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Results for “Compressive Strength”

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PubMed1979

The strength of fifteen amalgam alloys.

The compressive and tensile (by diametral compression) strengths of amalgams prepared from fifteen conventional and higher copper alloys are compared and the rate at which these amalgams develop strength is investigated. Alloys of the single melt high copper type generally possess the greatest strength at all times of testing. The amalgams tend to achieve maximum tensile strength more rapidly than maximum compressive strength. The major increase in strength takes place between one hour and one day.

Chemical Phenomena↗

PubMed1999

Crosslinking characteristics of an injectable poly(propylene fumarate)/beta-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement.

We investigated the crosslinking characteristics of an injectable composite paste of poly(propylene fumarate) (PPF), N-vinyl pyrrolidinone (N-VP), benzoyl peroxide (BP), sodium chloride (NaCl), and beta-tricalcium phosphate (beta-TCP). We examined the effects of PPF molecular weight, N-VP/PPF ratio, BP/PPF ratio, and NaCl weight percent on the crosslinking temperature, heat release upon crosslinking, gel point, and the composite compressive strength and modulus. The maximum crosslinking temperature did not vary widely among formulations, with the absolute values falling between 38 degrees and 48 degrees C, which was much lower than that of 94 degrees C for poly(methyl methacrylate) bone cement controls tested under the same conditions. The total heat released upon crosslinking was decreased by an increase in PPF molecular weight and a decrease in N-VP/PPF ratio. The gel point was affected strongly by the PPF molecular weight, with a decrease in PPF molecular weight more rapidly leading to a gel point. An increase in initiator concentration had the same effect to a lesser degree. The time frame for curing was varied from 1-121 min, allowing the composite to be tailored to specific applications. The compressive strength and compressive modulus values increased with decreasing N-VP/PPF, increasing NaCl content, and increasing BP/PPF ratio. For all formulations, the compressive strength values fell between 1 and 12 MPa, and the compressive modulus values fell between 23 and 265 MPa. These data suggest that injectable PPF/beta-TCP pastes can be prepared with handling characteristics appropriate for clinical orthopedic applications and that the mechanical properties of the cured composites are suitable for trabecular bone replacement.

Biodegradation, Environmental↗

PubMed1993

Effect of mixing speed on mechanical properties of encapsulated glass-ionomer cements.

It is well established that the strength of encapsulated dental amalgam is affected by the speed of mixing. An investigation into the effects of mixing speeds on the compressive strength of three encapsulated glass-ionomer cements was carried out. The working and setting time and compressive strength at 24 hours and 7 days were evaluated for the three materials at four mixing speeds. There appeared to be little variation in working and setting times at the different mixing speeds. The early compressive strength of one material, Ketac-fil, increased as the speed of mixing increased. The variation in mixing speed did not appear to affect the early compressive strengths of the other two materials. Seven-day compressive strengths of all three materials were not affected by variations in mixing time.

Aluminum Silicates↗

PubMed1983

Tensile strength and compression of coated pharmaceutical powders: tablets.

A study has been made of the tensile strength and compression during tableting of lactose, sodium chloride and calcium phosphate powders after they had been coated with small amounts of stearic acid, polyethylene glycols and polyvinylpyrrolidones. The properties of the systems were measured over a range of temperatures. The tensile strength and the compression behaviour depended not only on the amount and type of the coating material but also on the homologous temperature of processing. The changes in tensile strength have been explained in terms of changes in interparticle separation, changes in interparticle forces and the formation of welded bonds by the coatings. The compression results have been analysed in terms of the Heckel and the Cooper & Eaton equations.

Drug Compounding↗

PubMed2002

Study on some mechanism of leucite microcrystallization to reinforce dental glass ceramics.

