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PubMed2006

Pozzolanic reactivity of the synthetic slag from municipal solid waste incinerator cyclone ash and scrubber ash.

This study investigates the pozzolanic reactions and compressive strength of the blended cement manufactured using synthetic slag obtained from municipal solid waste incinerator (MSWI) cyclone ash and scrubber ash as partial replacement of portland cement. The synthetic slag was made by co-melting the MSWI scrubber ash and cyclone ash mixtures at 1400 degrees C for 30 min. Following pulverization, the different types of slag were blended with cement as cement replacement at ratios ranging from 10 to 40 wt %. The synthetic slag thus obtained was quantified, and the characteristics of the slag-blended cement pastes were examined. These characteristics included the pozzolanic activity, compressive strength, hydration activity, crystal phases, species, and microstructure at various ages. The 90-day compressive strength developed by slag-blended cement pastes with 10 and 20 wt % of the cement replaced by the synthetic slag outperformed ordinary portland cement by 1-7 MPa. X-ray diffraction species analyses indicated that the hydrates in the slag-blended cement pastes were mainly portlandite, the calcium silicate hydrate gels, and calcium aluminate hydrate salts, similar to those found in ordinary portland cement paste. Differential thermal and thermogravimetric analysis also indicated that the slag reacted with portlandite to form calcium silicate hydrate gels.

Air Pollution↗

PubMed1999

High-resolution computed tomography for architectural characterization of human lumbar cancellous bone: relationships with histomorphometry and biomechanics.

The aim of the present study on human vertebral cancellous bone was to validate structural parameters measured with high-resolution (150 microm) computed tomography (HRCT) by referring to histomorphometry and to try to predict mechanical properties of bone using HRCT. Two adjacent vertical cores were removed from the central part of human L2 vertebral body taken after necropsy in 22 subjects aged 47-95 years (10 women, 12 men; mean age 79 +/- 14 years). The right core was used for structural analysis performed by both HRCT and histomorphometry. Two cancellous bone specimens were extracted from the left core: a cube for HRCT and a compression test, and a cylinder for a shear test. Significant correlations were found between HRCT and histomorphometric measurements (BV/TV, trabecular thickness, separation and number, and node-strut analysis), but with higher values for most of the tomographic parameters (BV/TV and trabecular thickness determined by HRCT were overestimated by a factor 3.5 and 2.5 respectively, as compared with histomorphometry). The maximum compressive strength and Young's modulus were highly correlated (rho = 0.99, p<0.0005). Significant correlation was obtained between bone mineral density (determined using dual-energy X-ray absorptiometry) and the maximum compressive strength (rho = 0. 64, p = 0.002). In addition the maximum compressive strength and architectural parameters determined by HRCT or histomorphometry showed significant correlations (e.g., for HRCT, BV/TV: rho = 0.88, p<0.0005, N.Nd/TV: rho = 0.73, p<0.001). The shear strength was significantly correlated with BV/TV (rho = 0.62, p = 0.002), Tb.Sp (rho = -0.58, p = 0.004) and TSL (rho = 0.55, p = 0.006) measured by HRCT. In conclusion, an HRCT system with 150 microm resolution is not sufficient to predict the true values of the structural parameters measured by histomorphometry, although high correlations were found between the two methods. However, we showed that a resolution of 150 microm allowed us to predict the mechanical properties of human cancellous bone. In vivo peripheral systems with such a resolution should be of interest and would deliver an acceptable radiation dose to the patient.

Aged↗

PubMed1986

Biomechanical optimization of a model particulate composite for orthopaedic applications.

