Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Casting

  • alloy casting
  • corrosion casting
  • die casting
  • film casting
  • freeze casting
  • ray casting
  • slip casting
  • solution casting
  • solvent casting
  • tape casting

  • Terms modified by Casting

  • casting doubt
  • casting machine
  • casting method
  • casting process
  • casting technique
  • casting temperature

  • Selected Abstracts

    Comparing botulinum toxin A with casting for treatment of dynamic equinus in children with cerebral palsy

    Jeffrey D Ackman MD
    The purpose of this study was to compare the cumulative efficacy (three treatment sessions) of botulinum toxin A (BTX-A) alone, casting alone, and the combination of BTX-A and casting in the management of dynamic equinus in ambulatory children with spastic cerebral palsy (CP). Thirty-nine children with spastic CP (mean age 5y 10mo, range 3 to 9y) were enrolled in the study. A multicenter, randomized, double blind, placebo-controlled prospective study was used. Children were randomly assigned to one of three treatment groups: BTX-A only (B), placebo injection plus casting (C), or BTX-A plus casting (B+C). The dosage for the BTX-A injections was 4U/kg per extremity. Assessments were performed at baseline, 3,6,7.5, and 12 months with a total of three treatments administered after the evaluations at baseline, 3, and 6 months. Primary outcome measures were ankle kinematics, velocity, and stride length. Secondary outcome measures were ankle spasticity, strength, range of motion, and ankle kinetics. Group B made no significant change in any variable at any time. Groups C and B+C demonstrated significant improvements in ankle kinematics, spasticity, passive range of motion, and dorsiflexor strength. Results of this 1-year study indicate that BTX-A alone provided no improvement in the parameters measured in this study, while casting and BTX-A/casting were effective in the short- and long-term management of dynamic equinus in children with spastic CP. [source]


    Summary. The discovery presented in this paper may reshape the stylistic history of Greek art. It is that the torso and limbs of the Riace Bronzes were cast from life, rather than having been previously modelled in clay. [source]

    Plant Location and the Advent of Slab Casting by U.S. Steel Minimills: An Observation-Based Analysis

    ECONOMIC GEOGRAPHY, Issue 4 2006
    Frank Giarratani
    Abstract: The advent of slab casting for steel that is produced in electric furnaces resulted in a wave of new investments in the construction of steel minimills. From 1989 to 2001, 10 new plants were constructed in the United States on the basis of new technologies. Some were built in established steel industry agglomerations, while others were built in greenfield locations,regions that had little or no prior steelmaking activity. This research brings new evidence to bear on location decisions concerning modern steelmaking. The findings are based on direct observation and visits to the plants of all the new mills that were created by these investments. While the analysis reinforces the importance of transfer costs in decision making, it also argues that critical locational elements cannot be fully understood unless analyses take account of the characteristics of specific products, plants, and firms. [source]

    Tape Casting of Graphite Material: A New Electrochemical Sensor

    ELECTROANALYSIS, Issue 16 2006
    M. Chicharro
    Abstract Tape casting is a feasible method for preparing ceramic tapes with different electrical and magnetic properties for multilayer ceramic devices. This paper describes the tape casting process for the preparation of a new kind of self-standing carbon electrodes (SSCE) using different ratios of graphite and the organic additives generally used in the non-aqueous tape casting process. [source]

    Modeling of Hot Ductility During Solidification of Steel Grades in Continuous Casting , Part I,

    Dieter Senk
    The present paper gives an overview of the simultaneous research work carried out by RWTH Aachen University and ThyssenKrupp Steel Europe AG. With a combination of sophisticated simulation tools and experimental techniques it is possible to predict the relations between temperature distribution in the mould, solidification velocity, chemical steel composition and, furthermore, the mechanical properties of the steel shell. Simulation results as well as experimentally observed microstructure parameters are used as input data for hot tearing criteria. A critical choice of existing hot tearing criteria based on different approaches, like critical strain and critical strain rate, are applied and developed. The new "damage model" is going to replace a basic approach to determine hot cracking susceptibility in a mechanical FEM strand model for continuous slab casting of ThyssenKrupp Steel Europe AG. Critical strains for hot cracking in continuous casting were investigated by in situ tensile tests for four steel grades with carbon contents in the range of 0.036 and 0.76,wt%. Additionally to modeling, fractography of laboratory and industrial samples was carried out by SEM and EPMA and the results are discussed. [source]

