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Results for “Compressive Strength”

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PubMed1976

Polymer-ceramic composite for tooth-root implant.

A new polymer-ceramic composite suitable for tooth-root implants has been developed in this study. This material exhibited the desirable combination of good mechanical properties, controlled porosity, and ease of processing. A thermal processing technique was utilized to polymerize acrylic acid (AA) in the presence of either 0.3 or 0.05 mu alumina particles. Porosity and pore size distribution were influenced by the alumina particle size and the processing technique. For a 50 vol % AA solution, the composite had an average compressive strength of 18,000 psi and 38% porosity when 0.3 mu filler particles were used. In comparison, the 0.05 mu alumina-filled composite had an average compressive strength of 28,000 psi with a 15% porosity. Data on the physical and structural characteristics of the composite are presented in this study. Based on these results, the composite material shows good potential for use in tooth-root implants as well as other orthopedic implant applications.

Absorption↗

PubMed2001

Stress distribution changes in bovine vertebrae just below the endplate after sustained loading.

OBJECTIVE: To describe the pattern of stress distribution in the vertebral body just behind the endplate, and to document its changes due to sustained loading. METHODS: Twelve fresh bovine coccygeal motion segments were dissected and tested. Each specimen was axially loaded with a sustained compressive force of 50% of its estimated compressive strength. Before loading, after 1.5 h and after 3 h of loading, the distribution of the axial pressure under the bottom vertebra (i.e., just below its top endplate) was recorded at three force levels (25%, 37.5% and 50% of the estimated compressive strength), using pressure-sensitive film. RESULTS: Stress distribution over the endplate was found to be fairly uniform. At low compression forces, the stress was the highest centrally. With increased compression and after sustained compression the uniformity improved through a significant redistribution of stress to the periphery. No stress peaks were found to occur after sustained loading. CONCLUSION: Stress peaks after sustained loading cannot explain the occurrence of endplate fractures in sustained cyclic compression in non-degenerated discs. Competing explanations, such as creep, and fatigue failure, would appear more likely candidates. RELEVANCE: It has been hypothesised that compression induced fractures of the lumbar vertebral endplate constitute an important etiological factor for low back pain. Competing theories exist on the fracture mechanism in sustained loading and these would have different implications with respect to prevention. The present study evaluated one of these theories.

Analysis of Variance↗

PubMed1992

Effects of palladium addition on properties of dental amalgams.

Palladium-containing amalgam alloys were developed utilizing the atomization method. Single-compositional type alloys were fabricated and palladium was substituted for silver in concentrations up to 5 w/o. Alloy powder with a particle size of less than 45 microns was collected and triturated with mercury. Creep, compressive strength and dimensional change tests were performed according to ADA Specification No. 1 along with controls of Tytin, Valiant and Valiant-Ph.D. Values for creep decreased and compressive strength increased markedly with additions of palladium. Current densities of the experimental amalgams containing palladium were determined to be an order of magnitude less than the original amalgams in the electrochemical test. A trend of positive relationships between properties and palladium additions was indicated.

Corrosion↗

PubMed1997

Biomechanical assessment of bone ingrowth in porous hydroxyapatite.

Porous hydroxyapatite (Endobon) specimens were implanted into the femoral condyle of New Zealand White rabbits for up to 6 months. After sacrifice, specimens were sectioned for histology and mechanical testing, where the extent of reinforcement by bony ingrowth was assessed by compression testing and fixation was assessed by push-out testing. From histological observations, it was established that the majority of bone ingrowth occurred between 10 day and 5 weeks after implantation and proceeded predominantly from the deep end of the trephined defect, with some integration from the circumferential sides. At 3 months, the implants were fully integrated, exhibiting bony ingrowth, vascularization and bone marrow stroma within the internal macropores. After 5 weeks, the mean ultimate compressive strength of retrieved implants (6.9 MPa) was found to be greater than that of the original implant (2.2 MPa), and by 3 months the fully integrated implants attained a compressive strength of approximately 20 MPa. Push-out testing demonstrated that after 5 weeks in vivo, the interfacial shear strength reached 3.2 MPa, increasing to 7.3 MPa at 3 and 6 months.

Journal Article↗

PubMed2006

Freeze casting of hydroxyapatite scaffolds for bone tissue engineering.

Although extensive efforts have been put into the development of porous scaffolds for bone regeneration, with encouraging results, all porous materials have a common limitation: the inherent lack of strength associated with porosity. Hence, the development of porous hydroxyapatite scaffolds has been hindered to non-load bearing applications. We report here how freeze casting can be applied to synthesize porous scaffolds exhibiting unusually high compressive strength, e.g. up to 145 MPa for 47% porosity and 65 MPa for 56% porosity. The materials are characterized by well-defined pore connectivity along with directional and completely open porosity. Various parameters affecting the porosity and compressive strength have been investigated, including initial slurry concentration, freezing rate, and sintering conditions. The implications and potential application as bone substitute are discussed. These results might open the way for hydroxyapatite-based materials designed for load-bearing applications. The biological response of these materials is yet to be tested.

