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Results for “Compressive Strength”

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PubMed2003

The physical properties of conventional and resin-modified glass-ionomer dental cements stored in saliva, proprietary acidic beverages, saline and water.

Specimens of three conventional and one resin-modified glass-ionomer cement were prepared for both compressive strength and biaxial flexure strength determination. They were stored either in neutral media (water, saline, unstimulated whole saliva or stimulated parotid saliva) or in acidic beverages (apple juice, orange juice or Coca-Cola) for time periods ranging from 1 day to 1 year. In neutral media, the compressive and biaxial flexural strengths of all cements studied showed similar results, with significant increases apparent in compressive strengths at 6 months and which continued to 1 year, but no significant differences between the media; and no significant differences with time for biaxial flexure strength in all media. These findings show that interactions of these cements with saliva, which are known to result in deposition of calcium and phosphate, do not affect strength. Results for specimens stored in Coca-Cola were the same as for those stored in neutral media. By contrast, in orange and apple juice specimens underwent severe erosion resulting in dissolution of the conventional glass-ionomers after 3-6 months, and/or significant loss of strength at 1-3 months. Erosion of the resin-modified glass-ionomer, Vitremer, led to a significant reduction in strength, but not in dissolution, even after 12 months. The chelating carboxylic acids in these fruit juices were assumed to be responsible for these effects.

Beverages↗

PubMed2004

Industrial sludge solidification by using clinoptilolite.

The sludge from metal plating industry is generally considered as "hazardous waste" due to its toxic heavy metal content. Solidification/stabilization techniques which are applied as prior to landfill give good results for the disposal of especially inorganic sludges into the landfill in a safe manner. The research is aimed to investigate an effective and low cost solidification technique for the sludge of a metal plating factory by using different particle sizes of clinoptilolite. Clinoptilolite is a kind of natural zeolite and it was used due to its good pozzolanic characteristic and its abundant reserves in Turkey. According to the results, clinoptilolite was found as a successful solidification additive yielding products with high unconfined compressive strength and low leaching.

Compressive Strength↗

PubMed2006

The biomechanical evaluation of calcium phosphate cements for use in vertebroplasty.

OBJECT: The authors evaluate the biomechanical properties of vertebral bodies (VBs) stabilized with calcium phosphate (CaP) cements for use in vertebroplasty in comparison with polymethylmethacrylate (PMMA). METHODS: In the first phase of the study, 73 VBs (T3-L2; thoracic region [T3-8] and thoracolumbar region [T9-L2]) were collected from seven fresh human cadavers. Compression tests were performed before and after vertebroplasty using PMMA (compression strength 80 MPa) and three kinds of CaP cements-CaP1 (5 MPa), CaP2 (20 MPa), and CaP3 (50 MPa). The authors compared the maximal compression loads (MCLs) and stiffness before and after vertebroplasty in each of the four cement groups. In the second phase of the study, 18 paired spinal units (PSUs) were collected from three fresh human cadavers, and the authors injected two types of cement selected from the first phase of the study into the lower level of six PSUs. They compared the MCLs of the untreated and two treated groups (there were six PSUs in each type of group) to analyze the tendency of inducing compression fractures in the upper level of the PSUs. The MCLs of the PMMA-injected vertebrae were significantly increased after vertebroplasty. The MCL levels of the CaP3-injected vertebrae and the CaP2-injected thoracolumbar vertebrae were decreased from those of untreated vertebrae without being significant. The MCLs of CaP1-injected vertebrae and CaP2-injected thoracic vertebrae were significantly decreased after vertebroplasty. The stiffness of all cement groups was decreased after vertebroplasty compared with initial stiffness, significantly so in all three thoracic CaP groups. In the second compression test with PSUs, the MCLs of the CaP2- and CaP3-injected PSUs were not significantly different from those of the untreated control PSUs. CONCLUSIONS: The CaP3-injected vertebrae restored the MCLs of human vertebrae closer to their initial levels than the PMMA-injected vertebrae did. The CaP2- and CaP3-injected PSUs showed no tendency to induce compression fractures in adjacent VBs.

Aged↗

PubMed1998

Anterior vertebral body screw pullout testing. A comparison of Zeilke, Kaneda, Universal Spine System, and Universal Spine System with pullout-resistant nut.

