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Results for “Compressive Strength”

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At least 1,261 records · Page 70Linked to original sources

PubMed1979

[Correct timing of work on a hard plaster of Paris model].

Of the individuals in Hamburg questioned, 48% waited an average of 1 to 2 hours after making a stone cast before proceeding with work on it; 38%, 1 day; and only 2%, more than 1 day. The material test however showed that 5 or 6 days of storage at room temperature are necessary before optimal values are obtained for compressive strength, ball-thrust hardness, and abrasive hardness. The greatest amount of expansion with type IV stone plaster, removed from the cast after 30 minutes, was measured between 8 and 24 hours at room temperature, after the plaster had been mixed. The least changes in dimension were recorded after a 5-day contractive phase. Given these results, the stone cast should be stored for 5 to 6 days at room temperature before work is resumed on it if precision work is to be done.

Calcium Sulfate↗

PubMed1979

[Mechanical and dimensional properties of thermosetting resins for crown (author's transl)].

The various mechanical and dimensional properties of seven thermosetting methacrylic resins for crown and one heat-curing methacrylic resin as the control were investigated. The obtained results were as follows. 1. The water sorption, namely amount of sorption water and linear expansion by water sorption of hydrophobic poly-bis-MEPP resins were 50 to 70% of that of the control. But hydrophilic poly-EDMA resins indicated the water sorption about 1 to 1.5 times as much as the control. And a poly-UDMA resin was also hydrophilic as poly-EDMA resins, indicated about 1.3 times as much as the control. 2. The properties of poly-bis-MEPP resins were more excellent than that of poly-EDMA resins especially in the wet condition, at least were equal. 3. A poly-UDMA resin contained so-called organic composite fillers, indicated more excellent properties than other resins on hardness, abrasion resistance, linear coefficient of thermal expansion, compressive strength and bending strength in the dry condition. But, in the wet condition, some of these properties of a poly-UDMA resin were approximately equal to those of other resins.

Acrylates↗

PubMed1988

An analysis of the biomechanical mechanism of tibial stress fractures among Israeli infantry recruits. A prospective study.

The biomechanical mechanism of tibial diaphyseal stress fractures was studied prospectively in a group of 286 Israeli recruits. Before training each recruit had roentgenograms taken of his tibiae. Measurements of total tibial and cortical widths in the anteroposterior (AP) and mediolateral planes were made on these roentgenograms at two levels: at the point of the narrowest tibial width on AP roentgenograms (Level 1) and at the point of the narrowest width on lateral roentgenograms (Level 2). The tibial cross section was idealized as an eccentric ellipse within an ellipse, and on the basis of measurements taken from the roentgenograms, the cross-sectional area (compression strength), area moments of inertia about AP and mediolateral axes of bending (bending strength), and the area polar moment of inertia (torsional strength) were calculated for each cross section. During the course of 14 weeks of training, 20% of the recruits sustained tibial diaphyseal stress fractures, all of which were along the medial cortex. Using stepwise logistic regression analysis the tibia's bending strength along an AP axis of bedding at Level 2 was found to be the most significant factor determining whether or not a recruit would develop a tibial stress fracture.

Adult↗

PubMed1987

[The effect of selected disintegrants on the properties of three hydrochlorothiazide tablet formulations].

The admixture of disintegrants was investigated in three different hydrochlorothiazide formulations with respect to tablet properties. Sodiumcarboxymethyl starchs, Na-CMS (Explotab, Primojel, Na-CMS AB-G.D.R.), cross-linked polyvinylpyrrolidone, CL PVP (Polyplasdone) and potato starch were applied. The investigations were especially aimed at the alteration of tablet properties in dependence on compressive force. Considering the values of decomposition and compressive strength Polyplasdone XL has been proved to be the most effective disintegrant for the hydrochlorothiazide formulations investigated. Potato starch shows the worst results. There are only slight differences between the three Na-CMS.

Drug Compounding↗

PubMed1979

Silver polymethyl methacrylate antibacterial bone cement.

