SEARCH · PubMed Health

Results for “Compressive Strength”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67Linked to original sources

PubMed2000

Improved orthopaedic bone cement formulations based on rubber toughening.

Poly(methylmethacrylate) (PMMA) bone cements have been used for the fixation of hip and knee implants since the early 1960s. Aseptic loosening, related to fracture of the PMMA, continues to be the primary mode of failure for these prostheses. Failed prostheses must be replaced causing additional expense and patient trauma. Furthermore, the average lifetime of the revised prosthesis is significantly lower than that of a primary prosthesis. Recent work by Moseley and co-workers led to the development of a promising new rubber toughened cement. It is comprised of a matrix of the traditional PMMA with dispersed rubber particles to modify mechanical properties and, in particular, improve fracture toughness. The fracture toughness of the experimental material was 167% greater than the toughness of a nontoughened control; however, the elastic modulus and compressive strength were reduced. The reductions in properties should not pose a clinical problem based on results of the implant model reported by Moseley. More serious concerns were mixing and delivery problems and high residual monomer concentrations. The formulation and chemical/mechanical characterization of new toughened acrylic formulations that have residual monomer levels equivalent to Simplex and better mixing properties are reported.

Bone Cements↗

PubMed2005

Did we push dental ceramics too far? A brief history of ceramic dental implants.

Humankind has developed and used ceramics throughout history. It currently has widespread industrial applications. Dental ceramics are used for fabricating highly esthetic prosthetic denture teeth, crowns, and inlays. However, ceramic's biocompatibility and compressive strength are offset by its hardness and brittleness. Nonetheless, a single crystal sapphire aluminum oxide endosseous implant was developed in 1972 as an alternative to metal. It was more esthetic than its metallic counterparts and was eventually produced in a variety of shapes and sizes. Clinical studies demonstrated its excellent soft and hard tissue biocompatibility, yet the range of problems included fractures during surgery, fractures after loading, mobility, infection, pain, bone loss, and lack of osseointegration. Ultimately, single crystal sapphire implants fell into irredeemable disfavor because of its poor impact strength, and dentists and surgeons eventually turned to other implant materials. However, bioactive ceramic coatings on metal implants have kept ceramics as a key component in dental implantology.

Biocompatible Materials↗

PubMed1998

Biomechanical and histological evaluation of a calcium phosphate cement.

It is often difficult to achieve stable fixation of a comminuted fracture associated with a metaphyseal defect. The injection of a resorbable cement into an osseous defect may help to stabilize the fracture and to maintain osseous integrity as the cement is resorbed and replaced by bone. The purpose of the present study was to evaluate the repair of a metaphyseal defect after treatment with an injectable calcium-phosphate cement. The injectable cement undergoes isothermic curing in vivo to form a carbonated apatite (dahllite) with a compressive strength of twenty-five megapascals. Either the cement or allograft bone was placed in proximal tibial metaphyseal and distal femoral metaphyseal defects in seventy-two dogs and was evaluated from twenty-four hours to seventy-eight weeks postoperatively. Histological examination showed that the cement was osteoconductive; nearly the entire surface area was covered with bone two weeks after the injection. The resulting bone-cement composite underwent gradual remodeling over time in a pattern that was qualitatively similar to the remodeling of normal cortical and cancellous bone. Osteoclasts were found to resorb the cement and were usually associated with adjacent new-bone formation. With increasing time in vivo, the cement was penetrated by small blood vessels that became surrounded by circumferential lamellae of bone and that closely resembled evolving haversian systems. This process occurred more rapidly in the cortex than in the medulla. Mechanical testing showed that, by eight weeks, the tibiae that had been treated with cement had reached nearly 100 per cent of the torsional strength of the contralateral, control (intact) tibiae; this finding paralleled the histological observations of bone apposition to the cement and rapid restoration of the cortex. At no time was fibrous tissue present between the cement and the bone, and there was no evidence of acute inflammation. Small particles of cement were present within occasional macrophages during the process of cement resorption, but the macrophages disappeared over time and were not associated with fibrosis or unexpected resorption of bone. Resorption of the cement was incomplete in the medullary area at seventy-eight weeks, but the pattern of cement resorption and bone-remodeling suggested gradual restoration of a physiological proportion of bone and marrow in both the cortical and the medullary region with maintenance of mechanical function.

Animals↗

PubMed2003

rhBMP-2 release from injectable poly(DL-lactic-co-glycolic acid)/calcium-phosphate cement composites.

