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PubMed1994

Recovery from pamidronate (APD): a two-year study in the dog.

The goal of this study was to find out if bone can recover after long-term administration of bisphosphonate. Disodium pamidronate (APD) was given orally by gavage to mature beagle dogs at doses of 0, 2.5, 12.5, and 25 mg/kg/day for 1 year (0.1% concentration) and the animals were allowed to recover for another year. At sacrifice, the os ilium was used to determine bone mineralization profile and, subsequently, each density fraction was analyzed chemically. The ribs were used to determine the lattice parameters and the size of the apatite crystals of bone. The sternum was used to determine selected morphometric parameters using image analysis of specimen X-ray films and, subsequently, to determine bone mechanical properties using a 3-point bending technique. We found that the 12.5 and 25 mg/kg/day doses exhibit a significant shift towards greater mineralization versus control, whereas the lower dose (2.5 mg/kg/day) was indistinguishable from the controls. The lattice parameters and crystal size of bone apatite remained unchanged. The image analysis shows a dose-related increase in trabecular volume and thickness. The connectivity increased with dose but the anisotropy of bone remained unchanged. Both the elastic modulus and the maximum stress of bone remain unaffected by APD. We conclude that when dogs are treated with APD for 1 year, their bones can reestablish their physical-chemical characteristics (mineralization profile, chemistry, and crystal size/strain) after 1 year of recovery, provided that the treatment dose is 2.5 mg/kg/day. In addition, the mechanical properties of the bone remained unaffected and the gains in trabecular volume and thickness are maintained.

Animals↗

PubMed1995

Properties of heat-treated composites after aging in water.

OBJECTIVES: Post-cure heat treatments have been shown to increase the fracture toughness and elastic modulus of composites. The objective of this study was to determine if the increase remained after the composites were aged in water. METHODS. The fracture toughness (K(lc)), flexural modulus and flexural strength of four experimental and one commercial composite (Z-100, 3M Dental Products) were tested after 1, 7, 30, 60 and 180 d of aging in 37 degrees C water. The four experimental composites were made with a BisGMA/TEGDMA resin and were characterized as follows: Micro = 38 vol% silane-treated silica, Fine = 65 vol% silane-treated quartz of 1-2 micrometer average size, Hybrid = 65 vol% silane treated quartz of a mixture of 1-2 micrometer average and 8 micrometer average size, and Large = 65 vol% quartz of 8 micrometer average size (of which only 75% were silane-treated). All specimens were light-cured (normal-cured; Triad II - 80 s). One set of each composite was further heat-cured at 120 degrees C for 10 min (heat-cured). A third set of the Hybrid was heat-cured with simultaneous light exposure (Elipar, Espe) for the first 3 min. RESULTS: By 30 d, normal-cured and heat-cured specimens showed significant (ANOVA/Tukey's test; p < or = 0.05) reductions in fracture toughness (avg. 16% and 22%, respectively), flexural modulus (avg. 11% and 11%, respectively) and flexural strength (avg. 25% and 29%, respectively). Further aging had little effect. The use of additional light-curing during heating did not affect the properties more than heat-curing alone. SIGNIFICANCE: The improvements in some of the properties of composites produced by heat-treating are of only short-term benefit, and are for the most part negated due to an alteration of the resin matrix as the composite equilibrates with water.

Analysis of Variance↗

PubMed2003

Human enamel dissolution in citric acid as a function of pH in the range 2.30< or =pH< or =6.30--a nanoindentation study.

The objective of this study was to investigate the dissolution of human enamel in citric acid solutions over a wide range of pH. The in vitro conditions are considered to be relevant to soft drink-induced enamel erosion. Nanoindentation was used to investigate changes in the nanomechanical properties of polished enamel surfaces after exposure to citric acid solutions. Solutions used had 38.1 mmol l-1 citric acid and pH greater than 2.3 but less than 6.3 (2.30 < or = pH < or = 6.30). Samples were exposed to rapidly stirred, constant composition solutions for 120 s. Statistically significant changes in enamel hardness and reduced elastic modulus were observed after exposure to all solutions. There was an approximately linear dependence of enamel hardness on solution pH for 2.90 < or = pH < or = 6.30. Below pH 2.90, enamel is thought to have reached the lowest possible hardness value. The reduction in enamel dissolution caused by an increase in pH of a soft drink is likely to be small. Product modification to reduce the erosive potential of drinks may require additional methods such as addition of calcium salts.