An improved antibacterial bone cement was sought based on the addition of low concentrations of inorganic silver compounds to polymethyl methacrylate. Composites with AgCl, Ag-AgCl, Ag2O, Ag2SO4 and Ag3PO4 in concentrations of 0.05% to 1% by weight, were tested in vitro against bacterial cultures. All were effective, but Ag2SO4 was especially so, even after 7 weeks of incubation in normal saline. Compressive strength of the cement was not affected by these additions, except in the case of Ag2O. Biocompabibility tests in rabbit muscle for up to 12 weeks showed no significant difference between the Ag -PMM and plain PMM in tissue reactivity, both being minimal. These features, coupled with the broad spectrum of antibacterial activity and low allergic potential of silver, make Ag-PMM an attractive alternative to conventional organic antibiotic/bone cement composites.

Acrylic Resins↗

PubMed1980

[Area of contact between osteosynthesis plate and bone in internal fixation (author's transl)].

The bone can be protected against excessive stress if the plate is properly adapted to the surface of the contact area between plate and bone, thus ensuring good and longlasting repositioning of the fracture. The article describes an in-vitro method for the quantitative evaluation of the contact area between plate and bone in osteosynthesis. With four different bones and the requisite plates, six expert surgeons were able to obtain an area of contact between plate and bone which varied between 13 and 60%, the average being 32%. The available data allow us to conclude that the peak loads of pressure occurring with small contact areas may be so great that they exceed the maximum compressive strength of the bone.

Bone Plates↗

PubMed1983

[Influence of the pressing force on the physical features of sulfathiazole tablets and the dissolution rate of the active ingredient].

When the pressing force increased in the examined system, so did the mechanical firmness of the tablets. A logarithmic connection exists between the pressing force and the compression strength and between the pressing force and the porosity, while the connection between the pressing force and the abrasion loss was a connection of power-function. The changing of the pressing force don't alter significantly the disintegration time of the tablets and the dissolution rate of the drug. However there is a considerable difference between the dissolution rate of the sulfathiazolee-powder and that of the tablets. The binders used in the pressing process were surface-active, therefore they accelerated the dissolution by moistening the surface of the sulfathiazol crystals.

Drug Compounding↗

PubMed1980

[Optimizing the fibrinogen-thrombin adhesive system].

It was the aim of the present three series of investigations to determine conditions to improve the firmness of the clot produced by the fibrinogen-thrombin adhesive system. For methodological reasons the compressive strength and adhesive power of the clot, as well as the probability of a relation between deformation energy and tensile strength were examined. Furthermore, the influence of fibrinolysis on the effects of the adhesive system was investigated. The following factors proved to be relevant for the firmness of the clot: 1. Concentration of fibrinogen, 2. concentration of thrombin, 3. relation between volume of fibrinogen and of thrombin solution, 4. time of diffusion of constituents of mixture, 5. addition of blood-clotting factor XIII and solution of calcium ions. The following optimum concentrations of components of the adhesive system per ml of the mixture were established in the course of the investigations: Fibrinogen solution (approx. 10% clottable material) 0.86 ml Thrombin 100 E. Factor XIII 90 E. = 30 mg Ca++ 250 mMol A volume ratio of 6 parts of fibrinogen as cryoprecipitate to 1 part of a solution containing thrombin, factor XIII and calcium ions proved optimal for the preparation of the mixture.

Animals↗

PubMed1980

[Studies on Pd base ternary alloys for dental amalgam. (Part 2) On the corrosion resistivity (author's transl)].

