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AIM :The aim of this study was to assess the effect of acidic beverages on color stability and microhardness of various esthetic restorative materials. MATERIALS AND METHODS :A total of 60 samples were included in the present stud...
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AIM :The aim of this study was to assess the effect of acidic beverages on color stability and microhardness of various esthetic restorative materials. MATERIALS AND METHODS :A total of 60 samples were included in the present study. Group I: Microhybrid composite resin, Group II: Nanoceramic, Group III: ORMOCER (Organically Modified Ceramics). 10 mm internal diameter and 5 mm depth of cylindrical aluminum mold of were utilized to prepare the samples. All the esthetic restorative samples were submerged for 10 min in 25 ml of acidic drink (Coca-Cola) each day up to 15 days. Vickers diamond intender was used to measure the microhardness of each sample. These values were calculated with baseline, 7 th , and 15 th days for final microhardness values. RESULTS :The mean surface microhardness of 63.20 ± 0.46 was shown by Group III which was slightly more than that in Group II (60.08 ± 0.34) and Group I (58.10 ± 1.76). Analysis of covariance did not show any statistically significant difference between the groups. The samples in Group I showed the highest reduction in surface microhardness value after immersion into acidic drink, followed by Group II and Group III on 7 th day and 15 th day. A statistically significant difference ( P < 0.001) was found on the 7 th day. CONCLUSION :The present study concludes that the Organically Modified Ceramics esthetic restorative material showed the finest behavior after being dipped in the acidic drink followed next by Nanoceramic and Microhybrid composite resin. Copyright: ? 2021 Journal of Pharmacy and Bioallied Sciences.
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A model is proposed that makes it possible to calculate the temperature dependence of the microhardness of glass over the entire temperature range from the softening temperature to absolute zero. The calculation uses the temperatu...
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A model is proposed that makes it possible to calculate the temperature dependence of the microhardness of glass over the entire temperature range from the softening temperature to absolute zero. The calculation uses the temperature dependence of the glass enthalpy and the value of its microhardness at the glass transition temperature. The proposed model is tested on the example of glassy selenium. For this, the temperature dependence of the microhardness of selenium on the softening temperature up to 100 K, which is 50 K below its Debye temperature, is measured. Thus, a relationship is established between the strength and thermodynamic properties of glass.
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The rolling process is one of the most effective ways for strengthening a part’s surface. As the press force exerted on specimen in rolling process, material in the surface layer will deform plastically if the press force is suff...
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The rolling process is one of the most effective ways for strengthening a part’s surface. As the press force exerted on specimen in rolling process, material in the surface layer will deform plastically if the press force is sufficient. That might result in grain refinement, dislocation configuration change, or phase change in specimen surface layer material. Consequently, the surface material mechanical properties can be changed. The effects of rolling parameters on surface residual stress, micro-hardness, and surface roughness for a 210Cr12 shaft have been investigated. After the rolling process, the surface residual stress of the specimen changes from tensile stress to compressive stress, and a stable residual compressive stress layer is formed. The maximum absolute value of compressive stress can be up to 216MPa. With the increase of the value of contact stress exerted on shaft surface and the number of rolling cycles, the absolute value of residual compressive stress increases firstly and then becomes stable. With the increase of depth from shaft surface to interior, the absolute value of residual compressive stress increases initially, then decreases and disappears finally. The maximum absolute value of residual compressive stress exists at the position beneath specimen surface about 0.025mm. The depth of residual stress layer is about 0.2 mm. Research results indicate that shaft surface microhardness can be improved within small range, surface roughness can be reduced up to 67%.
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Dynamic and static mechanical spectra of polyvinylchloride (PVC)/acrylonitrile-butadiene rubber (NBR), PVC/styrene-butadiene rubber (SBR) and PVC/acrylonitrile-butadiene-styrene terpolymer (ABS) blends have been studied. The const...
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Dynamic and static mechanical spectra of polyvinylchloride (PVC)/acrylonitrile-butadiene rubber (NBR), PVC/styrene-butadiene rubber (SBR) and PVC/acrylonitrile-butadiene-styrene terpolymer (ABS) blends have been studied. The constituent compounding conditions were held constant. Mechanical investigations reveal that blends are partially compatible for 60 wt% PVC in the blends. UV absorption spectra for PVC/NBR blends have been investigated New bands were observed at 280 and 330 nm, which may be due to the formation of a compatible phase lying on the grain boundary between PVC and the NBR rubber domain, as observed by a polarized optical microscope. (C) 1996 Elsevier Science Ltd. [References: 16]
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Nanocrystalline magnetic materials because of their interesting functional properties such as their ductility, high wear resist- ance, mechanical strength and magnetic properties have attracted significant attention of many resear...