STUDY DESIGN: A biomechanical study of pullout of anteriorly implanted screws in cadaveric vertebral bodies. OBJECTIVES: To investigate and compare the pullout strength of the Zielke, Kaneda, Universal Spine System (USS) pedicle screw, and USS pedicle screw with a new pullout-resistant nut. SUMMARY OF BACKGROUND DATA: A common problem with anterior purchase regardless of the implant system is screw pullout at the proximal and distal ends of multilevel constructs. There is limited information on a solution to this problem. METHODS: The L1 to L4 vertebral bodies from four cadavers had one each of Zielke and Kaneda pedicle screws (Acromed Corp., Cleveland, OH), USS pedicle screw (Synthes Spine, Paoli, PA), and USS pedicle screw with pullout-resistant nut implanted transversely across the center of the vertebral body with bicortical purchase in a similar fashion as would be used clinically. The screws were extracted using a servohydraulic material testing system. The maximum axial forces were recorded. RESULTS: The Zielke and Kaneda screws had no significant difference in mean pullout strength (P = 0.542). The USS screw alone was less strong (P = 0.009). The USS screw and pullout-resistant nut increased the pullout strength by twofold (P = 0.00006). In the screw pullout tests, the mode of failure was at the screw thread's interface. The USS screw and pullout-resistant nut failed by imploding the body around the nut. With the USS screw and pullout-resistant nut, the pullout strength was determined by the compressive strength of the bone. CONCLUSIONS: The addition of a pullout-resistant nut to an anterior vertebral body screw improves the pullout strength by twofold and changes the mode of failure to rely ultimately on the inherent vertebral body strength rather than the screw's characteristics. The addition of a pullout-resistant nut may be applicable to multilevel implant constructs to prevent screw pullout at the top and bottom.

Biomechanical Phenomena↗

PubMed1980

The shear strength of dental porcelain.

The widespread use of porcelain in restorative dentistry is generally due to its esthetic appearance even though it is brittle. The transverse strength, or modulus rupture, averages around 108 MPa (16,000 psi) for aluminous porcelain and 88 MPa (13,000 psi) for feldspathic porcelain. The tensile strength, as determined by diametral compression, is approximately 29 MPa (4,200 psi) for opaque feldspathic porcelain and 40 MPa (5,800 psi) for gingival feldspathic porcelain. The compressive strength is reported to be 340 MPa (50,000 psi) for a feldspathic porcelain. These mechanical strength properties of dental porcelain confine its use to low stress-bearing restorations or to those restorations with a metal substrate.

Aluminum↗

PubMed1996

Preparation of glass ionomer cement using N-acryloyl-substituted amino acid monomers--evaluation of physical properties.

OBJECTIVES: The objectives of this study were (1) to develop polyacid formulations through the incorporation of amino acid-derived monomers with carboxylic acid groups at various distances away from the polymer backbone to allow for greater flexibility, less rigid ionic cluster formation and improved solubility, and (2) to test selected physical and handling properties of experimental ionomers with a conventional glass ionomer as a control. METHODS: The polycarboxylic acids prepared and used in glass ionomer formulation in this study included N-acryloylglutamic acid (AGA) and N-acryloyl-6-aminocaproic acid (AACA)- modified acrylic acid- ++itaconic acid copolymers, where the acrylic acid:itaconic acid:amino acid monomers were combined in different proportions. The characterization and purity of the monomers were determined by FTIR and their melting points. The characterization of synthesized polymers included molecular weight and relative viscosity determinations. The compressive strengths, diametral tensile strengths, flexural strengths and fracture toughness of the experimental ionomers and a commercially available ionomer (control) were measured after storage in water, at 37 degrees C for 1 h or 7 d. The working times and setting times of the experimental ionomers were compared to the control specimens. Separate analysis of variance and Tukey's tests were used to study the statistical significance of the physical strength parameters as a function of materials and storage times. RESULTS: Significant increases (p< 0.001) in diametral tensile, compressive, flexural strengths and fracture toughness were observed in the AGA co-polymers, while significant increases were observed in diametral and flexural strengths in the AACA co-polymers compared to the control Fuji II. The working and setting times of all except one experimental ionomer studied were comparable to the controls. SIGNIFICANCE: The use of amino acid-modified acrylic monomers to produce water soluble copolymers of acrylic-itaconic acid offers a new route of discovery to produce chemical-cured glass ionomers with improved physical properties. The spacer chain length, the hydrophobicity of the chains, the molecular weight and viscosity of the polymer all played important roles in determining the physical properties of the material.

Acrylates↗

PubMed1998

Effect of initiator concentration, exposure time and particle size of the filler upon the mechanical properties of a light-curing radiopaque dental composite.