Bone and Bones↗

PubMed1993

Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins.

Seven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane-based polymers sorbed substantially more water than the aromatic-based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water.

Absorption↗

PubMed1977

[Testing of various methods for the determination of processing time for amalgam].

Four different test methods for the determination of the processing time of freshly mixed amalgam pastes were examined with the view to their utility, using 9 commercial powder alloys of different setting speeds. The tests used were a schematised stuffing test, close to the procedure used in practise, the cutting test and the compressive strength test after 10 minutes, both of which are still quoted as alternatives in the provisional standard DIN 13904, as well as a Hg addition test described by Jørgensen. The compressive strength test proved to be the quickest and most accurate. It is therefore best suited for routine examinations and general control and is recommended for inclusion in the DIN. It is necessary to set up calibration curves with the help of the stuffing test in order to estimate the processing time. These have to be separately estimated for filing amalgam and globular amalgam. The cutting test proved to be relatively inaccurate. The Hg addition test, though giving usable values, consumed too much time and material.

Dental Amalgam↗

PubMed2005

[Development of a visible light-curing calcium hydroxide cement].

A visible light-curing calcium hydroxide cement is presented here and the effects of its resin matrix on the Ca2+ releasing, compressive strength of set material and the pH value of water in which set materials immersed are evaluated. Experimental results show that the effects of the selected resin matrix on Ca2+ releasing, compressive strength and pH value are significant. The calcium hydroxide cement containing BEMA or EMA and HEMA as resin matrix has good properties. The pulp capping test showed that an excellent dentin bridge appeared in dogs capped teeth at 70 days. pulp, pulp capping, calcium hydroxide, visible light-curing, dental materials

Animals↗

PubMed2005

Effect of resin-based material combination on the compressive and the flexural strength.

The mechanical properties, elasticity and compressive strength, of restorative materials play a crucial role during mastication for clinical performance of materials in particular stress bearing areas at posterior regions. This in vitro study was objected to evaluate the changes in the compressive and flexural strength of tooth-coloured resin-based dental restorations placed on flowable composites. Specimens in the control group were produced in cylindrical form for testing compressive strength and in quadrangular prism form for flexural strength test. Tetric Ceram, Charisma, Surefil, Admira and two compomers; Dyract AP and Compoglass F in test group specimens were fabricated by placing the control materials on different flowables. The material combinations were as follows: Tetric Ceram/Tetric Flow Charisma/Flowline, Surefil/Dyract Flow, Admira/Admira Flow, Dyract AP/Dyract Flow, Compoglass F/Compoglass Flow. Compressive strength values were measured at the Instron Testing Machine with a cross-head speed of 10 mm min(-1) while flexural strength were determined in three-point bending with a cross-head speed of 1 mm min(-1). One-way anova and Tukey's multiple comparison tests were performed for the statistical analysis. The flexural strength values of Tetric Ceram/Tetric Flow (135.9 +/- 3.2), Charisma/Flowline (120.4 +/- 5.6) and Compoglass F/Compoglass Flow (108.2 +/- 5.2) combinations were statistically greater than Tetric Ceram (110.8 +/- 10.5), Charisma (95.3 +/- 5.3) and Compoglass F (86.9 +/- 4.9). The results of the present study support the idea that the placement of flowable composite as a liner under the resin-based composite restoratives increase the flexural strength.

Compomers↗

PubMed1992

Additional mechanical tests of bone cements.

A revision of the ISO-standard for bone cement testing has been proposed to include compressive strength after 24 hours in air and 4-point bending testing after 50 hours in a 37 degrees water bath. Nine commercially available bone cements were tested in accordance with the new program. Compressive strength varied from 78 to 100 MPa, bending strength from 48 to 74 MPa and bending modulus from 2.2 to 2.8 GPa. The highest strengths, but also the highest stiffness, were encountered with Simplex brands and low-viscosity cements.

Acrylic Resins↗

PubMed1990

Prostheses designed for vertebral body replacement.

Prostheses are proposed to restore the spinal stability of patients suffering from metastatic malignant tumours in their vertebral bodies. They are designed to replace only one vertebral body and two neighbouring intervertebral discs of the spine. Experiments performed on cervical, thoracic and lumbar sections, which were obtained from fresh cadavers, have shown that the reduction in average compressive strengths of these regions due to the placement of prostheses is about 9%. This seems acceptable for those patients in performing their daily activities. The same amount of reduction has also been observed in average compressive strengths of the neighbouring healthy vertebrae due to the placement of prosthesis heads by bone cement. Developed prostheses have a number of advantages over the existing fusion constructs for the cases considered in this work.