Particulate composites are a potential solution to the need for an injectable, biocompatible, resorbable material that could be used to reinforce fractures and defects in bone and temporarily to stabilize porous ingrowth prostheses. We have developed a model system for producing and testing particulate composites to determine if mechanical properties suitable for orthopaedic applications can be achieved. The experiments used bovine cortical bone and various forms of hydroxyapatite for the particulate phase and a collagen and particulate reinforce gelatin-resorcinol-formaldehyde (G-R-F) adhesive for the matrix phase. Using unconfined compression testing, we measured the effects of variation in particulate type, size, shape, and volume fraction on the material properties of the particulate composites. We found that compressive strengths greater than 10 MPa and compressive moduli greater than 100 MPa could be achieved in this model system. Rough and irregular particulates exhibited higher compressive strengths and moduli than smooth and spherical particulates. Mechanical properties were largely independent of particulate size in the range of 125-850 microns diameter. This model system suggests that, with the development of new biocompatible matrix materials, particulate composites with mechanical properties suitable for orthopaedic applications can be achieved.

Animals↗

PubMed2006

Starved air combustion-solidification/stabilization of primary chemical sludge from a tannery.

The high concentration of trivalent chromium along with organic/inorganic compounds in tannery sludge causes severe ground water contamination in the case of land disposal and chronic air pollution during incineration. In the present investigation, the sludge was subjected to flow-through column test to evaluate the concentration of leachable organics (tannin, COD and TOC) and heavy metal ions (Cr(3+), Fe(2+)) present in it. The dried sludge was incinerated at 800 degrees C in an incinerator under starved oxygen supply (starved-air combustion) to prevent the conversion of Cr(3+) to Cr(6+). The efficiency of starved air combustion was studied under different loading rates of sludge. The calcined sludge was solidified/stabilized using fly ash and Portland cement/gypsum. The solidified bricks were tested for unconfined compressive strength and heavy metal leaching. Unconfined compressive strength of the blocks was in the range of 83-156 kg/cm(2). The stabilization of chromium (III) in the cement gel matrix was confirmed with scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDX). Leachability studies on solidified bricks were carried out to determine the metal fixation and dissolved organic (as COD) concentration in the leachate.

Adsorption↗

PubMed1996

Laser-aided degradation of composite resin.

The removal of residual composite resin after debonding orthodontic brackets often creates surface scratches, enamel loss, and enamel tearouts. If the Nd:YAG laser could selectively degrade the resin without damaging the underlying tooth structure, these problems might be eliminated. The purpose of this study was to determine the effectiveness of the Nd:YAG laser in degrading composite resin within a time frame that will not cause pulpal damage. Minimal lasing times and optimum frequencies were determined by testing the compressive strengths of resin cylinders exposed to laser radiation for 2, 3, 5, 10, or 15 seconds at frequencies of 60, 80, or 100 Hz. The optimum condition was determined to be a 3 second lasing time at a frequency of 100 Hz. Cylinders of composite resin were divided into four groups consisting of: (1) resin, (2) resin with a laser enhancing dye, (3) resin lased for 3 seconds at 100 Hz, and (4) resin with the dye which was lased for 3 seconds at 100 Hz. The compressive strengths of the four groups were statistically compared. The resin groups that were lased for 3 seconds at 100 Hz showed a 75% reduction in compressive strength. The results of this study demonstrate that dual wavelength pulsed Nd:YAG laser energy, when used within the parameters described here, will degrade the mechanical properties of composite resin, thereby offering the potential for a quick and efficient method of removing residual composite resin.

Aluminum Silicates↗

PubMed1994

Experimental development of a chitosan-bonded beta-tricalcium phosphate bone filling paste.

Bone filling substances are needed to meet several requirements including nontoxicity, setting time, changes in pH values, and amount of dissolved elements as well as mechanical properties. In this study, the bone-generating composites were prepared by employing the in vivo absorbable beta-tricalcium phosphate as a parent matrix kneaded with CaO, MgO, and ZnO as bone mineral additives with different compositions. The setting time, pH values, compressive strength were investigated as a function of the amount of these bone mineral additives. It was found that the setting time was shortened by increasing CaO, MgO, and ZnO contents. Increasing ZnO contents resulted in the pH value lower, while the pH values increased by increasing CaO and MgO contents. Increasing ZnO contents caused the compressive strength stronger, on the other hand, the compressive strength was weakened by increasing MgO contents. Furthermore, calcium appears to be selectively released from the hardened composite sample.

Analysis of Variance↗

PubMed1994

Strength-probability-time (SPT) diagram--an adjunct to the assessment of dental materials?