BACKGROUND: In bone tissue engineering, poly(DL-lactic-co-glycolic acid) (PLGA) microparticles are frequently used as a delivery vehicle for bioactive molecules. Calcium phosphate cement is an injectable, osteoconductive, and degradable bone cement that sets in situ. The objective of this study was to create an injectable composite based on calcium phosphate cement embedded with PLGA microparticles for sustained delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2). METHODS: (125) I-labeled rhBMP-2 was incorporated in PLGA microparticles. PLGA microparticle/calcium-phosphate cement composites were prepared in a ratio of 30:70 by weight. Material properties were evaluated by scanning electron microscopy, microcomputed tomography, and mechanical testing. Release kinetics of rhBMP-2 from PLGA/calcium-phosphate cement disks and PLGA microparticles alone were determined in vitro in two buffer solutions (pH 7.4 and pH 4.0) for up to twenty-eight days. RESULTS: The entrapment yield of rhBMP-2 in PLGA microparticles was a mean (and standard deviation) of 79% +/- 8%. Analysis showed spherical PLGA microparticles (average size, 17.2 +/-1.3 micro m) distributed homogeneously throughout the nanoporous disks. The average compressive strength was significantly lower (p < 0.001) for PLGA and calcium-phosphate cement composite scaffolds than for calcium-phosphate cement scaffolds alone (6.4 +/- 0.6 MPa compared with 38.6 +/- 2.6 MPa, respectively). Average rhBMP-2 loading was 5.0 +/- 0.4 micro g per 75-mm (3) disk. Release of rhBMP-2 was limited for all formulations. At pH 7.4, 3.1% +/- 0.1% of the rhBMP-2 was released from the PLGA/calcium-phosphate cement disks and 18.0% +/- 1.9% was released from the PLGA microparticles alone after twenty-eight days. At pH 4.0, PLGA/calcium-phosphate cement disks revealed more release of rhBMP-2 than did PLGA microparticles alone (14.5% +/- 6.3% compared with 5.4% +/- 0.7%) by day 28. CONCLUSIONS: These results indicate that preparation of a PLGA/calcium-phosphate cement composite for the delivery of rhBMP-2 is feasible and that the release of rhBMP-2 is dependent on the composite composition and nanostructure as well as the pH of the release medium.

Bone Cements↗

PubMedDate not supplied

Incinerator slag formation and control of excursion temperatures.

An evaluation of slag formation was initiated to reduce incinerator slag. A factorial test was used to determine the effect of polymers, primary/secondary sludge ratio, and dewatering equipment on ash fusion temperatures (ASTM D-1857). None of the parameters affected the initial deformation or softening temperatures, 1141 and 1181 degrees C, respectively. Incinerators experience slag formation several hundred degrees lower than the measured ash fusion temperature test results. A new test was developed to determine ash fusion temperature. More than seventy 5-cm ash cubes were formed and heated in sets to temperatures of 816, 871, 899, 927, 954, 982, 1038, and 1093 degrees C. The compressive strength of each cube was measured to determine at what temperature fusion begins. A water spray system was built to control excursion temperatures and slag formation. Supplemental water for cooling excursion temperatures requires approximately 4 times less mass than air. Water injected to the incinerator condenses in the wet scrubber, therefore, there is no additional mass load to the incinerator fan. This process study defined the effect of temperature on slag formation.

Incineration↗

PubMed2002

Synthesis of organic-inorganic hybrid fillers at the molecular level and their application to composite resin.

The objective of this study was to synthesize a hybrid type filler composed of an organic component with inorganic component at the molecular level and to examine the properties of the filler. The composite resin was prepared by mixing synthesized filler with monomer and its physical properties were also examined. An organic-inorganic hybrid filler was synthesized by using 3-methacryloxypropyltrimethoxysilane (3-MPTS), methyltriethyoxysilane (MTES) and methanol silica sol. Firstly, poly3-methacryloxypropyltrimethoxysilane (poly3-MPTS) was synthesized by polymerization of 3-MPTS. A gelation product was obtained by graft-polymerization of poly3-MPTS with condensed organopolysiloxane after the hydrolysis of 3-MPTS, MTES and methanol silica sol. The gelation product was dried and ground to a filler. From the results of thermogravimetry-differential thermal analysis (TG-DTA), the organic-inorganic hybrid filler was found to be composed of 16.5 wt% organic component, 83.1 wt% inorganic component and 0.4 wt% residual water. A trial composite resin was prepared by mixing 55 wt% dimethacryloxyethyl 2,2,4-trimethylhexamethylene diurethane (UDMA), 15 wt% triethyleneglycol dimethacrylate (TEGDMA), 30 wt% 1-fluoro-1,3,3,5,5-penta (methacryloxyethyleneoxy) cyclotriphosphazene [P3N3(F)1 (EMA)5] as a base monomer and then 32.0 wt% of this monomer was mixed with 68.0 wt % of synthesized filler and a photo initiator, comphorquinone (CQ), was added. Compressive strength of the trial visible-light cured composite resin showed 397.0 MPa, and flexural strength and elastic modulus showed 142.5 MPa and 11.5 GPa, respectively. From the results, it was demonstrated that the present organic-inorganic hybrid filler at the molecular level can be used as a composite resin filler.

