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Cement
Kinds of Cement Terms modified by Cement Selected AbstractsQuality of root canal fillings performed by undergraduate dental students on single-rooted teeth,EUROPEAN JOURNAL OF DENTAL EDUCATION, Issue 2 2006C. D. Lynch Introduction:, Root canal therapy is an accepted and successful form of tooth conservation. Educational guidelines require dental schools to ensure that their graduates are competent on graduation at performing root canal therapy. The aim of this investigation was to assess the technical quality of root canal fillings placed by undergraduate students in single-rooted teeth. Materials and methods:, A total of 100 radiographs of root canal fillings placed by undergraduate students in single-rooted teeth were examined under even illumination in a darkened room using ×2 magnification. These were graded as ,adequate', where the root canal filling was within 2 mm of the radiographic apex, ,under-filled', where the root canal filling was >2 mm from the radiographic apex, and ,over-filled', where the root canal filling was extruded beyond the radiographic apex. The presence of voids, fractured instruments, and root perforations were also noted. Results:, All teeth were obturated with gutta-percha and sealer (Roth Cement), using a cold lateral condensation technique. Of 100 teeth, 10% (n = 10) had voids. Of the remainder, 70% (n = 63) were judged to be ,acceptable', 21% (n = 19) were ,under-filled', and 9% (n = 8) were ,over-filled'. There was no evidence of fractured instruments or root perforations in any root filling examined. Conclusions:, The quality of root canal fillings placed in single-rooted teeth by undergraduate dental students at the University Dental School and Hospital, Cork was acceptable (63% of root fillings placed in single rooted teeth were graded as ,adequate'). The probable reasons for this are multi-factorial, but may be linked to the amount of pre-clinical and clinical teaching in endodontics at the University Dental School and Hospital, Cork. It should be remembered that factors other than radiographic quality/evidence must be considered when determining the outcome of root canal therapy. [source] Fly ash concrete subjected to thermal cyclic loadsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2010M. S. KHAN ABSTRACT The present study describes the behaviour of concrete as well as fly ash concrete when subjected to varying number of high temperature heating cycles. A Concrete mix (1:2.37:2.98) with 340 kg/m3 cement and,w/cm,ratio 0.45 was prepared. Cement was replaced by varying percentages (0%, 20%, 40%, 50% and 60%) of fly ash by weight of cement. The concrete was subjected to a constant temperature of 200°C for 7, 14, 21 and 28 heating cycles. One heating cycle corresponds to 8 h heating and subsequent cooling in 24 h. Subsequently the effect of temperature on the properties of the concrete was investigated and compared with that of the properties of unheated concrete. The compressive strength of plain as well as fly ash concrete increased when it was subjected to thermal cyclic loads. Moreover, the compressive strength increased with an increase in number of heating cycles. Thermal conductivity of concrete was found to decrease with an increase in the fly ash content. [source] Residual compressive behavior of alkali-activated concrete exposed to elevated temperaturesFIRE AND MATERIALS, Issue 1 2009Maurice Guerrieri Abstract This paper reports the effect of elevated temperature exposures, up to 1200°C , on the residual compressive strengths of alkali-activated slag concrete (AASC) activated by sodium silicate and hydrated lime; such temperatures can occur in a fire. The strength performance of AASC in the temperature range of 400,800°C was similar to ordinary Portland cement concrete and blended slag cement concrete, despite the finding that the AASC did not contain Ca(OH)2 , which contributes to the strength deterioration at elevated temperatures for Ordinary Portland Cement and blended slag cement concretes. Dilatometry studies showed that the alkali-activated slag (AAS) paste had significantly higher thermal shrinkage than the other pastes while the basalt aggregate gradually expanded. This led to a higher thermal incompatibility between the AAS paste and aggregate compared with the other concretes. This is likely to be the governing factor behind the strength loss of AASC at elevated temperatures. Copyright © 2008 John Wiley & Sons, Ltd. [source] Using Rheology to Achieve Co-Extrusion of Cement-Based Materials with Graded Cellular StructuresINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Yunbo Chen Co-extrusion involves simultaneous extrusion of multiple layers and can be used to produce functionally graded materials whose layers have different properties. Rheological control is vital for successful co-extrusion. During extrusion, flow in the barrel and die land in a ram extruder should be plug-like, while the paste should be sheared and uniformly elongated in the die entry region. In the barrel of the extruder, the paste flow velocity field was inferred by direct observation of the paste left in the barrel, and evidence for plug flow in the barrel was seen only at low-extrudate velocities. In the die land, the Benbow nonlinear model was employed to assess the paste flow behavior, and plug flow was achieved only when the shear stress applied to the paste by the die land wall was smaller than its yield stress. For co-extrusion, a simple method using thin-walled tubes was found to be