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Nanocrystalline magnetic materials because of their interesting functional properties such as their ductility, high wear resist- ance, mechanical strength and magnetic properties have attracted significant attention of many researchers. Such materials find potential applications in diverse areas like medical, aerospace and microelectronic technologies as: sen- sors, thermal and chemical resistant materials, radio-frequency thin film inductors, micro-electromechanical systems (MEMS), microinductors, computer read/write heads and memory devices etc.There has been obviously great emphasis on investigating structure, properties and their relationship.
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AIM :This study aims at determining the amount of enamel decalcification in terms of microhardness. MATERIALS AND METHODS :Twenty patients requiring treatment by extraction method for Class I malocclusion with bimaxillary protrusi...
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AIM :This study aims at determining the amount of enamel decalcification in terms of microhardness. MATERIALS AND METHODS :Twenty patients requiring treatment by extraction method for Class I malocclusion with bimaxillary protrusion were selected for the study. Twenty patients were randomly divided into control group and experimental group. In the control group ( n = 40), extraction of permanent first premolars was done on day 1 of bonding to assess the Vickers hardness number (VHN) of enamel surface, and in the experimental group ( n = 40), extraction of the contralateral premolars was done on the 28 th day after bonding to assess the VHN of enamel surface. The values are tabulated and analyzed by SPSS software. RESULTS :There is significant surface enamel dissolution of enamel crystals in the experimental group compared to the control group, and a statistically significant difference in VHN is evident between the control and experimental groups. The surface enamel dissolution (VHN) is not significant difference noted between mandibular and maxillary premolars of the control and experimental groups. CONCLUSION :The present study has demonstrated a higher level of surface enamel dissolution in the experimental group. There is a marked difference in the VHN between the control and experimental groups, which is statistically significant. The scanning electron microscopy study also confirms the presence of surface enamel demineralization following orthodontic bonding. Copyright: ? 2021 Journal of Pharmacy and Bioallied Sciences.
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In the micro-hardness range of the load, the measurement is complicated by the occurrence of the Indentation Size Effect (ISE) - the measured value of the micro-hardness is affected by the value of the applied load. The paper aims...
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In the micro-hardness range of the load, the measurement is complicated by the occurrence of the Indentation Size Effect (ISE) - the measured value of the micro-hardness is affected by the value of the applied load. The paper aims to study the influence of the automatic testers on the character type and size of the ISE. Ten testers and five standard reference blocks were involved in the "round-robin test". Parameters of the ISE were evaluated using Meyer's, Hays-Kendall, and PSR methods and also by statistical methods (ANOVA, t-test, regression, and cluster analysis). Despite the assumptions, a statistically significant impact of the hardness tester was found not only on the measured value but also on the character and size of ISE.
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On the basis of microhardness (H) data measured at room temperature only for a number of polymers in the glassy state, a linear correlation between H and the glass transition temperature T_g has been found (H = 1.97T_g - 571). By ...
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On the basis of microhardness (H) data measured at room temperature only for a number of polymers in the glassy state, a linear correlation between H and the glass transition temperature T_g has been found (H = 1.97T_g - 571). By means of this relationship, the deviation of the H values from the additivity law for some multicomponent and/or multiphase polymeric systems can be accounted for. The latter usually contains a liquidlike soft component and/or phase with T_g below room temperature. A completely different deformation mechanism in comparison to systems with T_g above room temperature is invoked. A novel expression for the hardness of polymers in terms of crystallinity of the single components and/or phases, the T_g values, and the mass fraction of each component is proposed. This expression permits the calculation of (i) the room-temperature H value of amorphous polymers, mainly containing single bonds in the main chain, provided T_g is known, and of (ii) the contribution of the soft liquidlike components (phases) to the hardness of the entire multiphase system.
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摘要 :
On the basis of microhardness (H) data measured at room temperature only for number of polymers in the glassy state, a linear correlation between H and the glass transition temperature T_g has been found (H = 1.97T_g - 571). By me...
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On the basis of microhardness (H) data measured at room temperature only for number of polymers in the glassy state, a linear correlation between H and the glass transition temperature T_g has been found (H = 1.97T_g - 571). By means of this relationship, the deviation of the H values from the additivity law for some multicomponent and/or multiphase polymeric systems can be accounted for. The latter usually contains a liquidlike soft component and/or phase with T_g below room temperature. A completely different deformation mechanism in comparison to systems with T_g above room temperature is invoked. A novel expression for the hardness of polymers in terms of crystallinity of the single components and/or phases, the T_g values, and the mass fraction of each component is proposed. This expression permits the calculation of (i) the room-temperature H value of amorphous polymers, mainly containing single bonds in the main chain, provided T_g is known, and of (ii) the contribution of the soft liquidlike components (phases) to the hardness of the entire multiphase system.
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