Viking Phase III. The Viking Primary Mission phase was concluded in November, , when the reins were passed on to the second phase - the Viking Extended Mission. The Extended Mission successfully carried spacecraft operations through the desired period of time needed to provided a profile of a full Martian year, but would have fallen a little short of connecting and overlapping a full Martian year of Viking operations which scientists desired as a means of determining the degree of duplicity in the red planet's seasons - at least for the summer period. Without this continuation of spacecraft data acquisitions to and beyond the seasonal points when the spacecraft actually began their Mars observations, there would be no way of knowing whether the changing environmental values - such as temperatures and winds atmospheric dynamics and water vapor, surface thermal dynamics, etc. This same broad interest can be specifically pursued at the surface - where hundreds of rocks, soil drifts and other features have become extremely familiar during long-term analysis.
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Measurement of the optical density of packable composites : comparison between direct and indirect digital systems. Directory of Open Access Journals Sweden. Twenty acrylic plates, with the proposed thicknesses, were used, each one containing a sample of each resin. Each acrylic plate was radiographed three times, under a standardized technique. Optical plates and films were scanned and three consecutive optical readouts were carried out, totalizing 1, readouts. The results were submitted to statistical analysis and revealed that the average optical density of the four resins always increased as thickness increased.
Fracture resistance of teeth restored with packable and hybrid composites. Full Text Available Background and Aim: With recent introduction of packable composites , it is claimed that they apply less stress on tooth structure because of reduced polymerization shrinkage, and similarity of coefficient of thermal expansion to tooth structure. However, the high viscosity may in turn cause less adaptation, so it is not clearly known whether these materials strengthen tooth structure or not.
The aim of this study was to evaluate fracture resistance of maxillary premolars, receiving hybrid or packable composite restorations with different methods of application and curing. Materials and Methods: In this experimental study, seventy five intact premolars were randomly assigned to five groups of 15 teeth each.
One group was maintained intact as the control group. Similar MOD cavities were prepared in the other teeth. After thermocycling, force to fracture was assessed and degree of conversion DC at the bottom of cavities was evaluated for different modes and methods.
The curing and placement methods in groups tested for DC A to D were the same as fracture resistance groups 2 to 5. This study evaluated the surface quality of four composite materials after polishing with six different polishing techniques. Five specimens of each material were polished using flexible Sof-Lex discs. Surface roughness was evaluated quantitatively by laser-stylus profilometry.
The polished surfaces were examined qualitatively by SEM. Five specimens were made for each shade of the materials. Subsequently, the specimens were removed from the plates and ground to powder and then pressed into holes measuring 4mm in diameter in a Teflon matrix, using the plates of the same material as base and cover. Specimens were evaluated under SEM with an x-ray detector for the spectroscopic test by energy dispersing. Kekerasan mikro resin komposit packable dan bulkfill dengan kedalaman kavitas berbeda.
Full Text Available Microhardness of packable and bulkfill composite resin with different cavity depths. Bulkfill composite resin restorations are increasingly popular because the material can be irradiated with a thickness reaching 4 mm, making it easier to apply. The objective of this study was to determine the differences in the microhardness between packable and bulkfill composite resin restorations with a cavity depth of 2 mm and 4 mm.
Group 1A, packable composite resin was applied to the mold with a cavity depth of 2 mm. Group 1B, bulkfill composite resin was applied to the mold with a cavity depth of 2 mm. Group 2A, packable composite resin was applied with a depth of 4 mm.
Group 2B, bulkfill composite resin was applied with a depth of 4 mm. The hardness of each sample was tested using Vickers indenter microhardness tester.
The results showed that bulkfill composite resin with a cavity depth of 2 mm has the highest average of microhardness The two-way ANOVA analysis showed that there are significant differences between the types of composite resin and cavity depths p composite resin and cavity depth p packable composite resin is lower than that of bulkfill at a cavity depth of 2 and 4 mm. Full Text Available Modern restorative dentistry has been playing an outstanding role lately since composite resins, allied to adhesive systems, have been widely applied on anterior and posterior teeth restorations.
The evolution of composite resins has mostly been verified due to the improvement of their aesthetic behavior and the increase in their compressive and abrasive strengths. In spite of these developments, the polymerization shrinkage inherent to the material has been a major deficiency that, so far, has been impossible to avoid.
The pycnometer Accupyc Micromeritics, USA precisely records helium displacement, allowing fast and reliable measurements of the volume of composite resin immediately before and after polymerization, without interference of temperature or humidity. Results were not found to be statistically different for the three tested resins, either for 2 mm or 10 mm-distance from the light source to the composite surface.
The restorative materials were placed to type A-cavity to buccal surfaces of permanent teeth Triadan system , , , , , The variables of composite materials were evaluated in 3 groups of animals, 2 animals in each, at different time intervals 1, 6 and 9 months after beginning of the experiment. In various time intervals, 12 teeth per group were extracted under general injection anaesthesia, 6 teeth from each animal.
Altogether 36 teeth were extracted throughout the experiment. During the experiment we observed neither cracks nor marginal discoloration in both Filtek P60 and Opticor New restorations. These materials are suitable as permanent restoration of dental cervical caries in sheep and other herbivores, such as those kept in zoological gardens and companion animals.
Surface geophysical methods, such as Electromagnetic Induction EMI and magnetometry, are typically applied to screen rehabilitation areas for UXO prior to excavation; however, the prevalence of innocuous magnetic clutter related to indigenous scrap, fragmentation, or geology can severely impede the progress and efficiency of these remediation efforts.
