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Results for “Compressive Strength”

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PubMed2005

[A comparative study on cyclic and static fatigue of dental ceramic by means of Hertzian's contact].

OBJECTIVE: To compare the difference in strength degradation and morphology damage of brittle dental ceramic after static load and cyclic fatigue. METHODS: Hertzian's contact technique with a tungsten carbide sphere was used to investigate the response of feldspathic dental porcelain to static load and cyclic fatigue. All specimens were subjected to static or cyclic loading in moist environment. Furthermore the surviving strength of specimens was examined by the three-point test and the morphology damage was observed. Statistical analyses were performed with ANOVA and a P-value less than 0.05 was considered to be significant. RESULTS: Outer cone crack and associated strength degradation simultaneously occurred both after the first cyclic loading and static loading. Up to 1,000 cycles, the specimens showed inner cone cracks and strength degradation was aggravated. No significant difference in the strength degradation among all static loading specimens and no inner cone cracks occurred in static loading specimens. CONCLUSIONS: Both static and cyclic fatigue influence dental ceramic strength, but cyclic fatigue is more deleterious.

Compressive Strength↗

PubMed1999

Tensile and shear stresses in the orthodontic attachment adhesive layer with 3D finite element analysis.

The tests commonly used for the evaluation of orthodontic adhesives measure tensile and shear bond strength. The two methods were compared with finite element analysis using a three-dimensional model and the effect of misalignment of the tensile and shear forces was calculated. Applying a shear load produces significant compressive and tensile stresses in the adhesive layer. Under ideal conditions of shear loading, the induced tensile stress is over 5 times the induced shear stress. The model shows that a tensile load induces predominantly tensile stresses in the adhesive layer. The calculations indicate that the tensile test method is a robust testing method with low sensitivity to misalignment of the applied load.

Adhesives↗

PubMed1999

The relationship between water absorption characteristics and the mechanical strength of resin-modified glass-ionomer cements in long-term water storage.

The purpose of this study is to elucidate the water absorption characteristics of resin-modified glass-ionomer cements and to also investigate the relationship between the characteristics and mechanical strength after long-term water storage. The mechanism of water diffusion in these cements is also discussed. Water absorption was measured using a gravimetric analysis for 12 m, while the diffusion coefficient was calculated using Fick's law of diffusion. Water solubility was determined based on the weight of the residue in the immersed water. The compressive and diametral tensile strength were measured at 1, 2, 6, and 12 m. A correlation was observed between the diffusion coefficient and equilibrium water uptake, which thus suggests the water in the cements to diffuse through micro-voids in accordance with the 'Free volumetric theory'. A correlation was seen between the solubility and diffusion coefficient of the cements. The deterioration ratio, defined as the ratio of the strength at 12 m versus that at 1 m, was also calculated. Finally, a negative correlation was observed between the deterioration ratio of the compressive strength and the diffusion coefficients of the cements.

Absorption↗

PubMed2003

Effect of bifunctional comonomers on mechanical strength and water sorption of amorphous calcium phosphate- and silanized glass-filled Bis-GMA-based composites.

This study seeks to elucidate structure-property relationships in a series of unfilled dental copolymers and their composites. The copolymers/composites were derived from photo-activated binary monomer systems based on 2,2-bis[p-2'-hydroxy-3'-methacryloxypropoxy)phenyl] propane (Bis-GMA) and equimolar amounts of a bifunctional, surface-active comonomer, i.e., 2-hydroxyethyl methacrylate (HEMA), glycerol dimethacrylate (GDMA) or ethylene glycol methacrylate phosphate (PHEMA). Triethyleneglycol dimethacrylate, a widely used comonomer for Bis-GMA, was used as a control. Two types of fillers were investigated: (1) a hydrophilic, silica-modified amorphous calcium phosphate (Si-ACP) and (2) a more hydrophobic, silanized nanosized silica (n-SiO(2)). Both the unfilled copolymers and their composites were evaluated for biaxial flexure strength (BFS), both dry and wet after 30 days immersion in buffered saline, and for water sorption (WS) and their WS kinetic profiles. The Bis-GMA copolymers and composites derived from HEMA and GDMA had BFS and WS values, as well as WS kinetic profiles, similar to the controls. Copolymers and composites based on Bis-GMA/PHEMA had lower BFS and higher WS values. Si-ACP composites had significantly lower BFS values (that were further diminished on soaking) than their copolymers. WS increased as the level of this filler was increased except for Bis-GMA/PHEMA composites. With n-SiO(2) as the filler, a more moderate reduction in BFS occurred compared to the unfilled copolymers. By contrast to Si-ACP composites, the WS of all the n-SiO(2) composites decreased with increasing filler level. From this study it is evident that both the chemical structure of the polymer matrix and the type of filler system can have significant effects on the strength and water-related properties of dental composites.

