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Results for “Compressive Strength”

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At least 433 records · Page 24Linked to original sources

PubMed1989

[Study on composite resin cores. Part 2. Effect of pressing composite resin].

In this study, we investigated effects of pressing in building composite resin cores on compressive strength, retention of prefabricated post and sealing ability. 1. Compressive strength increased by pressing in composite resin cores. 2. Prefabricated post to the retentive forces was not influenced by pressing, but increased when bonding agent was used. 3. Pressing was very effective to improve sealing ability of composite resin to tooth structure. 4. Sealing ability of light-cured composite resin was not influenced by pressing but by curing types of bonding agent.

Composite Resins↗

PubMed1989

[Composite resin cores. Part 1. Comparison of various composite resin cores].

This study evaluated compressive strength, sealing ability and tensile bond strength of various materials of composite resin cores. 1. Compressive strength of the various materials, after they were placed in air for 24 hours, underwent thermal cycling testing, or were soaked in water for 2 weeks, ranged from 2000 kgf/cm2 to 2900 kgf/cm2. 2. The sealing ability after thermal cycling testing and being soaked in water for 2 weeks varied among the materials. 3. The bond strength of all composite resin core materials to dentin was less than 50 kgf/cm2. 4. In this study, no relationship was found between sealing ability and tensile bond strength.

Composite Resins↗

PubMed2005

[IR study of the hardening and maturation of glass ionomer cement].

The set reaction of glass ionomer cement has been investigated by means of IR spectra. It has been found that the band intensity around 1413 cm(-1) due to the vibration of polyacrylate salt increased with aging, and the shoulder band at 950 cm(-1) due to the stretching vibration of Si-OH still appeared during the periods studied. The results are consistent with that of mechanical determination of compressive strength, which suggested that the crosslink density increase resulting from the slow diffusion of Ca2+ and Al3+ is responsible for compressive strength increasing with aging, and forming and maturing of interface layer comprising of silica gel also have a significant effect on the properties of glass ionomer cements.

Compressive Strength↗

PubMed2006

Physicochemical properties of TTCP/DCPA system cement formed in physiological saline solution and its cytotoxicity.

In this paper, the physicochemical properties and cytotoxicity of calcium phosphate cement (CPC), prepared by mixing cement powders of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA) with a cement liquid of physiological saline solution, were investigated. The microstructure evolution of various hardened cement bodies and their hydration crystals as a function of immersion time in similar physiological fluids, physiological saline solution (0.9% NaCl), or simulated body fluids (SBF), were also studied. Results show that the setting time of CPC is in the range of 12-15 min, which meets the clinical application demands. We also found that the mean compressive strength of the CPC samples immersed in SBF for 3 days is 104+/-10 MPa which reaches the transverse compressive strength, 106-133 MPa, of human long bone. The results obtained from both the X-ray powder diffraction analyses (XRD) and scanning electron microscopy (SEM) observations indicated that a reinforcing effect of some remaining TTCP particles in the early stages of immersion is mainly responsible for the increase in the initial strength. Although the CPC failed to keep this high level when immersed for a longer time, the initial reinforcing effect of the remaining TTCP particles provides advantages for clinical applications. This would be effective when the material is loaded at the very beginning of the implantation, especially for the material used as a fixation, which requires a certain initial strength in the early stages of the implantation. The cytotoxicity results showed that the relative growth rate (RGR%) of L929 cells on the CPC samples using physiological saline solution as a cement liquid was slightly superior to that of the samples using the 0.5 mol/L phosphate acid solution as the cement liquid. This was most likely caused by the pH difference between the two CPC samples immersed in a DMEM-BFS medium.

Animals↗

PubMed2002

Properties of encapsulated and hand-mixed zinc phosphate dental cement.

PURPOSE: Dental cements can be supplied as loose powder and liquid or as encapsulated syringes. This study assessed the compressive strength of a recently marketed zinc phosphate encapsulated cement compared with a hand-mixed system according to the American Dental Association Specification. MATERIALS AND METHODS: The mean fracture strength, standard deviations and associated Weibull Moduli (m) of the encapsulated and hand-mixed cements were determined by compressive fracturing 30 cylindrical specimens (height 6.0 +/- 0.1 mm, diameter 4.0 +/- 0.1 mm). Scanning electron microscopy was employed to assess crack growth from indentations and cement morphology. Image analysis was used to investigate the influence of mixing regime on pore distribution within the cement samples. RESULTS: The compressive strength data showed variation in magnitude and reliability ranging from 42 +/- 8 MPa (m = 5.2 +/- 1.0) for the encapsulated cement filled directly from the capsule to 71 +/- 11 MPa (m = 6.3 +/- 1.3) for the hand-mixed cement. The encapsulated cement matrix was extensively porous, consisting of pores between 0.1-0.5 microm diameter, compared with the non-porous hand-mixed cement matrix. Larger pores (over 18 microm diameter) were related to air entrapment in the encapsulated cement on mixing while small pores (0.1-0.5 microm diameter) were indicative of vaporization porosity commonly seen with exothermic reactions.