In the previous paper, the author reported the effect of composition of Pd base ternary alloys on the dimensional change, the compressive strength, hardness and microanalysis by EPMA. In this paper, corrosion resistivity of Pd base ternary alloy amalgam was studied by comparison of reflective light intensity, surface roughness and weight change before and after corosion test in 0.1% Na2S, 0.1% lactive acid and 1% NaCl solution. The main results obtained are as follows: (1) Pd base ternary alloy amalgam showed much higher corrosion resistivity than that of on the market silver-tin-copper amalgam. (2) On the (60 Pd-40 Ag)-Sn alloy amalgam, corrosion resistivity was gradually improved by addition of Sn up to 10 wt% Sn, and the best corrosion resistivity was observed in (60 Pd-40 Ag)-10 Sn among Pd base alloy amalgam tested in this study. (3) On the (60 Pd-40 Ag)-Cu alloy amalgam, corrosion resistivity decreased gradually with increment of Cu content. (4) Weight of (60 Pd-40 Ag)-Sn alloy amalgam was a little increased after corrosion test in 0.1% Na2S solution, but that of (60 Pd-40 Ag)-Cu alloy amalgam showed a tendancy to decrease. (5) Corrosion of Pd base alloy amalgam was observed mainly in the matrix. Tarnish on the core was observed a little. Since fine cut amalgam has the smaller rate of area of core than that of spherical amalgam, surface roughness was comparatively large.

Copper↗

PubMed1982

[Aluminous cement for dental application (author's transl)].

The various materials such as zinc oxide eugenol pastes, calcium hydroxide slurry and self hardening polymers have been used for the root canal filling and pulp capping. However, those materials have various problems in terms of biocompatibility and physical properties in clinical use. The development of root canal filling and pulp capping materials has been carried out with powder-liquid system which consisted of aluminous cement added to 20 wt% Ca (OH)2 and polyvinylalcohol solutions. The influence of polyvinylalcohol concentrations and L/P ratio on physical properties and biocompatibility were investigated. The results were as follows: 1. The initial setting time was showed between 3 and 20 minutes according to polyvinylalcohol concentration and L/P ratio and delayed linearly by increasing the L/P ratio. 2. The consistency was indicated between 18 and 51 mm with polyvinylalcohol concentration and L/P ratio. The lower the L/P ratio, the thicker was the consistency. 3. The solubilities in distilled water were 2.7-7.3% and 3.9-8.4%, respectively, after storage for 24 hours and 1 week, while those values in 199 medium were 2.9-6.2% and 4.4-9.9%, respectively, after storage for 24 hours and 1 week. 4. The pH values in distilled water were indicated high alkaline conditions of about 11.5 after storage for 24 hours and was not influenced by the repeated immersions. On the other hand, the pH values in 199 medium were showed high alkaline conditions of about 11.0 after storage for 24 hours, but decreased rapidly to the neutral conditions of about 8.0 with the repeated immersion. 5. The compressive strengths were increased by the use of higher polyvinylalcohol concentration and lower L/P ratio and indicated from 26 kg/cm2 and 278 kg/cm2. 6. By the use of the tissue culture method, mild response with the un-set cement was recognized from the morphological observation. In the case of the set cement, the cell morphological changes showed no significant difference in the cytotoxicity compared with that of control culture. The disappearance of the cytotoxicity was recognized in according to the progress of setting process.

Aluminum↗

PubMedDate not supplied

Some anatomical and mechanical considerations relevant to the surface replacement of the femoral head.

The internal structure of the arthrosic and normal femoral heads are grossly different although both are roughly circular. In particular bone is destroyed or defective superolaterally in the former. The compressive strength of the femoral head depends upon the medial trabecular system which runs through the head at approximately 20 degrees to the vertical i.e. the plane of the resultant of the major loads borne by the hip. Ideally a femoral resurfacing prosthesis should be placed in this axis. The bone of the arthrosic femoral head can be sustained by blood reaching it within the neck. Thus vessels on the intracapsular surface of the neck need not be preserved.

Biomechanical Phenomena↗

PubMed1995

Effect of particle variation on wear rates of posterior composites.

