scholarly journals Avaliação da influência do polimento químico na sorpção, solubilidade e microdureza de uma resina acrílica de termopolimerização

2021 ◽  
Vol 41 (1) ◽  
pp. 8-13
Author(s):  
Susana Maria Werner Samuel ◽  
Catia Rubinstein Selistre
Keyword(s):  
Silica Gel ◽  
Clinical Performance ◽  
Sorption Property ◽  
Acrylic Resin ◽  
International Organization ◽  
Distilled Water ◽  
Constant Mass ◽  
Knoop Microhardness ◽  
The Difference ◽  
The Moment

The purpose of this study was to evaluate the influence of the chemical polishing, when compared to the mechanical polish, in the sorption, solubility and microhardness of a heat-polymerizable acrylic resin. The heatactivated acrylic resin used was Clássico (Art. Odontológicos Clássico Ltda., S.P.). The properties of sorption and the solubility were tested in accordance with International Organization for Standartization (ISO) specification n. 1567, making 20 samples in the format of disks, divided aleatory in two groups, where the first group received lhe mechanical polish with abrasive pastes, and the second, the chemical polish during IOS, in the chemical polisher PQ 9000 (série 4868-2, Termotron do Brasil Ltda., Piracicaba, SP). The samples were maintained in a desiccator with silica gel, at 37 DC, until the moment they reached constant mass (M1), obtained in a scale with resolution of 0,0001g. The samples were submerged in distilled water, at 37 Uc, for 7 days, when it was Obtained new mass value (M2). The difference between M1 and M2 divided by the volume Of each sample resulted in the sorption. The samples were desiccated again until they reach constant mass (M3). The difference between M1 and M3 divided by the volume of each sample resulted in the solubility Of the same ones. For the Knoop microhardness measurement, were made 20 specimens of acrylic resin, of which 10 samples received the mechanical polish and the others, the chemical polish. The Knoop microhardness test was made with a NU Research Microscope (VEB Carl Zeiss JENAGermany). The results indicated that the technique of the chemical polish is acceptable when considered the sorption property, even so unviable with the solubility property, in accordance with the specification n.1567 of ISO. The chemical polish also reduced significantly the superficial microhardness of the acrylic resin, which consequences can interfere in the clinical performance of the material.

scholarly journals Effect of immersion in various disinfectant solutions on the properties of a heat-cured acrylic resin

2019 ◽  
Vol 67 ◽  
Author(s):  
Cláudia Jiménez PEREIRA ◽  
Bruna GENARI ◽  
Vicente Castelo Branco LEITUNE ◽  
Fabrício Mezzomo COLLARES ◽  
Susana Maria Werner SAMUEL
Keyword(s):  
Hydrogen Peroxide ◽  
Surface Roughness ◽  
Acrylic Resin ◽  
Distilled Water ◽  
Medium Term ◽  
Domestic Use ◽  
Knoop Microhardness ◽  
Level Of Significance ◽  
Microhardness Tester

ABSTRACT Objective: The aim of the present study was to evaluate the influence, of immersion in different disinfectant solutions, on microhardness and surface roughness of a heat-cured acrylic resin. Methods: Specimens were immersed in distilled water, commercial vinegar for domestic use, sodium hypochlorite and hydrogen peroxide, for 150 hours or 300 hours (n=10). After periods of immersion, Knoop microhardness and surface roughness were evaluated using a microhardness tester and a roughness tester, respectively. The data were analyzed using two-way ANOVA and Holm-Sidak, at a level of significance of 5%. Results: The microhardness values ranged from 16.90 ± 0.33 to 17.80 ± 0.51 and roughness values from 0.05 ± 0.01 to 0.08 ± 0.02. There is no difference in microhardness and roughness between groups and times (p>0.05). Conclusion: Within the limitations of this study, it is possible to conclude that vinegar and hydrogen peroxide, as alternative disinfectant solutions for acrylic resin devices, did not promote deleterious effects on microhardness and polishing of a heat-cured acrylic resin used for the fabrication of prostheses, neither in the medium term nor the long term.

scholarly journals Effect of sodium hypochlorite and edta irrigation, individually and in alternation, on dentin microhardness at the furcation area of mandibular molars