Absorption↗

PubMed2001

Strength over time of a resorbable bioscaffold for body wall repair in a dog model.

The change in strength over time of a biomaterial derived from the small intestinal submucosa (SIS) was determined in a dog model of body wall repair. Full-thickness body wall defects measuring 8 x 12 cm were surgically created and then repaired with a multilaminate eight-layer form of SIS in 40 dogs. Five dogs were sacrificed at each of the following time points: 1 day, 4 days, 7 days, 10 days, and 1, 3, 6, and 24 months. Ball burst tests that measured biaxial ultimate load-bearing capability were performed on the device prior to implantation and on the device/implant site at the time of sacrifice. The strength of the device at the time of implant was approximately 73 +/- 12 pounds. The strength of the implant site diminished to 40 +/- 18 pounds at 10 days, and then progressively increased to a value of 156 +/- 26 pounds at 24 months (P < 0.05). The clinical utility of a degradable biomaterial such as SIS depends on a balance between the rate of degradation and the rate of host remodeling. Naturally occurring extracellular matrix scaffolds such as SIS show rapid degradation with associated and subsequent remodeling to a tissue with strength that exceeds that of the native tissue when used as a body wall repair device.

Animals↗

PubMed2000

Improved reliability of leucite reinforced glass by ion exchange.

OBJECTIVES: The aim of this study was to develop an adequate process-, proof- and calculation technique for the chemical strengthening of dental ceramic materials in order to evaluate the efficiency of this method from the engineering point of view. METHODS: Ion exchange examinations below glass temperature have been done for the dental all ceramic system IPS-Empress (Ivoclar). In addition experiments on specimens were undertaken, which were stored in artificial saliva for the period of one month after the ion exchange treatment. The efficiency of the ion-exchange treatments has been evaluated based on the chemical composition of the surface layer, the residual stress distribution, the flexural- and the burst-strength and surface hardness. In addition, Weibull statistical analysis of the four-point bending and burst test data provides new information about the failure mechanisms of chemically strengthened dental ceramics. RESULTS: The ion-exchange process with a potassium salt increases the reliability of the dental ceramic material "IPS-Empress". By the KNO3 or Tuf-Coat ion exchange treatment potassium ions will be implanted as clusters directly into the crystal lattice which results in an increase of the binding energy and hence, in a pronounced increase in the surface hardness. In particular the stress bearing capabilities of dental all ceramic restorations, which are subject to high bending stresses, i.e. dental crowns and dental bridges, are largely improved by the induced residual stresses. This increase of residual stresses did not relax significantly after a one month storage in artificial saliva. SIGNIFICANCE: Enhanced load limits and a more narrow strength distribution spectrum is considered desirable for increasing the clinical longevity of all ceramics.

Algorithms↗

PubMed2006

Size effects on the mechanical behavior of nanoporous Au.

