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Results for “Compressive Strength”

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At least 1,153 records · Page 64Linked to original sources

PubMed2004

The current status of material used for depot delivery of drugs.

The ideal local antibiotic delivery system has not been created. Antibiotic-laden bone cement has become the gold standard in the treatment of infected orthopaedic implants and there are confirmatory laboratory and clinical data that support the use of these materials. Heat-stable antibiotics elute from antibiotic-laden bone cement and do not have a notable influence on the compressive strengths of bone cement if the antibiotics are used in appropriate amounts. If the proper antibiotic is chosen, placed in the appropriately porous materials in sufficient amounts, and implanted in bone, antibiotic levels in the surrounding bone are many times greater than can be achieved by safe systemic antibiotic doses. Although the materials that have been manufactured commercially have been used for over 30 years in Europe, until recently, they have not been available in the United States. Currently, there are five antibiotic-laden bone cement composites that have been approved by the FDA and that are available for clinical use. Studies are being done to search for biodegradable implants preferable to antibiotic-laden bone cement; however, these studies and the materials are still in early stages and development. Currently, there are no FDA-approved biodegradable materials available for use to treat infected orthopaedic implants. As new materials become available and their elution characteristics are recorded, it is important for surgeons to understand how the data were collected so they can have a clear understanding of the elution characteristics of the material used and how the material acts in different environments. Even with extensive historic, clinical, and research data that prove the effectiveness of antibiotic-laden cement, the ideal drug delivery system is neither agreed on nor available.

Absorbable Implants↗

PubMed2003

Ex vivo gene therapy in autologous critical-size craniofacial bone regeneration.

In therapeutic bone repairs, autologous bone grafts, conventional or vascularized allografts, and biocompatible artificial bone substitutes all have their shortcomings. The bone formed from peptides [recombinant human bone morphogenetic proteins (BMPs)], demineralized bone powder, or a combination of both is small in size. Tissue engineering may be an alternative for cranial bone repair. In this study, the authors developed an animal model to test the hypothesis that replication-defective, adenovirus-mediated human BMP-2 gene transfer to bone marrow stromal cells enhances the autologous bone formation for repairing a critical-size craniofacial defect. The mesenchymal stromal cells of miniature swine were separated from the iliac crest aspirate and expanded in monolayer culture 1 month before implantation. The cultured mesenchymal stromal cells were infected with recombinant, replication-defective human adenovirus BMP-2, 7 days before implantation. Bilateral 2 x 5-cm2 cranial defects were created, leaving no osteogenic periosteum and dura behind. Mesenchymal stromal cells at 5 x 10(7)/ml were mixed with collagen type I to form mesenchymal stromal cell/polymer constructs. Mesenchymal stromal cells used for the control site were infected with adenovirus beta-Gal under the same conditions. After 6 weeks and 3 months, 10 miniature swine were euthanized and the cranium repair was examined. Near-complete repair of the critical-size cranial defect by tissue-engineered mesenchymal stromal cell/collagen type I construct was observed. The new bone formation area (in square centimeters) measured by three-dimensional computed tomography demonstrated that the improvement from 6 weeks to 3 months was significantly greater on the experimental side than on the control side (2.15 cm2 versus 0.54 cm2, p < 0.001) and significantly greater at 3 months than at 6 weeks (2.13 cm2 versus 0.52 cm2, p < 0.001). The difference between the experimental and control groups was significant at 3 months (mean difference, 2.13 cm2; p < 0.001). The maximal compressive strength of the new bone was similar to that of the normal cranial bone when evaluated by biomechanical testing (cranium bone versus tissue-engineered bone, 88.646 +/- 5.121 MPa versus 80.536 +/- 19.302 MPa; p = 0.227). Adenovirus was absent from all constructs by immunochemical staining at 6 weeks and 3 months after implantation. The successful repair of cranial defects in this experiment demonstrates the efficacy of the integration of the autologous stem cell concept, gene medicine, and polymers in producing tissue-engineered bone.

Animals↗

PubMed2004

The chemistry of acrylic bone cements and implications for clinical use in image-guided therapy.