PURPOSE: To evaluate the relationship between filler size, shape, mechanical properties and wear resistance of posterior resin composite was evaluated. MATERIALS AND METHODS: Six UDMA/TEGDMA-based experimental resin composites consisting of different types of filler particles were investigated. These included four sized spherical fillers, (9.88 microns, 2.01 microns, 0.62 micron, 0.20 micron) and two irregular, (9.46 microns, 1.97 microns). Property measurements consisted of hardness and compressive strength. Wear resistance was evaluated by a three-bodied in vitro wear test. RESULTS: The composites containing the smallest sized spherical particle exhibited maximum mechanical strength and maximum wear resistance. The composites containing the largest spherical particle exhibited minimum wear resistance. There were no significant differences amongst those containing similar sized fillers regardless of particle shape. However, differences between the 0.20 microns spherical filled composite and other composites were statistically significant. SEM analysis showed that only the larger sized filler exhibited some exfoliation after wear testing. The smaller size spherical filler exhibited better mechanical strength and substantially higher wear resistance.

Analysis of Variance↗

PubMed1995

Bone density and osteoarthritis.

Osteoarthritis (OA) is a physiologic imbalance, a "joint failure" similar to "heart failure" in which mechanical as well as constitutional factors play a role. The initiation and progression of cartilage damage are distinct phenomena. One of the mechanisms of initiation of OA is subchondral bone stiffness, often a part of generalized inherited increased bone density. Evidence is accumulating that primary OA might initially be a bone disease rather than a cartilage disease. OA cases have a better preserved bone mass, even independent of body weight. Studies on iliac crest bone, a site far from load bearing forces, have shown differences in bone mass, biomechanical characteristics, biochemical composition, and mineralization profile according to the presence of OA in the hands. Women with OA had significantly more bone and the bone was significantly stiffer, they had higher compressive strength, higher osteocalcin, higher insulin-like growth factor I and II and transforming growth factor beta content, and a mineralization profile shifting to higher densities. These quantitative and qualitative differences in bone may produce disease by increasing subchondral bone stiffness and by making subchondral bone less deformable to impact leads. This stiff bone transmits more force to overlying cartilage, making it more vulnerable.

Bone Density↗

PubMed1976

A comparison of ultraviolet-curing and self-curing polymers in preventive, restorative and orthodontic dentistry.

Both self-cured and UV-cured resin-base dental materials are used in preventive, restorative, and orthodontic dentistry. Polymerization is initiated in both systems by free radicals. Self-curing materials generate free radicals by means of chemical compounds included in their formulation. UV-curing systems rely upon externally-supplied, long wavelength, ultraviolet radiation to produce free radicals within the material. Therefore, although the major chemical components of both systems are similar in many respects, each system has particular advantages and disadvantages over the other, which must be recognized by the practitioner. Substantial differences exist, for example, in the color stability of these two types of materials, because of the fact that the UV-cured system cannot include UV absorbers, which protect the self-cured systems from discoloration after exposure to sunlight. UV-cured systems require a limitation on the maximum depth of filled restorative that can be cured at one time, since the filler particles attenuate UV radiation. The limit-layer is generally established as 1-1-5 mm maximum thickness. Therefore, UV-cured filled systems are more time-consuming in restorations of deeper cavities. This liability is also in evidence as it affects the degree of polymerization of UV-cured filled systems. The uncertainty of complete polymerization is apparently responsible for highly erratic compressive strength data found with UV-cured restoratives. Normally, the amount of unpolymerized monomer is much less predictable in UV-cured systems, over that which is obtained in self-cured materials. The presence of a larger fraction of unpolymerized monomer creates a greater potential for pulpal injury from UV-cured restorative materials. The catalyst used in several UV-cured systems is benzoin methyl ether, a compound of rather high toxicity (LD50:300 mg/kg). The safety of using UV radiation in the vicinity of oral mucosa has not been firmly established. The design of the UV lamp should provide for focusing all radiation onto hard tissue. However, UV-cured systems do offer several advantages over self-cured systems. They normally are one-component systems and therefore are more convenient to use in certain types of applications, e.g., fissure sealing. UV-cured systems also provide an unlimited working time, an important advantage for specific applications.