effective to prepare layered feedrods. Functionally graded cellular structures of cement-based materials were successfully co-extruded by using a low-extrudate velocity when the paste had decreasing shear viscosity from inner to outer layers. [source] In vitro studies on the influence of precultural conditioning method on osteoblast reactions of a new type of injectable calcium cement materialJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006Feng Chai Abstract A new injectable dicalcium phosphate dehydrate (DCPD)-based cement material "PD" VitalOs Cement® was studied to elucidate the process of equilibrium occurring in the early stage of implantation. The present study investigated the pH variations of the cement sample-immersing culture medium at determined intervals, time-dependent calcium/phosphate release, cell proliferation, and vitality in the cells,cement coculture milieu, after different preculture conditionings of the samples. Measurement of pH variation showed that without renewing the medium, pH value of sample lixiviate medium first dropped and, after 70 h, gradually balanced. When medium was renewed each day, pH value of lixiviate medium first descended and, after 24 h, gradually returned to pH 7.2. The cell viability revealed an excellent cytocompatibility of the cement. Both cell proliferation and vitality test showed that the preculture conditioning treatment is important at least for good performance of osteoblasts growing on the surface of calcium phosphate hydraulic cement (CPHC) samples in vitro. The results of calcium and phosphate assays clearly showed that this cement material can continuously dissolve to release calcium and phosphate in the liquid cell culture environment. The decrease of proliferation in some experimental groups with short conditioning is due to an excess of acid, which still can have some influence on cell growth after 24 h, since the biological milieu is not continuously renewed as in in vivo conditions. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Cement, Yogurt, and MercuryJOURNAL OF INDUSTRIAL ECOLOGY, Issue 3 2007Reid Lifset No abstract is available for this article. [source] Cement Manufacture and the Environment: Part I: Chemistry and TechnologyJOURNAL OF INDUSTRIAL ECOLOGY, Issue 1 2002Hendrik G. van Oss Summary Hydraulic (chiefly portland) cement is the binding agent in concrete and mortar and thus a key component of a country's construction sector. Concrete is arguably the most abundant of all manufactured solid materials. Portland cement is made primarily from finely ground clinker, which itself is composed dominantly of hydraulically active calcium silicate minerals formed through high-temperature burning of limestone and other materials in a kiln. This process requires approximately 1.7 tons of raw materials per ton of clinker produced and yields about 1 ton of carbon dioxide (CO2) emissions, of which cal-cination of limestone and the combustion of fuels each con-tribute about half. The overall level of CO2 output makes the cement industry one of the top two manufacturing industry sources of greenhouse gases; however, in many countries, the cement industry's contribution is a small fraction of that from fossil fuel combustion by power plants and motor vehicles. The nature of clinker and the enormous heat requirements of its manufacture allow the cement industry to consume a wide variety of waste raw materials and fuels, thus providing the opportunity to apply key concepts of industrial ecology, most notably the closing of loops through the use of by-products of other industries (industrial symbiosis). In this article, the chemistry and technology of cement manufacture are summarized. In a forthcoming companion ar-ticle (part II), some of the environmental challenges and op-portunities facing the cement industry are described. Because of the size and scope of the U.S. cement industry, the analysis relies primarily on data and practices from the United States. [source] Effect of three adhesive primers for a noble metal on the shear bond strengths of three resin cementsJOURNAL OF ORAL REHABILITATION, Issue 1 2001K. Yoshida The purpose of this study was to evaluate the durability and shear bond strengths of the different combinations of three adhesive primers and three resin cements to a silver,palladium,copper,gold (Ag,Pd,Cu,Au) alloy. The adhesive primers Alloy Primer® (AP), Metal PrimerII® (MPII) and Metaltite® (MT), and the resin cements BistiteII® (BRII), Panavia Fluoro Cement® (PFC) and Super-Bond C&B® (SB) were used. Two sizes of casting alloy disks were either non-primed or primed and cemented with each of the three resin cements. The specimens were stored in a 37 °C water bath for 24 h and then immersed alternately in 4 and 60 °C water baths for 1 min each for up to 100 000 thermal cycles. Shear mode testing at a crosshead speed of 0·5 mm/min was then performed. The application of MPII or MT was effective for improving the shear bond strength between each of the three resin cements and the Ag,Pd,Cu,Au alloy compared with non-primed specimens. However, when primed with MPII or MT and cemented with SB, the bond strength at 100 000 thermal cycles was significantly lower than that at thermal cycle 0. When primed with AP, the specimens cemented with BRII or PFC showed lower bond strength than non-primed specimens and failed at the metal,resin cement interface at 100 000 thermal cycles. On the other hand, AP was effective in enhancing the shear bond strength of SB to the Ag,Pd,Cu,Au alloy. The five combined uses of an adhesive