Air↗

PubMed2004

Development of casting investment preventing blackening of noble metal alloys part 3. Effect of reducing agent addition on the strength and expansion of the investments.

Different reducing agents (B, Al, Si and Ti) were individually added to two gypsum-bonded investments to prepare investments preventing surface blackening of some noble cast alloys. The effect of different additive contents on green-body and burnout compressive strength, setting and thermal expansion of the investments were evaluated. The strength and expansion of the investments were changed by the additives. The compressive strength of Al-, Si- and Ti-added investments decreased with the increase of additive contents. The burnout strength of B-added investments significantly increased while green-body strength remained unchanged. The setting expansion of the B-added investments increased while those of the Al-, Si- and Ti-added investments decreased with the increase of additive contents. The thermal expansion of the Si- and Ti-added investments decreased, and that of the Al- and B-added investments remained unchanged. Further study is necessary to evaluate the effects of these additives on the accuracy of dental castings.

Aluminum↗

PubMed1984

Acid and water solubility and strength of calcium hydroxide bases.

The solubility in water and 37% phosphoric acid, and compressive strength of four brands of hard-setting calcium hydroxide base materials were studied. Results were highly variable among brands and no correlations appeared to exist between properties studied. One product was significantly different from the others with regard to acid solubility and compressive strength.

Calcium Hydroxide↗

PubMed1982

Correlation between strength of bonding to enamel and mechanical properties of dental composites.

The strength of bonding of dental composites to enamel was measured in shear. The compressive strength, proportional limit, elastic modulus, and tensile strength of the composites were measured for correlation with the bond strength. Conventional and microfilled composites with a range of filler concentrations were studied. The densities of the composites and their fillers and the concentrations of the fillers were determined. The mechanical properties that were most highly correlated with bond strength to enamel were proportional limit and elastic modulus. Tensile strength and filler concentration had lower correlation coefficients, and compressive strength was not correlated with bond strength. Using unfilled resins as bonding agents between the composites and enamel resulted in increased bond strength with half of the composites.

Composite Resins↗

PubMed2000

Controlled low-strength material using fly ash and AMD sludge.

Controlled low-strength material (CLSM) is a cementitious material with properties similar to stabilized soil. After hardening, CLSM provides adequate strength in bearing capacity and support but can also be easily excavated. To be classified as a CLSM, the material must have a compressive strength between 450 kPa (65 psi) and 8400 kPa (1200 psi). Typical CLSM contains coal-combustion fly ash (FA), cement, water and fine or coarse aggregate. In this paper, physical and strength properties of CLSM formed by combining sludge, a by-product from the treatment of acid mine drainage (AMD), with Class F FA are investigated. The sludge is a lime-based waste product that when combined with FA, exhibits self-hardening characteristics similar to cement. A main focus of this research is to develop a CLSM mix in which by-product material utilization is maximized while satisfying workability and performance requirements. A mixture of 10% AMD sludge, 2.5% Portland cement (PC), 87.5% Class F FA (dry wt.%) with water provided unconfined compressive strength values within the range for classification as CLSM. This mixture satisfies the excavatability and walkability requirements as well as the hardening time and stability criteria.

Calcium Compounds↗

PubMed2005

Optimising bioactive glass scaffolds for bone tissue engineering.

A 3D scaffold has been developed that has the potential to fulfil the criteria for an ideal scaffold for bone tissue engineering. Sol-gel derived bioactive glasses of the 70S30C (70 mol% SiO2, 30 mol% CaO) composition have been foamed to produce 3D bioactive scaffolds with hierarchical interconnected pore morphologies similar to trabecular bone. The scaffolds consist of a hierarchical pore network with macropores in excess of 500 microm connected by pore windows with diameters in excess of 100 microm, which is thought to be the minimum pore diameter required for tissue ingrowth and vasularisation in the human body. The scaffolds also have textural porosity in the mesopore range (10-20 nm). The scaffolds were sintered at 600, 700, 800 and 1000 degrees C. As sintering temperature was increased to 800 degrees C the compressive strength increased from 0.34 to 2.26 MPa due to a thickening of the pore walls and a reduction in the textural porosity. The compressive strength is in the range of that of trabecular bone (2-12 MPa). Importantly, the modal interconnected pore diameter (98 microm) was still suitable for tissue engineering applications and bioactivity is maintained. Bioactive glass foam scaffolds sintered at 800 degrees C for 2 h fulfill the criteria for an ideal scaffold for tissue engineering applications.

