PubMed · 11626301
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W Baroni. 1971. [Not Available].. https://pubmed.ncbi.nlm.nih.gov/11626301/
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Glass-ceramic materials are frequently used in prosthetic dentistry because of their excellent esthetics. Problematic aspects of glass ceramics are their limited strength, the scatter in their strength data, and their time-dependent strength decrease due to subcritical crack growth effects. The short-term strength level can be significantly increased by an ion-exchange process in a potassium salt. A dual ion-exchange process in KNO3/NaNO3 can additionally improve the scatter-in-strength. The objective of the present study was to examine the effect of a single and a dual ion-exchange process on the characteristic time-dependent strength decrease of a leucite-reinforced dental glass. The parameters of subcritical crack growth were evaluated by using the constant stress rate flexural strength test. Both ion-exchange processes showed a pronounced effect on the subcritical crack growth of the glass-ceramic material. The exponential crack parameter n was increased from 25 to 52 by the single-exchange and to 107 by the dual-exchange process, respectively. We conclude that the time-dependent strength decrease of a dental glass-ceramic material can be significantly limited by the ion-exchange process. This could improve the clinical reliability of dental restorations made from this class of materials.
A new method for rapid extraction of Volatile Organic Compounds (VOC) from low permeability, unconsolidated geologic media such as clayey soil has been developed and tested using trichloroethylene (TCE) as the model compound. The technique is based on a combination of sonication and mechanical agitation of the samples. The sample vials, mounted in a special holder attached to an orbital shaker, were immersed in an ultrasonic bath during extraction. The extracts were analyzed by gas chromatography with electron capture detection (GC-ECD). The method was validated using clay samples from a TCE-contaminated industrial site by comparing TCE recoveries to those obtained by the standard methanol extraction. In all cases, the recoveries obtained with the new method were the same or better than the recoveries obtained with the reference method. The extraction time was shortened from 5 days with the standard method to less than 2 h with the new method. The new technique makes it possible to analyze a large number of samples in a short time, without the need for sample preservation and prolonged storage. It has good potential for on-site analysis to facilitate decisions while field investigations are in progress.
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