Recent nanomechanical tests on submicron metal columns and wires have revealed a dramatic increase in yield strength with decreasing sample size. Here, we demonstrate that nanoporous metal foams can be envisioned as a three-dimensional network of ultrahigh-strength nanowires, thus bringing together two seemingly conflicting properties: high strength and high porosity. Specifically, we characterized the size-dependent mechanical properties of nanoporous gold using a combination of nanoindentation, column microcompression, and molecular dynamics simulations. We find that nanoporous gold can be as strong as bulk Au, despite being a highly porous material, and that the ligaments in nanoporous gold approach the theoretical yield strength of Au.

Compressive Strength↗

PubMed2006

A method for vibrational assessment of cortical bone.

Large bones from many anatomical locations of the human skeleton consist of an outer shaft (cortex) surrounding a highly porous internal region (trabecular bone) whose structure is reminiscent of a disordered cubic network. Age related degradation of cortical and trabecular bone takes different forms. Trabecular bone weakens primarily by loss of connectivity of the porous network, and recent studies have shown that vibrational response can be used to obtain reliable estimates for loss of its strength. In contrast, cortical bone degrades via the accumulation of long fractures and changes in the level of mineralization of the bone tissue. In this paper, we model cortical bone by an initially solid specimen with uniform density to which long fractures are introduced; we find that, as in the case of trabecular bone, vibrational assessment provides more reliable estimates of residual strength in cortical bone than is possible using measurements of density or porosity.

Aging↗

PubMedDate not supplied

Mechanical strength of single microcapsules determined by a novel micromanipulation technique.

A micromanipulation technique has been developed to measure the bursting force of single dry microcapsules coated onto a surface, such as those normally used in carbonless copying paper. For measuring the bursting force of a given microcapsule, a single fine probe with a flat end about 10 microns in diameter was used to squeeze the microcapsule against a flat surface until it burst. The force being imposed on the microcapsule was measured by a transducer connected to the probe. The bursting force and diameter of single dry microcapsules in two samples, different in size and wall thickness, were measured by this technique. The bursting force of the microcapsules in one sample ranged from 50 to 220 microN and the diameter from 1.3 to 7.0 microns, whilst the bursting force in the other was from 20 to 175 microN and the diameter from 0.7 to 3.7 microns. This technique makes it possible to compare the mechanical strength of microcapsules made of different formulations, and to infer information about microcapsule mechanical properties.

Capsules↗

PubMed1995

Tensile fatigue strength of light cure composite resins for posterior teeth.

The fatigue property of the composite resin has recently been a subject of research. In this study, the fatigue strength and the tensile strength of composite resins stored in water were investigated. Two types of light cure composite resins were used: a Hybrid type and am MFR type. Dumbbell-shaped specimens were prepared. After storage at 37 +/- 0.5 degrees C for 24 hours, 1 month, 3 months, 6 months and 12 months, the fatigue test and the direct tensile test were performed. The staircase method was employed to analyze the fatigue strength under a 10(5) cyclic load. The fatigue strength of the Hybrid type at 24h ours was 54.7 MPa; that of the MFR type was 28.1 MPa. Both fatigue strengths decreased during water storage. Otherwise, the tensile strength of the Hybrid type was 77.0 MPa; that of the MFR type was 53.5 MPa. After 12 months of storage, the tensile strength of the Hybrid type remained unchanged during water storage; however, that of the MFR type decreased.

Acrylic Resins↗

PubMedDate not supplied

Influence of muscle activity on the forces in the femur: an in vivo study.

Experiments were performed on two patients with custom-made instrumented massive proximal femoral prostheses implanted after tumour resection. In vivo axial forces transmitted along the prostheses were telemetered during level walking, single- and double-leg stance, and isometric exercises of the hip muscles. These activities varied the lever arms available to the external loads: minimum for double-leg stance and maximum for hip isometric exercises. Kinematic, force plate, EMG and telemetered force data were recorded simultaneously. The force magnification ratio (FMR; the ratio of the telemetered axial force to the external force) was calculated. The FMRs ranged from 1.3 (during double-leg stance) to 29.8 (during abductors test), indicating that a major part of the axial force in the long bones is a response to muscle activity, the strength of which depends on the lever arms available to the external loads. From these results, it was shown that the bulk of the bending moment along limbs is transmitted by a combination of tensile forces in muscles and compressive forces in bones, so moments transmitted by the bones are smaller than the limb moments. It was concluded that appropriate simulation of muscle forces is important in experimental or theoretical studies of load transmission along bones.