Citric Acid↗

PubMed2004

Physical properties of Escherichia coli P pili measured by optical tweezers.

The mechanical behavior of individual P pili of uropathogenic Escherichia coli has been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of approximately 10(3) PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. They are particularly important in the pathogenesis of E. coli colonizing the upper urinary tract and kidneys. A biological model system has been established for in situ measurements of the forces that occur during mechanical stretching of pili. A mathematical model of the force-versus-elongation behavior of an individual pilus has been developed. Three elongation regions of pili were identified. In region I, P pili stretch elastically, up to a relative elongation of 16 +/- 3%. The product of elasticity modulus and area of a P pilus, EA, was assessed to 154 +/- 20 pN (n=6). In region II, the quaternary structure of the PapA rod unfolds under a constant force of 27 +/- 2 pN (n approximately 100) by a sequential breaking of the interactions between adjacent layers of PapA subunits. This unfolding can elongate the pilus up to 7 +/- 2 times. In region III, pili elongate in a nonlinear manner as a result of stretching until the bond ruptures.

Bacterial Adhesion↗

PubMedDate not supplied

Finite element analysis studies of an all-ceramic crown on a first premolar.

PURPOSE: This study examined the effects of using four different core-ceramic materials on the stresses that developed in a single all-ceramic first premolar crown. MATERIALS AND METHODS: This was done by analyzing models constructed in an axisymmetric fashion with finite element analyses. The model had a 600-N vertical load applied uniformly over a circular area on top of the crown. Particular emphasis was placed on the tensile stresses that developed. RESULTS: For this particular type of model and loading configuration, radial tensile stresses were predominant in magnitude. Peak hoop and axial tensile stresses were approximately 80% and 2% of this value, respectively. The peak radial and hoop tensile stresses were located on the inside of the coping and scaled with the elastic modulus of the coping. For the axial component, the peak was located in the veneer ceramic on its outermost perimeter. CONCLUSION: Under normal loading, a near-uniform tensile stress field developed within the coping, directly beneath the contact area. The magnitude of this stress for realistic bite forces using current design recommendations was significantly lower than the fracture strength of the four ceramic materials investigated. The stresses developed within the porcelain were in all instances well below typical strength values.

Aluminum Oxide↗

PubMed1991

Cardiac hypertrophy and arterial compliance following drug treatment in hypertension.

The load of the heart in hypertension is related both to increased peripheral vascular resistance and decreased aortic compliance. From noninvasive studies involving determinations of pulse-wave velocity and systolic-diastolic variations of aortic arch diameter, it can be shown that increased aortic elastic modulus is strongly related to increased cardiac mass. The relationship is observed even after adjustment for the level of mean arterial pressure. It is suggested that decreased aortic compliance in hypertension causes a disproportionate increase in systolic pressure and end-systolic stress, thus contributing to promote cardiac hypertrophy. Such a possibility may have consequences for long-term antihypertensive therapy. Following converting enzyme inhibition and calcium blockade, important dissociations may be observed between the antihypertensive effect and the cardiac and arterial changes.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1987

A pulsed Doppler ultrasonic system for making noninvasive measurements of the mechanical properties of soft tissue.

In response to the need for a more precise means of predicting the interaction of a prosthetic socket with an amputee's residual limb, a gated Doppler ultrasonic motion sensing system was devised for making noninvasive measurements of the elastic modulus of soft tissue in vivo. Ultrasound was chosen for its ability to indicate the viscoelastic behavior of biological materials without damaging tissue. The system consists of a holding jig to support the limb being tested, a tissue vibrator, and an ultrasonic transducer to monitor the motion of the tissue. The ultrasonic transducer is controlled by an external computer to control the depth at which the sensor is measuring tissue displacement. This ultrasonic measuring technique provides as much information as more conventional techniques, but with more convenience and fewer restrictions.

Artificial Limbs↗

PubMed1998

Changes in the stiffness, strength, and toughness of human cortical bone with age.