Biocompatible Materials↗

PubMed2001

Directional bonding in compacted microcrystalline cellulose.

The mechanical properties of compacts of microcrystalline cellulose (MCC) and silicified microcrystalline cellulose (SMCC) were evaluated by tensile testing, diametric compression testing, and compression testing. For tensile and compression testing, cubic specimens were carefully machined from MCC and SMCC compacts, and the tensile and compression strengths were evaluated both normal and parallel to the compaction direction. The cubic tensile strengths were compared to values obtained from the diametric compression test. The results obtained using the diametric compression test suggested compacts of SMCC exhibit greater strength than those of MCC. In addition, the cubes machined from compacts of MCC and SMCC exhibited directional strength; the direction normal to the compaction direction display ed the greater tensile strength, and the parallel direction had greater compression strength. The diametric compression test afforded strength values with reduced spread compared to the values collected from the cubic tensile test, suggesting that the errors involved in collecting diametric compression test data of compacts are less than those for the cubic tensile test. Analysis of the cubes using X-ray diffraction (XRD) suggested that they display directional structural anisotropy, with the direction normal to the compaction direction being more crystalline than the parallel direction. However, it is not clear whether the difference in the directional strength is solely a consequence of the increased crystallinity or a culmination of crystallographic and mechanical keying effects.

Algorithms↗

PubMed1989

Mineral content and strength of lumbar vertebrae. A cadaver study.

Fifty-two cadaveric spine-motion segments were tested in compression alone and in combined compression-flexion to determine whether the compressive strength of lumbar vertebrae varied with the direction of the applied load, that is, whether similar relationships existed between the compressive strength and the amount of bone mineral depending on the direction of the loading. The bone mineral content (BMC) ranged between 1.6 and 5.8 g/cm and the ultimate strength between 810 and 10,090 N. The BMC of the motion segments was correlated with their strength irrespective of degree of flexion during testing (0-15 degrees). For compression-flexion within physiologic limits, the first part of the motion segment to fail was, with few exceptions, the end plate and the adjacent spongy bone.

Adolescent↗

PubMed2000

Biomechanics of stand-alone cages and cages in combination with posterior fixation: a literature review.

Interbody cages in the lumbar spine have met with mixed success in clinical studies. This has led many investigators to supplement cages with posterior instrumentation. The objective of this literature review is to address the mechanics of interbody cage fixation in the lumbar spine with respect to three-dimensional stabilization and the strength of the cage-vertebra interface. The effect of supplementary posterior fixation is reviewed. Only three-dimensional stabilization evaluations in human cadaveric models are included. These studies involve the application of different loads to the spine and the measurement of vertebral motion in flexion-extension, axial rotation, and lateral bending. There are no published studies which detected any differences between different cage designs. However, it does seem that cages inserted from an anterior direction provide better stabilization to the spine than those inserted from a posterior direction. In general, anterior cages stabilize better than posterior cages in axial rotation and lateral bending. Cages from both directions stabilized well in flexion, but not in extension. Supplementary posterior fixation with pedicle or translaminar screws substantially improves the stabilization in all directions. The strength of the cage-vertebra interface from studies using human cadaveric specimens is also reviewed. The axial compressive strength of this interface is highly dependent upon vertebral body bone density. Other factors such as preservation of the subchondral bony end-plate and cage design are clearly less important in the compressive strength. Supplementary posterior instrumentation does not enhance substantially the interface strength in axial compression.

Biomechanical Phenomena↗

PubMed2002

Self-curing acrylic formulations containing PMMA/PCL composites: properties and antibiotic release behavior.

Partially biodegradable acrylic composites containing poly(methyl methacrylate)-poly(epsilon-caprolactone) (PMMA/PCL) systems were prepared by mixing the corresponding PMMA/PCL beads (89:11, 86:14, 83:17, and 77:23 weight ratio) used as solid phase with methyl methacrylate (MMA) (liquid phase) in a solid/liquid ratio of 1.5:1. The physical and chemical microheterogeneity of these beads influenced significantly the curing parameters, because several aspects involved in the polymerization reaction are closely related to both morphology and size distribution of the particles. In vitro behavior was studied by immersion in simulated body fluid at pH = 7.4 and 37 degrees C for more than 8 weeks and the composition was followed by 1H-nuclear magnetic resonance spectroscopy. Approximately 2% wt/wt weight loss was observed after a period of 8 weeks for the composites richest in PCL. Mechanical properties of the dry and wet specimens were evaluated by compressive and tensile tests. In all cases, the presence of PCL in the composites provided a significant decrease in both compressive strength and elastic modulus compared with plain PMMA. Tensile and compressive strength also decreased significantly after 2 weeks of immersion in simulated body fluid compared with dry specimens. The self-curing composites based on PMMA/PCL beads and loaded with 3% wt/wt vancomycin were evaluated as carriers for local release of antibiotics. The composite prepared with beads of PMMA/PCL ratio 86:14 was the most effective. It eluted 64% of the initial drug within the first 5 h, allowing progressive release of nearly the total amount of the initial drug (90%) in approximately 2 months. The results obtained suggest that the described composites can be suitable for antibiotic release in non-load bearing graft applications.