Biomechanical Phenomena↗

PubMed1991

Tissue reaction to collagen-coated porous hydroxyapatite.

To give tenacity to high porosity (80%-90%) hydroxyapatite (HA) and to make a stronger bone substitute, a collagen-coated porous HA (C-HA) was prepared, and its compressive strength was examined. By implanting C-HA into the femoral condyle of adult rabbits, the capacity for new bone formation and foreign-body reactivity were quantitatively compared with those of HA alone. The compressive strength of C-HA was 4.3 times greater than HA. At four weeks after implantation, the mean areal ratio of the newly formed bone in the C-HA block in each rabbit was 9.9%, which was somewhat less than the 13.7% in the HA block; the mean number of multinucleated giant cells (MGC) per visual field at x25 in the C-HA-implanted specimens in each rabbit was 14.4, significantly larger than the 6.1 in the HA specimens. However, 12 weeks after C-HA implantation, the areal ratio of new bone increased to 32.7%, the number of MGC decreased to 9.4, and the differences compared to the values in HA cases, 31.5% and 6.8, disappeared. These results showed that C-HA is mechanically stronger than HA and that there is no difference between HA and C-HA in capacity for new bone formation or foreign-body reaction.

Animals↗

PubMed2000

Injectable biodegradable polymer composites based on poly(propylene fumarate) crosslinked with poly(ethylene glycol)-dimethacrylate.

New injectable, in situ crosslinkable biodegradable polymer composites were investigated consisting of poly(propylene fumarate) (PPF), poly(ethylene glycol)-dimethacrylate (PEG-DMA), and beta-tricalcium phosphate (beta-TCP). We examined the effects of the PEG-DMA/PPF double-bond ratio and beta-TCP content on the crosslinking characteristics of the composites including the maximum crosslinking temperature and the gel point, as well as the properties of the crosslinked composites such as the compressive strength and modulus, and the water-holding capacity. The maximum crosslinking temperature was constant averaging 39.7 degrees C for the composite formulations tested. The gel points varied from 8.0 +/- 1.0 to 12.6 +/- 2.5 min and were not affected by the relative amounts of PEG-DMA. The compressive strength at yield of PEG-DMA/PPF composites without beta-TCP increased from 5.9 +/- 1.0 to 11.2 +/- 2.2 MPa as the double-bond ratio of PEG-DMA/PPF increased from 0.38 to 1.88. An increase in compressive modulus was also observed from 30.2 +/- 3.5 to 58.4 +/- 6.2 MPa for the same range of the PEG-DMA/PPF double-bond ratio. Also, the addition of beta-TCP (33 wt%) enhanced the mechanical properties of all composites. The equilibrium water content of networks without beta-TCP increased from 21.7 +/- 0.2 to 30.6 +/- 0.2% for a double-bond ratio of PEG-DMA/PPF ranging from 0.38 to 1.88. However, the mechanical properties of the swollen composites under compression were smaller than the dry ones. These data demonstrate the feasibility of fabricating injectable biodegradable polymer composites with engineered mechanical properties for orthopedic tissue engineering.

Acrylates↗

PubMed1998

Influence of alkali metal ions on the fracture properties of glass polyalkenoate (ionomer) cements.

The influence of substituting sodium for calcium on the properties of glass polyalkenoate cements was investigated. Two series of glass compositions based on PSiO2 x QAl2O3 x 0.75P2O5 x (1 - Z)CaO x XCaF2ZNa2O were studied. The fluorine content was fixed at X = 0.50 and 0.75 and the sodium content varied by altering Z. The glass polyalkenoate cements formed from these glasses were characterized using a linear elastic fracture mechanics (LEFM) approach. In addition, compressive strengths of the cements were determined. The properties of the cements based on the high fluorine content glasses (X = 0.75) were relatively insensitive to sodium content. The Young's modulus, un-notched fracture strength and fracture toughness of the cements produced with the lower fluorine content glasses (X = 0.5) reduced with sodium content, which was consistent with sodium acting to disrupt ionic cross-linking in the polyacrylate matrix. The compressive strength was not as dependent on sodium content as the LEFM parameters.

Biocompatible Materials↗

PubMed1998

Studies in the setting of polyelectrolyte cements: part VII. The effect of divalent metal chlorides on the properties of zinc polycarboxylate and glass-ionomer dental cements.