OBJECTIVE: To research the influence of K(2)O composition in the raw material on leucite microcrystallization and to study the effect of leucite content on compressive strength of the dental glass ceramics reinforced by leucite microcrystallization. METHODS: The raw materials with different K(2)O content were treated by a decided thermal treatment system. The products were analyzed by polaring microscope and X-ray diffractometer, and their compressive strength was also tested. RESULTS: The microstructure of products from high K(2)O component was remarkably good, at microcrystal size of 0.8 micro m and the compressive strength was 206.6 MPa. A positive correlation was found between leucite volume and the compressive strength when leucite volume was less than 50% (Vol%). CONCLUSIONS: The component of K(2)O has a great effect on the microstructure and the properties of the leucite-microcrystal-reinforced dental glass ceramics and the content of leucite microcrystals has a notable influence on the compressive strength of the dental glass ceramics.

Compressive Strength↗

PubMed1999

The formation of hydroxyapatite-calcium polyacrylate composites.

Tetracalcium phosphate (TetCP, Ca4(PO4)2O) reacts rapidly with polyacrylic acid (PAA). Complete reaction results in the formation of hydroxyapatite (HAp) and calcium polyacrylate. Consequently, this combination of reactants can react to form a dental cement. However, reaction occurs so rapidly that it would be difficult to achieve a homogeneous mixture of reactants suitable for use in restorations. In order to explore extending the working time, the effects of prehydrating the TetCP to form surface layers of HAp on the TetCP particles was explored. Prehydration was found to be an effective means of allowing workability. Therefore, the effects of the proportions of TetCP and PAA, with and without HAp filler, on cement properties were investigated. The extents of the reactions were investigated by X-ray diffraction analysis; the extents of PAA neutralization were studied by Fourier transform infra-red spectroscopy (FTIR); pore structures were determined by mercury intrusion porosimetry; microstructures were observed by scanning microscopy, and compressive strengths were determined. After curing for 17 days at room temperature PAA neutralization was almost complete; however, residual TetCP could be detected by X-ray diffraction and PAA by FTIR. As expected, the compressive strengths of the cements showed a dependence on the liquid (water+polymer)-to-solid (TetCP+HAp filler) used. The presence of HAp filler caused a significant decrease in compressive strength and increasing the proportion of HAp filler resulted in a decrease in the compressive strength. The characteristics of the load-deflection curves showed a dependence on the presence of HAp filler. In the absence of filler, two slopes were observed in the curves whereas a linear curve, typical of a ceramic, was observed when HAp filler was present. Mercury intrusion porosimetry (MIP) indicated the majority of the porosity was present in pores larger than 0.1 microm. Porosity increased with increasing liquid-to-solids ratio and with an increasing proportion of HAp filler at a constant liquid-to-solids ratio. Microstructural observations indicated the effect of HAp filler on increasing porosity was the result of porosity present in the filler itself. Thus, poorly consolidated HAp filler contributed to increased porosity and reduced compressive strength.

Journal Article↗

PubMed1997

Mechanism of the hardening process for a hydroxyapatite cement.

The dynamics for the hydraulic process of calcium phosphate cement (CPC) were investigated by X-ray diffraction quantitative analysis. The results show that the hardening process of CPC is initially controlled by the dissolution of reactants in a 4-h period and subsequently by diffusion through the product layer of hydroxyapatite (HAP) around the grains. The compressive strength rises approximately linearly with the increase of the extent of conversion in a 4-h period, and a maximum compressive strength of about 51 MPa, which is superior to those reported by the references, is obtained in 4 h. Then the compressive strength drops a little with an increase in the extent of conversion. The final product of setting reaction is acicular HAP crystal. Crystal seed not only reduces the setting time but also drops the compressive strength. The variation of pH in CPC slurry from 7.5 to 10.5 reveals that the control step of the dissolution process in the hardening process is the dissolution of dicalcium phosphate anhydrous and the presence of crystal seed will reduce the supersaturation to produce HAP.

Biocompatible Materials↗

PubMed1985

Effect of filler content and size on properties of composites.

