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In this study, AISI 1018 steel with low carbon content was coated with the pack-boriding method at 950 °C for 2h and 4h. A two-layer structure was observed in the 2h boronized material: the thin FeB phase and the more prominent Fe2B phase. In addition to this two-phase structure, undesirable phases (SiC and Fe3O4) were detected in the material boronized for 4h. It was observed that the wear resistance and hardness of the boronized materials increased greatly, which is explained by the hard FeB and Fe2B phases. In addition, as the heat treatment time increases, the thickness of the FeB phase increases while the thickness of the Fe2B phase decreases.

In this research, the hardness and reduced modulus of Al-%wt.12-%wt.0.5Sb melt-spun alloy were evaluated by using depth sensing indentation and atomic force microscopy techniques. We considered two approaches, Oliver-Pharr and Work of Indentation, to analyse the load-displacement curves. The ratio of final depth to maximum depth was found to be higher than the reported critical value of 0.70, which mean that pile-up was dominant in the melt-spun. A pile-up around the deformed surface was observed from atomic force microscope, which is consistent with the aferomentioned result. The hardness calculated by Oliver-Pharr method was higher than that calculated by Work of Indentation Approach. According to the results, Work of Indentation Approach was more reliable than the Oliver-Pharr approach because of reducing pile-up affect.

Özet: Amaç: Minimal invaziv ve estetik bir tedavi seçeneği olan direkt kompozit rezin restorasyonlar diastema vakalarında başarıyla kullanılmaktadır. Bu olgu sunumunun amacı, ortodontik tedavisi tamamlanan hastada, vital ağartma sonrası direkt kompozit rezin restorasyonlarla estetik rehabilitasyonun sağlanmasıdır. Birey ve Yöntem: Ortodontik tedavisi tamamlanan 19 yaşında kadın hastanın anterior dişlerinde renklenme şikayeti için %16’lık karbamid peroksit içeren beyazlatma jeliyle 15 gün ev tipi ağartma tedavisi uygulanmıştır. Ağartma sonrası hands-free tekniğiyle kompozit rezin restorasyonlar uygulanmıştır. Bitirme ve cila işlemleri diskler ve polisaj lastikleriyle gerçekleştirilmiştir. Sonuç: Polidiastema ve renklenme şikayetiyle kliniğimize başvuran hastada ağartma tedavisi sonrası direkt kompozit rezin restorasyonlarla estetik rehabilitasyon sağlanmıştır.

Al-5Cu, 2xxx serisi Al-esaslı alaşım grubundan olup hafif ağırlığın gerektirdiği otomotiv ve havacılık endüstrisinde geniş bir kullanım alanına sahiptir. Al-5Cu alaşımlarının en belirgin özellikleri, düşük yoğunluk, yüksek erime sıcaklığı, iyi termal iletkenlik, yüksek dayanım ve tokluktur. Bu araştırmada, Al-5Cu alaşımının mekanik özelliklerinin geliştirilmesi amaçlanmıştır. Bu sebeple, ağ.% 0.5 ve 1.0 oranında Skandiyum (Sc) katkılı Al-5Cu alaşımı indüksiyonla ergitme yöntemi ile üretilmiştir. X-ışınımı kırınımı (XRD) analizlerinden, Al-5Cu alaşımında Al ve Al2Cu fazları gözlenirken, Sc katkılı alaşımlarda bu fazların yanında Cu2Sc fazı tespit edilmiştir. Taramalı elektron mikroskobu (SEM) analizlerinden, Sc katkısının, külçe alaşımların mikro yapısını büyük oranda incelttiği görülmüş ve ayrıca, Sc katkılı alaşımlarda yarı-kararlı iğnemsi θ'-Al2Cu fazlarına rastlanılmıştır. Ayrıca alaşımlarda gözlenen mekanik özelliklerindeki iyileşme, tane boyutu sertleşmesi ve çökelti sertleşmesi mekanizmaları ile açıklanmıştır. Nano çentme testi sonuçlarından, Sc elementinin Al-5Cu alaşımını mekanik özellikleri bakımından büyük oranda geliştirdiği anlaşılmıştır.

Humic acids, which are known for their use in agricultural areas and are very popular in this field, have the potential to be used for all living things. These acids are yellow to black in color and are a component of the humic substances found in the humus of the soil. They are fully decomposed remains of organic life and natural matters obtained as a result of the microbial degradation of plants. Humic acid refers to a complex mixture of many different organic acids soluble in alkaline solutions. These acids, we encounter in a different area every day, are important in the beekeeping sector, as well. Even though Türkiye has met all the requirements of the beekeeping sector in terms of both climate and wealth of flora, it is known that honeybees’ health and quality and production of honey have fallen below the targeted levels. The major factor behind the low level of production and failing to keep bee colonies’ health is that beekeepers insist on sticking to conventional methods. The nutrition and health of individuals in bee colonies directly affect the quality and amount of honey they make. For this reason, humic acids can be regarded as an alternative product in order to maintain their nutrition and health. In this review, the causes of Varroa destructor infestations, the applied control methods and the applicability of humic acids were examined.

In this study, the effects of Zr addition on phase transformation temperatures, microstructure of Ti-12V-4Al (wt. %) high temperature shape memory alloys (HTSMAs) manufactured using melt-spinning technique were investigated. During heating, differential scanning calorimetry (DSC) curves showed that austenite transformation temperature of Ti-12V-4Al (wt. %) melt-spun ribbon was single-stage transformation and Ti-12V-4Al-0.5Zr (wt. %) melt-spun ribbon was two-stage transformation. In the scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyzes, unveiled that the melt-spun ribbons consisted of martensite, austenite and R phases. Transmission electron microscopy (TEM) analysis showed that the thickness of martensite plates in ribbons was thinned by the addition of Zr.

