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Experimental Material (experimental + material)
Selected AbstractsPolymerization Contraction Stress of Resin Composite Restorations in a Model Class I Cavity Configuration Using Photoelastic AnalysisJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 6 2000YOSHIFUMI KINOMOTO DDS ABSTRACT Purpose: An important factor that contributes to deterioration of resin composite restorations is contraction stress that occurs during polymerization. The purpose of this article is to familiarize the clinician with the characteristics of contraction stress by visualizing the stresses associated with this invisible and complex phenomenon. Materials and Methods: Internal residual stresses generated during polymerization of resin composite restorations were determined using micro-photoelastic analysis. Butt-joint preparations simulating Class I restorations (2.0 mm ± 5.0 mm, 2.0 mm in depth) were prepared in three types of substrates (bovine teeth, posterior composite resin, and transparent composite resin) and were used to examine contraction stress in and around the preparations. Three types of composite materials (a posterior composite, a self-cured transparent composite, and a light-cured transparent composite) were used as the restorative materials. The self-cured composite is an experimental material, and the others are commercial products. After treatment of the preparation walls with a bonding system, the preparations were bulk-filled with composite. Specimens for photo-elastic analysis, were prepared by cutting sections perpendicular to the long axis of the preparation. Fringe patterns for directions and magnitudes of stresses were obtained using transmitted and reflected polarized light with polarizing microscopes. Then, the photoelastic analysis was performed to examine stresses in and around the preparations. Results: When cavity preparations in bovine teeth were filled with light-cured composite, a gap was formed between the dentinal wall and the composite restorative material, resulting in very low stress within the restoration. When cavity preparations in the posterior composite models were filled with either self-cured or light-cured composite, the stress distribution in the two composites was similar, but the magnitude of the stress was greater in the light-cured material. When preparations in the transparent composite models were filled with posterior composite and light-cured transparent composite material, significant stress was generated in the preparation models simulating tooth structure, owing to the contraction of both restorative materials. CLINICAL SIGNIFICANCE Polymerization contraction stress is an undesirable and inevitable characteristic of adhesive restorations encountered in clinical dentistry that may compromise restoration success. Clinicians must understand the concept of polymerization contraction stress and realize that the quality of composite resin restorations depends on successful management of these stresses. [source] The case for sequencing the genome of the electric eel Electrophorus electricusJOURNAL OF FISH BIOLOGY, Issue 2 2008J. S. Albert A substantial international community of biologists have proposed the electric eel Electrophorus electricus (Teleostei: Gymnotiformes) as an important candidate for genome sequencing. In this study, the authors outline the unique advantages that a genome sequencing project of this species would offer society for developing new ways of producing and storing electricity. Over tens of millions of years, electric fish have evolved an exceptional capacity to generate a weak (millivolt) electric field in the water near their body from specialized muscle-derived electric organs, and simultaneously, to sense changes in this field that occur when it interacts with foreign objects. This electric sense is used both to navigate and orient in murky tropical waters and to communicate with other members of the same species. Some species, such as the electric eel, have also evolved a strong voltage organ as a means of stunning prey. This organism, and a handful of others scattered worldwide, convert chemical energy from food directly into workable electric energy and could provide important clues on how this process could be manipulated for human benefit. Electric fishes have been used as models for the study of basic biological and behavioural mechanisms for more than 40 years by a large and growing research community. These fishes represent a rich source of experimental material in the areas of excitable membranes, neurochemistry, cellular differentiation, spinal cord regeneration, animal behaviour and the evolution of novel sensory and motor organs. Studies on electric fishes also have tremendous potential as a model for the study of developmental or disease processes, such as muscular dystrophy and spinal cord regeneration. Access to the genome sequence of E. electricus will provide society with a whole new set of molecular tools for understanding the biophysical control of electromotive molecules, excitable membranes and the cellular production of weak and strong electric fields. Understanding the regulation of ion channel genes will be central for efforts to induce the differentiation of electrogenic cells in other tissues and organisms and to control the intrinsic electric behaviours of these cells. Dense genomic sequence information of E. electricus will also help elucidate the genetic basis for the origin and adaptive diversification of a novel vertebrate tissue. The value of existing resources within the community of electric fish research will be greatly enhanced across a broad range of physiological and environmental sciences by having a draft genome sequence of the electric eel. [source] Translucency of glass-fibre-reinforced composite materialsJOURNAL OF ORAL REHABILITATION, Issue 8 2004T. Nakamura summary, The purpose of this study was to examine the translucency of glass-fibre-reinforced composite framework materials. Vectris and FibreKor, as well as an experimental material, were the glass-fibre-reinforced framework materials