2012 ◽  
Vol 23 (6) ◽  
pp. 654-658 ◽  
Author(s):  
Danilo Zaparolli ◽  
Paulo César Saquy ◽  
Antonio Miranda Cruz-Filho
Keyword(s):  
Sodium Hypochlorite ◽  
Ethylenediaminetetraacetic Acid ◽  
Acrylic Resin ◽  
Distilled Water ◽  
Water Control ◽  
Mandibular Molars ◽  
Significant Difference ◽  
Edta Solution ◽  
Maximum Decrease ◽  
Knoop Microhardness

The aim of this study was to evaluate the effect of irrigation regimens on dentin microhardness at the furcation area of mandibular molars, using sodium hypochlorite and ethylenediaminetetraacetic acid (EDTA), individually and in alternation. The occlusal surface and the roots of 20 non-carious extracted human permanent mandibular molars were cut transversally and discarded. The tooth blocks were embedded in acrylic resin and randomly assigned to 4 groups (n=5) according to the irrigating regimens: 1% NaOCl solution, 17% EDTA solution, 1% NaOCl and 17% EDTA and distilled water (control). Knoop microhardness of dentin at the furcation area was evaluated. Data were analyzed using one-way ANOVA and Tukey's multiple comparison tests (α=0.05). The results of this study indicated that all irrigation solutions, except for distilled water (control), decreased dentin microhardness. EDTA did not show a significant difference with NaOCl/EDTA (p>0.05), but showed a significant difference with NaOCl (p<0.01). EDTA and NaOCl/EDTA showed a maximum decrease in microhardness. The 17% EDTA solution, either alone or in combination with 1% NaOCl reduced significantly dentin microhardness at the furcation area of mandibular molars.

scholarly journals Comparison of Fracture Resistance in Thermal and Self-Curing Acrylic Resins—An In Vitro Study

Polymers ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1234
Author(s):  
António Sérgio Silva ◽  
Aurora Carvalho ◽  
Pedro Barreiros ◽  
Juliana de Sá ◽  
Carlos Aroso ◽  
...  
Keyword(s):  
Fracture Resistance ◽  
Research Work ◽  
Testing Machine ◽  
In Vitro Study ◽  
Dimensional Accuracy ◽  
Acrylic Resin ◽  
Thermosetting Resins ◽  
Acrylic Resins ◽  
The Difference

Thermal and self-curing acrylic resins are frequently and versatilely used in dental medicine since they are biocompatible, have no flavor or odor, have satisfactory thermal qualities and polishing capacity, and are easy and fast. Thus, given their widespread use, their fracture resistance behavior is especially important. In this research work, we comparatively analyzed the fracture resistance capacity of thermo and self-curing acrylic resins in vitro. Materials and Methods: Five prosthesis bases were created for each of the following acrylic resins: Lucitone®, ProBase®, and Megacryl®, which were submitted to different forces through the use of the CS® Dental Testing Machine, usually mobilized in the context of fatigue tests. To this end, a point was defined in the center of the anterior edge of the aforementioned acrylic resin bases, for which the peak tended until a fracture occurred. Thermosetting resins were, on average, more resistant to fracture than self-curable resins, although the difference was not statistically significant. The thermosetting resins of the Lucitone® and Probase® brands demonstrated behavior that was more resistant to fracture than the self-curing homologues, although the difference was not statistically significant. Thermosetting resins tended to be, on average, more resistant to fracture and exhibited the maximum values for impact strength, compressive strength, tensile strength, hardness, and dimensional accuracy than self-curing resins, regardless of brand.

scholarly journals Elastic Simulation of Joints with Particle-Based Fluid

2021 ◽  
Vol 11 (15) ◽  
pp. 6900
Author(s):  
Su-Kyung Sung ◽  
Sang-Won Han ◽  
Byeong-Seok Shin
Keyword(s):  
Principal Stress ◽  
Human Body ◽  
Yield Condition ◽  
Maximum Principal Stress ◽  
Human Motion ◽  
The Difference ◽  
The Moment ◽  
External Forces ◽  
Physical Changes ◽  
Elastic Simulation