Toleration, which allows people to live together despite their differences, has paradoxes in itself. The concept of toleration is primarily a guide on how I should behave towards being not like me. It is clear that people are different; toleration preliminary accepts me and the other’s difference. Besides, the concept of toleration is an improved attitude towards intoleration. The emergence of the concept of tolerance is to get rid of the negative effects of toleration. However, it is noticed that toleration can not bring about the positive effects that it wants to reveal due to the intoleration which is the opposite of toleration within the process. The effects of the paradoxical structure can be seen here. In connection with any situation or situation, a person will tolerate a situation different from his or her own values or acceptance. In this case, the person will be able to make it worthless to himself or to move away from the life he / she accepts. As a result of tolerated subjects, there may not be a topic to be tolerated. Because, If the person, the group, the society, moving away from their own selves, they can accept what they have tolerated as their own truth. In addition to this, the question, “is there a limit to what I will tolerate” is on the agenda. Can intoleration be tolerated? Should I tolerate a crime committed against humanity, a nation, society, community? Toleration to intoleration will bring about disappearance of toleration. In this case it is unclear what will determine differance between toleration and intoleration. If I do not tolerate what is intolerant, the things that make me different from will come off spontaneously. Likewise, if I show toleration to intoleration, a structure will be formed against my loss and even toleration. In this case, I will have to set a limit on what I will tolerate. The paradoxical structure of the concept of tolerance still appears. Is it possible to determine this limit? Or how will the content of the border be determined? Is it always possible to keep the border the same? It is understood that it is very difficult to determine what this boundary is. First of all, it can be very difficult if the accepted limit applies to everyone. The culture, beliefs, philosophical views people belong to, the power relations they are in will be decisive about what the boundary should be. Furthermore, if a boundary is accepted and this boundary is not tight enough to prevent harm from social values, then the characteristics determine the quality of the society will be removed and there will be no situation where Intoleration will be shown. The values that sould be tolerated will become dominant values, in a sense, intoleration will be out of toleration. If this limit is rather limited and tight, the possibility of doing a tolerant behavior will be greatly reduced. Besides, is toleration an expression of superiority? The person who will show toleration has a more effective power than tolerated. Toleration appears to be a principle in determining the dominance / power relation in this sense. If toleration is determined according to dominance / power relation, the limit of it can be determined in relation to the interests of the stronger one. To see tolerated as weak, it may also bring to the agenda that it is defective, imperfect or faulty. Tolerance can then lead to intoleration. Ernesto Laclau (1935-2014) states that tolerantion is undecidability. Evaluating the concept of toleration in relation to intoleration, Laclau refers to the paradoxical nature of this concept. In this presentation, based on the paradoxical situations involved in toleration and the views of Ernosto Laclau and Habermas, an inquiry will be made on what the toleration is and is not.

WOS:000456351800022 In this research, cylinder liners of a diesel engine were coated with a 150 mu m thick Fe2B layer using boronizing method. The upper surface of the piston was coated with a 300 mu m thick CoNiCrAlYttra + NiCrBSi layer by using plasma spraying method. D-2, biodiesel (PSME-100) and blend (PSME-50) were used as test fuels. PSME fuel was produced through alkali catalyzed transesterification method. As-prepared fuels were used separately in coated (CE) and standard engines (SE) to compare performance and exhaust emission of both engines. In order to see the isolation effect of Fe2B layer, 3-D finite element transient-state analyses were carried out. According to the results, brake thermal efficiency (BTE) and exhaust gas temperature (EGT) of coated engine were considerably enhanced while brake specific fuel consumption (BSFC), CO, HC and smoke emission were decreased compared to those of standard engine. However, NOx emission of CE was higher than that of uncoated one, which was attributed to high combustion temperature and long combustion process in CE. These results were further confirmed with finite element simulation. The decreasing BSFC and increasing BTE for coated engine has been attributed to the elevated temperature of the combustion chamber by the effect of thermal insulation. (C) 2018 Elsevier Ltd. All rights reserved.

This study analyzes the influences of Zr addition on the martensitic transformation behavior, microstructural evolution, mechanical properties and superelasticity effect of arc-melted Ti-12V-4Al-xZr (x = 0, 0.5, 1, 1.5 and 2 wt.%) high temperature shape memory alloys (HTSMA). The results revealed that the austenite transformation temperatures and activation energy values decreased linearly when the Zr addition was greater than 0.5 wt.%. The Ti-V-4Al (wt.%) and Ti12V-4Al-0.5Zr (wt.%) alloys were composed of α″ martensitic phase, while the others consisted of predominant α″ martensitic phase and a small amount of the β austenite phase. The thickness of martensitic plates in the alloys reduced with increased Zr addition. Hardness and reduced elastic modulus values calculated from load-depth curves of the alloys also decreased with increasing Zr addition. Along with the increase in the Zr addition, the alloys’ superelasticity behavior decreased at room temperature (24 °C), while this behavior increased at the high temperatures (450 °C).

Aim: This study aimed to evaluate the status of receiving education on rational drug use, the criteria in medical drug selection, and the level of knowledge of dentists working in a dentistry faculty in Turkey. Materials and Methods: This was a descriptive study based on a questionnaire. One hundred seventeen (74%) dentists volunteered to participate in the study. The questionnaire consisted of 20 questions investigating sociodemographic features and rational drug use. Results: The mean age of the dentists was 30.8±7.2 years, and 62.4% of them were men. The mean period of professional experience was 8.9±7.1 years. The most frequently used resources of references while prescribing medicine were Vademecum (medical drug guide) (61.5%), the internet (59.0%), and colleagues (49.6%).According to the responses of the dentists about their level of knowledge of drugs, the most frequently reported condition described as ‘good’ was drug indications (43.6%). The dentists had a moderate level of information about posology and administration route (48.7%), pharmacologic features (48.7%) and contraindications (46.2%). The number of dentists who stated that they considered the cost while prescribing was low (always, 6%, and frequently, 15.4%). 23.9% of the dentists received education for rational drug use. Conclusion: It was determined that dentists did not receive adequate and effective education on rational use of drugs. Regular and continuous education before and after graduation is a necessity for both dentists and their patients.