Concentration of camphorquinone initiator, exposure time of the light source and particle size of a radiopaque glass filler have been varied for an indigenously developed light-curing dental composite and the changes in the microhardness, compressive strength and diametral tensile strength studied. Higher initiator concentration and exposure times are found to improve the microhardness values while a concentration above 0.25% does not signify any drastic improvement in compressive and diametral strength. Changes in properties are found to be statistically significant at low initiator concentrations. A filler particle size around 1 microm is found to give better properties compared with larger sizes.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1999

Strength and microstructure of gallium alloys.

This study investigated the physical and mechanical properties and the microstructure of four different gallium alloys. For all gallium alloys, the compressive strengths measured at one hour (86-223 MPa) and 24 hours (265-286 MPa) after specimen preparation were found to be well within the range exhibited by many high-copper amalgams. The creep values and dimensional change of the gallium alloys were comparable to those of leading amalgams, except for the dimensional change value of one alloy. The set gallium alloys consisted of a multi-phase structure including beta-Sn, CuGa2, In4Ag9, Ag72Ga28, and Ga5Pd (except for one product that did not contain Pd) that was more complicated than the structure of dental amalgams. Although the gallium alloys had physical and mechanical properties comparable to those of high-copper amalgams, the microstructure, coupled with the instability of the element gallium itself, could make these materials more prone to corrosive attack compared to amalgams.

Analysis of Variance↗

PubMed2005

Predicting the compressibility behaviour of tire shred samples for landfill applications.

Tire shreds have been used as an alternative to crushed stones (gravel) as drainage media in landfill leachate collection systems. The highly compressible nature of tire shreds (25-47% axial strain on vertical stress applications of 20-700 kPa) may reduce the thickness of the tire shred drainage layer to less than 300 mm (minimum design requirement) during the life of the municipal solid waste landfill. There hence exists a need to predict axial strains of tire shred samples in response to vertical stress applications so that the initial thickness of the tire shred drainage layer can be corrected for compression. The present study performs one-dimensional compressibility tests on four tire shred samples and compares the results with stress/strain curves from other studies. The stress/strain curves are developed into charts for choosing the correct initial thickness of tire shred layers that maintain the minimum thickness of 300 mm throughout the life of the landfill. The charts are developed for a range of vertical stresses based on the design height of municipal waste cell and bulk unit weight of municipal waste. Experimental results also showed that despite experiencing large axial strains, the average permeability of the tire shred sample consistently remained two to three orders of magnitude higher than the design performance criterion of 0.01cm/s for landfill drainage layers. Laboratory experiments, however, need to verify whether long-term chemical and bio-chemical reactions between landfill leachate and the tire shred layer will deteriorate their mechanical functions (hydraulic conductivity, compressibility, strength) beyond permissible limits for geotechnical applications.

Compressive Strength↗

PubMed2005

Rheological enhancement of mechanically activated alpha-tricalcium phosphate cements.

Most biocements are two- or three-component acid-based systems with large differences in the component particle sizes, which occurs by virtue of the differing processing routes. This work aimed to improve injectability and strength of a single reactive component cement, that is, mechanically activated alpha-tricalcium phosphate (TCP)-based cement by adding 13-33 wt % of several fine-particle-sized (d(50) of 0.5-1.1 microm) fillers [dicalcium phosphate anhydrous (DCPA), titanium dioxide (TiO(2)), and calcium carbonate] to the monomodal alpha-TCP matrix (d(50) = 9.8 microm). A high zeta-potential was measured for all particles in trisodium citrate solution. The fraction of alpha-TCP cement "injected" through an 800-microm hypodermic needle was found to be only 35% at a powder-to-liquid ratio of 3.5 g/mL. In contrast, the use of fillers decreased cement viscosity to a point, where complete injectability could be obtained. Mechanistically, these additives disrupted alpha-TCP particle packing yet decreased the interparticle spacing by a factor of approximately 5.5 such that the electrostatic repulsion effect was enhanced. A strength improvement was found when DCPA and TiO(2) were used as fillers despite the lower degree of conversion of these cements. Compressive strengths of precompacted cement samples increased from 70 MPa for unfilled alpha-TCP cement to 140 (110) MPa for 23 wt % DCPA (or TiO(2)) fillers as a result of porosity reduction. Strength improvement for more clinically relevant uncompacted cements was achieved by higher powder-to-liquid ratio mixes for filled cements such that maximum strengths of 90 MPa were obtained for 23 wt % DCPA filler compared with 50 MPa for single-component alpha-TCP cement.

Biocompatible Materials↗

PubMed2006

Evaluation of concrete incorporating bottom ash as a natural aggregates replacement.