Arthroplasty, Replacement, Hip↗

PubMed2002

Flexural strength of provisional crown and fixed partial denture resins.

STATEMENT OF PROBLEM: Provisional prostheses are subject to flexure under function. Selection of the appropriate material for their fabrication is difficult given the limited evidence-based information on the flexural strength of provisional resins. PURPOSE: This study compared the flexural strength of 5 methacrylate-based resins and 8 bis-acryl resins used to fabricate provisional crowns and fixed partial dentures. MATERIAL AND METHODS: Bar-type specimens were fabricated according to American National Standards Institute/American Dental Association specification 27. After being immersed in artificial saliva at 37 degrees C for 10 days, the specimens were fractured under 3-point loading in a universal testing machine at a crosshead speed of 0.75 mm/min. Maximal loads to fracture in Newtons were recorded. Mean flexural strengths were calculated in MPa (n = 10 per group). Comparisons were made with analysis of variance and Duncan's multiple range test (P<.05). RESULTS: Mean flexural strengths ranged from 56.2 to 123.6 MPa. There were 4 statistically similar groups. The group with the highest strengths consisted of 4 bis-acryl materials (Provipont, Integrity, Protemp 3 Garant, and Luxatemp). CONCLUSION: Within the limitations of this study, flexural strengths were material- rather than category-specific. Some, but not all, bis-acryl resins demonstrated significantly superior flexural strength over traditional methacrylate resins.

Acrylic Resins↗

PubMed2006

A mild magnesium deprivation affects calcium excretion but not bone strength and shape, including changes induced by nickel deprivation, in the rat.

An experiment was performed to determine the effect of a mild magnesium deprivation on calcium metabolism and bone composition, shape, and strength in rats, and whether nickel deprivation exacerbated or alleviated any changes caused by the magnesium deprivation. Weanling male rats were assigned to groups of 10 in a factorial arrangement, with variables being supplemental nickel at 0 and 1 mg/kg and magnesium at 250 and 500 mg/kg of diet. The basal diet contained about 30 ng Ni/g. Urine was collected for 24 h during wk 8 and 12, and rats were euthanized 13 wk after dietary treatments began. Mild magnesium deprivation decreased the urinary excretion of calcium and increased the tibia concentration of calcium but did not affect femur shape or strength (measured by a three-point bending test). Dietary nickel did not alter these effects of magnesium deficiency. Nickel deprivation increased the urinary excretion of phosphorus and the femur strength variables maximum force and moment of inertia. Strength differences might have been the result of changes in bone shape. Magnesium deprivation did not alter the effects of nickel deprivation on bone. The findings indicate that a mild magnesium deficiency affects calcium metabolism but that this does not markedly affect bone strength or shape, and these effects are not modified by dietary nickel. Also, nickel deprivation affects phosphorus metabolism and bone strength and shape; these effects apparently are not caused by changes in magnesium metabolism or utilization.

Animals↗

PubMed1997

A review of all-ceramic restorations.

To select the most appropriate type of all-ceramic system for clinical use, the clinician must be familiar with the differences between systems. This article discusses five categories of all-ceramic restorative systems relative to their processing techniques, strength and wear characteristics. The authors present and compare results of published in vitro studies and short-term clinical studies.

Compressive Strength↗

PubMed2006

Reduced tabletability of roller compacted granules as a result of granule size enlargement.

