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At least 775 records · Page 43Linked to original sources
PubMed2000

Compressive shear strength of core materials and restoring techniques.

In this study, ninety extracted endodontically treated mandibular molars were mounted in acrylic resin blocks. Five groups of eighteen extracted teeth were prepared by two different techniques. A peripheral shelf 2 mm deep and 1.4 mm wide was prepared as a first technique, while TMS pins were used in the second group. The teeth were then restored with five different core materials: silver-reinforced glass-ionomer, resin-modified glass-ionomer, self-cured glass-ionomer, polyacid-modified composite resin, and titanium-reinforced composite resin. An Instron testing machine was used to apply shear force at a crosshead speed of 2 mm/min until fracture occurred. The results were obtained statistically using analysis of variance and least significant difference tests. According to the results of this study, Ti-core and composite resin were the strongest core materials when subjected to shear forces, and the most retentive preparation design was the vertical-pin design. The fractures of these materials with a vertical-pin design were mostly seen at the core and the tooth.

Analysis of Variance↗
PubMed2001

[Cytotoxic and genotoxic activity of certain preservative agents in cosmetics].

Cytotoxic effects of the preservative compounds for cosmetics JMAC TD, Bronopol, CA 24, and Euxyl K100 were studied. Bronopol demonstrated the highest cytotoxic effect on the proliferation of V79 and VH10 fibroblast cell lines--the IC100 values being 10 mg/l during the whole experiment. The preservatives CA 24 and Euxyl K100 showed 4-times and 5-times smaller cytotoxic activity than Bronopol IC100 = 42 or 50.3 mg/l). The preservative compounds on silver chloride ions JMAC TD manifested the lowest cytotoxicity of the preservatives tested (IC100 = 150 mg/l); 15-times smaller than Bronopol, 3.5-times smaller than CA 24 and 3-times smaller than Euxyl K100. The biocide JMAC TD did not exhibit mutagenic effects on the bacteria Salmonella typhimurium TA 98 and TA 100.

Animals↗
PubMed2002

Comparison of the resistance to infection of rifampin-bonded gelatin-sealed and silver/collagen-coated polyester prostheses.

PURPOSE: The purpose of this study was to compare the efficacy of rifampin-bonded gelatin-sealed and silver acetate/collagen-coated knitted polyester prostheses for the prevention of bacteremic graft infection in an animal model. METHODS: Eighteen 6.0-mm polyester grafts (length, 5.0 cm) were implanted in dogs end-to-end into the infrarenal aorta. The dogs were divided into four groups as a function of type of prosthesis implanted. The dogs in groups I (n = 3) and II (n = 3) received control gelatin-sealed or collagen-coated polyester prostheses, respectively. In group III (n = 6), the dogs received rifampin-bonded gelatin-sealed polyester prostheses. In group IV (n = 6), the dogs received silver/collagen-coated polyester prostheses. Two days after implantation, the grafts were challenged with 6 x 10(9) Staphylococcus aureus intravenously. One week after implantation, the grafts were harvested with sterile technique. Quantitative cultures were obtained from all the harvested grafts. The results were expressed as colony-forming units per cm(2) of graft material. Bacteriologic study was also performed on various tissue samples. The chi(2) test was used to compare the culture proven infection of control and antimicrobial grafts. RESULTS: All the control grafts were infected with S aureus at the time of removal. Five of the six silver/collagen-coated grafts were infected, whereas none of the six rifampin-bonded gelatin-sealed grafts grew S aureus (P <.01). There was no significant difference in the number of positive culture results of organ samples between the different groups of dogs. CONCLUSION: These results indicate that rifampin-bonded gelatin-sealed polyester grafts are significantly more resistant to bacteremic infection than are silver/collagen-coated polyester grafts in a highly challenging model.

Acetates↗
PubMed2002

Comparative study of the physical properties of core materials.

This study was undertaken to measure physical properties of materials used for direct core buildups, including high-copper amalgam, visible light-cured resin composite, autocured titanium-containing composite, polyacid-modified composite, resin-modified glass-ionomer, and silver cermet cement. Compressive strength, diametral tensile strength, and flexural strength of six core materials of various material classes were measured for each material as a function of time up to 3 months at different storage conditions, using a standard specification test designed for the materials. Three different storage conditions (dry, humid, wet) at 37 degrees C were chosen. Materials were manipulated according to manufacturers' instructions for use as cores. Mean compressive, diametral tensile, and flexural strengths with associated standard deviations were calculated for each material. Multiple comparison and Newman-Keuls tests discerned many differences among materials. All materials were found to meet the minimum specification requirements, except in terms of flexural strength for amalgam after 1 hour and the silver cermet at all time intervals.