This investigation sought to construct and compare strength-probability-time (S-P-T) diagrams for four dental materials. Three of these were resin composites and one was dental plaster. In the case of dental plaster a total of 90 compressive specimens as fabricated whereas for each of the other materials a total of 75 specimens was prepared. The compressive strength of equal sized groups of each material was then determined at the crosshead (XHD) speeds of 1, 5 and 10 mm min-1 respectively. The data was subjected to Weibull analysis to relate the probability of failure to the applied stress. Where strong correlations were found between the (i) mean compressive strength and crosshead speed, (ii) individual compressive strengths and failure times, the data was used to determine the crack velocity exponent (n) and produce a S-P-T diagram. Although only one of the materials (P-50) evaluated fulfilled all the necessary criteria and yielded a value of n = 16.13 (7.22), it is suggested that this method may enable comparisons to be made amongst other materials satisfying the required conditions. As such diagrams are based upon a crack growth law they may be of value in assessing the likely clinical wear resistance of new formulations. Consideration, however, should always be given to what levels are deemed acceptable for the intended clinical application of the material. Thus, before this technique can be employed fully, to the evaluation of new restorative materials, further work is necessary to determine appropriate design criteria.

Composite Resins↗

PubMed1982

Heat treatment of glass ionomer, silicate, zinc phosphate and zinc polycarboxylate cements.

The compressive strength and erosion resistance of glass ionomer, silicate, zinc phosphate or zinc polycarboxylate cements, submitted to heat treatments at 50 degrees or 70 degrees C after mixing, have been assessed. Zinc phosphate cement specimens showed a marked reduction in compressive strength properties and erosion resistance, while minor improvements in compressive strength were observed for various brands of the other types of cements. For silicate cement a considerable improvement in erosion resistance was noted. One brand showed a reduction in the release of phosphate amounting to approximately a factor of 20. The various improvements observed may be clinically exploited by exposing the restoration after insertion to radiation from an external heat source which deposits radiation energy in the surface or bulk of the restoration.

Chemical Phenomena↗

PubMed2005

The influence of some dentin primers on calcium hydroxide lining cement.

UNLABELLED: Dentin primer is applied as a routine procedure prior to bonding to improve the sealing properties of direct polymerizing resins. Some primers contain acetone or alcohol that may affect the properties of calcium hydroxide liner which is placed as a direct or indirect pulp cap. If calcium hydroxide is softened or smeared over the cavity walls, the bonding will be impaired. Therefore, if this occurs, the cement must be removed, the walls must be cleansed, and the procedure must be repeated with careful application of dentin primer. OBJECTIVE: The purpose of this study was to determine the wear and compressive strength of a calcium hydroxide liner after exposure to different kinds of dentin primers for different periods of time. METHODS: The calcium hydroxide used in this study was Dycal. It was mixed according to the manufacturer's instructions and placed in plastic rings of 0.5 mm x 5 mm and allowed to set at 37 degrees C for 15 min under 500 gm load. To determine erosion, the height for each sample before and after application of primers was recorded using a Digital Height Measuring Instrument "Digmar" 817. Compressive strength specimens were also prepared. RESULTS: Calcium hydroxide treated with Optibond (alcohol based) or Syntac (acetone based) for 1 min or 5 min had the highest erosion values and the lowest compressive strength values. Gluma CPs (water based primer) had the least effect on calcium hydroxide values.

Analysis of Variance↗

PubMed1999

Mechanical properties of trabecular bone in the human mandible: implications for dental implant treatment planning and surgical placement.