Advances in image-guided therapy for vertebral fractures and other bone-related disorders have made acrylic bone cement an integral part of the interventional armamentarium. Unfortunately, information on the properties and chemistry of these compounds is mostly published in the biomaterial sciences literature, a source with which the interventional community is generally unfamiliar. This review focuses on the chemistry of bone cement polymerization and the properties of components in polymethylmethacrylate (PMMA)-based polymers, the most commonly used bone cements in interventional procedures such as percutaneous vertebroplasty. The effects of altering the concentration of components such as methylmethacrylate monomers, PMMA beads, benzoyl peroxide activator, N,N-dimethyl-p-toluidine (DMPT) initiator, and radiopacifiers on the setting time, polymerization temperature, and compressive strength of the cement are also considered. This information will allow interventional radiologists to manipulate bone cement characteristics for specific applications and maximize the clinical potential of image-guided interventions.

Bone Cements↗

PubMed2006

Bioactive and bioresorbable cellular cubic-composite scaffolds for use in bone reconstruction.

We used a novel composite fibre-precipitation method to create bioactive and bioresorbable cellular cubic composites containing calcium phosphate (CaP) particles (unsintered and uncalcined hydroxyapatite (u-HA), alpha-tricalcium phosphate, beta-tricalcium phosphate, tetracalcium phosphate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrate or octacalcium phosphate) in a poly-D/L-lactide matrix. The CaP particles occupied greater than or equal to 70 wt% (greater than or equal to 50 vol%) fractions within the composites. The porosities of the cellular cubic composites were greater than or equal to 70% and interconnective pores accounted for greater than or equal to 70% of these values. In vitro changes in the cellular geometries and physical properties of the composites were evaluated over time. The Alamar Blue assay was used to measure osteoblast proliferation, while the alkaline phosphatase assay was used to measure osteoblast differentiation. Cellular cubic C-u-HA70, which contained 70 wt% u-HA particles in a 30 wt% poly-D/L-lactide matrix, showed the greatest three-dimensional cell affinity among the materials tested. This composite had similar compressive strength and cellular geometry to cancellous bone, could be modified intraoperatively (by trimming or heating) and was able to form cortico-cancellous bone-like hybrids. The osteoinductivity of C-u-HA70, independent of biological growth factors, was confirmed by implantation into the back muscles of beagles. Our results demonstrated that C-u-HA70 has the potential as a cell scaffold or temporary hard-tissue substitute for clinical use in bone reconstruction.

Absorbable Implants↗

PubMed2003

Sustainable development of the cement industry and blended cements to meet ecological challenges.

The world production of cement has greatly increased in the past 10 years. This trend is the most significant factor affecting technological development and the updating of manufacturing facilities in the cement industry. Existing technology for the production of cement clinker is ecologically damaging; it consumes much energy and natural resources and also emits pollutants. A new approach to the production of blended or high-volume mineral additive (HVMA) cement helps to improve its ecological compatibility. HVMA cement technology is based on the intergrinding of portland cement clinker, gypsum, mineral additives, and a special complex admixture. This new method increases the compressive strength of ordinary cement, improves durability of the cement-based materials, and--at the same time--uses inexpensive natural mineral additives or industrial by-products. This improvement leads to a reduction of energy consumption per unit of the cement produced. Higher strength, better durability, reduction of pollution at the clinker production stage, and decrease of landfill area occupied by industrial by-products, all provide ecological advantages for HVMA cement.

Construction Materials↗

PubMed2004

Shock pressures induced in condensed matter by laser ablation.

The Trident laser was used to induce shock waves in samples of solid elements, with atomic numbers ranging from Be to Au, using pulses of 527 nm light around 1 ns long with irradiances of the order of 0.1 to 10 PW/m(2). States induced by the resulting ablation process were investigated using laser Doppler velocimetry to measure the velocity history of the opposite surface. By varying the energy in the laser pulse, relations were inferred between the irradiance and the induced pressure. For samples in vacuo, an irradiance constant in time does not produce a constant pressure. Radiation hydrodynamics simulations were used to investigate the relationship between the precise pulse shape and the pressure history. In this regime of time and irradiance, it was possible to reproduce the experimental data to within their uncertainty by including conductivity-dependent deposition of laser energy, heat conduction, gray radiation diffusion, and three temperature hydrodynamics in the treatment of the plasma, with ionizations calculated using the Thomas-Fermi equation. States induced in the solid sample were fairly insensitive to the details of modeling in the plasma, so Hugoniot points may be estimated from experiments of this type given a reasonable model of the plasma. More useful applications include the generation of dynamic loading to investigate compressive strength and phase transitions, and for sample recovery.