    Modelling of Hot Ductility during Solidification of Steel Grades in Continuous Casting , Part II,

    Bernd Bttger
    In continuous casting, the probability of hot cracks developing strongly depends on the local solidification process and the microstructure formation. In ref. 1, an integrative model for hot cracking of the initial solid shell is developed. This paper focuses on solidification modelling, which plays an important role in the integrated approach. Solidification is simulated using a multiphase-field model, coupled online to thermodynamic and diffusion databases and using an integrated 1D temperature solver to describe the local temperature field. Less-complex microsegregation models are discussed for comparison. The results are compared to EDX results from strand samples of different steel grades. [source]

    Slip Casting of ZrB2,SiC Composite Aqueous Suspensions

    Valentina Medri
    Slip casting of concentrated aqueous suspensions was set up as forming technique for the production of crucibles from ZrB2,SiC composite powder. The dispersion effectiveness and the effect on the final microstructures of two commercial ammonium polyacrylates (Duramax D3005 and Dolapix PC33) used as dispersants were investigated. The first goal was pursued by evaluating the zeta potential of the powders in water at different concentrations of additives, while the second one was assessed by analyzing the microstructure. Duramax D3005 resulted more effective than Dolapix PC33 in electrostatically stabilize the suspensions. Correspondently, almost homogeneous microstructures and lower final porosity of the sintered crucibles were obtained with Duramax D3005, while ZrB2 layers on the vertical surfaces initially in contact with the plaster molds were observed using Dolapix PC33. Moreover, the use of this latter dispersant did not allow the preparation of thick crucible walls due to the sample rupture during the binders pyrolysis stage. [source]

    Hydroxyapatite/SiO2 Composites via Freeze Casting for Bone Tissue Engineering,

    Silke Blindow
    Freeze casting is a fabrication method that allows producing near-net-shaped ceramics with variable porosity. Hydroxyapatite (HA) was modified by the addition of different amounts of SiO2 nanoparticles during freeze cast preparation. The addition of SiO2 introduced a partial phase transformation of HA to , -tricalcium phosphate and improved the form stability due to less shrinkage after sintering. The impact of surface roughness of pure HA ceramics and the influence of SiO2 introduction during freeze casting on adhesion, proliferation, and differentiation of human osteoblast-like cells (MG-63) was investigated. While both cell attachment and proliferation of smooth pressed HA was significantly enhanced compared to rough freeze cast HA, the addition of SiO2 improved the cell numbers of the latter. The expression of cell differentiation markers osteocalcin and collagen I was found to be supported by rough surfaces (Ra,=,5,6,m) in particular on ceramics containing SiO2 [source]

    Preparation of Titanium Foams by Slip Casting of Particle Stabilized Emulsions,

    Bram Neirinck
    Bulk titanium foams were prepared by emulsion templating during slip casting. The emulsion template was stabilized using partially hydrophobized titanium particles while the continuous phase consisted of a titanium hydride powder suspension. Sintering was performed in inert atmosphere. The use of titanium hydride resulted in lower sintering temperatures and denser, stronger struts. Both homogeneous foams with high compressive strength and structures with a gradient in pore size were obtained. [source]

    Optimization of Mechanical Properties of NiAl-base Alloy by Suction Casting,

    W. Huai
    The suction-cast NiAl-Cr(Mo)/Hf alloy exhibits a refined microstructure and extended solid solubility. Significant improvement in room temperature ductility and strength was achieved by adopting suction casting technique. In addition, their elevated temperature strength also got slightly increase. The optimized mechanical properties can be attributed to the fine interlamellar spacing, the extended solid solubility and the increased cell eutectic zone as well as the refined Heusler phase. [source]

    Role of Manganes in the Soldering Reaction in Magnesium High Pressure Die Casting,