PURPOSE: This study sought to establish the relationships between bone density, elastic modulus, and ultimate compressive strength of trabecular bone in the human mandible, and to determine the influence that the cortical plates have on these values. MATERIALS AND METHODS: Nine fresh-frozen human mandibles between the ages of 56 and 90 years were cut into anterior (incisors and canine), middle (premolars), and distal (molars) sections. Seventy-six cylindrical trabecular bone specimens with bone marrow in situ were then prepared and tested in compression in the vertical direction. These tests were performed at a constant strain rate of 0.01 s(-1) with and without the presence of the cortical plates. RESULT: The density of mandibular trabecular specimens with bone marrow in situ ranged from 0.85 to 1.53 g/cm3, with a mean value of 1.14 g/cm3 (SD = 0.15). With the cortical plates present, the elastic modulus ranged from 24.9 to 240.0 megapascals (MPa), with a mean value of 96.2 MPa (standard deviation (SD) = 40.6). Without the cortical plates present, the elastic modulus ranged from 3.5 to 125.6 MPa, with a mean value of 56.0 MPa (SD = 29.6). The ultimate compressive strength of the trabecular bone ranged from 0.22 to 10.44 MPa, with a mean value of 3.9 MPa (SD = 2.7). CONCLUSION: This study indicates that the trabecular bone in the human mandible possesses significantly higher density, elastic modulus, and ultimate compressive strength in the anterior region than in either the middle or distal regions. The absence of cortical plates decreases the bone elastic modulus. These findings quantitatively confirm the need for clinical awareness in altering implant treatment plans and/or design in relation to bone density and the presence of the cortical plates.

Adolescent↗

PubMed2005

Effect of 10 wt% spherical silica filler addition on the various properties of conventional and resin-modified glass-ionomer cements.

In this study, we evaluated the effects of 10 wt% spherical silica filler (SSF) addition on 24-h compressive strength, modulus of elasticity, water uptake, and immediate setting shrinkage of conventional glass-ionomer (Fuji II and Experimental) and resin-modified glass-ionomer (Fuji II LC EM) cements. The glass-ionomer cement powders were modified by being mixed with 10 wt% SSFs with an average particle diameter of 0.3 microm. The materials were mixed to consistencies similar to the flow of Fuji II mixed with a powder-liquid ratio of 2.7:1 (w/w). The 24-h compressive strength, modulus of elasticity, water uptake, and immediate setting shrinkage were observed and the results compared with the original materials mixed with similar flow. The addition of SSF increased the compressive strength value to 1.1 times, while the increase of moduli of elasticity was 1.10 to 1.35 times. In general, the addition of SSF decreased the 24-h water uptake to 80-90% and reduced the immediate setting shrinkage to 70-79% of the original materials. The addition of 10 wt% SSF improved the characteristics of conventional and resin-modified glass-ionomer cement.

Compressive Strength↗

PubMedDate not supplied

Evaluation of curing units used in private dental offices.

It is well known that numerous factors influence the light output of curing units, but many dentists are unaware that the output of their curing lights are inadequate. This study was conducted to evaluate the light intensity of visible-light curing units in private dental offices and to assess their curing efficiency by measuring compressive strength of a light-cured resin. Also, in order to determine the maximum light intensity of the curing units, lamps, filters, and fiber optic bundles were replaced by new ones and curing efficiency remeasured. Light intensity was measured by employing a Quantum Radiometer LI-189 at a wavelength of 470 +/- 40 nm using a bandpass filter. Compressive strength of a light-cured resin using the light units was measured employing an Instron Testing Machine at a crosshead speed of 1.0 mm/min. From the evaluation of 105 light units, the light intensity ranged from 28 to 1368 W/m2 (0 approximately 500 W/m2; 41.9%, 500 approximately 1000 W/ m2; 45.7%, 1000 approximately 1500 W/m2; 12.4%). Light intensity of the light unit in private offices decreased 15.9 approximately 82.1% compared to brand-new units. Reduction of light intensity impaired compressive strength of the light-cured resin to varying degrees (148.3 approximately 279.9 MPa) compared with the highest value (317 MPa) obtained from brand-new light units. The replacement of the parts increased the light intensity, with maximum increases of 36.0% for lamps, 157.7% for filters, 46.2% for fiber optics, and 322.7% for all three parts. The results of this study indicated that the light intensities of the curing units used in private practice were lower than expected.

Composite Resins↗

PubMed1987

[Biomechanical properties of the sacroiliac joint].