A study on the incorporation of coal bottom ash from thermoelectric power stations as a substitute material for natural sand in the production of concrete is here presented. The normally coarse, fused, glassy texture of bottom ash makes it an ideal substitute for natural aggregates. The use of bottom ash in concrete presents several technical challenges: the physical and mineralogical characteristics of the bottom ash; the effect on water demand and the participation on cements hydratation. In the production of the concrete, substitutions in volume were used. Two different ways to employ bottom ash were used to make up the mix proportions: one considering the natural humidity present in the porous particles and the other not considering it, seeking to maintain the same strength. These considerations are fundamental given that the process of bottom ash extraction is carried out through moisture. Mechanical tests by compressive strength were performed and the elastic modulus was determined. An analysis of the influence of bottom ash in the formation of pores was carried out through tests for the water loss by air drying and water uptake by capillary absorption. The results show that the higher the bottom ash contents in the concrete, the worse the performance regarding moisture transport. However, for one bottom ash concrete type, the mechanical properties were maintained.

Adsorption↗

PubMedDate not supplied

A study of the physical and chemical properties of four resin composite luting cements.

PURPOSE: This study evaluated the surface microhardness and flexural and compressive strengths of five luting cements and compared the degree of conversion of dual and autopolymerized forms of four resin-based luting cements. MATERIALS AND METHODS: Four resin composite luting cements-Panavia F, Variolink 2, RelyX Unicem Applicap, and RelyX ARC-and a polycarboxylate cement (Durelon, control group) were used in three-point bending, compression, and Vickers hardness tests following water storage for 1 week. Resin composite cements were additionally investigated with both dual and autopolymerization techniques under Fourier transformed infrared spectroscopy. Differences were analyzed using one-way ANOVA. RESULTS: The highest flexural strengths were obtained with Variolink 2 (90 MPa, SD 22), whereas the lowest were observed with Durelon (28 MPa, SD 4). RelyX Unicem showed the highest hardness values (44 HV, SD 5), whereas Variolink 2 gave the lowest (32 HV, SD 6). The highest compressive strengths were obtained with RelyX Unicem (145 MPa, SD 32), whereas the lowest were observed with Durelon (41 MPa, SD 17). For both dual and autopolymerized groups, RelyX ARC showed the highest degrees of conversion (81% and 61%, respectively) and RelyX Unicem had the lowest (56% and 26%, respectively). CONCLUSION: Resin composite luting cements of similar chemical characterizations differed in their physical properties, and polymerization method influenced their degree of conversion.

Analysis of Variance↗

PubMed2003

Mechanical evaluation of novel spinal interbody fusion cages made of bioactive, resorbable composites.

Osteoconductive and totally bioresorbable spinal/cervical interbody fusion cages were fabricated from a forged composite of raw particulate hydroxyapatite/poly L-lactide (u-HA/PLLA) with an u-HA 40wt% fraction (F-u-HA 40). The mechanical strengths of three types of cages, designed for open-box, screw and cylinder constructs, were compared with those of existing metal and carbon-fiber/polymer cages. Compressive strengths of these composite cages surpassed those of existing metal and carbon-fiber cages. Fatigue resistance to alternate and static compressive loading persisted for longer than the minimum period (6 months) necessary for spinal devices in simulated body fluid (SBF) at 37 degrees C. These novel interbody fusion cages await clinical application in humans.

Absorbable Implants↗

PubMed2006

Precooling of the femoral canal enhances shear strength at the cement-prosthesis interface and reduces the polymerization temperature.

Preheating of the femoral stem in total hip arthroplasty improves the cement-prosthesis bond by decreasing the interfacial porosity. The main concern, however, is the potential thermal osteonecrosis because of an increased polymerization temperature. In this study, the effects of femoral canal precooling on the characteristics of the cement-stem interface were evaluated in an experimental model for three test conditions: precooling of the femoral canal, preheating of the stem (44 degrees C), and a control in which stems were inserted at room temperature without thermal manipulation of the implant, cement, or bone. Compared to the control group, precooling of the femoral canal and preheating of the stem had similar effects on the cement-stem interface, with greater interfacial shear strength and a reduced porosity. Femoral canal precooling also produced a lower temperature at the cement-bone interface. No difference was found in the ultimate compressive strength of bone cement for the three preparation conditions. Based on this laboratory model, precooling of the femoral canal could improve shear strength and porosity at the stem-cement interface, minimize thermal injury, and maintain the mechanical strength of the cement.

Arthroplasty, Replacement, Hip↗

PubMed2004

A water setting tetracalcium phosphate-dicalcium phosphate dihydrate cement.