Acrylic Resins↗

PubMed1993

Alloy particle shape and sensitivity of high-copper amalgams to manipulative variables.

Compressive strength, dimensional change during hardening and residual mercury content of three high-copper spherical particle amalgams (Tytin, Logic and Valiant), two admix amalgams (Dispersalloy and Permite C) and a conventional lathe-cut amalgam (New True Dentalloy) were determined as a function of condensation pressure and trituration time. The properties of the three amalgams containing non-spherical particles were markedly dependent on condensation pressure in the range 3 MPa to 14 MPa. Specimens condensed at 3 MPa showed substantially lower strength, greater expansion during hardening and higher residual mercury contents than did specimens condensed at 14 MPa. The three high-copper spherical particle amalgams, on the other hand, were comparatively insensitive to condensation pressure. Variations in trituration time between 5 and 12 seconds had little effect on the properties of any of the amalgams.

Copper↗

PubMed1976

[REM and Hommel tester studies of the dental enamel surfaces after removal of dental calculus with 2 different scalers].

Removal of gingival calculus was performed with two different scalers on teeth that had been extracted previously. Using scanning electron microscopic prints and the Hommel tester, it was demonstrated that the dental surface had obtained a clearly visible roughness. This is determined by the dental surface, the compressive strength and the characteristics of the various scalers. The use of a Tompkin reamer to smooth the surface produced even deeper criss-cross grooves than the scaler, and not a satisfactory smooth surface.

Dental Calculus↗

PubMed1994

Mechanical properties of articular cartilage in knees with unicompartmental osteoarthritis.

We studied the mechanical properties of cartilage from the apparently unaffected compartment of knees with unicompartmental osteoarthritis (OA). Plugs of cartilage and subchondral bone, 8 mm in diameter, were obtained from the tibial plateau of seven patients treated by total knee replacement. Control specimens were obtained from eight cadaver knees of similar age. Specimens were loaded by a plane-ended indentor in a hydraulic materials testing machine; we measured thickness, 'softness', rate of creep, and compressive strength of the articular cartilage. We found that the 'unaffected' cartilage from OA knees was significantly thinner and softer than control cartilage, and it was slightly, although not significantly, weaker. We conclude that the apparently unaffected cartilage in knees with unicompartmental OA is mechanically inferior to normal cartilage, even although clinically, radiologically and morphologically it appears to be sound.

Adult↗

PubMed1993

Preparation and characterization of porous apatite ceramics coated with beta-tricalcium phosphate.

Hydroxyapatite (Ca10(PO4)6(OH)2; HA) is one of the most biocompatible materials with bones, and porous HA is promising bone substitute materials for clinical applications. While there are reports that beta-tricalcium phosphate (Ca3(PO4)2; TCP) has higher resorbability than HA when the material is implanted in a bone defect. In the present study, porous HA coated with beta-TCP was prepared by our unique method. The porous HA of about 60% porosity with interconnecting pore structure was soaked in diammonium hydrogen phosphate solution, and then the HA was sintered at 900 degrees C for 3 h. beta-TCP was revealed by X-ray diffractometry on the surface of porous HA. It was possible to control the content of surface-formed beta-TCP arbitrary by varying the concentration of the solution. The obtained HA coated with 33 wt% beta-TCP (33TCP) had about 60% open porosity with the pore size from 150 to 400 microns. The average compressive strength of this porous ceramics was 17.5 MPa. Surface coated HA with beta-TCP deprived of the brittleness in handling. The weight of HA implanted into muscles was increased obviously at 4 weeks because of formation of carbonate hydroxyapatite on the surface of HA. The weight of 33TCP was scarcely changed up to 12 weeks, but the weight tended to increase at 24 weeks. The carbonate hydroxyapatite was not formed on 33TCP at 4 weeks, but formed on it at 24 weeks. Therefore beta-TCP coated porous HA behaved like beta-TCP initially after implantation, and then behaved like HA.

Animals↗