The purpose of this study was to investigate the biomechanical properties of the bony and cartilagenous elements of the sacroiliac joint. The materials were obtained from human fresh cadavers en bloc, and they were analysed on cartilage thickness, dynamic viscoelasticity, static compressive strength, and bony trabecular structure. The results were as follows: Cartilage thickness of the joint was well correlated with viscoelasticity, and the results of viscoelasticity and static compressive strength were highly equivalent to the results of analysis of the trabecular bone. The values of viscoelasticity, static compressive strength and bone area were higher in the iliac side of the joint than in the sacral side, and markedly high values were obtained in the middle part of the iliac side. In conclusion, the middle part of the sacroiliac joint may play an important role in the support and transmission of the load.

Adolescent↗

PubMed2005

Change of mechanical properties during short-term natural weathering of MSWI bottom ash.

The present work describes the change of mechanical properties during the natural weathering of freshly quenched processed bottom ash. An unconfined uniaxial compression to failure test of the unbound material was used to determine compressive strength and modulus of elasticity. Three main stages of mechanical behavior were determined. In the first stage, during a period lower than 30 days, mechanical properties suddenly increase, with a compressive strength and elastic modulus 7 times greater than the initial parameters. During the second stage, compressive strength and modulus of elasticity lightly increase until approximately 90 days of curing time. Starting from this period both mechanical properties remain steady and independent of the curing time. The neoformed phases, the elevated water content, and the improvement of particle contact after compaction act as a binder layer among particles, increasing the mechanical parameters during the short-term natural weathering process. Because of this, the freshly compacted bottom ash progresses from behaving as an unbound material into a bound pavement material. These mechanical properties obtained from freshly quenched bottom ash are 6-7 times greater than those obtained from previously weathered bottom ash. The bottom ash expansion and leaching of metals were also evaluated.

Construction Materials↗

PubMed1997

Fixation of carbon fibre-reinforced carbon composite implanted into bone.

The push-out test of three types of biomaterials: carbon fibre-reinforced carbon (CFRC), hydroxyapatite (HA), and surgical steel (SS) implanted into rabbits' femurs was carried out. Hydroxyapatite was used as a positive control (good fixation expected in bone) and surgical steel was a negative one (potentially no fixation in bone). Regeneration of bone in contact with all implants was found three months after implantation. The shear strength between CFRC implants and bone was lower than with the HA implants and higher than the shear strength between the surgical steel and bone. Compressive strength of CFRC implants removed after the observation period was significantly lower than the compressive strength of non-implanted samples. It is concluded that the mechanical bonding between the CFRC implants and host tissues exists 3 months after intrabone implantation and is accompanied by a decrease of the strength of implants.

Journal Article↗

PubMed2002

Transforming growth factor-beta1 incorporation in an alpha-tricalcium phosphate/dicalcium phosphate dihydrate/tetracalcium phosphate monoxide cement: release characteristics and physicochemical properties.