metal primer and resin cement (combinations of MPII or MT and BRII or PFC and AP and SB) are applicable to the cementation of prosthodontic restorations without complicated surface modification of the noble alloy. [source] Creep dominates tensile fatigue damage of the cement,bone interfaceJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2004Do-Gyoon Kim Abstract Fatigue damage from activities of daily living has been considered to be a major cause of aseptic loosening in cemented total hip arthroplasty. The cement,bone interface is one region where loosening could occur, but to date the fatigue response of the interface has not been examined. Cement,bone specimens were prepared from fresh frozen human cadaver tissue using simulated in vivo conditions. Tensile fatigue tests to failure were performed in an environmental chamber. Loss of specimen stiffness (stiffness damage) and permanent displacement after unloading (creep damage) were found in all specimens. At failure, creep damage accounted for the majority (79.9 ± 10.6%) of the total strain damage accumulation at failure (apparent strain, , = 0.0114 ± 0.00488). A power law relationship between strain-damage rate and time-to-failure showed that the strain-damage rate was an excellent predictor of the fatigue life of the cement,bone interface. The S,N response of the interface was obtained as a function of the applied stress ratio and the initial apparent strain. The total motion between cement and bone (72.2 ± 29.8 ,m) prior to incipient failure due to both stiffness and creep fatigue damage may be sufficient to result in fibrous tissue formation and contribute to eventual clinical loosening. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] An Analysis of the Effect of a Vent Hole on Excess Cement Expressed at the Crown,Abutment Margin for Cement-Retained Implant CrownsJOURNAL OF PROSTHODONTICS, Issue 1 2009Dipan Patel BDS Abstract Purpose: The labial margins of anterior implant-retained crowns are often positioned subgingivally for a superior esthetic appearance. One of the consequences of subgingival margins is the increased risk of leaving excess cement behind following cementation. This can lead to potential problems, including peri-implant inflammation, soft tissue swelling, soreness, bleeding or suppuration on probing, and bone loss. The purpose of this laboratory study was to investigate the effect of placement, location, and diameter of a vent hole on the amount of cement being expressed at the margin of an anterior implant abutment-retained crown. Materials and Methods: Three implant crown copings were fabricated to fit on the same custom abutment. Three vent diameters (0.75, 1.25, and 1.65 mm) and three locations on the palatal surface of the coping (cervico-palatally, mid-palatally, inciso-palatally) were chosen for vent hole placement. For each test, the coping was cemented onto the abutment under standardized conditions. A preweighed thin coating of cement was applied to the fit surface of the coping. The amount of cement expressed at the margin and vent hole was measured by weight and calculated as a proportion of the amount of cement placed in the coping before seating. The procedure was completed 15 times for each variable. The results were statistically analyzed using univariate ANOVA with post hoc Bonferroni-adjusted independent samples t -tests. Results: The presence of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05). The location of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05), with the exception of the mid-palatal and inciso-palatal positioning where there was no significant difference (p= 0.61) between groups. The diameter of the vent hole did not significantly influence the proportion of cement expressed at the coping margin (p= 0.096). Conclusions: When using anterior cement-retained implant crowns, the use of a 0.75-mm mid-palatal or inciso-palatal vent hole to minimize the amount of cement expressed at the margin during cementation should be considered. [source] Laboratory strength of glass ionomer and zinc phosphate cementsJOURNAL OF PROSTHODONTICS, Issue 3 2001Andree Piwowarczyk Dr med dent Purpose The present in vitro study examined 3 mechanical properties, namely compressive, flexural, and diametral tensile strength, of various commercially available cements and core materials as a function of time after mixing. Materials and Methods The examined materials were 2 cermet cements (Ketac Silver [ESPE, Seefeld, Germany] and Chelon Silver [ESPE]), 1 metal-reinforced glass ionomer cement (Miracle Mix [GC Dental Industrial Corp, Tokyo, Japan]), 2 conventional glass ionomer cements (Ketac Bond [ESPE] and Ketac Cem [ESPE]), 1 standard cure zinc phosphate cement (Harvard Cement [Richter and Hoffmann, Berlin, Germany]), and 1 zinc phosphate cement with the addition of 30% silver amalgam alloy powder (Harvard Cement 70% with Dispersalloy 30% [Richter and Hoffmann/Johnson and Johnson, East Windsor, NJ]). Properties were measured using a universal testing machine at 15 minutes, 1 hour, and 24 hours after first mixing. Results Compressive strengths varied widely between the 3 times of measurement from 5.8 ± 6.6 MPa for Ketac Cem to 144.3 ± 10.2 MPa for Ketac Silver. Twenty-four hours after mixing, the Bonferroni test showed significant (p, .01) differences between Ketac Silver and all other materials tested. Diametral tensile strengths ranged widely from 4.4 ± 0.9 MPa for Ketac Cem to 11.5 ± 2.2 MPa for Chelon Silver. At 15 minutes, 1 hour, and 24 hours after first mixing, the analysis of variance