthodontic adhesives - Formation and characterisation of apatites using MAS-NMR and SEM.

OBJECTIVES: To study the dissolution and fluoroapatite (FAP) formation of a new bioactive glass (BAG)-resin adhesive in an acidic solution in reference to neutral solutions, using the magic angle spinning-nuclear magnetic resonance (MAS-NMR) and the scanning electron microscopy (SEM). METHODS: BAG composite disks (n = 90) were prepared from, novel fluoride-containing BAG-resin. Three sample groups (n = 30) of the disks were immersed in Tris buffer pH = 7.3 (TB), neutral artificial saliva pH = 7 (AS7) and acidic artificial saliva pH = 4 (AS4) at ten time points (from 6 h to 6 months). Half of the immersed disks at each time point were crushed into a powder and investigated by the solid state MAS-NMR. SEM studies were undertaken by embedding the other half of the immersed disk in a self-cure acrylic where the fracture surface was imaged. RESULTS: MAS-NMR results show that the BAG composite degraded significantly faster in AS4 compared to TB and AS7. At the end of the immersion period (6 months), around 80% of the glass particles in AS4 had reacted to form an apatite, evidenced by the sharp peak at 2.82 ppm in 31P signals compared to a broader peak in TB and AS7. It also shows evidence of fluorapatite (FAP) formation, indicated by 19F signal at -103 ppm, while signal around -108 ppm indicated the formation of calcium fluoride, from the excess Ca2+ and F- especially on longer immersion. SEM images confirm higher degradation rate of the BAG composite in AS4 and reveal the impact of time on the dissolution of more glass particles. The images also indicate apatite formation around the glass particles in TB and AS4, while it forms predominantly over the disk surface in AS7. SIGNIFICANCE: BAG composite demonstrate smart reactivity in response to pH change which has a potential clinical benefit against demineralization and promoting remineralisation to form more stable fluorapatites.

[AEROMONAS BACTERIA ISOLATED FROM BITHYNIIDAE MOLLUSKS AND THEIR HABITATS: SPECIES COMPOSITION AND BIOLOGICAL PROPERTIES. COMMUNICATION 1].

The purpose of this investigation was to study the species composition and biological properties of Aeromonas bacteria isolated from Bithyniidae mollusks and their habitat (a water reservoir). The Bithyniidae mollusks and water from their habitat were the material to be studied. A total of 176 Aeromonas strains were isolated from the mollusks and water. A. veronii, A. hydrophila, and A. ichthiosmia were most common in the mollusks and A. veronii and A. ichthiosmia were in the water. All the strains isolated had hemolytic activity and no lysozyme or plasma coagulase activity. The magnitude of lecithinase and antilysozymic activities and biofilm formation of the Aeromonas bacteria varied with the isolation source of their strains.

[THE STRUCTURE AND SOME BIOLOGICAL PROPERTIES OF GRAM-NEGATIVE BACTERIA CONSTITUTING THE MICROSYMBIOCENOSIS OF PROSOBRANCHIA MOLLUSKS (BITHYNIIDAE). COMMUNICATION 2].

The goal of this investigation was to study the structure and biological properties (antilysozymic, activity and biofilm formation) of gram-negative bacteria isolated from Bithyniidae mollusks and their habitat (water reservoir waters and soil). A total of 160 gram-negative bacterial strains isolated from the mollusks of the Bithyniidae family and their habitat were the material to be, studied. Psedomonas, Comamonas, and Acinetobacter held the lead in the structure of microbiocenosis of Bithyniidae mollusks, the first intermediate host of Opisthorchis filineus, while Acinetobacter did in the habitat. The antilysozymic activity of the water strains was shown to be an order of magnitude higher than that of the strains isolated from the mollusks.

Structure and solubility behaviour of zinc containing phosphate glasses.

