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Results for “Compressive Strength”

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At least 883 records · Page 49Linked to original sources

PubMed1983

Multiaxial strength characteristics of trabecular bone.

Bovine trabecular bone specimens were tested in multiaxial stress, including pure shear, in a special test device. Shear strength was proportional to apparent density to the exponent 1.65, in approximate agreement with theoretical and experimental studies on the shear strengths of porous foams. The mean shear strength was 6.60 +/- 1.66 MPa, after normalizing for apparent density. This compares well with normalized shear strengths from Saha and Gorman's (1981) study on human femora. A scanning electron microscope study indicated random trabecular architecture and a complex fracture mechanism at the level of the individual trabecular struts. Hoffmann's (1967) 3-D isotropic failure criterion was applied to the multiaxial test data, along with data from uniaxial compression tests, indicating a compressive strength approximately three times the tensile strength.

Animals↗

PubMed1978

Stress/strain behavior of dental amalgams.

The stress/strain behavior at different strain rates and the creep rate of dental amalgams were evaluated and compared to the microstructure. The results indicate that substantial differences exist both in strength and strain at fracture. The strain at fracture for high strain rates was associated with the nature of the particle-matrix interface, in that amalgams with an interpenetrating interface exhibited some ductility, while amalgams with an abrupt interface exhibited practically no plastic deformation at fracture. The correlation between creep and slow compressive strength was verified and it was suggested that grain boundary sliding was the deformation mechanism in both cases.

Dental Amalgam↗

PubMed1995

A physiological analysis of articulatory dysfunction in dysarthric speakers following severe closed-head injury.

A physiological analysis of the lip and tongue function of a group of 18 severely closed-head injured (CHI) subjects was performed using lip and tongue force transduction systems. Lip and tongue strength, endurance and rate of repetitive movements were assessed on four non-speech tasks: maximum strength, sustained maximum strength, repetition of 10 maximum strength compressions, and maximum repetition rate. The values recorded were compared to those achieved by a group of 18 non-neurologically impaired subjects, matched for age and sex, who served as the controls. The results of the study indicated that the CHI subjects demonstrated a significant impairment of lip and tongue function based on strength, endurance and rate of repetitive movements, compared to the controls. While lip function was found to be significantly impaired on several measures of strength and endurance, tongue function was noted to be more severely compromised. The CHI subjects were found to exhibit a significantly reduced rate of repetitive movements of the lips and tongue. The results are discussed in relation to the effects of CHI on neuromuscular function and differential subsystem impairment in dysarthria. The clinical implications of these findings are also discussed in relation to the treatment of articulatory disturbances following severe CHI.

Adult↗

PubMed2006

An in vitro optimized injectable calcium phosphate cement for augmenting screw fixation in osteopenic goats.

This study reports the proportioning and standardized mixing procedures for preparing a hydroxylapatite cement (tetracalcium phosphate and dicalcium phosphate) of desired viscosity and mechanical strength reproducibly for application in trauma surgery. The behavior and the biomechanical properties of the resulting bone cement in screw augmentation were then evaluated in our osteopenic goat model. The use of a shaker standardized the mixing procedure. The optimal volume of Na2HPO4 used to prepare the injectable cement was 0.45 mL/g, with averaged in vitro compressive strength of 48.29 +/- 5.62 MPa. Histology showed increasing tightly-coupled bone apposition on the cement surface without fibrous encapsulation as observed in the screw-only controls with time in the osteopenic goat model. The cement increased the initial screw pull-out force (54.7%, p = 0.005) significantly and the energy required to failure (54.7%, p < 0.05) significantly, and remained higher than the screw-only controls after 3 months (9.8% and 20.2%, respectively) and 6 months (20.2% and 44.7%, respectively). These results imply potential in the prevention of interfacial micromotions and subsequent fibrous tissue formation at the implant-bone interface resulting in a decreased risk of implant failure. The optimized cement in this study may serve as a good candidate for augmenting fixation of osteoporotic bone.

Animals↗

PubMed1999

Technical note: biomechanical analysis of two absorbable fracture fixation pins after long-term canine implantation.