    C. Tang
    The significance of soldering in high pressure die casting (HPDC) of magnesium alloys could have a major economic impact on die casters and a study of the soldering phenomenon during HPDC of magnesium alloys has been undertaken. In this paper results of dip tests are presented involving the immersion of samples made from H13 tool steel into molten magnesium alloys with different aluminium and manganese contents. [source]

    Tape Casting and Dielectric Properties of Zn2Te3O8 -Based Ceramics with an Ultra-Low Sintering Temperature

    Johanna Honkamo
    The suitability of dielectric ceramics made of zinc tellurate (Zn2Te3O8) and titanium dioxide (TiO2) with an ultra-low sintering temperature (650C) for tape casting and thus for the multimodule technique with Al electrodes was investigated. The properties of the tape before and after sintering as well as the amount of organic additives for the casting process and a thermal analysis of the tape up to 1000C are reported. In addition, electrodes on a multilayer module made on stacked tapes were prepared using Al paste and postfiring, followed by relative permittivity and loss tangent measurements to verify the electrical performance of the whole structure. The dielectric properties of the stacked module without any electrodes were also measured. The results show that the composition is well suited for the tape process but extra care should be taken especially with the proper sintering temperature for optimized electrical performance. [source]

    Anthropometry of fetal vasculature in the chorionic plate

    JOURNAL OF ANATOMY, Issue 6 2007
    Z. Gordon
    Abstract Normal fetal development is dependent on adequate placental blood perfusion. The functional role of the placenta takes place mainly in the capillary system; however, ultrasound imaging of fetal blood flow is commonly performed on the umbilical artery, or on its first branches over the chorionic plate. The objective of this study was to evaluate the structural organization of the feto-placental vasculature of the chorionic plate. Casting of the placental vasculature was performed on 15 full-term placentas using a dental polymer mixed with colored ink. Observations of the cast models revealed that the branching architecture of the chorionic vessel is a combination of dichotomous and monopodial patterns, where the first two to three generations are always of a dichotomous nature. Analysis of the daughter-to-mother diameter ratios in the chorionic vessels provided a maximum in the range of 0.6,0.8 for the dichotomous branches, whereas in monopodial branches it was in the range of 0.1,0.3. Similar to previous studies, this study reveals that the vasculature architecture is mostly monopodial for the marginal cord insertion and mostly dichotomous for the central insertion. The more marginal the umbilical cord insertion is on the chorionic plate, the more monopodial branching patterns are created to compensate the dichotomous pattern deficiency to perfuse peripheral placental territories. [source]

    Centrifugal Gel Casting: A Combined Process for the Consolidation of Homogenous and Reliable Ceramics

    Saeed Maleksaeedi
    In this work, a combined process, called centrifugal gel casting (CGC), was proposed for the fabrication of homogenous and reliable monolithic and composite ceramics starting from submicrometer-sized powders. This method exploits the advantages of both conventional gel casting (GC) and centrifugal slip casting (CSC), while overcoming the limitations associated with the two methods. Via this process, a relatively low centrifugal force is applied to form a highly concentrated slurry in the mold cavity, which is then followed by in situ polymerization of slurry during gelation. In this work, concentrated alumina slurries with different solid contents from 45 to 65 vol% were consolidated by the three forming methods mentioned above. Various properties of green and fired products were measured and compared. Shorter processing time, lower centrifugal force, higher green strength, and minimal segregation are observed to be the characteristics of CGC in comparison with CSC. In situ elimination of bubbles with no need for degassing and the ability to remove heterogeneities, on top of high reliability and the potential to process higher viscosity slurries, are the main advantages of this method over the conventional GC. [source]

    Fabrication and Characterization of Anode-Supported Tubular Solid-Oxide Fuel Cells by Slip Casting and Dip Coating Techniques