The structure of phosphate glasses of general composition 10Na2O : (20 + x/2)ZnO : (20 + x/2)CaO : (50 -x)P2O5 (0 ≤x≤ 20) has been investigated using IR spectroscopy, 1D 31P and 43Ca MAS Bloch decay, 31P-31P double quantum MAS-NMR and 43Ca and 67Zn static NMR techniques, as well as neutron diffraction analysis. Zinc is shown to aid glass formation in this system. Glass transition temperature and density increase with increasing cation : phosphate ratio. However, free volume calculations show structures becoming significantly more compact from x = 5 to x = 10. The structural data confirm depolymerisation of the glasses with increasing cation : phosphate ratio. Zinc oxide is found to act in a network forming role in the system, with 67Zn NMR and neutron diffraction analysis confirming zinc exhibits predominantly four-coordinate geometry. Solubility in deionised water and tris/HCl buffer solution is seen to decrease significantly with increasing x-value. This is discussed in terms of water ingress and the degree of structural openness, associated with increased cross-linking and a decrease in concentration of P-O-P linkages. pH measurements confirm invert phosphate compositions maintain physiological pH levels on immersion in water and buffer solutions for up to four weeks.

[BIOLOGICAL PROPERTIES OF BACTERIA OF THE FAMILY ENTEROBACTERIACEAE AS COMPONENTS OF MICROSYMBIOCENOSIS OF THE FIRST INTERMEDIATE HOSTS OF O.FELINEUS].

The objective of the investigation was to study the biological properties (antilysozyme activity (ALA), biofilm formation (BFF), and virulence factors) of different Enterobacteriaceae species isolated from Bithyniidae mollusks and their habitats. A total of 117 strains isolated from Bithyniidae mollusks of the genera Codiella and Bithynia and those from their habitats were the material to be studied. Thus, comparison of the mean values of ALA in Enterobacteriaceae species suggests that the strains isolated from the mollusks and their aqueous habitat did not virtually differ in this indicator. Also, there were no statistically significant differences in the detection rate of the Enterobacteriaceae strains having a pronounced antilysozyme activity and in that of mollusks circulating in the aqueous habitat when compared with the strains isolated from the mollusks. Comparison of BFF in the aqueous bacterial strains and mollusk microbiota representatives revealed the highest values in the former; just lower value was noted in the latter. Soil Enterobacteriaceae isolates had very low BFF values.

[RATIONAL ASPECTS OF BACTERIOPHAGES USE].

AIM: Analysis of existing aspects of bacteriophage use and study features of their lytic activity by using various techniques. MATERIALS AND METHODS: Effect of monophages and associated bacteriophages (staphylococci, piopolyvalent and piocombined, intestiphage, pneumonia klebsiella and polyvalent klebsiella produced by "Microgen") was studied with 380 strains of Staphylococcus aureus and 279 cultures of Klebsiella pneumoniae in liquid and solid nutrient media. From patients with intestinal disorder, sensitivity was analyzed to 184 strains of Salmonella genus bacteria 18 serological variants to salmonella bacteriophages, 137 strains of Escherichia coli (lactose-negative, hemolytic), as well as some members of OKA groups (21 serovars) to coli-proteic and piopolyvalent bacteriophages. Lytic ability of the piobacteriophage against Klebsiella and Proteus genus bacteria was determined. RESULTS: Staphylococcus aureus was sensitive to staphylococcus bacteriophage in 71.6% of cases and to piobacteriophage--in 86.15% of cases. A 100% lytic ability of salmonella bacteriophage against Salmonella spp. was established. Sensitivity of E. coli of various serogroups to coli-proteic and piobacteriophage was 66 - 100%. Klebsiella, Proteus genus bacteria were sensitive to piobacteriophage in only 35% and 43.15% of cases, respectively. CONCLUSION: A more rational use of bacteriophages is necessary: development of a technique, evaluation of sensitivity of bacteria to bacteriophage, introduction of corrections into their production (expansion of bacteriophage spectra, determination and indication of their concentration in accompanying documents).

[Microsymbiocenosis of Codiella mollusks as a basis for symbiotic relations in the parasite-host system in opisthorchiasis].