The design requirements for bioabsorbable fracture fixation devices for specific applications are as yet unknown. Therefore, a range of initial mechanical properties and degradation kinetics may provide developers with additional choices for the design of absorbable fracture fixation devices. This study evaluated the changes in push-out strength, polymer mechanical properties, and bone mechanical properties of self-reinforced poly(glycolide) (SR-PGA) and poly(ortho ester) (POE) fracture fixation pins implanted into the canine femoral canal for 18 months. Mechanical testing indicated that SR-PGA pins had degraded to a pasty consistency by 3 months, showing complete loss of all mechanical properties. Meanwhile, POE pins showed a simultaneous linear decrease in both compressive strength and stiffness to almost zero by the end of the study period, suggesting that these devices were undergoing surface erosion. However, changes in specimen diameter, which would support this mechanism, were not apparent. The decrease in polymer density after 12 months suggests that there was an increase in bulk erosion for POE devices. This was further supported by the observation of internal polymer resorption noticed in specimen cross-sections after 18 months. This observation appears to be related to the method of polymer processing; hot-compression molding of fine powdered polymer. The appearance of grain boundaries would provide a path for water to penetrate into the bulk polymer and cause autocatalysis in the interior of the implant.

Absorption↗

PubMed1993

Composite resins in the 21st century.

Human enamel and dentin should be used as the physiologic standards with which to compare composite resins, especially in the posterior region. The intrinsic surface roughness of composite resins must be equal to or lower than the surface roughness of human enamel on enamel-to-enamel occlusal contact areas (Ra = 0.64 microns). Roughness determines the biologic strength of composite resins. The nanoindentation hardness value of the filler particles (2.91 to 8.84 GPa) must not be higher than that of the hydroxyapatite crystals of human enamel (3.39 GPa). Composite resins intended for posterior use should have a Young's modulus at least equal to, and preferably higher than, that of dentin (18.500 MPa). The compressive strength of enamel (384 MPa) and dentin (297 MPa) and the fracture strength of a natural tooth (molar = 305 MPa; premolar = 248 MPa) offer excellent mechanical standards to select the optimal strength for posterior composite resins. The in vivo occlusal contact area wear rate of composite resins must be comparable to the attritional enamel wear rate (about 39 microns/y) in molars. Differential wear between enamel and composite resin on the same tooth is a new criterion for visualizing and quantifying the wear resistance of composite resins in a biologic way. Posterior resins must have a radiographic opacity that is slightly in excess of that of human enamel (198% Al). Based on these standard criteria, it can be concluded that in the 21st century the ultrafine compact-filled composite resins may be the materials of choice for restoring posterior cavities.

Analysis of Variance↗

PubMed1976

Influence of application technique on microstructure and strength of acrylic restorations.

An investigation was made of the influence of application techniques on the microstructure and properties of an acrylic tooth restorative. Mixtures of acrylic powder and monomer ("Sevriton Simplified") were applied by the brush technique of Nealon (J. Prosth. Dent., 2, 513, 1952) and by two bulk flow techniques. While similar porosities (about 4%) were observed, the brush technique resulted in a greater quantity of grains from the acrylic powder. Despite this, there was little difference in values of compression modulus, compressive yield stress, and diametral compressive strength. The mechanical strength of the materials studied was less than one-half that of high molecular weight poly(methyl methacrylate) (PMMA). Crack propagation studies established that the interface between the grains and matrix was not a source of weakness. However, as the matrix was crosslinked this could not be checked by solution methods of polymer characterization.

Acrylic Resins↗

PubMed1991

Biomechanics of fracture risk prediction of the hip and spine by quantitative computed tomography.