Cermet Cements↗
PubMed2002

Resonance scattering spectral analysis of chlorides based on the formation of (AgCl)n(Ag)s nanoparticle.

A novel resonance scattering spectral method has been proposed for the determination of trace amounts of chlorides in the range of 2 x 10(-7)-8 x 10(-6) mol/l. It was based on the photochemical reaction system of AgNO3-NaCl-sodium oxalic to form the (AgCl)nucleus (n)(Ag)shell (s) nanoparticle. There is a strongest resonance scattering peak at 470 nm and a maximum absorption peak at 425 nm. The concentration of chlorides is proportional to the intensity of resonance scattering at 470 nm. The nonlinear resonance scattering peaks of the nanoparticle system have been also considered, according to the theory of the interaction between the surface electron of nanoparticle and the incidence photon.

Chlorides↗
PubMed1973

Solid state AgCl detectors for nuclear tracks with on- and off-response at choice: applications to life sciences.

A new concept of trackforming solid state detectors is presented. These detectors record and accumulate tracks of ionizing particles which can be revealed if they are irradiated with yellow light during the passage of the particle through the detector; otherwise the tracks are dropped by fading. Tracks stabilized by yellow light are stable for months. The detectors consist of thin layers of 200-300 micrometers of Cd-doped AgCl crystals, supported by a thin plate of quartz glass. The invisible latent tracks in these detectors are revealed at microscopically visible size by ultraviolet light. The sensitivity of the crystals against particles of different specific energy transfer depends upon the concentration of Cd; these have rather good thresholds, which permit selective recording in a well-known manner. These AgCl(Cd) crystals have a unique property amongst trackforming detectors; their response can be switched on and off at choice, for instance by electronic triggering of the stabilizing accompanying yellow light. This allows a time assignment of particle tracks, or restriction to tracks of desired particles. Examples of tracks and of applications in cosmic ray research, heavy ion physics, radiobiology and dosimetry are given.

Bacillus subtilis↗
PubMed2002

[Decontamination of dental unit waterlines using disinfectants and filters].

Bacterial contamination of the dental unit water system can become a health problem for patients, particularly if they are immunodepressed. The present study has had the purpose of evaluating the effectiveness of methods of chemical decontamination using different disinfectants (peracetic acid, hydrogen peroxide, silver salts, chloramine T, glutaraldehyde T4) and methods of physical decontamination using synthetic membranes for the filtration of water. A preliminary removal procedure of the biofilm present in the waterline has been followed in a dental unit prepared on purpose for the research; subsequently different 2-week long maintenance procedures were applied using disinfectants injected by a pump and finally the bacterial contamination of the water flowing from the waterline was evaluated. The physical decontamination was performed using 0.22 mm membrane filters, which have been installed also in another dental unit, and the filtered water was analyzed to detect bacterial contamination. The preliminary procedure of biofilm removal succeeded obtaining germ-free water. Among the disinfectants used for the maintenance of the water quality only glutaraldehyde T4 was able to reduce the bacterial contamination under the limit suggested by the ADA. The membrane filter system was not able to purify the water, but when a disinfectant (peracetic acid) was used in the last part of the waterline good results were obtained. At present no decontamination system of dental waterline is available, and glutaraldehyde T4 seems to be the best disinfectant only if integrated with periodic biofilm removal for the maintenance of the water quality.

Biofilms↗
PubMed1977

Assignment of particle tracks to spores of Bacillus subtilis on silver chloride detectors.

In Biostack III B, flown in the Apollo-Soyuz Test Project, AgCl detectors were used to study ionizing effects of HZE particles on spores of Bacillus subtilis or eggs of Artemia salina. The tracks of these particles inside the detectors are used to extrapolate the path of the particle near the biological objects which are fixed at the detector surface. The closest distance to the geometric centre of the object, the so-called impact parameter, is determined with a mean accuracy of 0.3 micrometers for 1 micrometers spores. From knowledge of the lateral distribution of the energy transferred by primary and secondary ionization effects of the particle, the energy deposit and its localization at the objects can be determined. We describe some technical aspects of a video-electronic scanning system, Quantimet 720, which has been adjusted to the particular requirements of these experiments. The main improvements achieved are increased precision of coordinate measurements, objective focusing of the microscopic image combined with measurements of the density profile of particle tracks, and finally speeding up of the measurements by automatic data transfer.

Animals↗
PubMedDate not supplied

A comparative study of plaque mutans streptococci levels in children receiving glass ionomer cement and amalgam restorations.