Aging adversely affects the elastic and ultimate properties of human cortical bone as seen in uniaxial tests in quasi static loading, high strain rate impact or fatigue. Little is known about the full effects of aging on toughness and its relationship with strength. In the present article the elastic modulus (E), strength (sigma f), fracture toughness (KC and J-integral), and work of fracture (Wf) were determined in specimens of male human femoral bone aged between 35-92 years. In this way we investigated whether fracture of bone in three situations, allowing various amounts of damage prior to fracture, can provide a better insight into the fracture process and also the relative importance of these experimental methods for assessing the soundness of bone material. We found a steady and significant decrease with age for all these mechanical measures. E fell by 2.3%, from its value of 15.2 GPa at 35 years of age, per decade of later life; sigma f fell similarly from 170 MPa by 3.7%; KC from 6.4 MPa m1/2 by 4.1%; J-integral from 1.2 kJ m-2 by 3%, and the Wf from 3.4 kJ m-2 by 8.7%. In aging bone there was a deterioration in the elastic properties of the material. This reduced the (elastically calculated) critical stress intensity level (KC) required to initiate a macrocrack, or the nonlinear energy associated with the onset of fracture (J). The macrocrack was preceded by less damage, and once created needed less energy to drive through the tissue (Wf).

Adult↗

PubMed1981

Erythrocyte membrane elasticity during in vivo ageing.

Changes in the ability of senescent erythrocytes to pass through the microcirculation may cause them to be trapped in the spleen and removed from the blood. To help understand this process we have measured erythrocyte membrane elasticity, to see whether it changes during in vivo ageing. Human and rabbit red cells were fractionated by isopycnic sedimentation to obtain samples of aged and young cells. These were subjected to micropipette analysis in order to determine their membrane shear elastic modulus. We found that the membrane rigidity did not significantly alter as red cells aged. Previously we have also demonstrated that the changed size and shape of aged cells is unlikely to explain their removal from the circulation (Nash, G.B. and Wyard, S.J. (1981) Biorheology, in the press). Thus we conclude that the lifespan of erythrocytes is not determined by factors related to membrane flexibility or cell shape but may depend on changes in their viscous properties (as suggested by Williams, A.R. and Morris, D.R. (1980), Scand. J. Haematol. 24, 57--62).

Animals↗

PubMed2005

Rheology of Microcrystalline Cellulose and Sodiumcarboxymethyl Cellulose hydrogels using a controlled stress rheometer: part II.

Rheological properties of two different commercial grades of Microcrystalline Cellulose/Sodiumcarboxymethyl Cellulose (MCC/NaCMC) hydrogels were investigated. Viscoelastic characterization of the hydrogels using a controlled stress rheometer revealed that structure formation in the gels could be detected at a concentration as low as 1.0% w/w MCC/NaCMC in purified water. The elastic modulus (G') and the linear viscoelastic region (LVR) increased with increase in hydrogel concentration. The frequency sweep study of the hydrogels exhibited a flat G', indicating a stable structure at 1.5% w/w and 2.0% w/w concentrations. The oscillation time sweep study indicated that the rate of structure build up was dependent on the concentration of hydrogel. Structure buildup at various temperatures indicated that structure formation was rapid at higher temperature (40 degrees C), and the gel point was reached fairly quickly. Phase volume of the hydrogel significantly influenced structural recovery at different temperatures.

Carboxymethylcellulose Sodium↗

PubMed1997

The mechanical properties of elastic arteries in Ehlers-Danlos syndrome.

OBJECTIVE: To study whether measurements of wall mechanics can be used as an indicator of disturbed vessel wall integrity and predictor of vessel fragility in Ehlers-Danlos Syndrome (EDS). METHODS: The wall mechanics of the abdominal aorta (AO) and common carotid artery (CCA) were estimated from the indices Ep (pressure strain elastic modulus) and stiffness (beta) in twelve individuals with EDS of different subtypes and compared with the results of a healthy reference population. Ep and beta were calculated from diameter and pulsatile diameter change determined non-invasively with the aid of an ultrasonic echo-tracking system and blood pressure obtained by the auscultatory method. RESULTS: Compared with normal individuals and their confidence intervals, subjects with EDS had unaltered diameter, Ep and beta in the AO, as well as in the CCA. Analysis of covariance (ANCOVA) also showed unaltered results. AO: diameter (males p = 0.66, females p = 0.27), Ep (males p = 0.81, females p = 0.27) and beta (males p = 0.95, females p = 0.12). CCA: diameter (males p = 0.36, females p = 0.46), Ep (males p = 0.93, females p = 0.48) and beta (males p = 0.86, females p = 0.47). CONCLUSIONS: This investigation could not demonstrate any alteration in wall mechanics as a sign of disturbed vessel wall integrity of elastic arteries in EDS. This might indicate that the structural defect in the arterial wall collagen, and thus the tendency to vessel fragility, cannot be revealed under normal physiological pressure conditions.