used. Targis, Sculpture and Estenia were the types of particulate filler composites veneered onto frameworks. Specimens were fabricated from each material, 0·5 and 1·0 mm thick. In addition, laminate specimens, 1·5 mm thick, were fabricated. The translucency of each specimen was evaluated by determining its contrast ratio. The laminate specimens were examined for colour differences. The experimental framework material was more translucent than the enamel composite when it was not coloured, and was nearly as translucent as the dentine composite when coloured. The commercial tooth-coloured framework materials were nearly as translucent as the dentine composite. It was found that it was possible to reproduce the same colour as the veneering dentine composite, when the framework thickness was 0·5 mm, except in the case of FibreKor. Within the limitations of this study, tooth-coloured, glass-fibre-reinforced framework materials are nearly as translucent as the veneering dentine composite, but these materials affect the colour of the prosthesis if the thickness of the framework material is increased beyond a certain point. [source] Effects of Tisseel and FloSeal on Primary Ischemic Time in a Rat Fasciocutaneous Free Flap Model,THE LARYNGOSCOPE, Issue 2 2004Aaron W. Partsafas BS Abstract Objectives: Free flaps are the technique of choice for reconstruction of defects resulting from extirpation of tumors of the head and neck. Advances in microsurgical technique have resulted in success rates of greater than 95%. Numerous intraoperative factors, ranging from technical issues to topically applied agents, can complicate the outcome of microsurgical free tissue transfer. Synthetic tissue adhesives and hemostatic agents are playing an ever-increasing role in reconstructive surgery. The safety of these factors in free flap surgery has not been ascertained. Study Design: Animal Care Committee live rat model. Methods: Male Sprague-Dawley rats were divided into three groups: group I, Control; group 2, FloSeal; group 3, Tisseel. In each group, a 3 × 6 cm ventral fasciocutaneous groin flap based on the left superficial epigastric artery was elevated and the experimental material applied beneath the flap and around the flap pedicle prior to suturing of the flap back to the wound bed. The experimental materials consisted of 0.2 mL saline in the control group, 0.5 mL FloSeal, and 0.2 mL Tisseel. In phase I of this study, the effect of each treatment on flap survival was assessed by survival at postoperative day 4. In phase II of the study, the effects of these agents on ischemic tolerance was investigated. Five rats in each treatment group were exposed to ischemic times of 6, 8, 10, and 12 hours. Survival of the flap was assessed 7 days after reversal of the ischemia. Probit curves and the critical ischemic time (CIT50) were calculated. Results: All flaps survived the 2-hour period of ischemia and were viable at postoperative day 4. Flap survival from group 1 (Control), group 2 (FloSeal), and group 3 (Tisseel) at the various ischemic times was as follows: at 6 hours, 80%, 80%, and 80%, respectively; at 8 hours, 80%, 80%, 60%; at 10 hours, 60%, 33%, 40%; at 12 hours, 20%, 20%, 0%. The CIT50 for the Control, FloSeal, and Tisseel groups was 9.4, 9.0, and 7.0 hours, respectively. Conclusions: FloSeal, a thrombin-based hemostatic agent, and Tisseel, a fibrin glue, displayed no adverse effect on flap survival in this model. [source] Cytotoxicity of MTA and Portland cement on human ECV 304 endothelial cellsINTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2005G. De Deus Abstract Aim, To evaluate the cytotoxic effects of two brands of mineral trioxide aggregate (MTA) (Pro-Root MTA® and MTA Angelus®) and Portland cement (PC) on the human ECV 304 endothelial cell line. Methodology, Endothelial ECV 304 cells were incubated at 37 °C in an atmosphere of 95% air, 5% carbon dioxide and 100% humidity for 7 days and grown in F12 medium supplemented with 10% fetal bovine serum with 50 ,g mL,1 of gentamicin sulphate. Effects of the materials on mitochondrial functions were measured by a colorimetric assay. At each experimental time interval (24, 48 and 72 h), a dimethyl-thiazol-diphenyl tetrazolium bromid assay was conducted to measure cell viability. All assays were repeated three times to ensure reproducibility. Results were expressed as average absorbance (A570\,nm) ± SD and the data were analysed statistically by one-way analysis of variance and the Bonferroni post-test. A P -value <0.05 was considered statistically significant. Results, No statistically significant difference was shown between any of the experimental materials (P > 0.05). Conclusions, The two brands of MTA analysed, as well as the PC, initially showed a similar elevated cytotoxic effect that decreased gradually with time allowing the cell culture to become reestablished. [source] Fallacies in probability judgments for conjunctions and disjunctions of everyday eventsJOURNAL OF BEHAVIORAL DECISION MAKING, Issue 3 2009Fintan J. CostelloArticle first published online: 16 OCT 200 Abstract The conjunction fallacy occurs when people judge a conjunction B-and-A as more probable than a constituent B, contrary to probability theory's ,conjunction rule' that a conjunction cannot be more probable than either constituent. Many studies have demonstrated this fallacy in people's reasoning about various experimental materials. Gigerenzer objects that from a ,frequentist' standpoint probability theory is not valid for these materials, and so failure to follow the conjunction rule is not a fallacy. This paper describes three experiments showing that the conjunction fallacy occurs as consistently for conjunctions where frequentist probability theory is valid (conjunctions of everyday weather events) as for other conjunctions. These experiments also demonstrate a reliable correlation between the occurrence of the conjunction fallacy and the disjunction fallacy (which arises when a disjunction B-or-A is judged less probable than a constituent B). This supports a probability theory,+,random variation account of probabilistic