Composite Resins↗

PubMed1978

Stress/strain behavior of some dental luting cements.

The compressive strength, modulus of elasticity and the plastic strain at fracture have been studied for several dental luting cements. Stress/strain diagrams of cylindrical specimens using two different crosshead speeds (2 mm/min and 0.1 mm/min) at 23 degrees and 37 degrees C showed that large differences existed between various luting cements. A zinc phosphate cement exihibited high strength, high modulus of elasticity and a small plastic strain at fracture. A resin cement also had high strength, but elastic and plastic strains were high. A polycarboxylate and an EBA-cement both showed low values of strength and modulus of elasticity combined with a high degree of plastic deformation at fracture. Testing with low strain rate at 37 degrees C accentuated the differences between these two materials and the zinc phosphate cement.

Composite Resins↗

PubMed1980

Properties of amalgams made from lathe-cut, high Cu amalgam alloys.

Two alloys for dental amalgams made from lathe-cut powder with high Cu content have been developed. The alloys have been characterized with respect to physical properties and microstructure. The strongest amalgam exhibited minimal dimensional changes during setting and had low flow and creep values. It had the highest Cu content of the two amalgams investigated and no gamma 2 phase. The epsilon and eta' phases may dispersion-strenthen the amalgam which in compressive strength was comparable to the strongest amalgams available. A new mechanism for gamma 2 disappearance is suggested where Cu replaces Hg directly in the gamma 2 phase thus forming the eta' phase.

Copper↗

PubMed1995

Dual-cure resin cements: in vitro wear and effect of quantity of remaining double bonds, filler volume, and light curing.

The present study measured in vitro occlusal wear, quantity of remaining double bonds, and volumetric filler content of eight dual-cure resin cements. Furthermore, the effect of light curing on wear and quantity of remaining double bonds was evaluated. The filler content varied between 31 vol% and 66 vol%. In vitro wear varied between 30 microns and 65 microns, and quantity of remaining double bonds between 19% and 38% when resin cements had been both chemically cured and light cured. When light curing had been omitted, wear varied between 36 microns and 74 microns, and quantity of remaining double bonds between 25% and 56%. One resin cement did not harden when not cured by light. Light curing improved the wear resistance of three resin cements by up to 44% and reduced the quantity of remaining double bonds of six cements by up to 36%. A three-dimensional regression analysis found wear to decrease with decreasing quantity of remaining double bonds and increasing volumetric filler content. A negative correlation was shown between compressive strength and wear.

Acrylic Resins↗

PubMed1998

Agreement between radiographic and photographic trabecular patterns.

PURPOSE: It has been hypothesized that photographs can facilitate the interpretation of the radiographic characteristics of trabecular bone. The reliability of these photographic and radiographic approaches has been determined, as have various agreements between the two approaches and their correlations with biomechanical characteristics. MATERIAL AND METHODS: Fourteen vertebral bodies were obtained at autopsy from 6 women and 8 men aged 22-76 years. Photographs (n = 28) and radiographs (n = 28) were taken of midsagittal slices from the third lumbar vertebra. The radiographs and photographs were digitized and the geometric properties of the trabecular architecture were then determined with a digital image analysis technique. Information on the compressive strength and ash density of the vertebral body was also available. RESULTS: The geometric properties of both radiographs and photographs could be measured with a high degree of reliability (Cronbach's alpha > 0.85). Agreement between the radiographic and photographic approaches was mediocre as only the radiographic measurements showed significant correlations (p < 0.05) with the biomechanical characteristics. We suggest that optical phenomena may result in the insignificant correlations between the photographs and the biomechanical characteristics. CONCLUSION: For digital image processing, radiography offers a superior description of the architecture of trabecular bone to that offered by photography.