Journal Article↗

PubMed2000

Investigation of the radial compression of carbon nanotubes with a scanning probe microscope

Efforts have been made to characterize the mechanical properties of carbon nanotubes. Previous work has concentrated on the tubes' longitudinal properties, and studies of their radial properties have lagged behind. We have used a scanning probe microscope with an indentation/scratch function to investigate the radial compression of multiwalled carbon nanotubes under an asymmetric stress. In particular, we have determined the radial compressive elastic modulus at different compression levels and have estimated the compressive strength to be well beyond 5.3 GPa.

Journal Article↗

PubMed1978

In vitro studies of fluoridated amalgam.

Four types of fluoridated amalgam were assessed in vitro in terms of fluoride release, corrosion behaviour and compressive strength, and compared with amalgams prepared from the corresponding non-fluoridated alloys. Although corrosion susceptibility was found to be increased, steady release of the fluoride ion was demonstrated over a 16-week period, indicating that fluoridated amalgams might be prophylactically employed in clinical dentistry as a means of overcoming the problem of secondary caries associated with amalgam restorations.

Corrosion↗

PubMed1984

Antiplaque properties of sustained release SnF2: pilot studies.

Pilot studies examining the physical and clinical properties of an intracoronal sustained release fluoride delivery system were performed. After testing various percentages of SnF2 incorporated into polycarboxylate, zinc phosphate, and zinc oxide cements, 70% SnF2 polycarboxylate cement was found to have adequate compressive strength while releasing the greatest amount of fluoride in vitro. A 30-day in vivo trial, in which this fluoride cement was used as a temporary intracoronal restoration, produced elevated salivary fluoride levels with only transient elevation in urinary fluoride levels. Plaque scores decreased during the experimental period, suggesting that the released SnF2 affected bacterial growth or attachment. The SnF2-polycarboxylate cement was an adequate temporary restorative material without significant side effects.

Delayed-Action Preparations↗

PubMed2004

Physical properties and compatibility with dental stones of current alginate impression materials.

This study examined physical properties and compatibility with dental stones of two types of alginate impression materials. Five powder-type alginate impression materials (Alginoplast EM, Aroma Fine, Algiace Z, Coe Alginate, Jeltrate Plus) and a paste-type alginate impression material (Tokuso AP-1) were used. The dynamic viscosity immediately after mixing was measured by means of a controlled-stress rheometer. The gelation times were determined according to Japanese Industrial Standards (JIS) T6505, and recovery from deformation, strain in compression and compressive strength were determined according to the International Organization for Standardization (ISO) specification 1563. Detail reproduction and surface roughness of type III dental stones (New Plastone, New Sunstone) and a type IV dental stone (Die Stone) were evaluated using a ruled test block as specified in the ISO specification 1563 and a profilometer, respectively. The alginate impression materials evaluated in this study were all in compliance with the ISO specification 1563 and JIS T6505. The alginate impression materials had similar mechanical properties after gelation, whilst a wide range of dynamic viscosity immediately after being mixed, gelation times and compatibility with dental stones were found among the materials. The paste-type material had a higher dynamic viscosity and a shorter gelation time than the powder-type materials. The best surface quality was obtained with the paste-type material/type III dental stone cast combinations. The materials should be selected in consideration of initial flow, setting characteristics and compatibility with dental stones. The results suggested that a paste-type material would better meet the requirements of an alginate impression material.

Alginates↗

PubMed1980

Effect of thickness of peridental restorations on the casting precision.

The present study has shown that the precision of peridental gold alloy castings depends both on the specific properties of the investment used and on the thickness of the pattern. In all cases the inside diameter of the castings decreased with increasing thickness. The most accurate results were obtained with an experimental investment characterized by a setting expansion of 0.05%, a thermal expansion high enough to compensate for the alloy contraction during cooling from solidus to room temperature, and a compressive strength of only 27 kg/cm2 at 670 degrees C.

