An Investigation of the Dimensional Stability of Dental Alginates

Dimensional stability was defined by Nicholls (1977) as “the ability (of a material) to maintain accuracy over time”, and the result of loss of accuracy, “distortion”, as “the relative movement of a single point, or group of points, away from some originally specified reference position such that permanent deformation is apparent”. Maintaining dimensional stability of dental impression materials is vital if the impression cannot be cast (in stone) soon after removal from the mouth. Dental irreversible hydrocolloid (alginate) is a major dental impression material used worldwide in many clinical procedures. However, alginate is dimensionally unstable and changes its dimensions (suffers “distortion”) after removal from the mouth. With storage times of more than ten minutes, alginate begins to distort, and after one to three hours (depending on the product and storage conditions) cannot be used for many clinical purposes, especially fixed prosthodontics such as crowns and bridges (Hampson 1955, Skinner & Hoblit 1956, Wilson & Smith 1963, Rudd et al. 1969, Miller 1975, Inohara 1977, Schoen et al. 1978, Coleman et al. 1979, Linke et al. 1985, Habu et al. 1986, Peutfeldt & Asmussen 1989, Mathilde & Peters 1992, Khan & Aziz Sahu 1995, Eriksson et al. 1998, Schleier et al. 2001, and Donovan & Chee 2004). This loss of accuracy, due to dimensional instability, manifests as a time-dependent distortion of the poured stone cast, and thus any prosthesis fabricated will not fit in the mouth. With the introduction of the more stable elastomers in the 1950s (Stackhouse 1970, Glenner 1997, Brown 2003) that could be stored for days if necessary, without loss of accuracy, the alginates fell out of favour for fixed prosthodontics. Recently, there has been a resurgence of interest in alginate for use in dental procedures where dimensional stability is critical (Peutzfeldt and Asmussen 1989, Eriksson et al. 1998). This in part is due to the favourable properties of alginate not found in the elastomers. Of greatest significance is that alginate hydrocolloid is hydrophilic, whereas elastomers are hydrophobic (Phillips & Ito 1958, Glenner 2004). Thus, alginate materials are able to reproduce wet oral areas with greater precision and to produce a superior "fit" of, say, a gold casting produced by the Lost Wax technique (Skinner and Phillips 1982). A number of reports have been published which investigate newer alginate materials that are claimed to be more dimensionally stable than older formulations. Puetzfeldt and Asmussen (1989) found that a newer alginate , if stored at 100% relative humidity, retained accuracy over 24 hours that was equivalent to that of the elastomers. More recently, the manufacturer of another alginate has claimed equivalent dimensional stability to the elastomers for up to 100 hours, and, whilst this claim has not been reported on in the literature, the present thesis will show that, under favourable conditions of storage, the material maintained clinically useful accuracy for up to 100 hours. Another approach to improving the accuracy of alginate impressions has been to combine reversible hydrocolloid with alginate (the “Bilaminar” technique). Frederick and Caputo (1997) confirmed that the new agar reversible hydrocolloids are just as accurate (at the time of removal from the mouth) as the new elastomers. Mathilde et al. (1992) and Eriksson et al. (1998) have shown that several of the “bilaminar” impression techniques for fixed prosthodontics, where alginate is used as a tray material supporting a reversible hydrocolloid (agar) wash, are as accurate and dimensionally stable as elastomers for up to three hours. However, these studies are difficult to interpret due to lack of uniformity in the testing methods, and the fact that there is no regulatory standard available to measure dimensional stability for dental alginates. The International Standard (IS) for alginate impression materials (ISO 1563:1990E) contains no specification for dimensional stability, and thus places no requirement for manufacturers to state dimensional stability properties on their labels. In contrast, ISO 4823:1992(E) specifies the IS for elastomeric dental impression materials, and it does specify a requirement for dimensional stability (less than 1.5% distortion after 24 hours). Further, the IS sets a method for determination of dimensional stability. Briefly, this method (the Optical Method) uses a travelling optical microscope to measure the accuracy of the distance between score lines on an impression of a test grid, at various time periods. The American Dental Association Specification No. 19 for dental elastomeric impression materials is identical to the IS. There is currently no specific Australian Standard (AS) for the dimensional stability of any dental impression material. Overview of Experimental Methods A. The Optical Method The aim of Part A of this investigation was to: 1. Adapt the Optical Method of the IS for elastomers to be reproducible for dental alginates. This was achieved by using a perforated test tray (to simulate clinical conditions), and measuring the grid pattern on a dental stone button after casting the test impression, rather than direct measurement of the impression, as for the IS. 2. To measure and rank the dimensional stability of a number of locally available dental alginates. Measurements of the test stone buttons proved reproducible, and the results were different for each sample, allowing them to be ranked according to dimensional stability after 50 and 100 hours of storage. The results show that the traditional optical method for measuring dimensional stability, as specified in the IS for dental elastomers, can be adapted to measure the dimensional stability of dental alginates However, the Optical Method of measuring dimensional stability of dental alginates is cumbersome and time-consuming. It was hypothesised that dimensional stability of dental alginates could be measured more conveniently by finding a thermal property that is directly proportional to dimensional stability. This method could be useful for the rapid determination of relative performance, and allow comparison with a determined benchmark. B. The Thermal Method Recently, modern methods of Thermal Analysis, Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) have been used to rapidly age various polymers, including food alginates (Chinachoti 1996), in order to measure thermal stability. This thesis shows that thermal stability is an indicator of dimensional stability. The aim of Part B of this investigation was therefore to adapt thermal analysis techniques to dental alginates, and develop a method to measure their thermal stability. These results were then compared with those for dimensional stability measured by the Optical Method to determine the relationship between thermal and dimensional stability for dental alginates. The results show that current thermal analysis methods of TGA and DSC can be adapted to measure relative dental alginate dimensional stability, and are both rapid and convenient. This study also provides evidence that commercial products differ as regards the property of dimensional stability, and can be ranked accordingly. C. Practical Application of the Methods The aim of part C of this thesis was to validate the methods (both optical and thermal) developed in this study by using them to investigate the effect of varying the water/powder ratio on the dimensional stability of dental alginates. It was shown that dimensional stability is affected by changes to the recommended water/powder ratio, that both the methods detected and measured the changes, and that the results were proportional, in that any percentage change detected by the optical method, was mirrored by the thermal method, confirming that the more convenient thermal methods can be used to measure dimensional stability