Biocompatible Materials↗

PubMed2001

A comparison of the mechanical properties of a gallium-based alloy with a spherical high-copper amalgam.

OBJECTIVES: The aim of the present study was to investigate how the mechanical properties of a palladium free gallium-based alloy (Galloy) compare with a leading spherical high-copper amalgam (Tytin). METHODS: Cylindrical specimens were mechanically condensed, according to the ISO 1559:1986 standard, to measure compressive strength, Vickers hardness, static creep and dimensional change on setting. Disc and beam shaped specimens were manually prepared to assess the diametral tensile and flexural strengths of the investigated alloys. RESULTS: The mean hardness, 1h compressive fracture strength, 24 h diametral tensile and 24h flexural strengths of Galloy were significantly lower (P<0.001) than Tytin. No significant differences in modulus of elasticity, creep, dimensional change on setting, 24 and 168 h compressive fracture strength for the two alloys were identified. SIGNIFICANCE: The significant reduction in the 1 h mean compressive fracture strength and hardness identified for Galloy compared with Tytin possibly indicate a slower setting reaction in the gallium-based alloy. Manual condensation of the gallium-based alloy produced specimens with inferior mechanical properties possibly due to the increased likelihood of introducing voids within the test specimens. Previous reports indicating poor corrosion resistance and moisture sensitivity of gallium-based alloys highlight the need for further research to investigate the effect of the oral environment on the gallium-based alloy.

Compressive Strength↗

PubMed2003

Immobilization of mercury and zinc in an alkali-activated slag matrix.

The behavior of heavy metals mercury and zinc immobilized in an alkali-activated slag (AAS) matrix has been evaluated using physical property tests, pore structure analysis and XRD, TG-DTG, FTIR and TCLP analysis. Low concentrations (0.5%) of mercury and zinc ions had only a slight affect on compressive strength, pore structure and hydration of AAS matrixes. The addition of 2% Hg ions to the AAS matrix resulted in a reduction in early compressive strength but no negative effects were noticed after 28 days of hydration. Meanwhile, 2% Hg ions can be effectively immobilized in the AAS matrix with the leachate meeting the USEPA TCLP mercury limit. For a 2% Zn-doped AAS matrix, the hydration of the AAS paste was greatly retarded and the zinc concentration in the leachate from this matrix was higher than 5mg/l even at 28 days. Based on these results, we conclude that the physical encapsulation and chemical fixation mechanisms were likely to be responsible for the immobilization of Hg ions in the AAS matrix while only chemical fixation mechanisms were responsible for the immobilization of Zn ions in the AAS matrix.

Compressive Strength↗

PubMed1998

Die stone disinfection: incorporation of sodium hypochlorite.

PURPOSE: Previous research has shown that dental gypsum casts may be effectively disinfected by the substitution of 10% of the gauging water with 5.25% solution of sodium hypochlorite. The purpose of this investigation was to determine the properties of gypsum produced from such a solution as opposed to tap water alone. MATERIALS AND METHODS: Tests included setting time, compressive strength, rigidity, diametral tensile strength, setting expansion, hardness, and detail reproduction. RESULTS: The addition of sodium hypochlorite to the gauging water resulted in a statistically significant increase in the compressive strength and rigidity, and a decrease in setting time (p < or = .5). All other properties remained unchanged. CONCLUSIONS: This substitution may be an effective and convenient method of disinfecting gypsum casts in the laboratory without adversely effecting physical and mechanical properties.

Calcium Sulfate↗

PubMed1990

A study of the method of making dental prosthetic appliances by sintered titanium alloys: effect of copper powder content on properties of sintered titanium alloy.

The effects of added copper powder to the properties of the sintered titanium alloys were investigated by measuring the compressive strength and densities of the green and sintered compacts, the thermal expansion curves and dimensional changes in the sintered compacts, and the accuracy of the crown-type restorations. The compressive strengths of green compacts ranged from 55 to 75 MPa. The expansion of green compacts increased with increased copper content. The sintered density was lower than the green density. The compressive yield strength of sintered compacts ranged from 260 MPa to 410 MPa. The sintered compacts expanded from 0.35% to 1.03% and the expansion increased with increased copper content. The dimensional accuracy of crown-type restorations showed the same dimensional change tendencies as did the sintered compacts. These results showed that the fit and the strength of sintered titanium alloy restorations could be improved.

Copper↗