Adolescent↗

PubMed1976

Physical properties of a nickel-base alloy prepared by isostatic pressing and sintering of the powdered metal.

The physical and mechanical properties of samples of a nickel-base alloy fabricated by powder metallurgy were determined. The particle sizes of the powders used to make the samples varied from -80/ +200 mesh to -325 mesh. The compaction pressure varied from 138 to 414 MN/m2 and the sintering temperature varied from 1150 to 1250 degrees C. The shrinkage during processing, the porosity, tensile strength, yield strength, elongation, and elastic modulus were used to characterize the samples. The strength of the samples generally increased with decreasing particle size of the powder and increasing compaction pressure and sintering temperatures. The porosity and strength, therefore, could be varied over a wide range by controlling the various parameters. The properties of the samples prepared by powder metallurgy were compared with those of the cast alloy and compact bone. Conditions can be selected that will yield equivalent or better properties by powder metallurgy than by casting.

Bone and Bones↗

PubMed1995

Alterations in systemic arterial mechanical properties during septic shock: role of fluid resuscitation.

The effects of septic shock (endotoxin; EDTX) on arterial mechanical properties were studied in anesthetized rabbits, both in the absence (EDTX alone) and presence (EDTX + fluids) of fluid resuscitation. Aortic pressure-flow (n = 20) and pressure-diameter (n = 10) measurements were used to calculate systemic arterial and regional aortic mechanical properties. At 3 h of EDTX shock, EDTX-alone rabbits had elevated total peripheral resistance (TPR, + 30%, P < 0.05), reduced cardiac output (CO, -40%, P < 0.05), and increased aortic characteristic impedance (Zc, +78%, P < 0.05). In contrast, the EDTX + fluids group responded with decreased TPR (-30%, P < 0.05), a tendency to increase CO (+23%), and elevated Zc (+46%, P < 0.05). A reduction in aortic diameter (-20%, P < 0.05) and an increase in elastic modulus (+50%, P < 0.05) and water content (+23%, P < 0.02) of the aortic wall were observed following endotoxemia. Thus following EDTX 1) "hyperdynamic" septic shock profile (i.e., low TPR, high CO) was observed only when concomitant fluid replacement was provided, 2) aortic wall stiffening was present due to both increased smooth muscle tone and vessel wall edema, and 3) fluid resuscitation resulted in discordant changes in TPR and Zc, suggesting differential flow-induced vasodilation between arteriolar and aortic smooth muscle.

Animals↗

PubMed1979

Effect of methacholine chloride on rheology and transport of canine tracheal mucus.

The effect of methacholine chloride (M) on tracheal mucus was investigated in three conscious tracheostomized dogs. Aerosols of M in concentrations of 2--32 mg/ml were delivered intratracheally for 1 min. Mucus was sampled with a cytology brush at 2 min postchallenge and at irregular intervals thereafter. The mechanical properties of each sample were determined in the magnetic microrheometer, and correlated with mucociliary transportability as assayed by the frog palate technique. With high doses of M, there was an increase in volume of secretion collected per unit time. The elastic modulus (G') at 2 min postchallenge went up (to 1.5 x 2.3 x control for 16 and 32 mg/ml, respectively) then fell below control before returning to base line after 30 or 45 min. With low doses of M (2--8 mg/ml) the secretion rate was also above control, but only a decrease in G' (to 0.54 x control) was observed. The decrease in G' at low doses did not significantly alter the frog palate transport rate; however, the increase at higher doses did impede mucociliary transport.

Animals↗

PubMed2005

Influence of fibrillin-1 genotype on the aortic stiffness in men.