The establishment of variant surface glycoprotein monoallelic expression revealed by single-cell RNA-seq of Trypanosoma brucei in the tsetse fly salivary glands

International audienceThe long and complex Trypanosoma brucei development in the tsetse fly vector culminates when parasites gain mammalian infectivity in the salivary glands. A key step in this process is the establishment of monoallelic variant surface glycoprotein (VSG) expression and the formation of the VSG coat. The establishment of VSG monoallelic expression is complex and poorly understood, due to the multiple parasite stages present in the salivary glands. Therefore, we sought to further our understanding of this phenomenon by performing single-cell RNA-sequencing (scRNA-seq) on these trypanosome populations. We were able to capture the developmental program of trypanosomes in the salivary glands, identifying populations of epimastigote, gamete, pre-metacyclic and metacyclic cells. Our results show that parasite metabolism is dramatically remodeled during development in the salivary glands, with a shift in transcript abundance from tricarboxylic acid metabolism to glycolytic metabolism. Analysis of VSG gene expression in pre-metacyclic and metacyclic cells revealed a dynamic VSG gene activation program. Strikingly, we found that pre-metacyclic cells contain transcripts from multiple VSG genes, which resolves to singular VSG gene expression in mature metacyclic cells. Single molecule RNA fluorescence in situ hybridisation (smRNA-FISH) of VSG gene expression following in vitro metacyclogenesis confirmed this finding. Our data demonstrate that multiple VSG genes are transcribed before a single gene is chosen. We propose a transcriptional race model governs the initiation of monoallelic expression

The Transcriptional and Epigenomic Foundations of Ground State Pluripotency

SummaryMouse embryonic stem (ES) cells grown in serum exhibit greater heterogeneity in morphology and expression of pluripotency factors than ES cells cultured in defined medium with inhibitors of two kinases (Mek and GSK3), a condition known as “2i” postulated to establish a naive ground state. We show that the transcriptome and epigenome profiles of serum- and 2i-grown ES cells are distinct. 2i-treated cells exhibit lower expression of lineage-affiliated genes, reduced prevalence at promoters of the repressive histone modification H3K27me3, and fewer bivalent domains, which are thought to mark genes poised for either up- or downregulation. Nonetheless, serum- and 2i-grown ES cells have similar differentiation potential. Precocious transcription of developmental genes in 2i is restrained by RNA polymerase II promoter-proximal pausing. These findings suggest that transcriptional potentiation and a permissive chromatin context characterize the ground state and that exit from it may not require a metastable intermediate or multilineage priming

Evaluation of pH effect on solubility and precipitation of proteins from hemp (\kur{Cannabis sativa} L.) meal

In this thesis was examined the influence of pH on solubility and precipitation of proteins extracted from the flour of the Cannabis sativa L plant. For this experiment was chosen the pH in the range of 3 to 11. Monoecious breeds of canabis USO 31 and Fedora 17 were chosen for this purpose. Laboratory methods were applied after the protein extraction, in order to define the content of nitrate substances which was the highest at pH 11. Protein spectrums were detected by the SDS-PAGE analysis where especially in an alkaline environment, globuline fraction was present at a greater amount than was the albuminium one. The next step was the isoelectric precipitation of extracted proteins within the variances containing high values of nitrate substances. The content of the nitrate substances in the protein extract was spanning between 56,3 % to 92,9 %. Based on the results of the experiment, is is feasible to conclude that Fedora 17, which was extracted at the alkaline pH 11 and isoelectrically precipitate to pH value 5 and 6, contained the highest amount of protein