did not show any significant differences between Ketac Silver, Chelon Silver, and Miracle Mix. The 3-point flexural strength of Ketac Silver showed, at 15 minutes with 13.5 ± 3.9 MPa and at 24 hours with 27.2 ± 7.4 MPa, the highest values. Conclusions Setting time influences the mechanical properties of the materials tested in this study. Ketac Silver, a glass ionomer cement reinforced with sintered glass-silver particles, showed the highest mechanical properties of the examined materials. [source] Effects of Saccharide Set Retarders on the Hydration of Ordinary Portland Cement and Pure Tricalcium SilicateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Linghong Zhang The effects of aliphatic sugar alcohols (e.g., threitol, xylitol, sorbitol) on the hydration of tricalcium silicate (C3S) and ordinary portland cement (OPC) were investigated and compared with those of sucrose, a well-established cement set retarder. Only sugar alcohols which contain threo diol functionality retarded the setting of C3S and OPC, their efficacy increasing with the number of threo hydroxy pairs and, to a smaller extent, with the overall population of hydroxy groups. None, however, were as effective as sucrose. The initial and final setting times increased exponentially with the concentration of saccharide, although the hydration of OPC was less inhibited than that of C3S. Saccharides function as "delayed accelerators," that is, cement hydration is first inhibited and then proceeds faster than in saccharide-free cement. This behavior is consistent with the theory that the induction period is controlled by slow formation and/or poisoning of the stable calcium silicate hydrate (CSH) nuclei. The early inhibiting influence of saccharides on CSH precipitation is apparently stronger than on the growth of crystalline calcium hydroxide. Saccharides did not negatively affect the degree of hydration and compressive strength of fully set OPC paste; on the contrary, sorbitol yielded modest increases. [source] Chemistry and Morphology of Hydrogarnets Formed in Cement-Based CASH Hydroceramics Cured at 200° to 350°CJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2009Konstantinos Kyritsis We have studied the chemistry and the morphology of hydrogarnet crystals produced in cement-based hydroceramic materials at elevated temperatures (200°,350°C) with silica and alumina additions. Such materials lie within the hydrothermal CaO,Al2O3,SiO2,H2O (CASH) system. Hydrogarnet Ca3Al2(SiO4)3,y(OH)4y is the dominant aluminum bearing phase formed and its composition is influenced mainly by the curing temperature and to a lesser degree by the addition of silica. The composition parameter y was estimated by Rietveld refinement of X-ray diffraction (XRD) data. Electron probe microanalysis (EPMA) shows that the hydrogarnets incorporate minor elements such as Fe, Mg, and S. EPMA data confirmed the hydrogarnet composition estimated from XRD. Both octahedral and icositetrahedral forms are observed. The icositetrahedral form is associated with higher minor element content. [source] Control of Crystallinity of Hydrated Products in a Calcium Phosphate CementJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2009Tao Yu A novel calcium phosphate cement (CPC) was prepared by dry-mechanochemical rout in this work. With the different crystallinity, the CPC showed the different degradation ratio after setting. The degradation ratio of CPC was characterized by the calcium ion-dissolving ratio in deionized water after different soaking time. With the increment of crystallinity, the setting times of CPC were prolonged, and the different mechanical property of CPC were obtained. This novel CPC was supposed to match the new bone ingrowth in vivo and have the potential application in orthopedic surgery for filling non-load-bearing bone defects. [source] High-Pressure Device for Fluid Extraction from Porous Materials: Application to Cement-Based MaterialsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Martin Cyr A high-pressure device, reaching an axial pressure of 1000 MPa, intended to the extraction of the pore solution of rigid and slightly porous materials, has been developed to improve the efficiency of extraction. This paper gives an application of fluid extraction from mortars made with Portland cement. It includes an experimental study of the performance of the apparatus, and an analysis of the results in terms of efficiency of extraction, repeatability of measurement, and effect of the squeezing pressure on the pore solution composition. Results shows that: (1) the squeezing efficiency using our apparatus is higher than those found in the literature; (2) the measurement uncertainty ranges between 1.5% and 14%; (3) no significant effect of pressure (up to 1000 MPa) is observed for concentrations of Ca, Na, K, and Si. This paper suggests conducting extraction at 1000 MPa, especially on old concrete or concrete made with low W/C ratios. [source] Reinforcement of Calcium Phosphate Cement by Bio-Mineralized Carbon NanotubeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Xiupeng Wang Bio-mineralized carbon natotubes (CNTs) were prepared by soaking carboxyl functionalized CNTs in a simulating body fluid (SBF). A uniform hydroxyapatite layer was precipitated on the outer walls of CNTs after 7 days of soaking. The results showed that, by addition of the as-received CNTs and bio-mineralized CNTs, the compressive strength of the calcium phosphate cement (CPC) increased by 24% and 120%, respectively. The modified interfacial bonding between the