In this review, we have made use of some simple engineering concepts to summarize current efforts relating QCT measures to bone density and strength. From a variety of in vitro experiments on cadaveric vertebrae and femora, it is evident that both apparent and ash densities are strong linear functions of QCT measures, with coefficients of determination ranging from 0.49 to 0.90 and relative errors from 44.9% to 7.1%. QCT data also can be used (with somewhat less confidence) to determine the compressive modulus (R2s from 0.36 to 0.68, relative errors from 45.0% to 35.5%) and compressive strength (R2s from 0.58 to 0.70, relative errors from 56.5% to 39.9%) of trabecular bone from the proximal femur and vertebral body. In cortical bone, material properties are only correlated weakly with QCT measures. Experiments designed to relate QCT data to failure loads for the proximal femur and vertebral body have been remarkably successful. Coefficients of determination have ranged from 0.32 to 0.93, with relative errors from 31.1% to 13.9%. However, when the in vitro failure loads determined in these experiments are compared against available estimates of in vivo loads on the spine and hip, it is apparent, at least in the elderly, that in vivo loads are relatively close to those that cause fracture in vitro. To assess the possibility of developing QCT-based clinical predictors of fracture risk for individual patients, we have introduced the concept factor of risk often used in engineering design to account for uncertainties in estimates of service loads and component strength. The factor of risk for a particular loading condition is defined as the ratio of expected service loads to the known failure loads. To extend this concept to densitometric fracture risk prediction in vivo, it is important to recognize that densitometric data must not only be used to predict the ultimate load carrying capacity of the region of interest, but that this ultimate load must then be compared to the forces expected in vivo under comparable loading conditions. One difficulty with this approach is that little is known about the in vivo forces that are associated with atraumatic age-related fractures of the hip and vertebrae and even less about the forces applied to the hip and spine during traumatic events such as falls. However, from available estimates of in vivo loads during bending and lifting, it is apparent that in the elderly, factors of risk for the spine can easily approach 1.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMedDate not supplied

Variable reduced metal support for collarless metal ceramic crowns: a new model for strength evaluation.

A newly designed specimen allowed strength testing of simulated collarless metal ceramic crowns. The design provided precision replication of specimens having ceramic veneers that were completely supported by metal or that were extended 1 and 2 mm beyond the metal support. Twelve specimens of each design were loaded to failure at angles of 90, 45, and 6 degrees. Specimens with unsupported extensions approximated the compressive strength of those with complete framework support (means of 291.6 MPa, 320.2 MPa, and 335.9 MPa, respectively, for 1 mm, 2 mm, and 0 mm of porcelain extension) when tested at 90 degrees. However, for corresponding porcelain lengths, mean resistance to fracture at an angle of 45 degrees was 7.3, 11, and 5.8 times smaller, and at an angle of 6 degrees, 45, 60, and 25 times smaller. The differences were highly significant (P < .001). These results suggest that collarless metal ceramic crowns having up to 2 mm of unsupported porcelain could resist the same axial pressure as those restorations with complete metal support, provided a 90-degree shoulder tooth preparation is used.

Analysis of Variance↗

PubMed2001

Biomechanical compression tests with a new implant for thoracolumbar vertebral body replacement.

The authors present an investigation into the biomechanical functioning of a new titanium implant for vertebral body replacement (Synex). Possible indications are fractures and/or dislocations with damage of the anterior column, posttraumatic kyphosis and tumors of the thoracolumbar spine. The construction must be supplemented by a stabilizing posterior or anterior implant. For best fit and contact with adjacent end-plates, Synex is distractable in situ. We performed comparative compression tests with Synex and MOSS ("Harms mesh cage") on human cadaveric specimens of intact vertebrae (L1). The aim of the study was to measure the compressive strength of the vertebral body end-plate in uniaxial loading via both implants to exclude collapse of Synex in vivo. Twelve human cadaveric specimens of intact vertebrae (L1) were divided into two identical groups (matched pairs) according to bone mineral density (BMD), determined using dual-energy quantitative computed tomography (DE-QCT). The specimens were loaded with an axial compression force at a constant speed of 5 mm/min to failure, and the displacement was recorded with a continuous load-displacement curve. The mean ultimate compression force (Fmax) showed a tendency towards a higher reading for Synex: 3396 N versus 2719 N (non-significant). The displacement until Fmax was 2.9 mm in the Synex group, which was half as far as in the MOSS group (5.8 mm). The difference was significant (P < 0.001). The compression force was twice as high, and significantly (P < 0.05) higher with Synex at displacements of 1 mm, 1.5 mm and 2 mm. A significant (P < 0.001) correlation (R = 0.89) between Fmax and BMD was found. Synex was found to be at least comparable to MOSS concerning the compressive performance at the vertebral end-plate. A possible consequence of the significantly higher mean compression forces between 1 and 2 mm displacement might be decreased collapse of the implant into the vertebral body in vivo.