The development of a calcium phosphate cement, comprising tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD), that hardens in 14 min with water as the liquid or 6 min with a 0.25 mol/L sodium phosphate solution as the liquid, without using hydroxyapatite (HA) seeds as setting accelerator, is reported. It was postulated that reduction in porosity would increase cement strength. Thus, the effects of applied pressure during the initial stages of the cement setting reaction on cement strength and porosity were studied. The cement powder comprised an equimolar mixture of TTCP and DCPD (median particle sizes 17 and 1.7 microm, respectively). Compressive strengths (CS) of samples prepared with distilled water were 47.6 +/- 2.4 MPa, 50.7 +/- 4.2 MPa, and 52.9 +/- 4.7 MPa at applied pressures of 5 MPa, 15 MPa, and 25 MPa, respectively. When phosphate solution was used, the CS values obtained were 41.5 +/- 2.3 MPa, 37.9 +/- 1.7 MPa, and 38.1 +/- 2.3 MPa at the same pressure levels. Statistical analysis of the results showed that pressure produced an improvement in CS when water was used as liquid but not when the phosphate solution was used. Compared to previously reported TTCP-DCPD cements, the greater CS values and shorter setting times together with a simplified formulation should make the present TTCP-DCPD cement a useful material as a bone substitute for clinical applications.

Adhesives↗

PubMed1997

Effect of mixing method on selected properties of acrylic bone cement.

The present study was an investigation of the effect of the method of mixing the constituents of CMW3 bone cement on selected physical and mechanical properties of the fully polymerized cement. Five such methods were used: hand mixing; "active" vacuum mixing; mixing in a machine that allowed simultaneous mechanical mixing and centrifugation; mixing using this machine followed by application of a "passive" vacuum; and application of a passive vacuum followed by mixing in the machine. It was found that the best overall results were obtained from cement that had been mixed using the second and fifth methods and the values of the properties were: density, 1220 to 1246 kg/m3; areal porosity, 0.02 to 7.04%; ultimate compressive strength, 84 to 112 MPa; ultimate compressive strain, 5.1 to 6.4%; and compressive modulus of elasticity, 2249 to 2877 MPa.

Acrylates↗

PubMed2001

Structure, metallurgy, and mechanical properties of a porous tantalum foam.

This study evaluated a porous tantalum biomaterial (Hedrocel) designed to function as a scaffold for osseous ingrowth. Samples were characterized for structure, Vickers microhardness, compressive cantilever bending, and tensile properties, as well as compressive and cantilever bending fatigue. The structure consisted of regularly arranged cells having struts with a vitreous carbon core with layers of CVI deposited crystalline tantalum. Microhardness values ranged from 240-393, compressive strength was 60 +/- 18 MPa, tensile strength was 63 +/- 6 MPa, and bending strength was 110 +/- 14 MPa. The compressive fatigue endurance limit was 23 MPa at 5 x 10(6) cycles with samples exhibiting significant plastic deformation. SEM examination showed cracking at strut junctions 45 degrees to the axis of the applied load. The cantilever bending fatigue endurance limit was 35 MPa at 5 x 10(6) cycles, and SEM examination showed failure due to cracking of the struts on the tension side of the sample. While properties were variable due to morphology, results indicate that the material provides structural support while bone ingrowth is occurring. These findings, coupled with the superior biocompatibility of tantalum, makes the material a candidate for a number of clinical applications and warrants further and continued laboratory and clinical investigation.

Biocompatible Materials↗

PubMed2007

Preparation and characterization of porous PDLLA/HA composite foams by supercritical carbon dioxide technology.

A composite poly(D,L)lactic acid (PDLLA)/hydroxyapatite (HA) biomaterial was prepared by in situ polymerization of D,L-lactide monomer and HA. Supercritical CO2 (SC CO2) technology was developed to prepare the biodegradable composite foams for use in tissue regeneration. In this technology, NaCl particles were used as porogen to produce an open-pore structure. Organic solvents were not used and high temperature was not necessary. The problem with pore interconnectivity was resolved. High-porosity composite foams (up to 90% +/- 2% porosity) were obtained with pore sizes ranging from 100 to 300 microm suitable for cell seeding. The microstructure and morphology of the composite foams could be controlled by saturation pressure, saturation time, and temperature as well as amount of NaCl particles. The compressive strength and water absorbability of the composite foams were also determined. With an increase in HA amount, the molecular weight of PDLLA/HA composite foams decreased, but the mechanical strength and hydrophilicity increased slightly.

Biocompatible Materials↗