Two series of dental composites, along with the unfilled resin matrix, were examined to determine the effects of filler level and size on selected properties. Both series were prepared by incorporating a silanated barium borosilicate filler into a visible-light-activated polyphenylene polymethacrylate resin matrix. One series had a filler particle size of 2 microns, with filler levels of 20, 40, 45, 50, and 53% (vol). The second series contained a 15-microns filler in amounts of 20, 40, 50, 60, and 65% (vol). Tests conducted included: depth of cure as evaluated by hardness, water sorption, compressive strength, stress-strain behavior under slow compression, toothbrush abrasion, and wear by hydroxyapatite. Analysis of the data indicated that increased filler levels resulted in increased hardness, compressive strength and stiffness, and decreased water sorption. Also, there was a slight trend toward improved depth of cure. Incorporation of the 2-microns filler decreased the abrasion resistance of the resins to toothbrushing as compared with the unfilled resin, while addition of the 15-microns filler improved resistance. All filled resins exhibited a significant improvement in resistance to wear by hydroxyapatite as compared with the unfilled resin. There was a trend for increased wear with increased filler level. The particle size of the filler appeared to have a moderate influence on the properties. When compared with 15-microns filled resins of the same filler levels, the 2-micron filled series appeared to have inferior properties in terms of depth of cure, compressive strength, water sorption, and resistance to toothbrush abrasion. Properties which were less affected by particle size were hardness, stiffness, and wear resistance to hydroxyapatite.

Chemical Phenomena↗

PubMed2001

Compression shear strength and tableting behavior of microcrystalline cellulose agglomerates modulated by a solution binder (polyethylene glycol).

PURPOSE: To investigate the possibility of modulating the compression shear strength of agglomerates by the incorporation of a solution binder and to study the subsequent effect on the deformation behavior and tablet forming ability of the agglomerates. METHOD: Various concentrations (0.5 to 10%) of polyethylene glycol were incorporated as a solution binder into microcrystalline cellulose agglomerates of different porosity (10 and 20%) and the shear strength of the agglomerates, as evaluated by the 1/b value of the Kawakita equation, and the permeability to air and tensile strength of tablets formed from them were determined. RESULTS: Increased agglomerate porosity and concentration of polyethylene glycol reduced the 1/b values, which led to the formation of tablets with a lower permeability. A decreased tablet permeability corresponded to an increased tablet tensile strength except that the highest binder content was associated with a drop in the tablet tensile strength. CONCLUSIONS: The solution binder reduced the agglomerate shear strength, which was expressed as an increased degree of agglomerate deformation during compression. The latter seemed to be controlled by both agglomerate porosity and shear strength. The main role of the solution binder in improving the agglomerate compactability was to increase the degree of deformation of agglomerates during compression.

Cellulose↗

PubMedDate not supplied

[Determination of the elasticity of the femoral cortex of Adam's arc in patients with osteoarthritis].

In this study, the compressive strength, the compressive force as well as cortical thickness of prismatic specimens from Adam's arc of the femur were determined in patients with osteoarthrosis. Correlations were evaluated between the cortical bone parameters, which depend on age and sex. Supported by histomorphometric data of cancellous bone, the great variability of mechanical properties revealed the variable osteological status prior to implantation of hip endoprostheses. Its eventual consequences for alloarthroplastic surgery had been discussed.

Adult↗

PubMed2005

Evaluation of blends tincal waste, volcanic tuff, bentonite and fly ash for use as a cement admixture.

The evaluation of blends tincal waste (TW), fly ash (FA), bentonite (BE), volcanic tuff (VT) for use as a cement admixture was investigated. The properties examined include setting time, expansion, water requirement, specific surface and compressive strength of cement mixtures. The results revealed that the early compressive strength decrease with increasing tincal waste, due to tincal waste increasing initial setting time of the cement. The tincal waste and volcanic tuff of cement mixtures increased and there was reduction in compressive strength. The more the tincal waste increased the greater retardation there was initial setting time this may be attributed to containing high amount B2O3 and MgO content. The tincal waste and fly ash increased with expansion increased. Water requirement increased as the Blaine fineness of the cement mixtures increased. The results obtained were compared with standards and five batches were advised as suitable for the standard.