Dental Casting Investment↗

PubMed1983

Working time of dental amalgams.

The purpose of the present work was to study the setting of amalgams made from several different commercial alloys by recording the rate of initial mercury consumption, and then to compare the findings with those from other methods of defining the early setting process. The results show that the rate of initial mercury consumption is well correlated with clinicians' classification of the rate of setting of amalgams, but not correlated with mechanical tests like early compressive strength and guillotine setting time used till now in estimating the working time of amalgams. Based on these findings an appropriate method of determining the mercury:alloy proportion and working time of dental amalgams is suggested.

Chemical Phenomena↗

PubMed1975

A comparison of methods for determining setting rate of amalgam.

Four methods were compared for determining the setting rate of amalgams. The resultant order of preference as a standard method was compressive strength at 30 minutes after preparation of the specimen, the time to the last transverse cut on a cylindrical specimen with a "guillotine" blade and the time to nonfracture of a ball of a amalgam with a final set Gillmore needle. A mercury absorption method was unacceptable. Alloys labelled fast and standard setting could be separated and limits between fast and standard alloys have been examined for each method.

Absorption↗

PubMed1975

An adhesive paint-on restorative for tooth surface defects.

The physical properties of an adhesive paint-on restorative material have been examined and it is shown that the adhesion to enamel is good, its compressive strength about equal to silicate, hardness is less than for composite resins, and stain resistance is good.

Acrylic Resins↗

PubMed1976

Improvement in the properties of gypsum casts by polymer impregnation.

It is known that porous solids such as Portland cement, concrete, and ceramic tile bodies can be strengthened by polymer impregnation. The solid material is infiltrated with a liquid monomer, which is then polymerized in situ. In the present investigation, it has been found that this process is effective for strengthening gypsum casts prepared from ordinary laboratory plaster. Impregnation with poly(methyl methacrylate) confers marked improvements in tensile and compressive strength and abrasion resistance. The process would be particularly applicable to the preservation of study casts for record purposes.

Calcium↗

PubMed1982

Evaluation of 50 low and high copper amalgams according to Standards.

The content and rationale of Standards for Dental Amalgam Alloys are discussed. The properties of amalgams made from 50 alloys used in Australia were determined according to methods in the Standards and the results are presented to enable comparison between low and high copper amalgams. The limits for the physical tests are discussed in the light of the range of values obtained. In general, the high copper amalgams showed higher one hour compressive strengths, lower creep and plastic deformation than low copper amalgams. No difference in dimensional change was found.

Chemical Phenomena↗

PubMed1999

Finite element analysis of anterior tooth root stresses developed during endodontic treatment.

Vertical tooth root fractures are diagnostically challenging, frustrating, and an increasingly common cause of failure of tooth restoration. These vertical root fractures have been associated with many causes, including the endodontic process itself. To investigate these endodontic causes, various phases of crown replacement for an anterior tooth were modeled using nonlinear, plane strain finite element (FE) analysis. Stresses developed during obturation, post positioning, crown placement, and masticatory and occlusal loading of the restored tooth were estimated using this analysis method. The minimum (compressive) principal stress was greatest during obturation of cones 1 and 2, and during mastication of the restored tooth. Although these stresses were significant (-150 to -280 MPa), they did not exceed the compressive strength of dentin. The maximum (tensile) principal stresses, 160 to 300 MPa, were also observed during obturation of cones 1 and 2. These peak stresses exceed the dentin tensile strength.

Crowns↗

PubMed2005

Super-compressible foamlike carbon nanotube films.

We report that freestanding films of vertically aligned carbon nanotubes exhibit super-compressible foamlike behavior. Under compression, the nanotubes collectively form zigzag buckles that can fully unfold to their original length upon load release. Compared with conventional low-density flexible foams, the nanotube films show much higher compressive strength, recovery rate, and sag factor, and the open-cell nature of the nanotube arrays gives excellent breathability. The nanotube films present a class of open-cell foam structures, consisting of well-arranged one-dimensional units (nanotube struts). The lightweight, highly resilient nanotube films may be useful as compliant and energy-absorbing coatings.

Journal Article↗