    Lan Zhang
    High-performance anode-supported tubular solid-oxide fuel cells (SOFCs) have been successfully developed and fabricated using slip casting, dip coating, and impregnation techniques. The effect of a dispersant and solid loading on the viscosity of the NiO/Y2O3,ZrO2 (NiO/YSZ) slurry is investigated in detail. The viscosity of the slurry was found to be minimum when the dispersant content was 0.6 wt% of NiO/YSZ. The effect of sintering temperature on the shrinkage and porosity of the anode tubes, densification of the electrolyte, and performance of the cell at different solid loadings is also investigated. A Ni/YSZ anode-supported tubular cell fabricated from the NiO/YSZ slurry with 65 wt% solid loading and sintered at 1380C produced a peak power output of ,491 and ,376 mW/cm2 at 800C in wet H2 and CH4, respectively. With the impregnation of Ce0.8Gd0.2O2 (GDC) nanoparticles, the peak power density increased to ,1104 and ,770 mW/cm2 at 800C in wet H2 and CH4, respectively. GDC impregnation considerably enhances the electrochemical performance of the cell and significantly reduces the ohmic and polarization resistances of thin solid electrolyte cells. [source]

    Comparison of Water-Based and Solvent-Based Tape Casting for Preparing Multilayer ZnO Varistors

    Lanyi Wang
    Water-soluble acrylic was used as the binder of the water-based (aqueous) slurry while polyvinyl butyral was the binder of the solvent-based (nonaqueous) slurry. Both types of slurry exhibited shear thinning properties suitable for tape casting. The casting parameters for them were different when the same thick green sheets were cast. Thermogravimetric analysis was used to find the binder burnout temperatures of the aqueous and nonaqueous green tape. Scanning electron microscopy (SEM) studies revealed that both types of green tapes have smooth defect-free surfaces but the aqueous green tape is denser than the nonaqueous one. The multilayer ZnO varistors prepared by aqueous tape casting display comparable good electrical properties to those prepared by nonaqueous tape casting because both types of ceramic have a uniform, fine grain microstructure with a homogeneous dopant distribution indicated using SEM and transmission electron microscopy. [source]

    Novel Coagulation Method for Direct Coagulation Casting of Aqueous Alumina Slurries Prepared Using a Poly(Acrylate) Dispersant

    Kuttan Prabhakaran
    Coagulation of concentrated aqueous alumina slurries prepared using an ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC). A small amount of MgO (0.2 wt% of alumina) increased the viscosity of the concentrated alumina slurry with time and finally transformed it into a stiff gel. The mechanism of coagulation is proposed such that the time-delayed in situ generation of Mg2+ ions from the sparingly soluble MgO forms Mg,poly(acrylate) with the unadsorbed ammonium poly(acrylate) molecules in solution that shift the poly(acrylate) adsorption equilibrium toward the left by depleting the poly(acrylate) molecules adsorbed on the alumina particle surface. This leads to insufficient dispersant coverage on the particle surface and coagulation of the slurry. DCC using MgO is possible only if the slurry is prepared at a dispersant concentration higher than that required for optimum dispersion as the slurries prepared at the optimum dispersant concentration underwent premature coagulation. The gelation time could be tailored within 20 min to a few hours by maintaining the temperature in the range of 70,30C. The wet coagulated bodies prepared from 50 vol% alumina slurry showed a compressive strength of nearly 0.05 MPa. [source]

    Fabrication of a Porous Bioactive Glass,Ceramic Using Room-Temperature Freeze Casting

    Ju-Ha Song
    The room-temperature freeze-casting method was used to fabricate porous bioactive glass,ceramics. In this method, a glass/camphene slurry prepared at 60C was cast into a mold at 20C, resulting in the production of a rigid green body that was comprised of three-dimensional dendritic camphene networks surrounded by highly concentrated glass powder walls. After the sublimation of camphene, the samples were sintered for 3 h at elevated temperatures ranging from 700 to 1100C. As the sintering temperature was increased to 1000C, the densification of the glass,ceramic wall was remarkably enhanced, while its highly porous structure was preserved. The sample sintered at 1000C showed a high porosity of 53% and pore channels with a size of several tens of micrometers, as well as dense glass,ceramic walls. In addition, the fabricated samples effectively induced the deposition of apatite on their surfaces when immersed in simulated body fluid, implying that they are very bioactive. [source]

    Room-Temperature Freeze Casting for Ceramics with Nonaqueous Sublimable Vehicles in the Naphthalene,Camphor Eutectic System