Adult↗

PubMed1980

Dual photon absorptiometry in lumbar vertebrae. Evaluation of the baseline error.

In connection with determination of the bone mineral content in the third lumbar vertebra by dual photon absorptiometry, the fat in the adipose capsules of the kidneys is assumed to cause erroneous positioning of the baseline, leading to overestimation of the bone mineral content. The bone mineral content in L3 was measured in situ (BMC1) and vitro (BMC2) in 14 cadavers. The difference between BMC1 and BMC2 was significantly greater than zero, the median value being 0.32 g/cm at the confidence level of 94.4 per cent. It is concluded that at correlation between bone mineral content and compressive strength in vitro, the in vivo strength is overestimated by about 250 N.

Absorption↗

PubMed1977

Mechanical property changes of barium titanate (ceramic) after in vivo and in vitro aging.

Since barium titanate (BaTi03) can be made piezoelectric, it may be used to substitute hard tissues directly. As a first step in testing this concept, a series of in vivo and in vitro aging and biocompatibility studies were performed. The mean compressive strength of samples implanted subcutaneously in the backs of rabbits decreased to 138 MPa after 20 weeks from a control value of 281 MPa. Similar, though less drastic losses of strength were seen when specimens were aged in distilled water (182 MPa at 28 weeks) and Ringer's solution (159 MPa at 28 weeks). The most rapid decrease of strength in all cases was seen prior to 4 weeks. Thereafter, the decrease was much slower. Histological evaluation of the tissue surrounding the implant revealed a thin fibrous capsule and no evidence of tissue inflammation.

Animals↗

PubMed1978

Structural role of bone apatite in human femoral compacta.

Tensile and compressive strength of human femoral compacta have been shown to be related (P is greater than 0.005) to the average bone apatite crystallite length (D002) as determined by X-ray diffraction line breadth measurement. However, statistical variance of crystallite length was not sufficient to explain observed differences in mechanical properties, these differences being primarily due to variation in mineral density. Average bone apatite crystallite length was not found to change significantly with biological age (P=0.30) over the range 3 1/2 to 87 years. It is concluded that increased bone apatite crystallite length is detrimental to the structural role of the skeleton but that this is not a major factor in determining fracture incidence in the elderly.

Adolescent↗

PubMed1982

Zn and Cu content in human cancellous bone.

Duplicate cancellous bone samples from the iliac crest were obtained from autopsies of 88 persons with a normal mineral status and 50 having osteoporotic change due to chronic immobilizing diseases. The following parameters were determined: the minimal density with gamma-ray attenuation, the compressive strength with a strain transducer, the concentrations of Ca, Mg, Cd, Co, Cu, Mn, Ni, Li, Pb, Sr and Zn with an atomic absorption spectrophotometer and the concentration of F with an ion-selective electrode. The data were analyzed with linear multiple regression analysis. Altogether 34.8 per cent of the Zn concentration was accounted for in all the variables. The selected variables, after the nonsignificant and those with very low explanatory power were removed, explained 38.3 per cent. The two most important variables were the F concentration (16.1 per cent) and Cu concentration (13.7 per cent). The third variable was Mn concentration (8.5 per cent). All variables explained 41.7 per cent of the Cu concentration and five selected variables 40.7 per cent, respectively. The concentration of Zn explained itself as much (20.1 per cent) as four other variables (Ca 7.7 pe cent, Mn 5.9 per cent, Sr 3.9 per cent and Co 3.2 per cent) together. Age and sex did not significantly affect the concentration of Zn and Cu. No remarkable difference was found between the bone samples representing a normal mineral status and osteoporosis.

Adolescent↗

PubMed2000

A bone replaceable artificial bone substitute: morphological and physiochemical characterizations.