bio-mineralized CNTs and CPC accounted for the significant improvement in the mechanical property by addition of the bio-mineralized CNTs as compared with the as-received CNTs. [source] Chemical Speciation of Trace Zinc in Ordinary Portland Cement Using X-ray Absorption Fine Structure AnalysisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004Isao Tsuyumoto Chemical change of trace zinc in ordinary portland cement (205.1 ppm) was investigated in hydration process using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Intensities of the peaks appearing at the same energy of ZnO in XANES spectra were decreased with cement hydration. The interatomic distances and the coordination numbers of the first and the second shells calculated from EXAFS spectra indicated that ZnO hydrolyzed to zincate ion [Zn(OH)4]2, with cement hydration keeping their fundamental structure of ZnO4 tetrahedra. [source] Cement-Based 0-3 Piezoelectric CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Zongjin Li To meet the requirements of development for smart or intelligent structures in civil engineering, new functional materials that have good compatibility with civil engineering structural materials are needed. In this study, for the first time in the field of piezoelectric materials, cement-based 0-3 piezoelectric (PZT) composites were fabricated by the normal mixing and spreading method. The new materials have very good compatibility with portland cement concrete. The cement-based 0-3 piezoelectric composites were shown to have a slightly higher piezoelectric factor and electromechanical coefficient than those of 0-3 PZT/polymer composites with a similar content of PZT particles; thus, they are adequate for sensor application. There is potential for the application of cement-based 0-3 PZT composites in civil engineering because of their better piezoelectric properties and good compatibility with portland cement concrete. [source] Processing of Lightweight, High-Strength Porcelains Using an Alumina Cement to Replace Feldspars and ClaysJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2000Weon-Pil Tai New lightweight, high-strength porcelain bodies, using only nonplastic raw materials such as glass microspheres, quartz, and alumina cement, were fabricated and the effect of quartz particle size was investigated. Decreases in the green strength, relative to an increasing content of glass microspheres, were attributed to the decrease in the density and the relative decrease in the volume of alumina cement. The phases in the fired body were glass, ,-quartz, cristobalite, anorthite, and a small amount of ,-alumina. The large quartz particles (10,32 ,m in size) could not be densified to closed porosity, because of underfiring, whereas smaller quartz particles (4,10 ,m in size) permitted densification to closed porosity at 1300°C. The high flexural strength when using medium-sized quartz particles (6,20 ,m, content of 30 wt%) was attributed to a stronger prestress and higher density that was due to better vitrification. [source] Canal Wall Reconstruction with Mimix Hydroxyapatite Cement: Results in an Animal Model and Case Study,THE LARYNGOSCOPE, Issue 12 2003John Dornhoffer MD Abstract Objective/Hypothesis To assess Mimix hydroxyapatite cement for its applicability in canal wall reconstruction using the gerbil as a canal wall model. A case is presented to illustrate a novel technique of canal wall reconstruction using Mimix on the basis of the findings of our animal research. Study Design This was a preclinical study. Methods Ten Mongolian gerbils were implanted with Mimix, with the left side used to simulate mastoid obliteration and the right side used to simulate canal wall reconstruction. Pre- and postsurgery auditory-evoked brainstem responses were used to assess ototoxicity, and hematoxylin-eosin staining of histologic sections was used to assess inflammatory and foreign-body response and new bone formation. Results Rapid wound healing was achieved with each of the nine animals evaluated, with no erythema, edema, or drainage. Inspection of the ear canal at the time of sacrifice revealed no signs of otitis media and no middle ear effusions. Microscopic examination showed no inflammatory response or foreign-body reaction, good mucosalization on the side of the implant facing the bulla, and minimal fibrosis adjacent to the skin. Eight of nine specimens showed new woven bone ingrowth at the bone implant interface, with active osteoblasts and viable lacunae cells. There were no apparent fractures in the implanted material. Conclusions Mimix hydroxyapatite cement is biocompatible and suitable for canal wall reconstruction in the animal model. The characteristics of this cement, namely its ability to set quickly in a moist environment, offer advantages over previously used cements for canal wall reconstruction. [source] Fiber Reinforced Calcium Phosphate CementARTIFICIAL ORGANS, Issue 3 2000Luís Alberto Dos Santos Abstract: The term calcium phosphate cement was introduced by Gruninger et al. (1). This type of cement can be prepared by reacting a calcium phosphate salt with an aqueous solution, which causes it to set by the crossing of the precipitated crystals. These cements offer a series of advantages that allow their use as grafts and substitutes of damaged parts of the bone system. However, these cements have low mechanical strength compared to human bones. This work studied the influence of the use of polyamide fibers in the mechanical properties of a calcium phosphate cement based on ,-tricalcium phosphate as