Dimensional stability of elastomeric impression materials: a critical review of the literature.

The aim of the present paper was to review the literature concerning the dimensional stability of dental elastomeric impression materials, to support recommendations to control the variables that influence the accuracy of these materials. An electronic search of the Scopus and PubMed databases was performed in November 2010. Articles were selected according to the following inclusion criteria: investigation of the dimensional stability of dental elastomers, an experimental study, sample size reported, laboratory tests described, and published in an English language peer-reviewed journal. The search resulted in 47 articles published between 1958 and 2008; of these, 24 were selected for inclusion in the present study. Great variability was discovered in the experimental methodologies used, such as different working times, temperatures and storage mediums for the impressions, impression techniques, material thicknesses, tray types, and methods of evaluation. Despite the lack of standardization among the studies, this review supports the following recommendations to control the dimensional stability: impressions should be stored at temperatures between 21 +/- 2 degrees C; polyether impressions should be stored in an environment with a relative humidity below 50%; time until pouring has been settled for each elastomer material.

Performance trade-offs in in situ chemostat NMR.

Investigating cell cultures with NMR requires high cell densities to provide adequate signal-to-noise, or scans must be summed over long time periods and short-term events are lost. The mixing within a chemostat can be used to shorten the time required to acquire informative in situ NMR spectra from cell cultures. However, performance trade-offs can occur between net signal, spectral resolution, and oxygenation due to sampling volume, conductivity, gas bubble, and fluid flow effects. These trade-offs and the effect of different mixing regimes were theoretically analyzed to quantify how device design decisions impact performance. The results were found to concur with data from cell-free NMR experiments performed in 18 mS/cm conductivity medium. The results also guided the redesign of an NMR bioreactor in terms of relative radio frequency (rf) coil and sample dimensions and other factors. The design, which entails using chemostat mixing to shunt sample through a rf coil in ca. 0.4 s, provides adequate oxygenation for the 4-16% (v/v) cell suspensions examined. Gains realized include lower conductive losses, better magnetic field homogeneity, and the exclusion of gas bubbles from the sampling zone. These gains enable the acquistion of spectra from dilute (3-4% v/v) Saccharomyces cerevisiae chemostat cultures in 6.9 min with high resolution in both the orthophosphate and the beta-NTP regions. Samples with 16% (v/v) cells also yield useful spectra within 0.5-1.0 min.

Mechanisms of clearance of Treponema pallidum from the CSF in a nonhuman primate model.

OBJECTIVES: To establish a model of CNS invasion by Treponema pallidum and to use it to investigate the immune mechanisms responsible for clearance. METHODS: Four macaques were intrathecally inoculated with 0.6 to 2.1 x 10(8) T. pallidum and underwent clinical examinations and blood and CSF collections every 1 to 2 weeks for 12 to 13 weeks. The following were determined: serum Venereal Disease Research Laboratory (VDRL) and microhemagglutination-T. pallidum reactivities, CSF-VDRL, CSF white blood cell (WBC) count, and the presence of viable T. pallidum in CSF by the rabbit infectivity test (all animals), as well as the presence of T. pallidum in CSF by reverse transcriptase (RT)-PCR, WBC phenotype by fluorescence-activated cell sorter, WBC cytokine production by RT-PCR, and brain MRI at 10 weeks (two animals). RESULTS: All animals became systemically infected and developed CSF pleocytosis that resolved after 8 weeks. CSF T. pallidum was detected from 2 to 8 weeks. CSF T lymphocytes were predominantly CD4+. Interferon-gamma (IFN-gamma) mRNA was consistently detected in CSF WBCs, but interleukin (IL)-4 and IL-5 were not. All animals remained clinically well. MRIs were normal. CONCLUSIONS: In this model, T. pallidum is cleared from the CNS just as in most humans with early syphilis. Local production of IFN-gamma likely participates in this process. This model could be used to clarify the effect of retrovirus-induced immunodeficiency on clearance of T. pallidum from the CNS and on the local CNS immune response.

In situ 31P nuclear magnetic resonance for observation of polyphosphate and catabolite responses of chemostat-cultivated Saccharomyces cerevisiae after alkalinization.

The proposed pH buffering and phosphagenic functions of polyphosphate were investigated by subjecting chemostat-cultivated Saccharomyces cerevisiae to alkalinization (NaOH addition) and anaerobiosis. The subsequent changes in intracellular phosphate-containing species were observed in situ by nuclear magnetic resonance (NMR) spectroscopy by using the NMR cultivator we developed. For the alkalinization experiments, changes in catabolite secretion were also measured in parallel experiments. Additionally, a range of potential neutralization capacity was investigated: a dilute culture and concentrated cultures with low or high polyphosphate content. The concentrated cultures displayed increased cytosolic pH and rapid polyphosphate degradation to small chains. The pH changes and extent of polyphosphate degradation depended inversely on initial polyphosphate content. The dilute culture restored extracellular pH rapidly and secreted acetate. The concentrated culture with low polyphosphate reserves also secreted acetate. In contrast to the alkalinization-induced polyphosphate dynamics, anaerobiosis resulted in the complete hydrolysis of polyphosphate to P(i), as opposed to small chains, and reduced cytosolic pH. The results and calculations suggest that the bulk of NMR-observable polyphosphate (vacuolar) degradation to short polymers conceivably contributes to neutralizing added alkalinity. In other circumstances, such as anaerobiosis, degradation serves other functions, such as phosphorylation potential regulation.