The purpose of the first step of microparasitocenosis investigation was to study the microbiocenosis of the first intermediate hosts of O. felineus--prosobranch gastropods of the genus Codiella, as well as their habitats. Materials were collected in the Iryum River of the Ob-Irtysh basin. The microflora of mollusks, water, and soil from their habitats was examined. The predominant flora was Aeromonas species in the biocenosis of mollusks and Enterobacteriaceae in the microbiocenosis of the water basin and soil. Examination of the microbial communities in the mollusks and their habitats showed that the range of microbial populations of mollusks was wider in species composition as compared to the microbiocenosis of soil and water.

Crystallisation in oxide glasses - a tutorial review.

Glasses and glass-ceramics have had a tremendous impact upon society and continue to have profound industrial, commercial and domestic importance. A remarkable number of materials, with exceptional optical and mechanical properties, have been developed and enhanced using the glass-ceramic method over many years. In order to develop glass-ceramics, glass is initially prepared via high temperature synthesis and subsequently heat treated, following a carefully designed and controlled process. A glass-ceramic system comprises crystalline and non-crystalline phases; in multicomponent systems these phases are significantly different from the initial glass composition. The properties of glass-ceramics are defined by microstructure, crystal morphology as well as the final chemical composition and physical properties of the residual glass. Knowing the mechanism of glass crystallisation, it is possible to predict and design a glass-ceramic system with near-ideal properties that exactly fulfil the requirements for a particular application. This tutorial review is a basic introduction to the crystallisation in glasses and mainly focuses on silicate and closely related oxide glasses. The review describes and discusses key learning points in five different sections, which facilitate the understanding of glass crystallisation and development of glass-ceramics.

Effects of fluoride on in vitro enamel demineralization analyzed by ¹9F MAS-NMR.

The mechanistic action of fluoride on inhibition of enamel demineralization was investigated using (19)F magic angle spinning nuclear magnetic resonance (MAS-NMR). The aim of this study was to monitor the fluoride-mineral phase formed on the enamel as a function of the concentration of fluoride ions [F(-)] in the demineralizing medium. The secondary aim was to investigate fluorapatite formation on enamel in the mechanism of fluoride anti-caries efficacy. Enamel blocks were immersed into demineralization solutions of 0.1 M acetic acid (pH 4) with increasing concentrations of fluoride up to 2,262 ppm. At and below 45 ppm [F(-)] in the solution, (19)F MAS-NMR showed fluoride-substituted apatite formation, and above 45 ppm, calcium fluoride (CaF2) formed in increasing proportions. Further increases in [F(-)] caused no further reduction in demineralization, but increased the proportion of CaF2 formed. Additionally, the combined effect of strontium and fluoride on enamel demineralization was also investigated using (19)F MAS-NMR. The presence of 43 ppm [Sr(2+)] in addition to 45 ppm [F(-)] increases the fraction of fluoride-substituted apatite, but delays formation of CaF2 when compared to the demineralization of enamel in fluoride-only solution.

Real time neutron diffraction and NMR of the Empress II glass-ceramic system.