Bentonite↗

PubMed1980

Strength and biocompatibility of polymethacrylate-silica composite dental implant materials.

A study was made of the strength properties of several composite dental implant materials composed of silica microspheres (6%, 24%, and 48% by weight) and PMMA. Prepared specimens of the materials were tested for compressive strength and tensile strength as a function of the curing methods. Compressive strength was reduced only slightly when the 6% mixture was used, as compared to 100% PMMA, but the compressive strengths of the 12% and 24% mixtures were reduced by approximately 30% when compared to 100% PMMA. The compressive strengths of these materials were reduced even further after curing in a microwave oven, and the tensile strengths decreased to a greater degree. The 6% mixture was reduced by 38% in the heat-cured specimens and was reduced by 27% in the microwave-cured specimens. Tooth replica implants were placed in baboons and the peri-implant tissues were studied histologically after 6 months. Inflammation was minimal. Peri-implant alveolar bone was viable and active, and both connective tissue and epithelial attachment to the implant surface was evident.

Alveolar Process↗

PubMed1997

Effects of hydroxypropyl methylcellulose and other gelling agents on the handling properties of calcium phosphate cement.

The calcium phosphate cement (CPC) used in this study was formed by combining equimolar amounts of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). This powder, when mixed with water, sets to a hard cement in about 30 min. However, the water-based CPC paste is not highly cohesive and is vulnerable to washout until hardening occurs. The objectives of this study were to investigate the effects on handling properties, washout resistance, cement hardening behavior, and mechanical properties of adding several gelling agents to CPC paste. Aqueous solutions that contained a mass fraction of 2-4% of hydroxypropyl methylcellulose (HPMC), carboxyl methylcellulose (CMC), chitosan acetate, and chitosan lactate were used as cement liquids. Hardening time was measured by the Gilmore needle test; resistance to washout was evaluated by the disintegration of the cement specimen in water with agitation; and mechanical strength was evaluated by the measurement of diametral tensile strength and compressive strength. Handling properties were greatly improved by the addition of HPMC, CMC, chitosan acetate, and chitosan lactate. Hardening time was retarded by the additions of HPMC and CMC, and mechanical strength was weakened by the addition of either the chitosan lactate or the chitosan acetate.

Biocompatible Materials↗

PubMed1986

Influence of mixing technique on some properties of PMMA bone cement.

PMMA bone cements (Refobacin-Palacos R, Sulfix 6, AKZ, and CMW bone cement, types I and II), from six different clinics, were investigated in three stages. In the first stage, studies of density, hardness, flexural strength, and compressive strength were made, as well as molecular weight measurements and microscopic investigations. These studies reflected the current state of techniques of application used in operating theaters. They revealed wide variations in the properties of the materials studied. Secondly, a comprehensive study of the process-technology in the laboratory was performed. The following variables were investigated or discussed: mixing vessel, order of the individual components, mixing time, rate of mixing, pressure application on the mixed bone cement, kneading, cement thickness, pouring into the syringe, contact force during polymerization, and preparation quantity. The third stage involved the development and clinical testing of an improved mixing technique. Using this improved mixing technique, all three selected clinics achieved far better results with reduced variability. A comparison between a centrifuging technique after mixing and our improved, but conventional, mixing technique, displays advantages for the latter. The question regarding a correlation between cement specimens of high porosity and early implant loosening could not be answered on the basis of the 43 PMMA bone cement explants investigated (implanted 6 months to 15 years). In some cases, the studies revealed that the bone cement manufacturers should be required to revise and quantify existing instructions for use. The users, on the other hand, should give more consideration to the mixing technique and its consequences.