Skinning, which is used in skeletal simulations to express the human body, has been weighted between bones to enable muscle-like motions. Weighting is not a form of calculating the pressure and density of muscle fibers in the human body. Therefore, it is not possible to express physical changes when external forces are applied. To express a similar behavior, an animator arbitrarily customizes the weight values. In this study, we apply the kernel and pressure-dependent density variations used in particle-based fluid simulations to skinning simulations. As a result, surface tension and elasticity between particles are applied to muscles, indicating realistic human motion. We also propose a tension yield condition that reflects Tresca’s yield condition, which can be easily approximated using the difference between the maximum and minimum values of the principal stress to simulate the tension limit of the muscle fiber. The density received by particles in the kernel is assumed to be the principal stress. The difference is calculated by approximating the moment of greatest force to the maximum principal stress and the moment of least force to the minimum principal stress. When the density of a particle increases beyond the yield condition, the object is no longer subjected to force. As a result, one can express realistic muscles.

scholarly journals Loading Effect of Prosthetic Feet’s Anthropomorphicity on Transtibial Osseointegrated Implant

2021 ◽  
Vol 186 (Supplement_1) ◽  
pp. 681-687
Author(s):  
Mark Pitkin ◽  
Laurent Frossard
Keyword(s):  
Free Flow ◽  
Convex Shape ◽  
Bone Implant ◽  
Concave Shape ◽  
Early Loosening ◽  
Osseointegrated Implants ◽  
Osseointegrated Implant ◽  
Quantitative Characteristics ◽  
The Difference ◽  
The Moment

ABSTRACT Introduction Osseointegrated implants for direct skeletal attachment of transtibial prosthesis carry risks that are yet to be fully resolved, such as early loosening, mechanical failure of percutaneous and medullar parts of implant, periprosthetic issues, and infections. Underloading could lead to early loosening and infection. Overloading might compromise the bone–implant interface. Therefore, Goldilocks loading regimen applied by transtibial bone-anchored prostheses is critical for safe and efficient development of osseointegration around the implant during rehabilitation and beyond. We hypothesized that Goldilocks loading could be achieved when ambulating with a so-called anthropomorphic prosthetic ankle showing moment–angle relationship similar to a sound ankle. Materials and Methods Quantitative characteristics of the moment–angle curve of the sound ankle during dorsiflexion phase of a free-pace walking were extracted for 4 able-bodied participants (experiment 1). A slope of the moment–angle curve (stiffness) was calculated twice: for the first half and for the second half of the moment–angle curve. The difference of stiffnesses (those at the second half minus at the first half) was called the index of anthropomorphicity (IA). By definition, positive IA is associated with concave shape of the moment–angle curve, and the negative IA is associated with convex shape. In experiment 2, the same recordings and calculations were performed for 3 participants fitted with transtibial osseointegrated fixation during walking with their usual feet and the Free-Flow Foot (Ohio Willow Wood). The Free-Flow Foot was selected for its anthropomorphicity demonstrated in the previous studies with amputees using traditional socket attachment. Results The IA was 5.88 ± 0.93 for the able-bodied participants, indicating that the stiffness during the first part of the dorsiflexion phase was substantially fewer than during the second parts, as the calf muscles resisted to angulation in ankle substantially less than during the second part of dorsiflexion phase. For amputees fitted with Free-Flow Foot, IA was 2.68 ± 1.09 and −2.97 ± 2.37 for the same amputees fitted with their usual feet. Conclusions Indexes of anthropomorphicity, while of different magnitude, were positive in control able-bodied group and in the amputee group wearing Free-Flow Foot, which was qualitatively associated with concave shape of their moment–angle curves. The 3 usual feet worn by the participants were classified as nonanthropomorphic as their individual moment–angle curves were convex and the corresponding IAs were negative. Furthermore, this study showed that a foot with anthropomorphic characteristics tends to decrease maximal loads at the bone–implant interface as compared to the nonanthropomorphic feet and possibly may minimize the risks to compromise the integrity of this interface.

Open access to scientific information: comparative study in DOAJ

2014 ◽  
Vol 35 (4/5) ◽  
pp. 364-374 ◽  
Author(s):  
Tereza Stoyanova Trencheva ◽  
Tania Yordanova Todorova
Keyword(s):  
Open Access ◽  
Comparative Study ◽  
Scientific Information ◽  
Comparative Approach ◽  
Content Type ◽  
Open Access Journals ◽  
Global Movement ◽  
The Difference ◽  
Important Position ◽  
The Moment