Aim: The purpose of this in vitro study was to evaluate the effect of different layering techniques (bulk, oblique, centripetal, split horizontal) on the marginal microleakage of Class II adhesive restorations. Methodology: Forty-eight standardized Class II cavities were prepared on both mesial and distal sides of extracted non-carious human molar teeth. Following preparation, all specimens were randomly divided into four groups (n=12). Group 1: bulk technique; Group 2: oblique incremental technique; Group 3: centripetal incremental technique; Group 4: split horizontal incremental technique. The teeth were restored with a total-etch adhesive system and a microhybrid composite resin. After thermocycling and immersion in a 0.2% methylene blue solution for 24 hours, the restorations were sectioned, and dye penetration was evaluated under a stereomicroscope. The microleakage scores (0 to 4) obtained from the occlusal and gingival margins were analyzed with Kruskal-Wallis and Mann-Whitney U tests (p0,05). Conclusions: Based on the results of the present study, none of the four placement techniques were found to be effective in eliminating marginal microleakage entirely in Class II restorations. All of the placement techniques showed similar results when the cavity margins were located on the enamel. How to cite this article: Misilli U, Yilmaz F. Evaluation of marginal microleakage in composite restorations with different placement techniques. Int Dent Res 2018;8(2):70-7. Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Yilmaz, Fikret/0000-0002-9621-4788; ozyurek, taha/0000-0003-3299-3361 WOS: 000431942400019 PubMed: 29571907 Introduction: The aim of this study was to compare the fracture strengths of mandibular molar teeth prepared using traditional endodontic cavity (TEC) and conservative endodontic cavity (CEC) methods and restored using SDR (Dentsply Caulk, Milford, DE) and EverX Posterior (GC Dental, Tokyo, Japan) base composite materials. Methods: A hundred mandibular first molar teeth were randomly divided into 5 groups. In group 1 (the control group), samples were kept intact. In group 2, TECs were prepared, and the samples were restored with EverX Posterior and composite resin. In group 3, CECs were prepared, and the samples were restored with EverX Posterior and composite resin. In group 4, TECs were prepared, and the samples were restored with SDR and composite resin. In group 5, CECs were prepared, and the samples were restored with SDR and composite resin. This load was applied on the samples at 1-mm/min speed using a 6-mm round-head tip until fracture. The forces resulting in fracture were recorded in newton units. The data were analyzed using Kruskal-Wallis and Pearson correlation tests at a 5% significance level. Results: The fracture strengths of the samples in the control group were significantly higher than the experimental groups (P < .05). There was no statistically significant difference in the endodontic access cavities prepared used the TEC and CEC methods and restored using the same composite base material (P > .05). Conclusions: CEC preparation did not increase the fracture strength of teeth with class II cavities compared with TEC preparation. The fracture strength of teeth restored with the SDR bulk-fill composite was higher than that of teeth restored with EverX Posterior.

In the present work, Cu and Ni nanofluids were synthesized using the pulsed wire evaporation (PWE) method in the different aqueous medias, namely (ethanol and ethylene glycol), and the effects of the aqueous media on the dispersion state, stability, and particle size of nanoparticles were studied. The size and morphology of synthesized nano-particles were investigated by transmission electron microscopy (TEM). Also, the dispersion stability of the nanofluids was evaluated by turbiscan analysis. The TEM results showed that the nano-particles were spherical in shape, and the average particle size was below 100 nm. The average particle size of the Cu nano-particles was smaller than that of Ni, which was attributed to a difference in the specific sublimation energy of the elements. Moreover, ethylene glycol (EG) exhibited higher suspension stability than ethanol. Finally, the dispersion stability of Cu@EG displayed the highest value due to lower particle size and greater viscosity.

The effects of Al content on microstructure, phase transformation and activation energy of Ti–12V-xAl (x = 2, 4 and 6 wt %) alloys produced by using the arc-melting technique have been investigated in the present study. These features of the alloys were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The XRD and SEM measurements showed that the alloys had simple of single orthorhombic α martensitic phase. In the DSC analysis, it was observed that the martensitic transformation temperature decreased depending on the heating rate in the alloys. The highest transformation temperature occured in the Ti–12V–4Al alloy. In TEM images, it was noteworthy that there were martensite structures arranged side by side in the structure of the alloys. The activation energies of the alloys were estimated using the Kissenger and Osawa method using the data obtained from DSC. Activation energies determined by these two methods were similar.

The LaNi5 intermetallic compound is an AB5 type hydrogen storage alloy which exhibits low operating temperature, easy activation, low pressure and tolerance to impurities. In this study, LaNi4.7-x Al0.3Bix (x = 0.0, 0.1, 0.2, 0.3) alloys were produced by melt-spinning technique and the effects of Al and Bi additions on the microstructure, thermal and hydrogen storage properties of LaNi5 were investigated. The results showed that substitution of Ni with Al led to a desired decrease in absorption/desorption plateau pressure and hysteresis without a decrease in hydrogen storage capacity. In contrast, Bi substitution with Ni increased the absorption/desorption plateau pressure, reduced the hydrogen capacity and increased pulverization resistance of the alloy due to the formation of BiLa and AlNi3 intermetallic phases at the grain boundaries.

In this study, the effect of Si amount on the microstructure, crystal structure and some mechanical properties of Al-(20,25,30 wt%)Si–5Fe powder mixtures produced by high energy ball milling method was investigated by determining the sintering temperature. In the X-ray diffraction analysis, no inter-metallic phases were found except for the Al, Si and Fe phases of the powder mixtures. The X-ray diffraction patterns were analyzed by the Rietveld method to determine amounts of the Al, Si and Fe elements in the powder mixtures. From the scanning electron microscopy analysis, it is seen that as the amount of Si increases, there is a marked decrease in the grain size of powders. In the micro-indentation tests performed at room temperature, the hardness and elastic modulus values of the pelletized powders were found to increase with the amount of Si. It was also found that the Al-20Si-5Fe powder mixture with the lowest Si content had the highest damping capability. The high temperature micro-indentation tests showed that the resulting Al-(20,25,30 wt%) Si-5 Fe powder mixtures started to consolidation at 200 °C and completed the consolidation at 400 °C. This method can be used as an alternative method in the determination of the sintering temperature of materials. © 2017, 110M517, This research was supported by TUBITAK (Project No.: 110M517 ).

In this study, dyeability of wool fabrics with walnut leaves extract have been investigated in presence of various acids including acetic acid, citric acid, maleic acid, oxalic acid, and formic acid. Each wool fabric was pretreated with 1 M of acid solution, separately. The pretreated fabrics were dyed with walnut leaves extract using various mordants by metamordanting method. Color strength values of the dyed fabrics were evaluated by measuring K/S values. Fastness properties (washing, rubbing, and light fastness) were also determined. The pretreated fiber sample surfaces were observed using a scanning electron microscope (SEM). The present study showed that citric acid pretreatment plays an important role for improving the dyeability of wool fabrics with walnut leaves extract. © 2015, The Korean Fiber Society and Springer Science+Business Media Dordrecht.