A composite material consisting of carbonate apatite (CAp) and type I atelocollagen (AtCol) (88/12 in wt/wt%) was designed for use as an artificial bone substitute. CAp was synthesized at 58 degrees C by a solution-precipitation method and then heated at either 980 degrees C or 1,200 degrees C. In this study, type I AtCol was purified from bovine tail skins. A CAp-AtCol mixture was prepared by centirfugation and condensed into composite rods or disks. The scanning electron-microscopic (SEM) characterization indicated that the CAp synthesized at 58 degrees C displayed a crystallinity similar to that of natural bone and had a high porosity (mean pore size: about 3-10 microns in diameter). SEM also revealed that the CAp heated at 980 degrees C was more porous than that sintered at 1,200 degrees C, and the 1,200 degrees C-heated particles were more uniformly encapsulated by the AtCol fibers than the 980 degrees C-heated ones. A Fourier transformed-infrared spectroscopic analysis showed that the bands characteristic of carbonate ions were clearly observed in the 58 degrees C-synthesized CAp. To enhance the intramolecular cross-linking between the collagen molecules, CAp-AtCol composites were irradiated by ultraviolet (UV) ray (wave length 254 nm) for 4 hours or vacuum-dried at 150 degrees C for 2 hours. Compared to the non cross-linked composites, the UV-irradiated or dehydrothermally cross-linked composites showed significantly (p < 0.05) low collagen degradation and swelling ratio. Preliminary mechanical data demonstrated that the compressive strengths of the CAp-AtCol composites were higher than the values reported for bone.

Animals↗

PubMed2004

Phosphate-bonded ZrSiO4 investments added with ZrC and ZrN for casting titanium.

In this study, new investments for titanium were developed by adding ZrC or ZrN as chemical additive for thermal expansion to a phosphate-bonded zircon (ZrSiO4) investment. The following effects were then examined: setting expansion, residual thermal expansion, and compressive strength of these experimental investments; surface roughness of cast plate; and casting accuracy of titanium crown. For residual thermal expansion, it occurred even while investments were cooled to room temperature after firing in air atmosphere. This was due to the additives' oxidation to ZrO2--suggesting that residual thermal expansion increased with increased amount of these additives. As for casting accuracy of full-crown cast into molds at room temperature, it correlated with the ZrN content. Hence by adding the right amount of ZrN, cast titanium crowns with low surface roughness and good adaptability could be obtained.

Analysis of Variance↗

PubMed1999

Porous bioactive glass matrix in reconstruction of articular osteochondral defects.

BACKGROUND AND AIMS: This study was carried out to investigate the use of porous bioactive glass implants in promotion of articular cartilage and subchondral bone repair in large osteochondral joint defects. MATERIAL AND METHODS: Two conical osteochondral defects (top diameter 3.0-3.2 mm) were drilled into the patellar grooves of the distal femurs in the rabbit. The defects, extending (approximately 6-7 mm) from the surface of the articular cartilage to the subchondral marrow space, were reconstructed with size-matched porous conical implants made of sintered bioactive glass microspheres (microsphere diameter 250-300 microm, structural implant compression strength 20-25 MPa) using press-fit technique. The implant surface was smoothened to the level of the surrounding articular cartilage. One of the two defects in each femur was left empty to heal naturally and to serve as the control. At 8 weeks, the defect healing was analyzed with use of a semiquantitative histological grading system, histomorphometry of subchondral bone repair, back-scattered electron imaging of scanning electron microscopy (BEI-SEM), and a microindentation test for characterization for the stiffness properties of the cartilage repair tissue. RESULTS: The porous structure of the bioactive glass implants, extending from the articular defect of the patellar groove into the posterior cortex of the femur, was extensively filled by new bone. Cartilage repair varied from near-complete healing by hyaline cartilage to incomplete healing predominantly by fibrocartilage or fibrous tissue. There were, however, no statistical differences in the histological scores of repair between the glass-filled and control defects, although the sum of the averages of each category was lowest for the bioactive glass filled defects. The indentation stiffness values of all the defects were also significantly lower than that of normal cartilage on the patellar groove. CONCLUSIONS: Porous textures made by sintering bioactive glass microspheres may expand the opportunities in reconstruction of deep osteochondral defects of weight-bearing joints. The implants act mechanically as a supporting scaffold and facilitate the penetration of stromal bone marrow cells and their chondrogenic and osteogenic differentiation. Ionic properties of the bioactive glasses make the substances highly potential even as delivery systems for adjunct growth factor therapy.

Animals↗

PubMed1976

[Compression of amalgam specimens under various loads].

To test the behavior of amalgam fillings under masticatory load, 72 cylindrical amalgam specimens (d=5mm, h=10mm) were exposed to alternating loads changing from zero pressure to a pressure of 10 N/mm2. The tests were made in a conventional and four silver amalgams rich in copper, in water baths of 30 degrees, 37 degrees, 50 degrees, and 60 degrees C. Compression of the specimens results, which increases proportionally to the cube root of the number of alternating loads and with rising temperature. The compression lies between 0.3 per cent to 5 per cent of the original length after 10,000 alternating loads, depending on amalgam and temperature. Compressive strength increased under alternating load.

Dental Amalgam↗