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    Color Changes of Dental Resin Composites before and after Polymerization and Storage in Water
    (Wiley-Blackwell, 2011) Celik, Esra Uzer; Aladag, Akin; Turkun, L. Sebnem; Yilmaz, Gokhan
    The aims of this study were to: (1) evaluate the A2 shades of various types and brands of resin composites to determine if any color differences occurred before and after polymerization and after 1 month of storage in water and (2) examine the correlation among the color changes and changes in Commission internationale de l'eclairage L*, a*, and b* values after polymerization and after 1 month of storage in water. One submicron-hybrid (Spectrum TPH3, DENTSPLY DeTrey, Milford, DE, USA), one nano-filled (Filtek Supreme XT, 3 M ESPE, St. Paul, MN, USA), three micro-hybrid (Filtek Z250, 3 M ESPE; Esthet X, DENTSPLY DeTrey; and Gradia Direct, GC, Tokyo, Japan), and five nano-hybrid (Ceram X, DENTSPLY DeTrey; Clearfil Majesty Esthetics, Kuraray, Osaka, Japan; Premise, Kerr Corporation, Orange, CA, USA; Tetric Evo Ceram, Ivoclar Vivadent, Schaan, Liechtenstein and Tetric N Ceram, Ivoclar Vivadent) light-curing resin composites were tested. The specimens (N = 10 for each composite) were prepared as discs, 12 mm in diameter and 2 mm in thickness, using round molds. The measurements were performed "before polymerization," "after polymerization," and "after 1 month of storage in water" using a contact type dental spectrophotometer (Vita Easyshade, Vident, Brea, CA, USA). The range of Delta E* values after polymerization (Delta E*1) and storage in water (Delta E*2) were 4.59 to 14.13 and 1.26 to 6.29, respectively. Nested analysis of variance and post hoc tests revealed that the type of resin composites significantly affected Delta a*1, Delta a*2, Delta b*1, Delta b*2, Delta E*2-values, whereas the brand of resin composites affected the changes in all color parameters (p < 0.05). In spite of many improvements in chemical compositions and fillers of the contemporary composites, color changes after polymerization were perceptible in all resin composites. However, color changes after storage in water were in the acceptable ranges for all resin composites except Clearfil Majesty Esthetic and Gradia Direct. CLINICAL SIGNIFICANCE In spite of many improvements in chemical compositions and fillers of the contemporary resin composites, the color changes after polymerization were still perceptible in all the resin composites tested in this study, regardless of their types and brands. Such changes may cause esthetic problems clinically, thus should be taken into account when the shade selections are performed. Alternatively, a piece of unpolymerized resin material can be placed on, or adjacent to the tooth to be restored and polymerized to confirm the selected shade of the esthetic material.
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    Effect of different types of superplasticizer on fresh, rheological and strength properties of self-consolidating concrete
    (Elsevier Sci Ltd, 2013) Mardani-Aghabaglou, Ali; Tuyan, Murat; Yilmaz, Gokhan; Arioz, Omer; Ramyar, Kambiz
    The effect of different types of superplasticizer on fresh, theological and strength properties of self-consolidating concrete (SCC) was investigated. The admixtures had same main chain and same polymer structure but different molecular weight and different side chain density of carboxylic acid groups. Fresh concrete properties were determined by using the slump-flow, V-funnel, slump-flow loss and L-box tests. Besides, the rheological parameters including apparent yield stress and plastic viscosity were measured by using a concrete rheometer. The compressive strength, ultrasonic pulse velocity and dynamic elastic modulus of SCC mixtures were determined at 1, 3, 7 and 28 day ages. Test results indicated that V-funnel flow time, plastic viscosity and slump retention of SCC mixtures were affected by the side chains density of polymer considerably. It was observed that the compressive strength of SCC mixtures was also influenced slightly with the incorporation of different types of superplasticizers. The effect was more pronounced at early ages. (C) 2013 Published by Elsevier Ltd.