In the present study, dyeing potential of waste water from distillation process was investigated for fresh and dried herbs of Menthaspicata (MS), Menthapiperita (MP), and Salvia officinalis (SO) species. Meta-mordanting method was used in the dyeing of wool and cotton fabrics in the presence of FeSO4·7H2O (iron) and AlK(SO4)2·12H2O (alum) mordants. The color of each dyed material was investigated in terms of the CIELab (L*, a*, b*, C, and h°) and K/S values. The surfaces of the samples were observed using a scanning electron microscope. It was observed that the color strength of fresh and dried plant is depended on the plant species, mordant, and fabric type. Best color intensity (K/S = 16.68) was obtained with iron mordant using fresh SO on cotton fabric. For wool fabric, the highest color strength (K/S = 9.62) was obtained with fresh SO in the presence of alum mordant. Presence of metal mordant for natural dyeing process of cotton with MS, MP, and SO extract has shown remarkable improvement in terms of dye adherence and fastness properties thus metal mordanting could be suitable alternative dyeing method for ecofriendly industrial application. © 2017 Taylor & Francis.

Ekmekci, Dursun/0000-0001-9045-7909 WOS: 000413562200034 This study aimed to investigate the mechanical properties of a surface modulation which was realized through compaction, and then sintering of copper powders. To this goal, Berkovich type of indenter and depth-sensing indentation technique were used in microindentation to measure the hardness and modulus of elasticity values at different features of compact. Indentations were performed with a peak force of 50 mN. Hardness values were obtained in 0.88-1.12 GPa range while the modulus of elasticity was recorded in the 70-111 GPa interval. Even though both modulus of elasticity and hardness values were noted to be different for copper powders and substrate, one-way ANOVA analyses showed that the differences in both modulus of elasticity and hardness values are insignificant. FE modeling of microindentation was also performed and validated. It was shown that the force-displacement values obtained from FE analyses are quite well in agreement with the experimental data.

Yilmaz, Fikret/0000-0002-9621-4788; Aytac Bal, Fatma/0000-0003-2379-4678 WOS: 000347131400009 Background/purpose: The aim of this study was to investigate the effects of different light curing units (LCUs) on the microleakage of different composite resins. Materials and methods: Forty-five freshly extracted human third molars were selected for this study. Standardized class V cavities were prepared on the buccal and lingual surfaces of each tooth. The teeth were randomly divided into three composite resin groups, comprising two dimethacrylate-based hybrid composites and a silorane-based composite. Each composite resin group was randomly divided into three subgroups for curing with three different LCUs (n = 5). Of the three different LCUs used, one was quartz-tungsten-halogen and two were light-emitting diodes (LEDs) with different power outputs. The teeth were immersed in a 2% methylene blue dye solution and examined under a stereomicroscope. Results were statistically analyzed using Kruskal-Wallis and Dunn tests. Results: When all composite resin groups were compared, the lowest marginal leakage scores were obtained with the Filtek Silorane composite group, and they statistically significantly differed from those of the other groups (P < 0.05). Among all groups, the lowest marginal leakage value was obtained for the LED 1055 subgroup of the Filtek Silorane composite group, and the highest marginal leakage value was obtained for the quartz-tungsten-halogen subgroup of the Aelite Aesthetic Enamel composite group. Conclusion: It was concluded that it is not possible to entirely prevent microleakage, but it can be minimized with silorane-based composite resins and high-density-output LED LCUs. Copyright (C) 2013, Association for Dental Sciences of the Republic of China. Published by Elsevier Taiwan LLC. All rights reserved.

In this study, the effects of different production methods like melt spinning, high-energy ball milling, and combined melt spinning and high-energy ball milling on the mechanical and microstructural properties of hypereutectic Al-20Si-5Fe alloys were investigated. While microstructural and spectroscopic analyses were performed using scanning electron microscopy and X-ray diffractometry, mechanical properties were measured using a depth-sensing indentation instrument with a Berkovich tip. Microstructural and spectroscopic analyses demonstrate that high-energy ball milling process applied on the melt-spun Al-20-Si-5Fe alloy for 10 minutes brings about a reduction in the size of silicon particles and intermetallic compounds. However, further increase in milling time does not yield any significant reduction in size. High-energy ball milling for 10 minutes on the starting powders is not enough to form any intermetallic phase. According to the depth-sensing indentation experiments, high-energy milling of melt-spun Al-20Si-5Fe alloys shows an incremental behavior in terms of hardness values. For the Al-20Si-5Fe alloys investigated in this study, the production technique remarkably influences their elastic–plastic response to the indentation process in terms of both magnitude and shape of P-h curves. © 2014, The Minerals, Metals & Materials Society and ASM International., 110M517, The authors would like to thank the Scientific and Technological Research Council of Turkey (TÜBİTAK) for funding the project (Project number 110M517).

In this work, rapidly solidified hypereutectic Al-20Si-5Fe-. XV (X=0, 0.5 and 1) alloys were fabricated by melt spinning under vacuum. Microstructural and spectroscopic analyses were performed using SEM, TEM, TEM-MAPing, TEM-EDS and XRD measurements. Mechanical properties of the alloys were determined using DSI measurements. Experimental results indicated that addition of 0.5. wt% V to melt-spun Al-20Si-5Fe alloys induced formation of a novel flower-like Si phase. And addition of higher amount V (1. wt%), caused formation of refined Si phases and mostly hindered formation of Fe-bearing intermetallics. Observations along with manuscript strongly indicate that V modifies the Si phases by the impurity induced twinning (IIT). Changes in the dynamic microhardness of the samples were mainly determined by the size of Si phases. Addition of vanadium led to quite lower elastic modulus in the vanadium added alloys compared to base alloy. © 2014 Elsevier B.V., Firat University Scientific Research Projects Management Unit 110M517 National Council for Scientific Research British Association for Psychopharmacology: 2010/111, The authors would like to thank the Scientific and Technological Research Council of Turkey (TÜBİTAK) for funding the Project (Project number 110M517 ). The authors would like to thank the Gaziosmanpaşa University Department of Scientific Research Projects (BAP) for funding the project (Project number 2010/111 ). The authors wish to record their grateful thanks to Prof. Soon-Jik Hong from Kongju National University (KNU) for TEM and SEM works.

WOS:000335666900002 Nanoindentation technique was used to characterize the mechanical properties of Gd-deposited bulk YBaCuO superconductors fabricated by solid-state reaction method. In order to determine the hardness and reduced modulus of the samples, load-displacement data were analysed by using the Oliver-Pharr method. The hardness values exhibited significant peak load-dependence especially at lower peak loads, while the reduced modulus values were found to be nearly constant at studied loading range. In order to find true hardness of the samples, the peak load-dependency of hardness was analysed by using Meyer's law, minimum resistance model, elastic/plastic deformation model, energy balance model, Nix-Gao model and Mukhopadhyay approach. Of the aforementioned models, energy balance model and Mukhopadhyay approach were found to be the most effective models to explain the load-dependency of hardness.