Biomechanical Phenomena↗

PubMed1998

Effect of clodronate treatment on established bone loss in ovariectomized rats.

The ability of clodronate to prevent bone loss and weakening of bone strength was studied in adult rats with established osteopenia. Six-month-old female Sprague Dawley rats were randomized into 13 groups. One group was killed at the start of the study, nine groups were ovariectomized (ovx), and three groups sham-operated (sham). After 4 months, the ovx rats were given either clodronate or vehicle subcutaneously (s.c.), once a week for 3 or 6 months, the cumulative doses of both dosing regimens being 36, 84, and 300 mg/kg. Clodronate reduced the increase in bone turnover as evidenced by serum osteocalcin and urinary deoxypyridinoline. Cancellous bone loss was more severe in distal femur than in lumbar vertebral body already at 4 months after ovx. Cortical osteopenia of femoral middiaphysis was significant at 7 and 10 months after operation and was in accordance with the impaired bending strength of the femoral shaft. In the tibia, the bending strength was, by contrast, increased at each timepoint after ovx. In distal femur, higher values of cancellous bone volume (BV/TV) were found after 6 months of clodronate treatment than in ovx/vehicle-treated rats. In lumbar vertebrae, only the lowest dose of clodronate slightly counteracted the ovx-induced further decrease in BV/TV, but reduced, at all dosages, the impairment of lumbar vertebral compression strength. The maximum load of femoral neck did not differ between vehicle-treated ovx and sham groups after clodronate treatment, but clodronate reduced the weakening of femoral shaft. A further increase in the bending strength of the tibia was found after clodronate treatment. There was a positive correlation between bending strength and ash weight in both the tibia and the femur. Histomorphometry further showed that long-term use of clodronate does not impair bone mineralization or affect modeling-dependent bone formation. In conclusion, clodronate treatment clearly slows down the progress of bone loss and prevents further weakening of bone strength in femoral shaft and vertebrae, even though it cannot completely reverse the effects of ovariectomy-induced changes in established osteopenia.

Amino Acids↗

PubMed2004

Anti-bone resorption activity of deer antler aqua-acupunture, the pilose antler of Cervus korean TEMMINCK var. mantchuricus Swinhoe (Nokyong) in adjuvant-induced arthritic rats.

Effect of deer antler aqua-acupunture (DAA), prepared from the pilose antler of Cervus korean TEMMINCK var. mantchuricus Swinhoe, a traditional immunosuppressive acupuncture, was evaluated to assess the reductions in bone mass, strength, and turnover in adjuvant-induced arthritic rats. For measuring the above parameters, a 20-day dosing experiment was performed using 6-week-old female Lewis rats. Arthritis was induced by injecting the adjuvant into the hind paw of the Lewis rats. The age-dependent increases in the body weight, lumbar bone mineral content and density (BMC and BMD) and compressive strength were disturbed in the arthritic rats. At 10 days, the histomorphometric parameters of bone formation (BFR/BS and BFR/BV) and the serum osteocalcin levels were significantly reduced compared with the baseline controls of Lewis rats. However, the BMC values corrected for body weight did not differ significantly between the arthritic and normal rats, and the bone minerals were not reduced when they were compared with the baseline controls. At 20 days, the parameters of bone minerals and strength of the lumbar body in the arthritic rats, both with and without correction for body weight, were significantly reduced compared with the baseline controls. The trabecular mineralizing surface remained significantly reduced and the osteoclast numbers were increased. DAA at the doses of 10, 20, 50 and 100 microg/kg, administered by Shinsu (B23) acupuncture daily from the start of the experiment, significantly prevented the development of the chronic paw edema at 20 days. The reductions in the parameters such as bone minerals, strength, and trabecular bone formation, and the increase in osteoclast number were alleviated by this DAA. Age-dependent increases in the lumbar height, disturbed by the adjuvant injection, were also maintained. These results indicated that a 20-day-period is necessary to obtain sufficient reductions in the bone mass and strength of the lumbar body concerning the model of secondary osteoarthritis in adjuvant arthritic rats. DAA was able to prevent these reductions by modulating the bone turnover in this arthritis model.