Aortic stiffness is a predictor of cardiovascular mortality. The mechanical properties of the arterial wall depend on the connective tissue framework, with variation in fibrillin-1 and collagen I genes being associated with aortic stiffness and/or pulse pressure elevation. The aim of this study was to investigate whether variation in fibrillin-1 genotype was associated with aortic stiffness in men. The mechanical properties of the abdominal aorta of 79 healthy men (range 28-81 yr) were investigated by ultrasonographic phase-locked echo tracking. Fibrillin-1 genotype, characterized by the variable tandem repeat in intron 28, and collagen type I alpha 1 genotype characterized by the 2,064 G>T polymorphism, were determined by using DNA from peripheral blood cells. Three common fibrillin-1 genotypes, 2-2, 2-3, and 2-4, were observed in 50 (64%), 10 (13%), and 11 (14%) of the men, respectively. Those of 2-3 genotype had higher pressure strain elastic modulus and aortic stiffness compared with men of 2-2 or 2-4 genotype (P = 0.005). Pulse pressure also was increased in the 2-3 genotype (P = 0.04). There was no significant association between type 1 collagen genotype and aortic stiffness in this cohort. In conclusion, the fibrillin-1 2-3 genotype in men was associated with increased aortic stiffness and pulse pressure, indicative of an increased risk for cardiovascular disease.

Adult↗

PubMed2000

Characterization of bioactive glass-reinforced HAP-polymer composites.

The effect of bioactive glass on the mechanical properties of hydroxyapatite-Ca polyacrylate composites was studied. Powder mixtures of tetracalcium phosphate (TetCP), poly(acrylic-co-itaconic) and bioactive glass (up to 50% by weight) were hot pressed for 30 min at 300 degrees C and 40 kpsi. Tensile strengths, elastic moduli, and microstructures of the composites produced were investigated. Results showed the mechanical properties of these composites were enhanced by the addition of bioactive glass. The highest values of tensile strength and elastic modulus were achieved with the addition of 10% bioactive glass. Composites were immersed in SBF for up to 10 days, then in 1.5 simulated body fluid (SBF) for a week. The changes in the concentrations of Ca, P, and Si ions of these solutions were measured. The microstructures of these composites after SBF immersion were also evaluated. Concentrations of Ca, P, and Si increased with the time of immersion in SBF owing to the formation of an apatite layer on their surfaces as found by SEM with energy-dispersive spectroscopy attachment.

Biocompatible Materials↗

PubMed2002

In vitro evaluation of dental bonding agents using shear and vibrational methods.

OBJECTIVE: To determine the suitability of two mechanical test methods for the in vitro evaluation of dental bonding agents. METHODS: The first method was the Iosipescu shear test in which a pure shear stress is induced in a notched beam sample, and the second was a multilayer vibrating reed test in which the effectiveness of bonding could be assessed by the magnitude of relative elastic modulus and mechanical damping factors. The tests were applied to bonded samples of high-copper amalgam, gallium alloy and composite resin with two different types of adhesive. Representative data is presented to show the capabilities of the test methods. RESULTS: Both methods were shown to generate more consistent data with lower scatter than that usually reported in this field. Each may be used to provide information of clinical relevance. CONCLUSION: With further development, these test methods could make a useful contribution to the assessment of dental bonding agents.

Composite Resins↗

PubMedDate not supplied

Assessment of trabecular structure using high resolution CT images and texture analysis.

PURPOSE: Our goal was to use high resolution (HR) CT images combined with texture analysis to investigate the trabecular structure of human vertebral specimens and to compare these techniques with bone mineral density (BMD) in the prediction of bone strength. METHOD: HR CT images with a slice thickness of 1 mm were obtained of 28 bone cubes. Four different groups of texture analysis techniques were used to assess these images. In addition, quantitative CT (QCT) was performed and elastic modulus (EM) was determined biomechanically. RESULTS: R2 between EM and BMD was 0.78 (p < 0.01). R2 values for EM versus most of the texture measures were also significant. Texture measures in addition to measures of BMD in a multivariate regression model significantly increased R2 up to 0.87. CONCLUSION: In an experimental setting, texture parameters calculated using HR CT images correlated significantly with EM. Combining texture measures with BMD improved the prediction of EM significantly.

Adult↗