OBJECTIVE: This study reports real time neutron diffraction on the Empress II glass-ceramic system. METHODS: The commercial glass-ceramics was characterized by real time neutron diffraction, ³¹P and ²9Si solid-state MAS-NMR, DSC and XRD. RESULTS: On heating, the as-received glass ceramic contained lithium disilicate (Li2Si2O5), which melted with increasing temperature. This was revealed by neutron diffraction which showed the Bragg peaks for this phase had disappeared by 958°C in agreement with thermal analysis. On cooling lithium metasilicate (Li2SiO3) started to form at around 916°C and a minor phase of cristobalite at around 852°C. The unit cell volume of both Li-silicate phases increased linearly with temperature at a rate of +17×10⁻³ ų.°C⁻¹. Room temperature powder X-ray diffraction (XRD) of the material after cooling confirms presence of the lithium metasilicate and cristobalite as the main phases and shows, in addition, small amount of lithium disilicate and orthophosphate. ³¹P MAS-NMR reveals presence of the lithiorthophosphate (Li3PO4) before and after heat treatment. The melting of lithium disilicate on heating and crystallisation of lithium metasilicate on cooling agree with endothermic and exotermic features respectively observed by DSC. ²9Si MAS-NMR shows presence of lithium disilicate phase in the as-received glass-ceramic, though not in the major proportion, and lithium metasilicate in the material after heat treatment. Both phases have significantly long T1 relaxation time, especially the lithium metasilicate, therefore, a quantitative analysis of the ²9Si MAS-NMR spectra was not attempted. Significance. The findings of the present work demonstrate importance of the commercially designed processing parameters in order to preserve desired characteristics of the material. Processing the Empress II at a rate slower than recommended 60°C min⁻¹ or long isothermal hold at the maximal processing temperature 920°C can cause crystallization of lithium metasilicate and cristobalite instead of lithium disilicate as major phase.

Preferential binding of fluorine to aluminum in high peralkaline aluminosilicate glasses.

For two series of fluoride-containing aluminosilicate glasses of high peralkaline type, we apply 27Al, 19F, 29Si, and 23Na NMR spectroscopy to understand the structural changes introduced by the addition of alkali fluorides. Adding fluoride in concentrations above the solubility limit causes crystallization of different phases in sodium and potassium glasses despite identical composition. However, the NMR spectra reveal that the structural evolution of the precrystallized states is similar in both series. In particular, fluorine coordinates exclusively to alkaline cations and aluminum. No indication of direct bonding with silicon was found from 19F --> 29Si cross-polarization experiments. In contrast to other glass systems, double resonance experiments in these peralkaline systems show that halide addition produces at most a minor fraction of tetrahedral aluminum containing fluorine in its coordination sphere. Instead, the fluorine addition prior to crystallization converts up to about 20% of the initial tetrahedral aluminum (1 mol % in absolute units) to 5- and 6-fold coordinated aluminum. A minor portion of five-coordinated aluminum groups is considered as the intermediate to the growing fraction of octahedral aluminum in the silicate matrix. The initialization of the crystallization process is correlated with the saturation of the silicate matrix by octahedral aluminum clusters segregating out under further doping by fluoride. It is suggested that the formation of the nonframework Al-F bonds is responsible for structural relaxation, reflected by the reduction of the glass transition temperature.

[The diagnostic value of serological studies in the clinical picture of tuberculosis]. / Diagnosticheskaia tsennost' serologicheskikh issledovanii v klinike tuberkuleza.

Circulating antituberculous antibodies in the sera from 89 patients with pulmonary tuberculosis and 11 patients with tumors and nonspecific inflammation in the lungs were evaluated using indirect hemagglutination and enzyme immunoassay. Specific antibodies were detected in 81.6 and 30% of tuberculous and nontuberculous patients, respectively.

[Clinical manifestations of tuberculosis in children and adolescents]. / Klinicheskie proiavleniia tuberkuleza u detei i podrostkov.

Clinical manifestations of tuberculosis in children and adolescents living in the Tumen region during 1984-1989 are analysed. Out of 432 of the patients, local forms of tuberculous infection were detected in 79.4% and pneumonia in 4.4% of the cases, while all the rest children proved to be just infected. The most prevailing among the pulmonary forms of the disease was intrathoracic lymphatic tuberculosis (52.3%) and among the non-pulmonary ones--tuberculous meningitis (3.5%). A complicated course of a tuberculous process was registered in 37.3% of the cases, especially in 2/3 of the patients with intrathoracic lymphatic tuberculosis (mainly of a bronchial type) as a consequence, in a number of cases, of the absence of BCG vaccination and the presence of tuberculous contact. Bronchoscopy undertaken in 244 children and adolescents made it possible to discover active changes in the bronchial mucosa in the first 1-2 months of therapy.