Acupuncture↗

PubMed2005

Daptomycin treatment of Staphylococcus aureus experimental chronic osteomyelitis.

BACKGROUND: Infection due to methicillin-resistant Staphylococcus aureus (MRSA) is increasingly common in nosocomial and community settings. Daptomycin is a cyclic lipopeptide anti-infective with activity against MRSA, approved for treatment of complicated skin and skin structure infections. Daptomycin may be useful in systemic or local treatment of chronic osteomyelitis. METHODS: We measured mechanical strength of daptomycin- and vancomycin-loaded polymethylmethacrylate (PMMA), assayed in vivo release of daptomycin and vancomycin from daptomycin- and vancomycin-loaded PMMA, respectively, and compared the efficacy of two systemic doses of daptomycin with that of vancomycin, each with or without the respective anti-infective loaded into PMMA, using a rat model of MRSA chronic osteomyelitis. RESULTS: Neither tensile nor compressive strength of PMMA was impacted by impregnation with these antimicrobials at a concentration of 7.5% by weight. The peak concentrations of daptomycin and vancomycin in rat tibial bone surrounding a 7.5% daptomycin- and vancomycin-loaded 3 mm PMMA bead were 178 and 49 mg/L, respectively. In the treatment of experimental osteomyelitis, rats assigned to no treatment, daptomycin 50 mg/kg subcutaneously twice daily, daptomycin 60 mg/kg subcutaneously twice daily, and vancomycin 50 mg/kg intraperitoneally twice daily had 6.4, 4.1, 4.0 and 4.5 median log10 cfu/g of bone at the end of 21 days of therapy. All systemic anti-infectives studied were more active than was no treatment. Daptomycin- or vancomycin-loaded PMMA did not, however, exhibit microbiological efficacy alone or adjunctively, as assessed 21 days after implantation. CONCLUSIONS: Daptomycin is released from PMMA in vivo at a rate similar to that of vancomycin. Systemic daptomycin is as active as vancomycin in a rat model of chronic MRSA experimental osteomyelitis.

Animals↗

PubMed1992

Decrease in bone strength of cadmium-treated young and old rats.

A decrease in mechanical strength of bones was observed both in young and old rats for long periods of administration of cadmium. Young (3-week-old) female rats were given 0 (control), 5 and 10 ppm cadmium in drinking water, respectively, for 20 weeks. Old (18-month-old) female rats were given 0 (control) and 40 ppm cadmium in drinking water, respectively, for 7 months. The compression strengths of bones of young rats which were given 10 ppm cadmium, and those of old rats which were given 40 ppm cadmium, significantly decreased at the distal end portion of femur. Cadmium contents in bones in the 10 ppm and 40 ppm groups were about 110 and 210 ng/g dry weight, respectively. The present result confirmed that cadmium has a lesional effect on the mechanical strength of bone at the concentration of 100-200 ng/g in dry weight of bone, for both young and old rats.

Aging↗

PubMed1997

Decreased bone mass and strength in ovariectomized cynomolgus monkeys (Macaca fascicularis).