This work reports the use of pulsed wire evaporation (PWE) method to prepare cobalt (Co) nano-particles. The effect of charging voltage on the average particle size and particle morphology was studied. The Co nano-particles were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET surface area analysis. SEM and TEM observations showed that the Co particles had spherical shape and were linked to each other because of their magnetic property. The XRD analyses confirmed that Co nano-particles had FCC structure without any presence of impurity phase. Average particle size was calculated by three methods; TEM, BET and XRD. The results showed that the particle size decreased with increasing charging voltage and then attempted to saturate, which was explained with crystallite size of the Co wire, superheating factor and specific energy input into the wire.

In this work, superconducting and mechanical properties of BSCCO superconducting whiskers were studied in detail. Nanoindentation properties of the whiskers were analyzed by the Oliver and Pharr Method and Work of Indentation (WI) method. More accurate results using the WI method for both the hardness and the reduced modulus were obtained due to reduction of the pile-up error. The correct hardness and reduced modulus values were determined by considering the indentation size effect and the substrate (epoxy resin) effect. The modified composite hardness model and the composite reduced modulus model are the most suitable models to investigate the nanoindentation properties of the whiskers.

The effects of cobalt addition on microstructure and mechanical properties of Al-20Si-5Fe-XCo (X = 0, 1, 3, and 5) alloys were reported in this study. The alloys were produced by both conventional sand casting and melt-spinning at 20 m/s disk velocity. Microstructures of the samples were investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Vickers micro-hardness tester was used for hardness measurements. Results showed that Co addition can alter morphology of Fe-bearing intermetallic compounds (IMCs) from long rod/needle-like structures to short rod-like ones, and lead to a more homogenous distribution in the microstructure. Addition of 5 wt% Co leads to a decrease in average size of the primary silicon phases in as-cast Al-Si alloys. In melt-spun alloys, with the addition of Co, the microstructure became finer and more homogenously distributed, while thickness of the featureless zone has seen great increase. The optimum Fe to Co ratio was found to be 1 for suppressing the undesirable effect of Febearing acicular/needle-like intermetallic compounds. (c) 2012 Elsevier B.V. All rights reserved.

In this study, microstructural evolution and mechanical properties of Al–20 wt%Si and pure Al powders fabricated by ultra high-energy ball milling technique were investigated as a function of milling time. The microstructure and mechanical properties of the as-milled powders were examined by scanning electron microscope (SEM), energy dispersive spectrometry (EDS), X-ray diffractometer (XRD) and Vickers hardness tester. SEM observation showed that the particle size increased at an early stage of milling, and then decreased drastically with further milling. XRD and cross-sectional EDS-mapping analyses revealed that Si particles were not dissolved but uniformly dispersed in the Al matrix in a milled state. Vickers hardness of both pure Al and Al–Si powder increases with milling time, which attributes to the grain size strengthening and dispersion strengthening.

WOS:000301482400001 Nanosized Ag particles were obtained in liquid medium, which is composed of deionized water and sodium hexametaphosphate, using pulsed wire evaporation within hundreds of microseconds from pure initial Ag wire (99.98%), with varying voltage. Changes in powder morphology and microstructure due to change in supply voltage was observed by FE-SEM and HR-TEM, and phase structure of powders was analyzed by XRD. The results revealed that average particle size slightly increased with increasing supply voltage without any impurity and oxide phase, which was explained in terms of addition of stabilizer into the coolant liquid. The experimental results also suggest that addition of sodium hexametaphosphate into the coolant liquid is good for enhancing the dispersibility property of silver nanopowders.

In this study, effects of simultaneous Mo and W substitution for Nb additions on the stability and magnetic properties of Fe–Co-based bulk metallic glass (BMG) alloys fabricated by centrifugal casting are investigated. The saturation magnetization ( J s ) and coercivity ( H c ) for the as-cast Fe 36 Co 36 B 19.2 Si 4.8 X 4 (X = Nb or Mo 0.5 W 0.5 ) BMG alloys and melt-spun Fe 36 Co 36 B 19.2 Si 4.8 Mo 2 W 2 were in the range of 1.02–1.57 T and 11.13–1685 A/m, respectively. The Fe 36 Co 36 B 19.2 Si 4.8 X 4 (X = Nb or Mo 0.5 W 0.5 ) BMG alloys in the shape of wedge with the maximum thickness of 1.5–2 mm were obtained successfully by means of conventional centrifugal casting. Replacing Nb with Mo 0.5 W 0.5 deteriorates magnetic properties in bulk form and reduces the GFA of the alloy due to promoting the precipitation of non-magnetic compounds, while it results in good soft magnetic properties in melt-spun ribbon form.

The effects of antimony (Sb) addition on the microstructure and mechanical properties of rapidly solidified eutectic Al–Si alloy were investigated. Al–12 wt.%Si– X wt.%Sb ( X = 0, 0.5 and 1.0) alloys were fabricated using a melt-spinner at rotating speeds of 20 m/s. The as-melt-spun ribbons were characterized by a combination of scanning electron microscopy (SEM), X-ray diffraction (XRD) and depth-sensing indentation (DSI) methods. SEM observations showed that 0.5%Sb addition refined the microstructure whereas 1.0%Sb addition led to the formation of coarse Si particles. The wheel side of the ribbons exhibited a finer microstructure than those on the free or air sides exposed to the atmosphere. According to the XRD results, the diffraction patterns of melt-spun ribbons consisted solely of α-Al and Si phases, and a possible volume fraction of AlSb or an intermetallic phase in the alloy was not observed. DSI tests were performed on the ribbons under different loads ranging from 200 to 1200 mN at room temperature. The resulting indentation load-displacement ( P – h ) curves were analyzed using the work of indentation approach (WIA) to evaluate the ribbons’ microhardness ( H ) and reduced modulus ( Er ). We found that the H and Er values of the ribbon decrease with increasing Sb content. This can be attributed to the over modification and changes in the microstructure of Al–12%Si alloy when a minimum of 1.0%Sb is present as a modifier.