Bone Cements↗

PubMed1990

Mechanical properties of bone after implantation of apatite-wollastonite containing glass ceramic-fibrin mixture.

Mechanical properties of bone implanted with a mixture of apatite-wollastonite containing glass ceramic (A-W.GC) granules and fibrin were examined by compression testing. A 1:1 mixture of A-W.GC granules and fibrin (Group 1), 1:4 mixture of A-W.GC granules and fibrin (Group 2), and 1:1 mixture of hydroxyapatite (HA) granules and fibrin (Group 3) were implanted in the distal femoral metaphyses of rabbits. Histomorphometric analysis suggested that A-W.GC has a greater osteoconductive potential than HA. Trabeculalike structures were observed 24 weeks after the operation in all groups but were most notable in Group 2. Twenty-four weeks after the operation, in Groups 1 and 3, the compressive strength and compressive stiffness were higher than that of normal cancellous bone, and the fracture toughness was comparable with that of normal cancellous bone. In Group 2, all three values were similar to those of normal cancellous bone. Implantation of A-W.GC granules at a low density induces the formation of bone tissue which is similar to normal bone in both mechanical properties and morphology.

Animals↗

PubMed1993

Preparation and in vivo evaluation of a newly developed bioglass ceramic.

This paper presents details of the fabrication of a glass ceramic, and its application as an artificial bone prosthetic material. This new bioglass ceramic, with composition of Na2O 8.4%, CaO 40.6%, P2O5 12% and SiO2 39%, had 160-190 MPa and 800-980 MPa of three-point bending strength and compressive strength respectively. The ceramic has a (Na, Ca) (P, Si) O3 crystalline phase with a uniform crystal size of about 10 microns, which was attributed to the high nucleation frequency. The rabbit condyle test showed that the material formed a tight chemical bond with biological texture and had good biocompatibility.

Animals↗

PubMed2002

Mechanical and in vivo performance of hydroxyapatite implants with controlled architectures.

Internal architecture has a direct impact on the mechanical and biological behaviors of porous hydroxyapatite (HA) implant. However, traditional processing methods provide minimal control in this regard. To address the issue, we developed a new processing method combining image-based design and solid free-form fabrication. We have previously published the processing method showing fabricated HA implants and their chemical properties. This study characterized the mechanical and the in vivo performance of designed HA implants. Thirteen HA implants with orthogonal channels at 40% porosity were tested on an Instron machine. The compressive strength and compressive modulus measured were 30+/-8 MPa and 1.4+/-0.4 GPa, comparable to coralline porous HA. Twenty-four cylindrical HA implants with two architecture designs, orthogonal and radial channels, were implanted in the mandibles of four Yucatan minipigs for 5 and 9 weeks. Normal bone regeneration occurred in both groups. At 9 weeks, bone penetrated 1.4mm into both scaffold designs. The percent bone ingrowth in the penetration zone was higher in the orthogonal channel design but not statistically different due to the low number of samples. However, the overall shape of the regenerated bone tissue was significantly different. In the orthogonal design, bone and HA formed an interpenetrating matrix, while in the radial design, the regenerated bone formed an intact piece at the center of the implant. These preliminary results showed that controlling the overall geometry of the regenerated bone tissue is possible through the internal architectural design of the scaffolds.

Animals↗

PubMed1993

Effects of post-curing by heat on the mechanical properties of visible-light cured inlay composites.

The aim of this study was to evaluate the effects of post-curing by heat on the mechanical properties of visible-light (V-L) cured three inlay composites and three posterior filling composites. One group was only photo-cured according to the manufacturers' recommended methods, while the other group was heat-treated at 100 degrees C for 15 min following initial cure by V-L. Knoop hardness, diametral tensile strength and compressive strength were measured to evaluate the mechanical properties. Cure performance was checked out by the solvent immersion test. Upon secondary-curing by heat, it was confirmed that the mechanical properties of the composites were increased moderately and the cure performance of the composites was also improved.

Composite Resins↗