Purpose – The purpose of the paper is to provide a comparative retrospective analysis of Bulgarian, Turkish and Croatian Open Access (OA) journals added in Directory of Open Access journals (DOAJ) in the period 2002-2013. Design/methodology/approach – First of all, the study is focussed on brief review of definitions and descriptions of the OA as a global movement. In the study were analyzed the three main OA initiatives and was shown the difference between Golden Road and Green Road. Second of all, the authors used the comparative approach and made a comparative study of the OA journals in Bulgaria, Turkey and Croatia and present the evaluation results and findings. Findings – Qualitative and quantitative data for the study are collected by the DOAJ. The data are analyzed in terms of quantity and period, and the results are presented graphically and tabular and finally there are made major specific conclusions and recommendations. Originality/value – The paper shows that OA in the digital space has an important position in scientific research. There are many discussion issues related to the problems of OA, but overall study of OA to scientific information, and in particular comparative study of Bulgarian, Turkish and Croatian journals in the DOAJ does not exist at the moment.

scholarly journals Against Declarativity

2020 ◽  
pp. 103-117
Author(s):  
Hans Kellner
Keyword(s):  
Literary Form ◽  
Literary Realism ◽  
Declarative Sentence ◽  
Romantic Literature ◽  
Realist Novel ◽  
Historical Discourse ◽  
The World ◽  
The Difference ◽  
The Moment ◽  
Declarative Statement

Historical discourse is a period phenomenon shaped by the rhetorical and genre understanding of the moment in which it became formalized and professionalized - that is, the second half of the nineteenth century. In the figurative arts, realist painting and its rival, photography, was dominant, and the literary form this notion of consciousness took was the realist novel. Literary realism devices replaced romantic literature devices, just as those latter devices had succeeded, but never replaced the eighteenth-century devices. Historical discourse and the very notion of proper history followed realism devices, mostly the single-lens photographic perspective, one viewer’s viewpoint. From a discourse perspective, this approach took the form of declarative, statement-making. Also, it is not to say that the declarative sentence which gives this term its name was rejected as the preferred way of making assertions about the world - far from it. Although a few self-conscious stylists (Derrida, for instance) work hard to avoid it, the declarative sentence is almost inevitable. Their readers work even harder. But just as narrativity encompasses a realm that extends far beyond narratives, so that narratives can proliferate in an environment that has, in a crucial sense, rejected grand narratives, so declarative statements will exist without entailing statement-making. The declarative act became the defining mark of professional history and remained its principal mode, just as it remains the predominant mode of literature and any number of other discourses. Indeed, this essay is written in the declarative rhetorical mode. However, literary modernism, philosophy, and a host of scientific developments have left this way of representing the world behind. Moreover, the same technological and intellectual changes that caused the modernist vision have, at the same time, created a different world to be depicted, a different sort of event to be represented historically. Not only the form but also the content have changed. The ethical and practical frustrations of representing such events have led to a theoretical challenge to the declarative form of knowing and to a challenge for the genre distinctions that constitute guild history: the idea of the past produced by academically professionalized individuals. For example, the difference between history and fiction - or rather, their respective relationship to truth and reality - has blurred. In contrast, history has adopted some of the modernist literature devices and the present’s practical demands.

scholarly journals Replacement depreciation and price regulation

2006 ◽  
Vol 17 (3) ◽  
pp. 10-20
Author(s):  
IJ Lambrechts
Keyword(s):  
The United States ◽  
Natural Monopoly ◽  
Price Regulation ◽  
Liquid Fuels ◽  
Economic Regulation ◽  
Tax Rates ◽  
Historical Cost ◽  
Investment Rates ◽  
The Difference ◽  
The Moment

Price regulation occurs quite commonly amongst natural monopolies which frequently include public utilities. In South Africa and in certain countries in Africa, there has recently been a revival of price regulation in certain industries and enterprises, where competition is limited or non-existent. Price regulation can be applied in a multitude of ways. Because of the importance of the price levels (historical and replacement) in the price setting exercise, the focus in this paper will be on the issue of depreciation to arrive at the final prices. The electricity utility industry was historically viewed as a highly mature and heavily regulated natural monopoly. In many parts of the world, electricity utilities have already been deregulated to a large extent and in the United States the process was preceded by a process of unbundling or ringfencing of the main divisions, i.e. generation and distribution. Even the network component of transmission, traditionally seen as natural monopolies, was deregulated to a large extent. The deregulation process, whether fully or partially, emphasised the requirement for a detailed explanation for a specific price level. The need for acceptable and transparent selling prices has, therefore, not disappeared. Regulatory pricing is consequently a vital component of pricing at this stage and in the restructured industry it will continue to play an important role because of a limited number of participants. In other sectors of the South African energy industry too, the deregulation process has either not started or has not been completed. Price regulation is presently and will in future be applicable to the liquid fuels industry, which includes the pipeline of Petronet as well as gas pipelines. Other industries which are being price regulated at the moment include water, medicine, telecommunication (fixed lines) and postal rates. Although the economic regulation for these industries may differ substantially, the principles applying to depreciation calculations would be similar. Replacement depreciation produces lower profit figures during periods of inflation. Quoted companies often oppose this system because of a lack of taxation recognition on income and the adverse effect on earnings per share. This paper covers the calculation of depreciation by price regulators where assets are not diversified (single assets). Shorter depreciation lifetimes based on historical cost result in an automatic provision for replacement depreciation. The extent of the provision would be a function of the difference between the actual and selected lifetimes, income tax rates, re-investment rates and the extent of the financial gearing ratio. Provision for replacement depreciation may be reduced significantly, if not reduced completely, by reducing depreciation lifetimes.