PURPOSE: The restorative materials amalgam (Standalloy F) and glass ionomer cements (Chelon Silver) were comparatively investigated to determine the number of mutans streptococci METHODS: Saliva and plaque were collected from patients before and 40 days after the insertion of their restorations. RESULTS: Total bateria and mutans streptococci counts were found to be statistically significantly reduced when compared with the prerestoration counts in the saliva samples (P<0.001). Microbiological analysis of the dental plaque showed that the number of mutans streptococci in the glass ionomer cements was significantly lower than in the amalgam restorations (P<0.001). CONCLUSIONS: This study showed that silver glass ionomer cements inhibited the growth of mutans streptococci.

Cermet Cements↗
PubMed2002

[Time resolution spectrum measurements of the process of photon acting on the silver halide materials].

The silver halide material is a very important optical information material. Silver halide material plays a very imperative role in the development of the information science and technology. The time characters of the photon action process determine the quality of the silver halide material to a great degree. We adopt the microwave absorption technology to measure the time characters of the process of the photon acting on silver halide material. A sample of the silver halide material is inserted into a microwave resonant cavity. With the excitation of excimer laser, photogenerated charge carriers are created in the silver halide material. The generation of the photogenerated charge carriers changes the dielectric function of the silver halide material. Therefore, the change of the dielectric function embodies the information of the time characters of the photogenerated change carries. At the same time, the change of the dielectric function results in an alteration of the cavity quality factor. This change leads to a reflected microwave. The reflected microwave contains the information of the time characters of the photon action process. Through the measurement of the reflected microwave, we can obtain the time resolution spectrum of the process of the photon acting on the silver halide material and study the time characters of the photon action process. The time resolution spectra of the process of the photon acting on various silver halide materials were obtained in our experiments. We analyzed the time characters of photon acting on the black-and-white film, color film and X-ray film.

Absorption↗
PubMed2003

[In situ diffuse reflectance FTIR spectroscopy study of the selective catalytic reduction reaction of NO over Ag/SAPO-34 catalysis].

An in situ diffuse reflectance FTIR spectroscopy (DRIFTS) study of the selective catalytic reduction (SCR) of NO with propene in the presence of excess O2 was carried out over Ag/SAPO-34 catalyst. The SCR reaction was investigated at temperatures from 573 to 773 K, and the role of oxygen in the NO reduction process was determined by comparing experiments using an initial reaction mixture containing oxygen and without oxygen. The results show that both NO and propene are easily activated in oxygen. Furthermore, the presence of oxygen is necessary to form organo-NOx adsorbed species. Based on these experiments, a reaction mechanism is proposed that NO, propene and oxygen react to form organo-nitro and organo-nitrito adsorbed species as key intermediates, and then these intermediates decompose to nitrogen.

Adsorption↗
PubMed2003

[Reversible temperature dependence of surface-enhanced Raman scattering of adenine, purine and pyrene].

The surface-enhanced Raman scattering (SERS) spectra of adenine, purine and pyrene adsorbed on a SERS-active silver surface roughened by nitric acid have been measured over the -190 degrees C-30 degrees C surface temperature range. The results show that the Raman shifts and SERS intensity of the vibrations, which are enhanced by electromagnetic mechanism, are affected by temperature, those by chemical mechanism are not. However, it has been found that the observed temperature dependence can be explained by postulating the reorientation of the absorbates. Adenine molecules and purine molecules prefer to adopt a more perpendicular stance on the surface at high temperature, but for a planar symmetric molecule, such as pyrene, the preferred orientation is parallel and temperature has no effect on its orientation.

Adenine↗
PubMed2003

[A study of aggregate behavior of green-sensitive dyes containing fluorine].

Five different-structure carboncyanine dyes containing fluorine in methanol solution and the aggregate behavior on the surface of AgIBr tabulate grains were investigated, the photographic capability determined and the sensitive multiple calculated. From the monomolecular absorption curves of dye1, dye2 and dye3 in methanol solution, it can be seen that when the substitute changed from C2H5 to CH3 to no substitute, the maximal absorption peak shifted to a shorter wavelength. Sensitive dye with ethylene (dyel) adsorbed on the AgBrI surface formed a higher peak of J-aggregate with a higher sensitive multiple. Sensitive dye with no substitute (dye3) did not form J-aggregate, which had a low sensitive multiple and reduced the sensitivity. Compared with dye5, dye4 had a sharper and narrower reflective spectrum and a higher sensitive multiple. The results showed that a different-structure dye adsorbed on silver halide grains formed a different J-aggregate. The sensitive dye of J-aggregate with a sharper absorption spectrum had a higher sensitive multiple.

Bromides↗