PubMed · 9560616
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G Freedman. 1997. Dentin and pulp simulation in ceramic restorations.. https://pubmed.ncbi.nlm.nih.gov/9560616/
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Microporous materials, such as zeolites and aluminophosphates, have many applications as molecular sieves and shape-selective catalysts. This is due to their three-dimensional frameworks, which contain regular pores and channels, to their high acidity, arising from Brønsted and Lewis acid active sites, and to the incorporation of transition metal atoms into framework sites. This review firstly provides an introduction into the nature and properties of these materials, and their important applications; the difficulties in their full characterization and possible methods of elucidating their structures are then outlined; finally, methods of characterization, utilizing 'softer X-rays' are introduced. The first method is the determination of low concentrations of transition metals, incorporated into the frameworks using single crystal anomalous dispersion crystallography; synchrotron radiation is used to tune to the absorption edge of the metal atom in question, in order to change its signal relative to that of the rest of the structure, thereby allowing the pinpointing of its positions and the determination of its concentration at each site in the framework. Secondly, the use of longer wavelengths in powder diffraction studies is described, which, by stretching out the powder pattern, thereby reduces the overlapping of the diffraction peaks, thus allowing the structure to be solved by conventional direct methods. Finally, the use of X-ray absorption spectroscopy to determine the metal incorporation and the nature of coordination at the metal atom sites, in Mn silicalite-1 and FAPO-36, are described.
Impressions, dentures and other dental appliances may be contaminated with oral micro-flora or other organisms of varying pathogenicity from patient's saliva and blood. Several approaches have been tried to control the transmission of infectious organisms via dental impressions and because disinfection is less effective and has several drawbacks for impression characterization, several sterilization methods have been suggested. This study evaluated the reproducibility of rubber impressions after sterilization by different methods. Dimensional accuracy and wettability of two rubber impression materials (vinyl polysiloxane and polyether) were evaluated after sterilization by each of three well-known methods (immersion in 2% glutaraldehyde for 10 h, autoclaving and microwave radiation). Non-sterilized impressions served as control. The effect of the tray material on impression accuracy and the effect of topical surfactant on the wettability were also evaluated. One-way ANOVA with Dunnett's method was used for statistical analysis. All sterilizing methods reduced the reproducibility of rubber impressions, although not always significantly. Microwave sterilization had a small effect on both accuracy and wettability. The greater effects of the other methods could usually be overcome by using ceramic trays and by spraying impression surfaces with surfactant before pouring the gypsum mix. There was one exception: glutaraldehyde still degraded dimensional accuracy even with ceramic trays and surfactant. We conclude that a) sterilization of rubber impressions made on acrylic trays was usually associated with a degree of dimensional change; b) microwave energy seems to be a suitable technique for sterilizing rubber impressions; c) topical surfactant application helped restore wettability of sterilized impressions.
Titania membranes, with a molecular weight cut-off of 15 kD were used in an ozonation/membrane system that was fed with water from Lake Lansing, which had been pre-filtered through a 0.45 microm glass fiber filter. The application of ozone gas prior to filtration resulted in significant decreases in membrane fouling. The effects of ozonation could not be explained by physical scouring of the filter cake. Decrease in the pH resulted in a concomitant increase in the dissolved ozone concentration in the feed water and in an improvement in permeate flux recovery. Increasing the ozone concentration beyond a threshold value had no beneficial effect on permeate flux recovery. Ozone decomposition, resulting in the formation of OH or other radicals at the membrane surface, is thought to result in the decomposition of organic foulants at the membrane surface and reduce the extent of membrane fouling.