scholarly journals Russia – China: A Difficult Way to Strategic Partnership (To the 70th Anniversary of the Establishment of Diplomatic Relations)

2021 ◽  
pp. 231-245
Author(s):  
Sergey Biryukov ◽  
Keyword(s):  
Political Development ◽  
Complex Dynamics ◽  
World Order ◽  
Strategic Partnership ◽  
General Situation ◽  
Republic Of China ◽  
Bilateral Relations ◽  
Political Analysis ◽  
The Difference ◽  
The Moment

Introduction. The article is devoted to the features and historical evolution of the SovietChinese (later Russian-Chinese) relations from the moment of the proclamation of the People’s Republic of China in 1949 to the present. The analysis of the complex of factors that determined the complex dynamics of the relations between the two countries was carried out by the author of the article. It is shown that the SovietChinese (later – Russian-Chinese) relations developed from close alliance to alienation and confrontation – with reaching a level of strategic partnership in the second decade of the 21st century. Methods and materials. The authors seek a combination of general theoretical and special methods, focusing on the historical, sociocultural and political analysis. They are based on the analysis of periodicals, as well as using books, articles and materials of researchers on the problems of the political development of China and the USSR (Russia) and on the transformation of the nature of their bilateral relations. The author analyzes the current situation in the relations between the two countries, according to which the nature of the development of the general situation in international relations and the objective foreign policy interests of China and Russia encourage them to build and deepen bilateral partnership. Results. According to the author, many of the reasons that gave rise to a conflict of interests and confrontation between the two countries in previous years are exhausted today. At the same time, the joint participation of China and Russia in the formation and adoption of a new, more equitable and sustainable world order, in the settlement of conflicts and crises, in the arrangement of the Greater Eurasia space seems to the author justified and promising. Among the factors defining the nature of the Sino-Soviet relations the author identifies the relationship between the leaders of the two countries, the difference of geopolitical concepts and approaches, ideological disputes and differences in the views on strategy and prospects of the communist movement, the logic of the socio-political and socio-economic development in the context of modernization. The changing and contradictory correlation of these factors determined the development of the Soviet-Chinese (later Russian-Chinese) relations from a close alliance to mutual distancing and confrontation – with the subsequent entry into strategic partnership.

scholarly journals Sin, hendes og KorpusDK

2017 ◽  
Vol 25 (24) ◽  
Author(s):  
Sten Vikner ◽  
Katrine Rosendal Ehlers
Keyword(s):  
Language Change ◽  
The Difference ◽  
The Moment ◽  
New Situation ◽  
National Corpus

We will briefly present our analysis of the four reflexive/non-reflexive types of pronouns in Danish (jf. Vikner 1985 and Ehlers & Vikner 2017), which each have to comply with two conditions: One type of condition on elements with/without selv (i.e. sig/hende vs. sig selv/ hende selv), and another type of condition on elements with/without sig (i.e. sig/sig selv vs. hende/hende selv). We will then show how the difference between the reflexive possessive and the non-reflexive possessives (sin vs. hendes) fits into this system, and we will examine how compatible our predictions are with data from the Danish national corpus, KorpusDK. We assume that sin corresponds to both sig and sig selv, and we argue against the view that there is a difference between sin and sin egen which corresponds to the difference between sig and sig selv. Finally we will discuss the language change that seems to be taking place at the moment, from a situation where sin may only have a singular antecedent to the new situation where sin may also have a plural antecedent.

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