    Kiyoshi Araki
    Freeze casting for Al2O3 was accomplished at room temperature with nonaqueous sublimable vehicles in the naphthalene,camphor eutectic system with a eutectic temperature of 31C. A fully dense sintered body (>99.5% of theoretical density (T.D.)) was obtained with a eutectic composition vehicle, whereas at most 90% T.D. was obtained with an off-eutectic (i.e., hypo- or hypereutectic) composition vehicle due to formation of large uniquely shaped voids. Microstructural observation suggested that growing pro-eutectic crystals rejected the suspended Al2O3 particles to form large voids during the solidification process. At the eutectic composition, formation of fine lamellar microstructure in a solidified vehicle is considered to inhibit particle rejection resulting in large voids. [source]

    Centrifugal Casting of Thin-Walled Ceramic Tubes from Preceramic Polymers

    Reinhold Melcher
    Thin-walled (wall thickness, 100,2000 ,m) mono- and bilayered ceramic tubes in the system Si,O,C,(N) were obtained by centrifugal casting of a polysiloxane/filler suspension. Si and SiC powders were dispersed in polyorganosiloxane/triethoxysilane solutions. After centrifugal casting in a Teflon tube with a rotational speed of 2000 rpm and subsequent cross-linking at 130C and 60 rpm, the tubes were pyrolyzed in argon or in nitrogen at 1400,1600C. Bilayered tubes with controlled variation of porosity were obtained by overcasting the monolayer green tubes with a modified slurry composition. [source]

    Effect of Oligosaccharide Alcohol Addition to Alumina Slurry and Translucent Alumina Produced by Slip Casting

    Yuji Hotta
    A slurry used to produce dense green compacts by slip casting should exhibit low viscosity, high solids content, and good dispersion. Slurries with good characteristics were produced in the present study by adding oligosaccharide alcohol to an Al2O3 slurry with an NH4+ salt of poly(methacrylic acid) (NH4+ -PMA). The role of NH4+ -PMA and oligosaccharide alcohol in the Al2O3 slurry was examined by DTA, ,-potential measurement, high-pressure liquid chromatography, and viscometry. The viscosity of the slurry with NH4+ -PMA and oligosaccharide alcohol was lower than that of the slurry with NH4+ -PMA at a high solids content. Oligosaccharide alcohol did not interact with the Al2O3 surface. However, the Al2O3 slurry with NH4+ -PMA was influenced by the addition of oligosaccharide alcohol. We found that the dispersibility of the slurry was greatly improved by adding oligosaccharide alcohol. The transmittance of the Al2O3 ceramics produced by slip casting using the slurry with both NH4+ -PMA and oligosaccharide alcohol was higher than that of ceramics produced by slip casting using the slurry with NH4+ -PMA alone. The increased optical property resulted from low viscosity, which was attributed to the addition of oligosaccharide alcohol, at a high solids content. [source]

    Thin Yttrium-Stabilized Zirconia Electrolyte Solid Oxide Fuel Cells by Centrifugal Casting

    Jiang Liu
    A centrifugal casting technique was developed for depositing thin 8-mol%-yttrium-stabilized zirconia (YSZ) electrolyte layers on porous NiO-YSZ anode substrates. After the bilayers were cosintered at 1400C, dense pinhole-free YSZ coatings with thicknesses of ,25 ,m were obtained, while the Ni-YSZ retained porosity. After La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-Ce0.9Gd0.1O1.95 (GDC) or La0.8Sr0.2MnO3 (LSM)-YSZ cathodes were deposited, single SOFCs produced near-theoretical open-circuit voltages and power densities of ,1 W/cm2 at 800C. Impedance spectra measured during cell tests showed that polarization resistances accounted for ,70%,80% of the total cell resistance. [source]

    Synthesis and Light-Emitting Properties of New Polyimides Containing Ethynylene Units in the Main Chain

    Jun Ho Chi
    Abstract Two new polyimides (ODA-PI and HDA-PI) having 1,4-phenylenediethynylene unit and octyloxy groups were synthesized. Judging from inherent viscosities of their precursor PAAs (1.42 and 1.62 dL,,g,1), the two PIs were very high in molecular weight. Casting and thermal imidization of PAAs results polyimides with good-quality films. They were stable up to 364,C and showed no crystallites. UV-vis and PL spectra in NMP solutions of both PIs showed maxima at 442 and 501 nm, respectively, while PL spectra in ,10 m thick films exhibited a maximum at 540 nm. CV indicates that two PIs were electrochemically active in redox region. The devices with construction of ITO/PEDOT/PIs/BAlq3/LiF/Al exhibited turn-on voltages of 6.5 V in ODA-PI and 7.5 V in HDA-PI and emitted a bright bluish-green light. ODA-PI and HDA-PI showed maximum luminescence of 256 and 316 cd,,cm,2, respectively, at the same voltage of 12 V. [source]