The osteoconductive properties of calcium phosphate cements (CPCs) may be improved by the addition of growth factors, such as recombinant human transforming growth factor-beta1 (rhTGF-beta1). Previously we have shown that rhTGF-beta1 was released from cement enriched with rhTGF-beta1 and subsequently stimulated the differentiation of pre-osteoblastic cells from adult rat long bones. It is unknown whether the addition of rhTGF-beta1 changes the material properties of this alpha-tricalcium-phosphate (alpha-TCP)/tetracalcium-phosphate-monoxide (TeCP)/dicalcium-phosphate-dihydrate (DCPD) cement, and what the characteristics of the release of rhTGF-beta1 from this CPC are. Therefore, in the present study we determined the release of rhTGF-beta1 from cement pellets in vitro. The possible intervening effects of the CPC modification for intermixing rhTGF-beta1 on physicochemical properties were studied by assessing the compressive strength and setting time, as well as crystallinity, calcium to phosphorus ratio, porosity and microscopic structure. Most of the previously incorporated rhTGF-beta1 in the cement pellets was released within the first 48 h. For all concentrations of rhTGF-beta1 intermixed (100 ng-2.5 mg/g CPC), approximately 0.5% of the amount of rhTGF-beta1 incorporated initially was released in the first 2 h, increasing to 1.0% after 48 h. The release of rhTGF-beta1 continued hereafter at a rate of about 0.1% up to 1 week, after which no additional release was found. The initial setting time, nor the final setting time was changed in control cement without rhTGF-beta1 (standard CPC) or in cement modified for rhTGF-beta1 (modified CPC) at 20 degrees C and 37 degrees C. Setting times were more than six times decreased at 37 degrees C compared to 20 degrees C. The compressive strength was initially low for both standard CPC and modified CPC, after which it increased between 24 h and 8 weeks. The compressive strength for the modified CPC was significantly higher compared with standard at 1, 2, and 8 weeks after mixing. X-ray diffraction revealed that both standard and modified CPC changed similarly from the original components into crystalline apatite. The calcium to phosphorus ratio as determined by an electron microprobe did not differ at all time points measured for standard CPC and modified CPC. In both standard CPC and modified CPC the separated particles became connected by crystals, forming a structure in which the particles could hardly be recognised in a densifying matrix with some small pores. The present study shows that the calcium phosphate cement is not severely changed by modification for the addition of rhTGF-beta1. The addition of rhTGF-beta1 in CPC enhances the biologic response as shown in our previous study and did not interfere with the aimed physical and chemical properties as shown in this study. We conclude that the addition of rhTGF-beta1 enlarges the potential of the CPC in bone replacement therapy.

Animals↗

PubMed1978

Surface texture and strength of vitreous carbon-poly(methyl methacrylate) dental implant materials.

A study has been carried out on the surface texture and the strength of several dental implant materials composed of vitreous carbon microballoons (6, 24, and 48 wt %)and poly(methyl methacrylate). Two sizes of microballoons were used--particle size less than 100 micrometer and particle size greater than 100 micrometer. Square wafers of the materials (10 X 10 X 1 mm) were studied with the surface sandblasted in half of the specimens. SEM studies revealed a rough porous surface with scattered moderately sized deep cavities in the 6% and 24% specimens with an increase in the number of cavities in the 24% specimens. The 48% specimens revealed a rough, porous surface composed of large shallow craters. Prepared specimens of the materials, processed by a gas-fired air oven and by a microwave oven, were tested for compressive strength and tensile strength using an Instron Universal Testing Machine. Compressive strengths of the various mixtures were similar, but mixtures using VC particle size over 100 micrometer demonstrated somewhat reduced compressive strength. Tensile strengths of the mixutres decreased significantly as the amount of VC increased, with a 20% reduction at 24 wt % and a 45% reduction at 48 wt %.

Carbon↗

PubMed2005

Synthesis of bioactive PMMA bone cement via modification with methacryloxypropyltri-methoxysilane and calcium acetate.

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is clinically used for fixation of implants such as artificial hip joints. However, it does not show bone-bonding ability, i.e., bioactivity. The lack of bioactivity would be one of factors which cause loosening between the cement and the implant. The present authors recently showed the potential of bioactive PMMA-based bone cement through modification with gamma-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. In this study, the effects of the kinds of PMMA powder on setting time, apatite formation and compressive strength were investigated in a simulated body fluid (Kokubo solution). The cement modified with calcium acetate calcined at 220 degrees C could set within 15 min when the PMMA powder had an average molecular weight of 100,000 or less. The addition of calcium acetate calcined at 120 degrees C in the PMMA powder required a much longer period for setting. The modified cements formed an apatite layer after soaking in the Kokubo solution within 1 day for cement starting from PMMA powder with a molecular weight of 100,000 or less. Compressive strengths of the modified cements were more than 70 MPa for cements starting from 100,000 and 56,000 in molecular weight. After soaking in Kokubo solution for 7 days, the modified cement consisting of PMMA powder of 100,000 in molecular weight showed a smaller decrease in compressive strength than that consisting of 56,000 in molecular weight. These results indicate that bioactive PMMA cement can be produced with appropriate setting time and mechanical strength when PMMA powders with a suitable molecular weight are used. Such a type of design of bioactive PMMA bone cement leads to a novel development of bioactive material for bone substitutes.

Acetates↗