well as the mechanisms involved in the increase of mechanical strength. The results demonstrate the feasibility of the use of polymeric fibers to increase mechanical strength and the need for coupling agents for the effective performance of the fibers as reinforcement in these materials. [source] Hydraulische Reaktionen des Zements in Mörtel bei verschiedenen ParameternBETON- UND STAHLBETONBAU, Issue 8 2010Analytische Betrachtungen mittels Kryotransfer-Rasterelektronenmikroskopie Allgemeines; Baustoffe Abstract Die Kryotransfer-Rasterelektronenmikroskopie wird mittlerweile sehr häufig zur Erforschung von Abbindereaktionen in Zementen und anderen Baustoffen eingesetzt und kann heute als Standardverfahren angesehen werden. Ein wesentliches Interesse für industrielle Anwendungen besteht unter anderem darin, Untersuchungen des Zementleims in-situ bereits ab der Wasserzugabe bzw. ab der ersten Minute der Hydratation in so genannten "Zeitschnitten" durchzuführen. In der vorliegenden Arbeit wird der Einsatz eines Kryotransfer-Systems bei der Untersuchung der Abbindereaktionen des Zements in einem herkömmlichen Beton aufgezeigt. Als unterschiedliche Parameter wurden modellhaft Abbindezeiten von 1 Minute, 5 und 60 Minuten bei Abbindetemperaturen von 4 °C, 22 °C und 40 °C gewählt. Hydraulic Reactions of Cement in Mortar at Different Parameters Analytical Observations by Means of Cryo-Transfer-Scanning-Electron-Microscopy For the investigation of hydraulic reactions of cements and other building materials the cryo-transfer scanning-electron-microscopy is frequently used by now. Today the cryo-transfer technique is considered as a reference procedure. An essential concern in industrial applications is , amongst others , the insitu investigation of the cement paste at the very early state of hydration , just after the addition of water, respectively during the first minutes within so-called "time-cuts". The present work illustrates the application of a cryo-transfer system for the investigations on hydraulic reactions of conventional concrete. Exemplary parameters were curing times of 1 minute, 5 and 60 minutes at curing temperatures of 4 °C, 22 °C and 40 °C. [source] Theory of Microbial Carbonate Precipitation and Its Application in Restoration of Cement-based Materials DefectsCHINESE JOURNAL OF CHEMISTRY, Issue 5 2010Chunxiang Qian Abstract Bacterial induced carbonate mineralization has been demonstrated as a new potential method for restoration of limestones in historic buildings and monuments. We claim here the formation of calcium carbonate was controlled by extracellular polymeric substances (EPS) isolated from Bacillus pasteurii. The process of crystallization nucleation was accelerated in the presence of cells and inhibited in the presence of EPS. The CaCO3 film deposited on cement paste surface was about 100 µm after 7 d treatment. The results of various restoring methods showed that higher decrease of water absorption of cement paste was gained in brushing application in the presence of agar, which could maintain urease with high activity in long term compared to spraying method. The coefficient of capillary suction of cement paste treated with brushing method was reduced by 90%. Mixed media consisted of sands, urea, Ca2+ and concentrated biomass, was injected into artificial cracks of cement paste followed by continual nutrient supplement, and CaCO3 particles were precipitated gradually between sands particles which were combined with cement matrix. The results showed that the compressive strength of recovered specimens was restored to 84%, which demonstrated that this kind of bio-restoration method is effective in repairing surface defects of cement-based materials. [source] Retrievability of implant-retained crowns following cementationCLINICAL ORAL IMPLANTS RESEARCH, Issue 12 2008Christian Mehl Abstract Objectives: The purpose of this study was to assess the retrievability of cemented implant crowns using two different removal devices. The influence of five cement types and two cement application techniques was evaluated. Methods: Forty copings were cast from a CoCr alloy for 40 tapered titanium abutments (5° taper, 4.3 mm diameter, 6 mm height, Camlog, Germany). Twenty copings were modeled as single crowns, whereas 20 copings were modeled with an extension to simulate fixed partial dentures (FPDs). Before cementation, the inner surfaces of the copings were air-abraded (50 ,m Al2O3 particles at 2.5 bars), while the abutments were used as delivered with machined surfaces. Copings were cemented with eugenol-free zinc oxide (Freegenol), zinc phosphate (Harvard), glass ionomer (Ketac Cem), polycarboxylate (Durelon) and so-called self-adhesive resin (RelyX Unicem) cement. Cement was applied in a thin film band of 1 or 3 mm to the cervical margin of the inner surface of the copings, respectively. After cementation, specimens were stored in saline solution for 24 h. The Coronaflex and a standardized custom-made removal device were used to remove the copings from the abutments. Results: Using the same cement, no statistically significant influence with regard to the type of restoration (crown/FDP), cement application mode and device was detected (P>0.05). Therefore, data of specimens cemented with the same cement were pooled. Median attempts to remove the copings were: zinc oxide: 3, self-adhesive resin: 3, zinc phosphate: 5, glass ionomer: 16 and polycarboxylate: 58. Four levels of significance (P<0.0001) were found: (1) zinc oxide/self-adhesive resin; (2) zinc phosphate; (3) glass ionomer; and (4) polycarboxylate. Conclusions: Zinc phosphate and glass ionomer cement might be suitable for a so-called ,semipermanent' (=retrievable) cementation, while polycarboxylate seems to provide the most durable cementation. [source] Effect of curing mode on bond strength of self-adhesive resin luting cements to dentinJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010T. R. Aguiar Abstract In this study, the in vitro bond strength of dual-curing resin cements to indirect composite restorations when the cement was either light polymerized or allowed to only autopolymerize was evaluated. Occlusal dentin surfaces of 56 extracted human third molars were flattened to expose coronal dentin. Teeth were assigned to eight groups (n = 7) according to resin cement products and polymerization modes: conventional cement (Panavia F 2.0; Kuraray Medical) and self-adhesive cements [RelyX Unicem (3M ESPE), BisCem (Bisco), and G-Cem (GC Corp.)]. Cements were applied to prepolymerized resin discs (2-mm-thick Sinfony; 3M ESPE), which were subsequently bonded to the prepared dentin surfaces. The restored teeth were either light-polymerized through the overlying composite according to manufacturers' instructions or were allowed to only self-cure. After 24 h, the teeth and restorations were sectioned to obtain multiple bonded beams (1.0 mm2) and tested in tension at a crosshead speed of 0.5 mm/min until failure. Data (MPa) were analyzed by two-way ANOVA and Tukey test (, = 0.05). Light activation of some cement systems (G-Cem and Panavia F 2.0) increased the bond strength, while the curing mode did not affect the bond strength for some (RelyX Unicem and BisCem). The bond strength in the autopolymerized mode varied among products. In general, the use of self-adhesive resin cements did not provide significantly higher bond strengths than that of a conventional material, and two self-adhesive cements yielded significantly lower bond values (regardless of cure mode) than the other products. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Graft copolymers of methyl methacrylate and poly([R]-3-hydroxybutyrate) macromonomers as candidates for inclusion in acrylic bone cement formulations: Compression testingJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006Sophie Nguyen Abstract Graft copolymers of methyl methacrylate and biodegradable, biocompatible bacterial poly([R]-3-hydroxybutyrate) (PHB) blocks were synthesized and evaluated as possible constituents in acrylic bone cements for use in orthopaedic applications. The copolymers were produced by conventional free radical copolymerization and incorporated in one commercially available acrylic bone cement brand, Antibiotic Simplex® (AKZ). Cements with formulations containing 6.7 and 13.5 wt % of PMMA- graft -PHB were prepared. The morphology of the graft copolymer particles was suggested to influence the ability of the modified cement to be processed. Formulations containing more than about 20 wt % of the graft copolymer resulted in cement doughs that, both after first preparation and several hours later, were either sandy or soft spongy in texture and, thus, would be unacceptable for use in orthopaedic applications. The morphologies of the powders and the volumetric porosity (p) and ultimate compressive strength (UCS) of the cured cements were determined. Micro computed tomography showed that the cements presented average porosities of 13.5,16.9%. It was found that, while the powder particle shape and size for the experimental cements were markedly different from those of AKZ, there was no significant difference in either p or UCS for these cements. The latter was determined to be about 85 MPa for the modified cements and 84 MPa for Antibiotic Simplex. Furthermore, the UCS of all the cements exceeded the minimum level for acrylic bone cements, as stipulated by ASTM F-451. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Characterization of new acrylic bone cements prepared with oleic acid derivativesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2002Blanca Vázquez Abstract Acrylic bone-cement formulations were prepared with the use of a new tertiary aromatic amine derived from oleic acid, and also by incorporating an acrylic monomer derived from the same acid with the aim of reducing the leaching of toxic residuals and improving mechanical properties. 4-N,N dimethylaminobenzyl oleate (DMAO) was used as an activator in the benzoyl-peroxide radical cold curing of polymethyl methacrylate. Cements that contained DMAO exhibited much lower polymerization exotherm values, ranging between 55 and 62 °C, with a setting time around 16,17 min, depending on the amine/BPO molar ratio of the formulation. On curing a commercial bone cement, Palacos® R with DMAO, a decrease of 20 °C in peak temperature and an increase in setting time of 7 min were obtained, the curing parameters remaining well within limits permitted by the standards. In a second stage, partial substitution of MMA by oleyloxyethyl methacrylate (OMA) in the acrylic formulations was performed, the polymerization being initiated with the DMAO/BPO redox system. These formulations exhibited longer setting times and lower peak temperatures with respect to those based on PMMA. The glass transition temperature of the experimental cements were lower than that of PMMA cement because of the presence of long aliphatic chains of both activator and monomer in the cement matrix. Number average molecular weights of the cured cements were in the range of 1.2×105. PMMA cements cured with DMAO/BPO revealed a significant (p<0.001) increase in the strain to failure and a significant (p<0.001) decrease in Young's modulus in comparison to Palacos® R, whereas ultimate tensile strength remained unchanged. When the monomer OMA was incorporated, low concentrations of OMA provided a significant increase in tensile strength and elastic modulus without impairing the strain to failure. The results demonstrate that the experimental cements based on DMAO and OMA have excellent promise for use as orthopaedic and/or dental grouting materials. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 88,97, 2002; DOI 10.1002/jbm.10092 [source] Bond Strength of Two Resin Cements on Dentin Using Different Cementation StrategiesJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2010RENATA MARQUES MELO MS ABSTRACT Purpose:, This study evaluated the microtensile bond strength of two resin cements to dentin either with their corresponding self-etching adhesives or employing the three-step "etch-and-rinse" technique. The null hypothesis was that the "etch-and-rinse" adhesive system would generate higher bond strengths than the self-etching adhesives. Materials and Methods:, Thirty-two human molars were randomly divided into four groups (N = 32, n = 8/per group): G1) ED Primer self-etching adhesive + Panavia F; G2) All-Bond 2 "etch-and-rinse" adhesive + Panavia F; G3) Multilink primer A/B self-etching adhesive + Multilink resin cement; G4) All-Bond 2 + Multilink. After cementation of composite resin blocks (5 × 5 × 4 mm), the specimens were stored in water (37°C, 24 hours), and sectioned to obtain beams (±1 mm2 of adhesive area) to be submitted to microtensile test. The data were analyzed using 2-way analysis of variance and Tukey's test (, = 0.05). Results:, Although the cement type did not significantly affect the results (p = 0.35), a significant effect of the adhesive system (p = 0.0001) was found on the bond strength results. Interaction terms were not significant (p = 0.88751). The "etch-and-rinse" adhesive provided significantly higher bond strength values (MPa) with both resin cements (G2: 34.4 ± 10.6; G4: 33.0 ± 8.9) compared to the self-etching adhesive systems (G1: 19.8 ± 6.6; G3: 17.8 ± 7.2) (p < 0.0001). Pretest failures were more frequent in the groups where self-etching systems were used. Conclusion:, Although the cement type did not affect the results, there was a significant effect of changing the bonding strategy. The use of the three-step "etch-and-rinse" adhesive resulted in significantly higher bond strength for both resin cements on dentin. CLINICAL SIGNIFICANCE Dual polymerized resin cements tested could deliver higher bond strength to dentin in combination with "etch-and-rinse" adhesive systems as opposed to their use in combination with self-etching adhesives. (J Esthet Restor Dent 22:262,269, 2010) [source] Flexural Strength, Elastic Modulus, and pH Profile of Self-etch Resin Luting CementsJOURNAL OF PROSTHODONTICS, Issue 4 2008Egle Saskalauskaite DDS Abstract Purpose: To determine the flexural strength, modulus of elasticity, and 24-hour pH profile of three self-etching resin luting cements and to obtain comparative data for representative conventional resin and resin-modified glass ionomer luting cements. Materials and Methods: Three self-etching resin luting cements [RelyX Unicem (3M ESPE), Maxcem (Kerr), Embrace Wetbond (Pulpdent)] were tested and compared with two conventional resin cements [RelyX ARC (3M ESPE), Linkmax (GC)] plus two resin-modified glass ionomer luting cements [Fuji Plus (GC), RelyX Luting Plus (3M ESPE)]. Flexural strength and modulus of elasticity were determined using bar-shaped specimens (2 × 2 × 25 mm3) at 24 hours, using an Instron universal testing machine. Setting pH was measured using a flat-surface pH electrode at 0, 2, 5, 15, and 30 minutes and 1, 2, 4, 6, and 24 hours after mixing. Testing was performed under both dual-cured and self-cured conditions for all dual-cure cements. Data analysis included ANOVA and Tukey's test (p < 0.05). Results: The self-etching cements showed similar flexural strength to the conventional resin cements, except for Embrace Wetbond self-cured, which was considerably lower. Modulus of elasticity results were both higher and lower than for conventional resin cements. All photopolymerized conventional and self-etch dual-cure cements showed markedly higher flexural strength and modulus than when solely self-cured. The resin-modified glass ionomer cements were characterized by lower flexural strength and elastic modulus. Self-etching resin cements showed lower initial pH (2.0 to 2.4) than conventional resin cements (4.8 to 5.2) and a wide range of final pH values (3.9 to 7.3) at 24 hours. One self-etching cement (Unicem) revealed a unique pH profile characterized by a more rapid rise in pH to neutrality both when dual-cured (15 minutes) and when auto-cured (1 hour). Conclusions: The self-etching resin cements evaluated in this study displayed disparate properties and cannot be considered a homogeneous group. Flexural strength properties were most uniform and were similar to those of the conventional resin cements, whereas moduli of elasticity showed greater variation. Setting pH profiles differed, depending on the brand and mode of cure, even within the same category of luting cement. All cements with dual-cure capability, both conventional and self-etch, showed significantly superior properties when photopolymerized. [source] Advances in Glass-ionomer CementsJOURNAL OF PROSTHODONTICS, Issue 3 2000David Covey DDS [source] | ||||||||||||||||||||||||||||