A study is reported in which a zinc polycarboxylate and a glass polyalkenoate dental cement, were prepared from aqueous solutions of divalent metal chlorides, namely ZnCl2, CaCl2, MgCl2 and SrCl2, all at 1.0 mol dm-3 concentration, as well as from pure water. Calcium chloride was employed at additional concentrations, i.e. 2.0, 0.5 and 0.1 mol dm-3. As was previously found for monovalent salts, setting of the zinc polycarboxylate was speeded up and water uptake generally enhanced by the presence of the divalent metal salts. However, the divalent salts were found to reduce the compressive strength at 24 h (from 86 MPa to about 60 MPa). The glass polyalkenoate showed broadly similar effects to those observed in the presence of monovalent salts, with the setting time being increased, water uptake inhibited and compressive strength at 24 h reduced; however, by contrast, the working time was generally reduced. These results occur because the rate of the neutralization process is increased by the divalent salts, a consequence of the reduced pH of the poly(acrylic acid) caused by these salts. Infrared spectroscopy demonstrated interactions between the metal chlorides and poly(acrylic acid), with various chelate structures being apparent from the position of the asymmetric carbonyl stretch.

Journal Article↗

PubMed2001

Evaluation of porous ceramic as microbial carrier of biofilter to remove toluene vapor.

Three kinds of porous ceramic microbe media are fabricated from fly ash, diatomite and a mixture of fly ash and diatomite powders. Water holding capacity, density, porosity, pore size and distribution, compressive strength and micro-structure of each of the fabricated media are measured and compared. The fly ash and diatomite mixture ceramic is evaluated as the best biofilter medium among the three media because of its high compressive strength. It is selected as an experimental biofilter medium inoculated with thickened activated sludge. The laboratory scale biofilter was operated for 42 days under various experimental conditions varying in inlet toluene concentration and flow rate of contaminated air stream. The experimental result shows that the removal efficiency reaches up to 96.6% after 4 days from the start-up. Nutrient limitation is considered as a major factor limiting biofilter efficiency. Biofilter efficiency decreases substantially at the build-up of backpressure, which is largely due to the accumulation of excess VSS within the media. Periodic backwashing of the biofilter is necessary to remove excess biomass and attain stable long-term high removal efficiency. The bed needs to be backwashed when the overall pressure drop becomes greater than 460.6 Pa at space velocity of 100 h-1. A maximum flow rate of 444.85 g m-3hr-1 of toluene elimination by the mixture ceramic biofilter, which is higher than the previously reported values. This indicates that the fly ash and diatomite mixture ceramic biofilter can be effectively applied for removing toluene vapor.

Air Pollutants↗

PubMed1994

Neutron attenuation characteristics of polyethylene, polyvinyl chloride, and heavy aggregate concrete and mortars.

Polyethylene and polyvinyl chloride pellets were introduced into concrete to improve its neutron attenuation characteristics while several types of heavy coarse aggregates were used to improve its gamma ray attenuation properties. Neutron and gamma ray attenuation were studied in concrete samples containing coarse aggregates of barite, pyrite, basalt, hematite, and marble as well as polyethylene and polyvinyl chloride pellets in narrow-beam geometry. The highest neutron attenuation was shown by polyethylene mortar, followed by polyvinyl chloride mortar; barite and pyrite concrete showed higher gamma ray attenuation than ordinary concrete. Broad-beam and continuous (infinite) medium geometries were used to study the neutron attenuation of samples containing polymers at different concentrations with and without heavy aggregates, the fitting equations were established, and from these the neutron removal coefficients were deduced. In a radiation field of neutrons and gamma rays, the appropriate concentration of polymer and heavy aggregate can be selected to give the optimum total dose attenuation depending on the relative intensities of each type of radiation. This would give much better design flexibility over ordinary concrete. The compressive strength tests performed on mortar and concrete samples showed that their value, in general, decreases as polymer concentration increases and that the polyvinyl chloride mortar showed higher values than the polyethylene mortar. For general construction purposes, the compression strength was considered acceptable in these samples.

Construction Materials↗

PubMed1982

Microstructure and strength properties of silicate and glass ionomer cements.

Microstructure characterization of silicate and glass ionomer cements has been carried out using, SEM, EDAX and ion microprobe techniques. The distribution of aluminum, calcium, fluorine, phosphorus or silicon was measured in the set cement surfaces. Cracks in the cement specimens produced by mechanical breaking, in contraction during setting, or as a result of SEM preparation were observed to occur mainly in the matrix and in the interface between matrix and particle. Powders of silicate and glass ionomer cements were separated into various fractions using sieves or cyclone separation technique. Compressive strength measurements of specimens made of powders with various size distributions have been assessed. The fractionation did not reveal any strong effect on the compressive strength properties either for the silicate or the glass ionomer cement.

Chemical Phenomena↗