    Casting the Nets of Symbolism

    NEW BLACKFRIARS, Issue 976 2002
    Christopher Dyczek
    First page of article [source]

    Casting Out Demons: The Native Anthropologist and Healing in the Homeland

    Tanya L. Ceja-Zamarripa
    This article addresses academic and social costs experienced by anthropologists studying their own ethnic group. It explores how one "native" anthropologist navigates her roles as ethnographer and insider while researching curanderismo, a religiously inflected form of ethnomedicine within increasingly secular and commercialized Mexican American urban spheres. Is academic credibility weakened because the anthropologist shares the cultural history of her/his informants? When your community entrusts you with their spiritual, emotional and social woes, do they see you as ethnographer, insider, or both? To be privy to the ritual knowledge and practices of healers and the individual struggles of clients to find respite from pain is a great responsibility as curanderismo has often been pathologized by anthropology as a "primitive" tradition used only by the ignorant and backward. Given this history, the native anthropologist must find a way to manage allegiance to her cultural as well as academic community. I suggest that doing "native" research is its own form of "exorcism," casting out demons in a field that often silences native voices and holds native anthropology in lower esteem. [source]

    Casting the Riace Bronzes: Modern Assumptions and Ancient Facts

    Herbert Hoffmann
    This article argues that classical archaeologists have seriously underestimated the output of heat required to melt a large quantity of bronze and therefore have wrongly reconstructed the ancient casting process. The idea that sufficient metal for casting a bronze of monumental proportions could be heated in a crucible with a charcoal fire ventilated by bellows is not realistic. The following observations are based on solid foundry experience: Nigel Konstam, a bronze sculptor, for many years supervised the casting of monumental bronzes comparable in size to those from Riace. This article has been written by Herbert Hoffmann drawing on Konstam's notes [source]

    Modeling the Porosity Formation in Austenitic SGI Castings by Using a Physics-Based Material Model,

    B. Pustal
    Abstract On solidification, microsegregations build up in solid phases due to changes in solid concentrations with temperature. Diffusion, which is a kinetic process, usually reduces the occurrence of microsegregations. This work is aimed at modeling such kinetic effects on the solidification of austenitic cast iron, using a holistic approach. For this purpose, a microsegregation model is developed and validated. Moreover, this model is directly coupled to a commercial process-simulation tool and thermodynamic software. A series of GJSA-XNiCr 20-2 clamp-rings is cast by varying the inoculation state and the number of feeders. The composition of this cast alloy is analyzed and the microstructure characterized to provide input data for the microsegregation model. In order to validate the software, cooling curves are recorded; differential thermal analysis, electron dispersive X-ray analysis and electron probe micro analysis are carried out. Furthermore, the porosity within the casting is analyzed by X-ray. By performing coupled simulations, the different cooling characteristics within the casting lead to pronounced differences in phase fractions and solidification temperatures which are due to dendrite arm coarsening. The hot spot effect below the feeders is assisted by a shift towards lower solidification temperatures over the solidification time. This shift is a result of the local cooling characteristics, which can only be predicted when process simulation is directly coupled with material simulation. The porosity predictions and the porosity analysis exhibit good agreement. A comparison between experimental and virtual cooling curves closes, implying that the novel coupling concept and its implementation are valid. [source]

    Simulation of Ni3Al-based Alloy and Investment Casting Process of its Thin Wall Castings

    Xi-e Zhang
    It is very difficult to produce thin wall complex castings of the Ni3Al-based alloy by investment casting. Defects such as incomplete mold filling and hot tears appear commonly. In this paper, physical parameters of Ni3Al-based alloy are obtained by experiments and simulations using JmatPro software. The calculation results of physical parameters are credible by comparing with test results and can be used in the pre-processing of casting simulaton software ProCAST of thin wall castings. Gating and feeding system is optimized to decrease hot tearing tendentiousness and ensure filling ability according to casting simulation results. [source]