A depth sensing indentation (DSI) test with associated analyses was used to investigate some mechanical properties (reduced elastic modulus, hardness and creep) of electrochemically synthesized polythiophene (PT). Internal friction (IF) and energy absorption representing the degree of anelastic deformation of the material were also determined using cyclic and step-load/unload (SLU) test procedure, respectively. The indentation load–displacement (P–h) curves of the sample were obtained under different peak loads with two load holding time, 70 and 300 s. Elastic modulus values were determined by analyzing of these curves with Oliver–Pharr (O–P) and Feng–Ngan (F–N) procedures. The obtained results pointed out that both methods yielded comparable results for 300 s, while the corresponding values of 70 s were not well-matched with each other. These results were explained by the saturation of creep effects within 300 s holding period. Creep analysis exhibited that creep displacement increases at a declining rate with time and finally reaches a constant rate. Cyclic test results indicated that IF values approach saturation after several cycles and the saturation value of IF was found to be depending on loading rate. From SLU tests, an upper limit of the normalized dissipated energy was observed.

In this study, we used depth-sensing indentation (DSI) technique to investigate some mechanical properties (reduced elastic modulus, indentation hardness, and creep) of polypyrrole (PPy) conducting polymer obtained with different support electrolyte concentration. The influence of support electrolyte concentration on these parameters was also determined. The order of doping degree of the samples was determined by cyclic voltammetry. The indentation load–displacement curves of the samples were obtained under different peak load levels with a 70 s holding time at maximum load. Reduced elastic modulus and hardness values were determined by analysis of these curves using the Feng–Ngan (F–N) and Tang–Ngan (T–N) methods, respectively. Both reduced elastic modulus (E r) and indentation hardness (H) exhibited significant peak load dependence, i.e., indentation size effect (ISE). It was found that both E r and H values decreased as the support electrolyte concentration was increased. This was explained by an increase in the free volume as the doping degree was raised. The creep behavior of the samples was monitored from the load holding segment of the load–unload curves. It was found that creep increases with the increasing support electrolyte concentration.

WOS: 000266117900096, In this study, ZnO molar wt% 0, 5,10,20,30, and 50 added Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10 superconductors were prepared by wet technique. The experimental works consist of powder X-ray diffraction (XRD) for phase analyses and c-axes parameters, scanning electron microscopy (SEM) for microstructure examination, and microhardness measurements for mechanical properties. These measurements showed that Zn-added material, in comparison with the pure sample, had increased c-axes parameters and decreased grain size. In addition, the experimental results of microhardness measurements were analyzed using Oliver-Pharr model. It was observed that the change of indentation hardness (H-rr) and reduced elastic modulus (E-r) values showed an increasing trend with ZnO addition and exhibited peak load dependence (i.e., indentation size effect (ISE)). (C) 2008 Elsevier B.V. All rights reserved., Turkish State Planning Organization (DPT) [2003K120510], The authors would like to acknowledge the financial support (Project No.: 2003K120510) by Turkish State Planning Organization (DPT). The authors also thank to Senol Akin for helpful comments on editing our manuscript and department of Physics, Karadeniz Technical University, Turkey, for producing the samples.

The present research aimed to characterize the microstructure of icosahedral quasicrystalline phase (i-phase) in different chemical compositions of Al–Cu–Fe alloys. The ternary alloys with the nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 (at%) were rapidly solidified by melt-spinning technique. The melt-spun ribbons were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). According to the XRD results, diffraction patterns of Al70Cu20Fe10 alloy showed the presence of the i-phase together with tetragonal θ-Al2Cu phase. However, XRD pattern of the melt-spun Al63Cu25Fe12 alloy showed the formation of i-phase together with a small amount of β-phase. The single quasicrystalline phase was observed only in the rapidly solidified Al65Cu20Fe15 alloy. The SEM examinations showed that the melt-spun Al70Cu20Fe10 and Al63Cu25Fe12 alloys composed of i-phase with an average grain size of 1–5 μm. However, for the Al65Cu20Fe15 alloy, the quasicrystalline particles in the star-shape dendritic formations were observed. The melting point of i-phase was determined as 890 °C by DTA examinations.

The nanomechanical properties of RuSr 2 RECu 2O8 (RE = Eu, Gd and Ho) prepared by ammonium nitrate melt technique (ANMT) were investigated using nanoindentation technique. The indentation load–displacement curves of the samples were obtained at different peak loads ranging from 10 to 400 mN. Reduced elastic modulus and hardness of the superconductors calculated from loading–unloading curves were peak load dependent, i.e., indentation size effect (ISE). We observed that Ho substitution led to a substantial improvement in mechanical properties of the RuSr2RECu2O8, which was attributed to the strong grain connectivity and dense and less porous structure of RE = Ho sample. © 2014, Springer Science+Business Media New York.

In this work, the effects of Be addition on the microstructure and phase transformation temperatures of Cu-12Al-xBe (x = 0.4, 0.5 and 0.6 wt.%) shape memory alloys fabricated by using the arc-melting and melt-spinning techniques have been investigated. X-ray diffraction analysis revealed that the arc-melted alloys consisted of austenitic ß1, martensitic ß1' and ?2 precipitate phases, whereas melt-spun ribbons were composed of a fully martensitic phase. The average grain size of martensitic phases in melt-spun ribbons was determined by electron microscopy images, showing a decrease with increasing Beryllium (Be) amount. Moreover, it was found that the Be addition in the arc-melted alloys had a distinct effect on the morphology of the ?2 precipitate phase. Transmission electron microscopy analysis showed that the thickness of martensitic plates in the melt-spun ribbons reduced with increasing Be addition. In a differential scanning calorimeter analysis, no martensitic transformation (Ms) peak was observed in arc-melted alloys, but it was clearly detected in melt-spun ribbons, in which Ms decreased dramatically with increasing Be addition. The improvement in the shape memory ability of melt-spun ribbons was explained in terms of the refinement in grain size and martensitic plates. © 2013 Elsevier Inc., Firat University Scientific Research Projects Management Unit: 2009/54, This work is supported by the Tokat Gaziosmanpasa University Scientific Research Project Unit (BAPB) under project no: 2009/54 .