Additionally, the variability in surface conditions and local topography necessitates the development of sensor technologies that can be applied to a range of sites including those that prohibit the use of vehicle-mounted or large array systems. The system is designed for operation in challenging site conditions and can be used in low ground-standoff modes to detect small and low-metal content objects. This high density data can also be used to provide characterization of target physical features, such as size, material content, and shape.
We summarize the development of this system for humanitarian demining operations and present results from preliminary system evaluations against a range of target types. Specifically, we assess the general detection capabilities of the EMPACT system and we evaluate the potential for target classification based on analysis of data and target model features.
Comparison of clasp retention on enamel and composite resin-recontoured abutments following repeated removal in vitro. Loss of prosthetic retention over time is a concern with removable prostheses.
Use of composite resin to modify an abutment contour receiving a removable partial denture clasp may offer a reasonable, less invasive method of improving removable prosthesis retention. The purpose of this study was to evaluate the removal force of clasps over composite resin-recontoured abutments during a simulated 4 years of service. A packable composite resin Filtek P60 was used to create a 0. Teeth in the natural abutment group were mounted in angulation to produce 0.
The chrome-cobalt framework consisted of 2 individually fabricated T-clasps. Both groups were subjected to cycles of repeated removal using a small shaker. Removal forces were recorded before the repeated removal test T 0 , after and cycles, and at cycle intervals thereafter. No debonding occurred during the test.
At T 0 , the highest and lowest force values were observed in the composite resin group 3. Retention loss was 3 times greater in the composite resin group than in the natural abutments group Within the limitations of the study, removal forces of the composite resin-recontoured abutments were threefold less than those of natural abutments after 4 years of simulated service.
Published by Mosby, Inc. All rights reserved. Full in-vitro analyses of new-generation bulk fill dental composites cured by halogen light. The objective of this study was to investigate the full in-vitro analyses of new-generation bulk-fill dental composites cured by halogen light HLG.
Samples were prepared for each analysis and test by applying the same procedure, but with different diameters and thicknesses appropriate to the analysis and test requirements. The surface morphology of the composites was investigated by scanning electron microscopes SEM and atomic-force microscopy AFM analyses. The sorption and solubility measurements were also performed after 1, 7, 15 and 30days of storage in water. In addition to his, the data were statistically analyzed using one-way analysis of variance, and both the Newman Keuls and Tukey multiple comparison tests.
The statistical significance level was established at pfill, resin-based dental composites. Longevity of dental amalgam in comparison to composite materials. Full Text Available Health political background: Caries is one of the most prevalent diseases worldwide. For direct restaurations of carious lesions, tooth-coloured composite materials are increasingly used. The compulsory health insurance pays for composite fillings in front teeth; in posterior teeth, patients have to bear the extra cost.
Scientific background: Amalgam is an alloy of mercury and other metals and has been used in dentistry for more than one hundred and fifty years. Composites consist of a resin matrix and chemically bonded fillers. They have been used for about fifty years in front teeth. Amalgam has a long longevity; the further development of composites has also shown improvements regarding their longevity.
Research questions: This HTA-report aims to evaluate the longevity failure rate, median survival time MST, median age of direct amalgam fillings in comparison to direct composite fillings in permanent teeth from a medical and economical perspective and discusses the ethical, legal and social aspects of using these filling materials.
Methods: The systematic literature search yielded a total of 1, abstracts. After a two-step selection process based on defined criteria 25 publications remained to be assessed. Results: The medical studies report a longer longevity for amalgam fillings than for composite fillings. However, the results of these studies show a large heterogeneity.
No publication on the costs or the cost-effectiveness of amalgam and composite fillings exists for Germany. The economic analyses NL, SWE, GB report higher costs for composite fillings when longevity is assumed equal for an observation period of five years or longer for amalgam compared to composite fillings.
These higher costs are due to the higher complexity of placing composite fillings. Discussion: Due to different study designs and insufficient documentation of study details, a comparison of different studies on longevity of direct amalgam and composite.
Food composition database development for between country comparisons. Full Text Available Abstract Nutritional assessment by diet analysis is a two-stepped process consisting of evaluation of food consumption, and conversion of food into nutrient intake by using a food composition database, which lists the mean nutritional values for a given food portion.
Most reports in the literature focus on minimizing errors in estimation of food consumption but the selection of a specific food composition table used in nutrient estimation is also a source of errors.
We are conducting a large prospective study internationally and need to compare diet, assessed by food frequency questionnaires, in a comparable manner between different countries. We have prepared a multi-country food composition database for nutrient estimation in all the countries participating in our study.
The nutrient database is primarily based on the USDA food composition database, modified appropriately with reference to local food composition tables, and supplemented with recipes of locally eaten mixed dishes.
By doing so we have ensured that the units of measurement, method of selection of foods for testing, and assays used for nutrient estimation are consistent and as current as possible, and yet have taken into account some local variations.
Using this common metric for nutrient assessment will reduce differential errors in nutrient estimation and improve the validity of between-country comparisons. Nutritional assessment by diet analysis is a two-stepped process consisting of evaluation of food consumption, and conversion of food into nutrient intake by using a food composition database, which lists the mean nutritional values for a given food portion.
Polymerization stress evolution of a bulk-fill flowable composite under different compliances.
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