Agents for prevention or treatment of osteoporosis must now be tested in a large animal species that exhibits bone remodeling. Ovariectomized, nonhuman primates provide one such model, and they consistently develop osteopenia accompanied by high bone turnover rates. The goal of this study was to further characterize this model, and particularly to determine the effect of ovariectomy on bone strength in vertebrae and femoral necks. Longitudinal evaluations of spinal bone mass and serum markers of bone turnover were performed in 19 sham-ovariectomized (SHAM) and 18 ovariectomized (OVX), domestically reared cynomolgus monkeys, aged > 9 years. OVX monkeys lost bone relative to both baseline values and SHAM controls. Serum markers of bone turnover were increased by OVX. After 72 weeks, both vertebral bone compressive strength and femoral neck breaking strength were significantly decreased in OVX animals compared with SHAM. Ovariectomized cynomolgus monkeys, like postmenopausal women, develop accelerated bone loss, increased bone turnover, and reduced bone strength, and provide a suitable large animal model for efficacy studies with agents for prevention or treatment of osteoporosis.

Alkaline Phosphatase↗

PubMed1976

The effects of pylon shape on bone-pylon interface performance in direct skeletal attachment.

The attachment of a prosthesis directly to the part of the skeleton remaining after an amputation offers many improvements over coupling schemes used in conventional prostheses. However, the stresses induced in the bone by the macrostructure of the attached prosthetic device must first be understood because they are a significant consideration in the design of a successful direct skeletal attachment (DSA) system. This investigation utilizes the finite element method of analysis to structurally model some possible DSA systems. Static stress-response models for an above-the-knee human femoral amputation are formulated to investigate the effect of variations in pylon macrostructure on system performance. The models approximate the initial stages of support following the insertion of a pylon into the medullary cavity of the bone and are also used to assess the bond strengths that must be developed between the bone and pylon for a "no-slip" condition to hold at their interface. The analyses indicate that either a shaped, marrow cavity-fit pylon or four 135 degree wedges with a complementary pylon are favorable geometries for a DSA system. The stress levels caused by these two geometries are on the order of 20% of the axial compressive strength of cortical bone. For each, local stress levels at the bone-biomaterial interface remain the critical parameters for investigation.

Artificial Limbs↗

PubMed1981

Mechanical testing of trabecular bone in knee replacement.

To measure the strength of the juxta-articular trabecular bone in knee replacement, an osteopenetrometer was developed. The principle of its function is tha a needle penetrates the bony tissue and during this penetration the pressure on and the displacement of the needle is registered. The instrument was tested on cadaveric specimens of the proximal tibia. Good agreement was found between the osteopenetrometer findings in 18 cases and compression tests on the same bony structure. Forty-five measurements at different sites of the tibial resection surface revealed that the force needed for the penetration varied according to a pattern known from the determination of the elasticity modulus and ultimate compressive strength of bone in the same area. Histological examination of the penetration canals in the bone disclosed only sparse upsetting of bone. Curves from corresponding bone proved to reflect, in height as well as shape, the morphology of the skeletal structure. The osteopenetrometer appears to be applicable fo objectively assessing the solidity of trabecular bone during the operation. Thereby it is possible, in each individual case, to form a basis for more varied planning of the postoperative treatment programme.

Biomechanical Phenomena↗

PubMedDate not supplied

Improved bioresorbable microporous intravascular stents for gene therapy.

Drug imbibing microporous stents are under development at a number of centers to enhance healing of the arterial wall after balloon coronary angioplasty procedures. The authors improved the mechanical strength and reservoir properties of a biodegradable microporous stent reported to this Society in 1994. A combined tubular/helical coil stent is readily fabricated by flotation/precipitation and casting/ winding techniques. A two stage solvent swelling technique allows precise adjustment of the surface hydrophilic/hydrophobic balance. These developments permit seven-fold improvement in drug capacity without significantly altering mechanical properties. Stents modified in this manner retain tensile and compressive strength and are suitable for remote deployment. Elution kinetics of these modified stents suggest they are suitable for gene delivery. Successful gene transfer and transmural expression have been demonstrated after implantation of stents impregnated with a recombinant adenovirus carrying a nuclear localizing beta-galactosidase reporter gene into rabbit carotid arteries. These studies suggest that surface modified, bioresorbable polymer stents ultimately may be useful adjunctive devices for gene transfer during percutaneous transluminal revascularization.

Angioplasty, Balloon↗