1,721,023 research outputs found
SEM evaluation of outer dentin-cementum layer at cervical margins of Class V and Class II restorations.
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Influence of thickness on color in multi-layering technique
No full textObjectives: The aim of the study was to evaluate the influence of layer thickness on the final color for different shade and opacity composite combinations in a laboratory set-up simulating a 2-layer stratification technique. Methods: Resin disks of different thicknesses were made. From one composite system (Point4, Kerr Co.), four dentin shades were selected (A1, A2, A3, A4). For each shade, disks were produced of 0.5-3.0 mm thickness, with increasing thickness steps of 0.5 mm. Moreover, from the three translucent shades of the same system (T1, T2, T3) disks were made of 0.5-2.0 mm thickness, again with increasing thickness steps of 0.5 mm. For all 288 combinations of base + translucent material color was determined with a spectrophotometer. Results: For a mounting layer thickness from 0.5 to 3.0 mm of the base material, differences till to ΔE = 5.1 were recorded. These differences increased when the layer thickness of the translucent material decreased. The translucent shade also influence the final aspect of the samples, whereas each translucent shade acted differently dependent on their shade and their thickness. Their layer thickness played a significant role in color perception. Significance: Layer thickness and the proportion of thicknesses of the dentin and translucent shade greatly influence the final aspect of a multi-layer composite restoration. Good understanding of the optical behavior of each composite system is essential in order to obtain high quality in aesthetic dentistry. © 2007
Sealing ability of two "compomers" applied with and without phosphoric acid treatment for Class V restorations in vivo
No full textStatement of problem. "Compomers" are bring used with increasing frequency in Europe and North America.
Purpose. This study evaluated the marginal seal of two compomers in vivo.
Material and methods. Periodontally involved teeth, scheduled for extraction, were selected. Four groups of a combination of materials were used (Dyract with Dyract-PSA primer, group 1; Dyract with prime and Bond 2.0, group 2; Compoglass with SCA primer, group 3; and Compoglass with Syntac Single Component, group 4). The restorations were made in a standardized shaped cavity: across the cementoenamel junction, and the teeth were extracted after 2 to 3 months of clinical service. The specimens were kept in a solution of 2% methylene blue for 24 hours. After being embedded in epoxy resin, sections were made with a low speed saw along the longitudinal axis of the teeth. The examination of dye penetration was made with a microscope at a magnification of x20 and scoring was done at both coronal and apical sites. Kruskal-Wallis statistical analysis was performed at 5% significance level.
Results. Groups 2 and 4 scored significantly less than groups 1 and 3 and for groups 2 and 4, 30% of the restorations exhibited leakage.
Conclusion. These restoration systems did not completely prevent leakage either at the incisal or the cervical margins. Therefore the use of an enamel-dentin bonding system in combination with the proprietary compomer is recommended
Mapping of tubule and intertubule surface areas available for bonding in Class V and Class II preparations.
No full textObjectives and Methods: The aim of this in vitro study was to evaluate the morphology of dentine in Class V and the Class II preparation walls in terms of tubule orientation, density and increase in surface area after conditioning. Six circular V-shaped preparations were cut al the cementum-enamel junction (CEJ) of anterior teeth and six Class II cavities with the cervical margin 1 mm below the CEJ were prepared in posterior teeth. The preparations were conditioned with 10% maleic acid. The samples were directly studied by SEM. The observations were organized according to location in the preparation, tubule density was counted and the increase in area available for bonding after acid etching was calculated.
Results: Dentine morphology of Class V and Class II preparation walls was mostly regular according to predictable patterns. Between the tubules, along the walls of the cavity, the etched dentine surface exhibited a porous network of collagen fibers. More than 50% of Class V and Class II cavity surfaces presented oblique or parallel tubule orientation with respect to the cut surface. Because of the presence of a structureless cementum layer, the morphology of the cervical area turned out to be less predictable. The tubule density varied considerably in different regions of the preparations. The intertubular dentine surface area increased after conditioning in Class V preparations from 20.9% to 50.3% on the walls where tubules were cut parallel to their long axis, and from 5.8% to 47.8% where tubules were cut perpendicularly. These same values for Class II preparations ranged from 0.6% to 46.4% on the walls where tubules were cut parallel to their long axis, and 29.8% of the tubules were cut perpendicularly.
Conclusions: Based on this morphological investigation, the increase in intertubular dentine surface area might very well be responsible for the enhanced bond strength after acid etching of dentine, but not all areas exhibited equal responses to etching. In particular, the bonding substrate at the gingival margins may contribute little in terms of micromechanical retention. (C) 1997 Elsevier Science Ltd
Effect of two etching times on the sealing ability of Clearfil Liner Bond 2 in Class V restorations
No full textPurpose: To investigate the sealing ability of the Clearfil Liner Bond 2 self-etching primer in Class V restorations placed under clinical and laboratory conditions. Materials and Methods: Firstly, the influence of two etching times of the self-etching primer were tested in vitro. In 10 Class V cavities (Group 1), the self-etching primer was applied for 30 seconds on the enamel and dentin, while in another 10 Class V cavities (Group 2) the etching time was 60 seconds. Since the Group 2 samples showed the best in vitro sealing ability at both the enamel and cementum-dentin sites, the teeth of Group 3 (10 restorations) were restored as in Group 2 under clinical conditions, applying the self-etching primer for 60 seconds. The sample teeth were extracted after 65-90 days, and then processed for leakage. Two other groups of 10 samples each were prepared under laboratory conditions to investigate hybrid layer, resin tags and adhesive lateral branch formation. A flat buccal surface on each extracted tooth was prepared. Group 4 samples were conditioned for 30 seconds, and those of Group 5 for 60 seconds. Results: In Group 1, 40% of the restorations showed leakage at the cementum-dentin site and 40% at the enamel site. Groups 2 and 3 showed statistically significant difference (less leakage) than Group 1. In Group 2 and 3 no leakage was found at the enamel site, and only a moderate leakage (10% and 20% of restorations, respectively) was found at the cementum-dentin site. The scanning electron microscopy observations of Group 4 samples showed a thin hybrid layer, with well-fitting and smooth resin tags and adhesive lateral branches only sporadically. Group 5 samples presented a thicker hybrid layer, rough and deep resin tags with many adhesive lateral branches. The etch enamel pattern was more uniform and rougher in Group 5 than in Group 4. The 60-second application time of the self-etching primer seems to be more reliable than a shorter conditioning time in day-to-day practice
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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