WOS: 000316536800003, The microstructure and microhardness evolution of melt-spun Al-25Si-5Fe alloy with Co addition (1, 3 and 5 wt.%) were investigated. Microstructural and spectroscopic analyses demonstrate that Co could refine primary Si grains and change their morphology because it causes higher constitutional undercooling and has large mixing enthalpy with Si. Especially, 3 wt.% Co addition causes homogeneously distributed fine spherical Si particles in the rapidly solidified Al-25Si-5Fe alloy. The size of the spherical silicon particles was from around 200 to 600 nm near the wheel side region, and it varied from 800 nm to 1.3 mu m at the air side. The optimum ratio of Si and Co should be between 6 and 8.3 to form spherical Si grains in Al-25/30Si-5Fe alloys. A considerable improvement in microhardness value (from 211 to 370 HV) was obtained with the addition of Co. (C) 2013 Elsevier Inc. All rights reserved., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [110M517]; Gaziosmanpasa University Department of Scientific Research Projects (BAP)Gaziosmanpasa University [2010/111], The authors would like to thank the Scientific and Technological Research Council of Turkey (TUBITAK) for funding the project (project number 110M517). The authors would also like to thank the Gaziosmanpasa University Department of Scientific Research Projects (BAP) for funding the project (project number 2010/111).

Polycrystalline superconducting Bi-Pb-Gd-Sr-Ca-Cu-O bulk samples with nominal composition Bi1.7Pb0.3-x Gd x Sr 2Ca3Cu4O12+y (x=0.00,0.01,0.05) were produced by the melt quenching method. The mechanical properties of the samples were characterized by depth sensing indentation technique under different peak loads ranging from 200 to 1800 mN. The experimental data were comparatively analyzed by the Oliver-Pharr method and a work of indentation approach. It was found that the work of indentation approach gave more reliable results because of the reducing pile-up effect. The results implied that both microhardness and reduced elastic modulus increased with increasing Gd substitution. © 2013 Springer Science+Business Media New York., Devlet Planlama Örgütü, Acknowledgements The authors would like to acknowledge the financial support (Project No.: 2003K120510) by Turkish State Planning Organization (DPT).

Yilmaz, Fikret/0000-0002-9621-4788 WOS: 000312267000010 PubMed: 22819955 Objectives: The aim of this in vitro study was to evaluate the effects of different finishing and polishing techniques on the surface roughness and color stability of nanocomposites. Methods: Two nanohybrid (Grandio, Aelite Aesthetic Enamel), two nanofill (Filtek Supreme XT Dentin and Translucent), and a microhybrid (Filtek Z250) composites were used. Two hundred and eighty disc-shaped specimens were cured under a mylar strip. Seven specimens of each resin composite were randomly assigned to one of the seven polishing systems. A profilometer was used for assessing surface roughness. Delta E was calculated with a colorimeter at baseline and 48 h after storage in a coffee solution. The results were analysed by two-way ANOVA and Tukey's HSD test (alpha = 0.05). Regression analysis was used to examine the correlation between surface roughness and color stability (alpha = 0.01). Results: There was no significant difference in R-a values between mylar strips and Sof-Lex polishing discs (p > 0.05). The highest Delta E and R-a values were obtained from Grandio (p < 0.05), and Aelite Aesthetic Enamel had the lowest DE values (p < 0.05). The Enhance system showed the lowest color differences among all the finishing systems. The highest DE values were found in the composite resin groups under mylar strips and finished with diamond burs (p < 0.05). Conclusions: While the Sof-Lex discs provided the lowest surface roughness, the Enhance Polishing system provided the most stain-resistant groups. Grandio presented the highest surface roughness and staining susceptibility after storage in coffee solution. Aelite Aesthetic Enamel, which did not include TEGDMA in its composition, showed the least discoloration. Clinical significance: The composites with smaller filler size did not necessarily show low surface roughness and discoloration. Staining of composite resins was dependent on monomer structure, as well as surface irregularities. (C) 2012 Elsevier Ltd. All rights reserved. The Scientific and Technological Research Council of TurkeyTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [107S314] The authors thank to The Scientific and Technological Research Council of Turkey for supplying financial support for commercial products used in this project (project no: 107S314) and Dr. Ahmet Umut Guler for sharing his valuable experiences and advices in this study. We also thank to Soner Cankaya for statistical advice and assistance.

PURPOSE The purpose of this study was to evaluate the effect of different acid etching times with 9.6% hydrofluoric acid gel and two adhesive systems on shear bond strengths of resin composite to porcelain.Ninety-eight 7 x 7 x 2 mm feldspathic porcelain blocks (VMK 95, Vita) were prepared. The specimens were divided into 7 groups: 1 control (no surface treatment) and 6 groups acid etched with 9.6% hydrofluoric acid gel for different etching times, including 30 s, 30+30 s, 60 s, 60+60 s, 120 s, and 180 s. Each of the etching time groups was divided into two bonding agent (Single Bond, AdheSE) subgroups (n = 7). Microhybrid composite (Filtek Z250) was condensed using a teflon mold and light polymerized for 20 s on the porcelain specimens. The prepared specimens were then stored in distilled water at 37 degrees C for 24 h before mechanical testing. Shear testing of all groups was performed on a universal testing machine (Lloyd LRX) at a crosshead speed of 0.5 mm/min. The bond strength data were analyzed with two-way ANOVA. The means were compared using the Tukey HSD test (alpha = 0.05).Acid etching time and bonding agent statistically significantly influenced bond strength (p0.05). In the Single Bond group, the bond strengths between group 0 (10.48 MPa) and Group 30 (11.17 MPa) did not differ significantly, with these groups exhibiting the lowest bond strength values. The highest bond strength in Single Bond group was observed in group 120 (15.07 MPa) and group 60+60 (15.42 MPa), which did not differ significantly from each other. In the AdheSE group, the bond strengths of group 0 (9.33 MPa) and group 30 (9.49 MPa) did not differ significantly, and these groups exhibited the lowest bond strength values. The highest bond strengths in the AdheSE subgroup were observed in group 120 (14.84 MPa) and group 60+60 (14.96 MPa), which were not significantly different. Comparing the two different adhesive systems, Single Bond exhibited higher bond strength values than did the self-etching adhesive AdheSE.Acid etching of porcelain with 9.6% hydrofluoric acid gel for 120 s provided adequate bond strength for composite repair with a microhybrid composite. When a porcelain restoration is repaired with composite, Single Bond adhesive should be preferred to the AdheSE self-etching adhesive system.