reasoning. Copyright © 2008 John Wiley & Sons, Ltd. [source] Integrating Formal and Functional Approaches to Language Teaching in French Immersion: An Experimental StudyLANGUAGE LEARNING, Issue 2001Elaine M. Day This experimental study was designed to evaluate the effect on French language proficiency of an integrated formal, analytic and functional, communicative approach (experiential) to second-language teaching in the immersion classroom. The impetus for the study arises from previous research indicating that immersion children show persistent weaknesses in their grammatical skills despite the fluent, functional proficiency they achieve in their second language. The experimental materials, which were custom-designed for our study, highlight form-function relations, promote noticing, encourage metalin-guistic awareness, and provide opportunities for language practice and thus relate to some of the theoretical issues that Rod Ellis (this volume) has indicated are important in SLA in the 90s. This classroom-based study on the conditional is one of a series of studies undertaken in Canadian French immersion to investigate the effectiveness of form-focused instruction in classrooms (see Swain, 2000). The results of our study, which was conducted in grade 7 early immersion, showed that the Experimental group performed significantly higher in writing than the Control group, in both the post- and the follow-up testing. Although this was not found for speaking, an examination of the individual class data revealed greater and more consistent growth in speaking for the Experimental than for the Control classes, suggesting that they benefited somewhat from the experi- mental treatment in this domain as well. Although Ellis (this volume) notes that research on form-focused instruc- tion in the 90s has tended to split pedagogy from theory, the immersion research in this area does not seem t o reflect this shift. In a recent article, Swain (2000) reviews the French Immersion (FI) studies and summarizes their re- sults as follows: "Overall, the set of experiments conducted in FI classes suggest that there is value in focusing on language form through the use of pre-planned curriculum materials in the context of content-based language learn- ing" (Swain, 2000, p. 205). Her reference to curriculum materials and to the specific context of content-based lan- guage learning should signal to the reader the orientation t o pedagogical considerations that characterize this research. As Ellis notes, hybrid research using both experimental and qualitative methods is becoming more common in SLA. Recently, the experimental materials in our study were implemented in a grade 8 immersion classroom, and the children's collaborative language activity was observed by a researcher working from a sociocultural theoretical per- spective (Spielman-Davidson, 2000). The uptake of our research by a researcher working in another paradigm introduces another kind of hybridity that we hope will also shed further light on questions in form-focused instruction and lead to appropriate changes in pedagogy and in the design of immersion curricula. [source] Osteogenic Evaluation of Glutaraldehyde Crosslinked Gelatin Composite with Fetal Rat Calvarial Culture ModelARTIFICIAL ORGANS, Issue 8 2001Hwa-Chang Liu Abstract: The cytotoxicity of the synthetic bone substitute composed of tricalcium phosphate and glutaraldehyde crosslinked gelatin (GTG) were evaluated by osteoblast cell culture. In a previous study, the GTG composites were soaked in distilled water for 1, 2, 4, 7, 14, 28, and 42 days, and then the solutions (or extracts) were cocultured with osteoblasts to evaluate the cytotoxicity of GTG composites by alive cell counting. In this study, the extracts were cocultured with the osteoblasts; thereafter, the concentration of transforming growth factor-, (TGF-,1) and prostaglandin E2 (PGE2) in the medium was analyzed to strictly reflect the biological effects of GTG composites on the growth of osteoblasts. In order to investigate the osteoconductive potential of the GTG composites on new bone formation in a relative short term, a model of neonatal rat calvarial organ culture was designed prior to animal experiments. Three experimental materials of 4, 8, and 12% GTG composites were evaluated by fetal rat calvarial organ culture for their ability for bone regeneration. Deproteinized bovine and porcine cancellous bone matrixes were used as the controlled materials. All the organ culture units were maintained in cultured medium for 5 weeks. Following the culture period, the morphology of tissue was observed under an optical microscope, and the quantitative evaluation of the new generation bone was determined by using a semiautomatic histomorphometeric method. Except in the initial 4 days, the concentration of TGF-,1 of 4% and 8% GTG composites was higher than that of the blank group for all the other experimental time periods. The PGE2 concentration for 4% and 8% GTG composites was lower than that of the blank group. It revealed that the 4% and 8% GTG composites would not lead to inflammation and would promote osteoblast growth. The morphology and activity of the osteoblasts were not transformed or changed by the 2 GTG composites. For the 12% GTG composite, the performance of the in vitro condition was inferior to the blank group and the other 2 GTG composites. Although the concentration of TGF-,1 and PGE2 was gradually back to normal after 14 days, the morphology of the osteoblasts was abnormal with features such as contracted cytoplast structures. The osteoblast was damaged perhaps in the initial stage. We suggested that the 4% and 8% GTG composites should be soaked in distilled water at least for 4 days before medical applications. The 12% GTG composite and the composites with a concentration of glutaraldehyde solution higher than 12% were not recommended as a medical prostheses in any condition. The fetal rat calvaria culture also showed the same results with the analysis of TGF-,1 and PGE2. From the study, we could predict the results of animal experiments in the future. [source] | ||||||||||