Formation en IUFM : les modes de groupement comme analyseur de la dynamique d'enseignement

is a document containing the supplementary figures, legends, tables, and methods. (PDF 13200 kb

Effects of Carvedilol Versus Metoprolol on Platelet Aggregation in Patients With Acute Coronary Syndrome: The PLATE-BLOCK Study

Platelet aggregation plays a pivotal role in acute coronary syndrome (ACS). In this setting, β-blockers (BBs) are used to counteract the effects of catecholamines on heart. Circulating catecholamines can also potentiate platelet reactivity, mainly through α2- and β2-adrenoceptors on human platelets’ surface, thus BB may affect platelet aggregation; however, the effects of different BBs on platelet aggregation in contemporary-treated patients with ACS have been poorly investigated. One hundred patients with ACS on dual antiplatelet therapy with aspirin and ticagrelor were randomized to receive treatment with carvedilol, a nonselective BB (n = 50), or metoprolol, a selective β1-blocker (n = 50), at maximum tolerated dose. Light transmission aggregometry was performed at randomization (T0) and at 30-day follow-up (T30), and the results were expressed as a percentage of maximum platelet aggregation (MPA). The primary end point was epinephrine-induced MPA at 30 days. Patients were predominantly men (80%), and mean age was 57.3 ± 9.7 years. The 2 randomized groups were well balanced for baseline characteristics. At T0, mean MPA was similar between the groups (18.96 ± 9.05 vs 18.32 ± 9.21 with 10 µM epinephrine, 14.42 ± 9.43 vs 15.98 ± 10.08 with 20 µM adenosine diphophate (ADP), and 13.26 ± 9.83 vs 14.30 ± 9.40 with 10 µM ADP for carvedilol and metoprolol, respectively, all p = NS). At 30 days, platelet aggregation induced by epinephrine was significantly lower in the carvedilol group than in the metoprolol group (23.52 ± 10.25 vs 28.72 ± 14.37, p = 0.04), with a trend toward the lower values of ADP-induced MPA (20 µM ADP 19.42 ± 13.84 vs 24.16 ± 13.62, p = 0.09; 10 µM ADP 19.12 ± 12.40 vs 22.57 ± 13.59, p = 0.19). In conclusion, carvedilol, a nonselective BB, reduces residual platelet reactivity in patients with ACS compared with the selective BB, metoprolol

List of TTE-MBD2 specific interactors identified from Mass Spectrometry.

<p>25 most significantly enriched TTE-MBD2 interactors, identified after Ty1 immunoprecipitation on both TTE-MBD2 and WT cells followed by mass spectrometry analysis. Results from triplicate pull-downs were analyzed with MaxQuant and label-free quantitation (LFQ) intensities were used to determine statistically enriched MBD2 interactors. Immunoprecipitation from wild type (WT) MCF-7 was used as a control.</p

Genome-wide binding of TTE-MBD2.

<p>a) Heatmap displaying tag densities in TTE-MBD2 (left and right) and input (middle) at MBD2 binding sites around 5 kb up- and downstream of the center of the peaks. b) Genomic location of peaks: each category is expressed as fold over random (y-axis), the random set consists of an equal number of sites having on average same length of the peaks. c) CpG content of each category expressed as percentage of the total binding sites (y-axis). d) Screenshots from the genome browser showing example of CGI promoters (KDM2A) and exons (MZF1, ZNF837, ZNF497) binding.</p

IL-7 receptor signaling drives human B-cell progenitor differentiation and expansion

Although absence of interleukin 7 (IL-7) signaling completely abrogates T and B lymphopoiesis in mice, patients with severe combined immunodeficiency caused by mutations in the IL-7 receptor α chain (IL-7Rα) still generate peripheral blood B cells. Consequently, human B lymphopoiesis has been thought to be independent of IL-7 signaling. Using flow cytometric analysis and single-cell RNA sequencing of bone marrow samples from healthy controls and patients who are IL-7Rα deficient, in combination with in vitro modeling of human B-cell differentiation, we demonstrate that IL-7R signaling plays a crucial role in human B lymphopoiesis. IL-7 drives proliferation and expansion of early B-cell progenitors but not of pre-BII large cells and has a limited role in the prevention of cell death. Furthermore, IL-7 guides cell fate decisions by enhancing the expression of BACH2, EBF1, and PAX5, which jointly orchestrate the specification and commitment of early B-cell progenitors. In line with this observation, early B-cell progenitors of patients with IL-7Rα deficiency still expressed myeloid-specific genes. Collectively, our results unveil a previously unknown role for IL-7 signaling in promoting the B-lymphoid fate and expanding early human B-cell progenitors while defining important differences between mice and humans. Our results have implications for hematopoietic stem cell transplantation strategies in patients with T− B+ severe combined immunodeficiency and provide insights into the role of IL-7R signaling in leukemogenesis.</p