The purpose of the present in vitro study was to examine shear bond strengths of resin composite to porcelain according to surface treatment.One hundred eight feldspathic porcelain blocks were prepared. Specimens were divided into nine surface treatment groups: sandblasting with 50- or 110-microm Al2O3, acid etching with hydrofluoric acid, applying silane agent, and combinations of these treatments. Microhybrid resin composite was condensed and light cured for 40 seconds on the porcelain specimens, which were then stored in distilled water at 37 degrees C for 24 hours before mechanical testing.The bond strengths were significantly different according to one-way ANOVA. The lowest bond strength was observed in the silane group (4.09 MPa); the highest bond strengths were observed with acid etching + silane (11.97 MPa) and sandblasting with 50-microm Al2O3 + acid etching + silane (12.34 MPa) (no significant difference between groups).Acid etching with 9.6% hydrofluoric acid gel or sandblasting with 50- or 110-microm Al2O3 particles alone did not provide adequate bond strength. Silane agent was effective in increasing the shear bond strength of resin composite to porcelain after sandblasting or acid etching. Porcelain treatment with a combination of 50-microm Al2O3 air abrasion, 9.6% hydrofluoric acid, and silane agent provided higher bond strengths than treatment with any of these procedures alone.

Yilmaz, Fikret/0000-0002-9621-4788 WOS: 000227751800012 PubMed: 15889665 Purpose: The purpose of the present in vitro study was to examine shear bond strengths of resin composite to porcelain according to surface treatment. Materials and Methods: One hundred eight feldspathic porcelain blocks were prepared. Specimens were divided into nine surface treatment groups: sandblasting with 50- or 110-mu m Al2O3, acid etching with hydrofluoric acid, applying silane agent, and combinations of these treatments. Microhybrid resin composite was condensed and light cured for 40 seconds on the porcelain specimens, which were then stored in distilled water at 37 degrees C for 24 hours before mechanical testing. Results: The bond strengths were significantly different according to one-way ANOVA. The lowest bond strength was observed in the silane group (4.09 MPa), the highest bond strengths were observed with acid etching + silane (11.97 MPa) and sandblasting with 50-mu m Al2O3 + acid etching + silane (12.34 MPa) (no significant difference between groups). Conclusion: Acid etching with 9.6% hydrofluoric acid gel or sandblasting with 50- or 110-mu m Al2O3 particles alone did not provide adequate bond strength. Silane agent was effective in increasing the shear bond strength of resin composite to porcelain after sandblasting or acid etching. Porcelain treatment with a combination of 50-mu m Al2O3 air abrasion, 9.6% hydrofluoric acid, and silane agent provided higher bond strengths than treatment with any of these procedures alone.

Yilmaz, Fikret/0000-0002-9621-4788; WOS: 000230994200004 PubMed: 16046965 Statement of problem. The ability of tooth-colored restorative materials for provisional restorations to resist stains is important when interim prostheses arc worn for a long period. Discoloration of provisional restorative materials may result in patient dissatisfaction and additional time and expense for replacement. However, the effect of different staining agents on the color difference of resin composite restorative materials has not been completely clarified. Purpose. The purpose of this study was to evaluate the stainability of auto- and light-polymerized composite provisional restorative materials, reinforced microfill, and microhybrid resin composite restorative materials upon exposure to different staining agents. Material and methods. Forty-five cylindrical specimens (15 X 2 mm) were prepared for each of an autopolymerized bis-acryl composite provisional restorative material (Protemp II), a light-polymerized composite provisional restorative material (Revotek LC), a reinforced microfill (Micronew), and a microhybrid composite (Filtek Z250, Herculite XRV) restorative material, using a brass mold. The specimens were wet-ground with 1000-grit silicon carbide abrasive paper for 10 seconds. The 5 restorative material specimens were divided into 9 groups (n = 5) and stored for 24 hours at 37 degrees C in different types of solutions: water, coffee, coffee with sugar, tea, tea with sugar, coffee with artificial creamer and sugar, cola, red wine, or sour cherry juice. Color of all specimens was measured before and after exposure with a colorimeter using CIE L*a*b* relative, and color changes (Delta E*) were then calculated. The data were analyzed with a 2-way analysis of variance (ANOVA), and mean values were compared by the Tukey HSD test (alpha=.05). Results. The interaction of provisional restorative materials and staining agents was statistically significant (P=.0001). For the 5 restorative materials tested, the lowest Delta E* values were observed in the water, cola, and Sour cherry juice groups. The highest color difference for all restorative materials was observed in the red wine groups. For microhybrid composite materials and light-polymerized composite provisional material, when tea and coffee groups with and without sugar were compared, both groups with sugar demonstrated a higher color difference than without sugar. When comparing the 5 different restorative materials, the reinforced microfill material group (Micronew) demonstrated significantly less color change than the other materials tested. The highest color difference in this study was observed for specimens in the light-polymerized composite provisional material group (Revotek LC). Conclusion. The reinforced microfill restorative material tested was found significantly more color stable than the autopolymerized bis-acryl, light-polymerized composite provisional restorative materials, and microhybrid composites tested. The largest color difference was observed in the light-polymerized composite provisional material. The presence of sugar in coffee and tea increased the color difference compared to coffee or tea without sugar for light-polymerized composite provisional material and microhybrid composites.

It is thought that externally applied bleaching agents may penetrate into the pulp chamber. This study was conducted to evaluate the diffusion of peroxide bleaching agents into the pulp chamber of teeth restored with various restorative materials. Sixty-five human extracted anterior maxillary teeth were separated into the 13 groups containing 5 teeth. Five teeth (control group) were not subjected to any cavity preparation and restoration. Standardized class V cavities were prepared in the other 60 teeth and restored using composite resin (Charisma), polyacid modified composite resin (Dyract), or resin-modified glass ionomer cement (Vitremer). All teeth were sectioned 3 mm apical to the cementoenamel junction to remove the intracoronal pulp tissue, and the pulp chamber was filled with acetate buffer to absorb and stabilize any peroxide that might penetrate. Vestibular crown surfaces of teeth in the experimental groups were subjected to four different bleaching agents for 30 min at 37 degrees C, whereas the teeth in the control groups were exposed only to distilled water. Then the acetate buffer solution in the pulp chamber of each tooth was removed, and the pulp chamber of each tooth was rinsed with 100 ml of distilled water twice. Leukocrystal violet and enzyme horseradish peroxidase were added to the mixture of the acetate buffer and rinse water. The optical density of the resulting blue solution was determined spectrophotometrically and converted into microgram equivalents of hydrogen peroxide. Higher hydrogen peroxide concentrations resulted in a higher pulpal peroxide penetration. The highest pulpal peroxide penetration was found in resin-modified glass ionomer cement groups, whereas composite resin groups showed the lowest pulpal peroxide penetration.