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    pH responsive glycopolymer nanoparticles for targeted delivery of anti-cancer drugs
    (Royal Soc Chemistry, 2018) Yilmaz, Gokhan; Guler, Emine; Geyik, Caner; Demir, Bilal; Ozkan, Melek; Demirkol, Dilek Odaci; Ozcelik, Serdar; Timur, Suna; Becer, C. Remzi
    Over the past decade, there has been a great deal of interest in the integration of nanotechnology and carbohydrates. The advances in glyconanotechnology have allowed the creation of different bioactive glyconanostructures for different types of medical applications, especially for drug delivery and release systems. Therefore, the use of more efficient biocompatible nanocarriers with high loading capacity, low overall toxicity and receptor-mediated endocytosis specificity is still in focus for the enhancement of the therapeutic effect. Conjugation of sugar derivatives onto gold nanoparticles presents unique properties that include a wide array of assembling models and size-related electronic, magnetic and optical properties. Here, pH-responsive drug-conjugated glycopolymer-coated gold nanoparticles were prepared by functionalization of gold nanoparticles with thiol-terminated glycopolymers and then subsequent conjugation of doxorubicin (DOX). Among the four different glycopolymers, their drug release, physicochemical characterization (spectroscopy, particle size and surface charge) and in vitro bioapplications with four different cell lines were compared. As a result, pH-sensitive drug delivery via sugar-coated AuNPs was performed thanks to hydrazone linkages between glycopolymers and DOX. Comparative viability tests also demonstrated the efficiency of glycopolymer-DOX conjugates by fluorescence cell imaging. The obtained results reveal that AuNP homoglycopolymer DOX conjugates (P4D) have significant potential, especially in human neuroblastoma cells in comparison to cervical cancer cells and lung cancer cells.
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    Poly(methacrylic acid)-Coated Gold Nanoparticles: Functional Platforms for Theranostic Applications
    (Amer Chemical Soc, 2016) Yilmaz, Gokhan; Demir, Bilal; Timur, Suna; Becer, C. Remzi
    The integration of drugs with nanomaterials have received significant interest in the efficient drug delivery systems. Conventional treatments with therapeutically active drugs may cause undesired side effects and, thus, novel strategies to perform these treatments with a combinatorial approach of therapeutic modalities are required. In this study) polymethacrylic acid coated gold nanoparticles (AuNP-PMAA), which were synthesized with reversible addition fragmentation chain transfer (RAFT) polymerization, were combined with doxorubicin (DOX) as a model anticancer drug by creating a pH-sensitive hydrazone linkage in the presence of cysteine (Cys) and cross linker. Drug-AuNP conjugates were characterized via spectrofluorimetry, dynamic light scattering and zeta potential, measurements as well as X-ray photoelectron spectroscopy. The particle size of AuNP-PMAA and AuNP-PMAA-Cys-DOX conjugate were calculated as found as 104 and 147 nm, respectively:. Further experiments with different pH conditions (pH 5.3 and 7.4) also showed that AuNP-PMAA-Cys-DOX conjugate could release the DOX in a pH-sensitive way. Finally, cell culture applications with human cervix adenocarcinoma cell line (HeLa cells) demonstrated effective therapeutic impact of the final conjugate for-both chemotherapy and radiation therapy by comparing free DOX and AuNP-PMAA independently. Moreover, cell imaging study was also an evidence that AuNP-PMAA-Cys-DOX could be a beneficial candidate as a diagnostic agent.
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    Stress Analysis of Fiber-reinforced Maxillary Dentures Under Different Loadings
    (Sage Publications Ltd, 2010) Akan, Ender; Gungor, Mehmet Ali; Yilmaz, Gokhan; Artunc, Celal; Benli, Semih
    The aim of this study was to compare maxillary dentures having different reinforcing materials in terms of stress distribution under concentrated forces applied to anterior and posterior regions. For this purpose, stress analyses of finite element models of 3 mm thick maxillary denture-bone systems were performed by using ANSYS software. First, concentrated forces making various angles, such as 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees, with horizontal axis were applied to the anterior incisor and the posterior molar tooth regions of a maxillary denture without reinforcement material. The results show that the highest stress in critical zones occur at 75 degrees and 45 degrees angles, under loadings of 150N to molar and 75N to incisor region, respectively. Secondly, four different reinforcing materials including unidirectional and woven glass fibers, unidirectional carbon fibers, and alloyed chrome-cobalt fibers were placed in the denture in two different positions. Under vertical loadings, the sigma(x) stress distributions occurring in critical zones were investigated. It is concluded from the stress analyses that use of Cr-Co as a reinforcing material at the center of the maxillary denture gives the best results in terms of stress distribution and strength.