The mechanism for the frequently observed "loss of reworkability or tabletability" of dry-granulated (DG) powders was investigated in detail using microcrystalline cellulose (MCC). It was hypothesized that granule size enlargement is the primary mechanism to the phenomenon. Detrimental effects of size enlargement on tabletability of plastic materials are predictable based on the physical model of interparticulate bonding within a tablet. In absence of extensive fracture of particles/granules, larger particles/granules exhibit lower surface area available for bonding thus lower tensile strength when compressed under identical conditions. Size effects were first demonstrated using different grades of MCC powders, both whole and sieved, of different particle size distributions. Regardless grade and sieve fraction, larger particles always resulted in lower tabletability, that is, lower tensile strength at the same compaction pressure. It was subsequently shown that enlargement of granules also reduced powder tabletability regardless grade of MCC. Tabletability of sieved granules after roller compacted for one, two, and four times decreased monotonically with increasing granule size but independent of the total number of roller compaction. Moreover, tabletability of fine granules (44-106 microm) was higher than that of coarse MCC powder (Avicel PH-200). These results suggest that the primary mechanism for reduced tabletabilty of DG granules of MCC is granule size enlargement rather than "work-hardening."

Cellulose↗

PubMed2005

Strength at the extracellular matrix-muscle interface.

Mechanical force is generated within skeletal muscle cells by contraction of specialized myofibrillar proteins. This paper explores how the contractile force generated at the sarcomeres within an individual muscle fiber is transferred through the connective tissue to move the bones. The initial key point for transfer of the contractile force is the muscle cell membrane (sarcolemma) where force is transferred laterally to the basement membrane (specialized extracellular matrix rich in laminins) to be integrated within the connective tissue (rich in collagens) before transmission to the tendons. Connections between (1) key molecules outside the myofiber in the basement membrane to (2) molecules within the sarcolemma of the myofiber and (3) the internal cytoplasmic structures of the cytoskeleton and sarcomeres are evaluated. Disturbances to many components of this complex interactive system adversely affect skeletal muscle strength and integrity, and can result in severe muscle diseases. The mechanical aspects of these crucial linkages are discussed, with particular reference to defects in laminin-alpha2 and integrin-alpha7. Novel interventions to potentially increase muscle strength and reduce myofiber damage are mentioned, and these are also highly relevant to muscle diseases and aging muscle.

Animals↗

PubMed2004

Effects of a fermented vegetable product on fat deposition and bone metabolism in ovariectomized rats.

We examined the effects of a fermented vegetable product (FVP), fermented by yeast as well as lactic acid bacteria, on body weight and fat deposition after ovariectomy in 10-wk-old Sprague-Dawley rats. The rats were divided into the following 5 groups: (1) ovari-ectomized rats fed as usual (OVX); (2) ones receiving FVP at a daily dose of 100 mg/kg (LOW); (3) ones receiving FVP at a daily dose of 1000 mg/kg (HIGH); (4) ones receiving a calcium-free diet (Ca-FREE); (5) sham-operated rats (SHAM). A slight increase in body weight was observed in the LOW group compared with the OVA group. The rate of increase in total fat content was lowest in the LOW group, but both bone weight and strength were similar to those in the other ovariectomized groups. In conclusion, the low dose of FVP turned out to reduce fat content without affecting bone weight and strength.

Adipose Tissue↗

PubMed2001

Experimental ammonia-free phosphate-bonded investments using Mg(H2PO4)2.

In previous study, we found that Mg(H2PO4)2 instead of NH4H2PO4 was available as a binder material for phosphate-bonded investments and possibly could be used to develop the phosphate-bonded investment without ammonia gas release. The purpose of the present study was to develop the experimental ammonia-free phosphate-bonded investments by investigating suitable refractories. Mg(H2PO4)2.nH2O and MgO were prepared as a binder. Cristobalite and quartz were selected as refractories. The power ratio of MgO/Mg(H2PO4)2.nH2O was set constant at 1.2 according to our previous findings. Fundamental properties of dental investment such as strength, manipulation and expansion were evaluated. Using cristobalite as the refractory material, further investigations were performed. The refractory/binder ratio was definitely effective. The increase of this ratio led to low mold strength and large mold expansion. The present findings suggested that C5 was desirable for dental investment.

Ammonia↗