    Cement Selection for Cement-Retained Crown Technique with Dental Implants

    James L. Sheets DDS
    Abstract Purpose: The purpose of this study was to assess and compare the retentive nature of common dental cements that have been adapted for use in the implant abutment cement-retained crown (CRC) technique with those specifically formulated for this purpose. Materials and Methods: Ten regular diameter implant analogs were embedded in stainless steel disks. Unmodified CRC abutments were attached and torqued to 30 Ncm. Test crowns were waxed and cast with base metal alloy. Castings were fitted, cleaned with aluminum oxide, and steam cleaned prior to application of the cement. The cements used were: (1) Temp Bond, (2) UltraTemp, regular, (3) UltraTemp firm, (4) ImProv with petroleum jelly coating of crown, (5) ImProv without petroleum jelly, (6) Premier Implant with KY Jelly coating of abutment, (7) Premier Implant without KY jelly, (8) TR-2, (9) Fleck's, (10) Ketac Cem Aplicap, and (11) Fuji Plus Capsule. After cementation, assemblies were stored for 24 hours. Each sample was subjected to a pull-out test using an Instron universal testing machine at a crosshead speed of 5.0 mm/min. Loads required to remove the crowns were recorded, and mean values for each group determined. A one-way ANOVA and a post hoc least square difference (LSD) test were done for pairwise comparison at a confidence interval of 95%. Results: The mean values (SD) of loads at failure (n = 10) for various cements were as follows (N): Ultratemp, regular 358.6 (38.2) (Group A), ImProv without petroleum jelly 172.4 (59.6) (Group B), Fleck's 171.8 (62.2) (Group B), Ketac Cem 167.8 (69.1) (Group B), UltraTemp firm 158.8 (62.7) (Group BC), Fuji Plus 147.5 (69.7) (Group BC), Premier without KY jelly 131.6 (31.8) (Group BC), ImProv using petroleum jelly 130.8 (42.5) (Group BC), Temp Bond 117.8 (48.3) (Group C), TR-2 41.2 (16.6) (Group D), and Premier with KY jelly 31.6 (24.8) (Group D). Groups with the same letter were not significantly different. Conclusions: Within the limitations of this in vitro study, it is not suggested that any one cement is better than another at retaining cement-retained crowns (CRCs) to implant abutments or that a threshold value must be accomplished to ensure retention. The ranking of cements presented is meant to be a discretionary guide for the clinician in deciding the amount of desired retention between castings and implant abutments. [source]

    The Effects of Abutment Wall Height, Platform Size, and Screw Access Channel Filling Method on Resistance to Dislodgement of Cement-Retained, Implant-Supported Restorations

    Mark Emms LDS
    Purpose: Factors affecting the retention of fixed prostheses to natural abutments are well understood. In contrast, little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that varying implant abutment wall height, platform size, and screw access channel filling method has on the retention of castings cemented to implant abutments using TempBond. Materials and Methods: Four 15 preangled abutments (Nobel Biocare Replace Select Esthetic) of each platform size,narrow (NP), regular (RP), and wide (WP),were used. In each group of abutments the screw access axial wall was either unadjusted, one-third removed, two-thirds removed, or completely removed. The screw access channels were either fully or partially filled with Memosil, a vinyl polysiloxane impression material. For each abutment a casting was constructed that incorporated an attachment to allow removal. Castings were cemented to abutments with TempBond. The tensile force required to separate the cemented castings from the abutments was measured using an Instron Universal load-testing machine. Results: The mean peak removal force for comparable abutments was significantly different ( p < 0.05): (1) where the screw access channel was completely filled with Memosil compared with those partially filled with Memosil; (2) with platform sizes,WP > RP > NP; (3) with alteration of axial wall height,1/3 removed > unadjusted = 2/3 removed > total wall removal. Conclusions: The retention of castings cemented to implant abutments with TempBond is influenced by the wall height, platform size, and the filling modality of the screw access channel. [source]