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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study measured the flexural and fatigue strengths of root canal posts of different alloy, design, and diameter. Fixed posts were loaded up to a preset force and the number of loadings endured until fracture was recorded at each loading force. The flexural strength was defined as the maximum force a post could endure before fracture when loaded once. The fatigue strength was determined as the maximum force a post could endure when loaded 10,000 times. Both modes of strength were found to increase with increasing diameter. Aluminum posts had lower flexural and fatigue strengths than posts of titanium, stainless steel, and a Ag-Pd alloy, all of which had strength values of about the same magnitude. Among the investigated brands, Triax and Radix were stronger than the others at comparable diameters. The high strength of Triax may be explained by the design of the post, whereas a superior alloy may account for the high strength of Radix.
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PMID:Flexural and fatigue strengths of root canal posts. 209 Dec 52

The authors tested the T clasp of Roach in three differents proportions among width and thickness: E1-1.7; E2-2.0 and E3-2.3, with a constant length of 15 mm. These clasps were casted with three cobalt-chromium alloys (L1-Biosil; L2-Steldent and L3-Duracrom), through two casting techniques (F1-oxygen-gas and F2-oxygen-acetylene). The fatigue of the clasps were verified by using and assay machine, that through movements, simulate the insertion and removal of the clasps for a pattern which were obtained from a premolar, prepared in a surveyor. This machine detect the fatigue of the clasps and count the number of cycles of insertion and removal realized. The obtained results of the interaction between the analysed factors, were submitted to the statistic analysis and the authors concluded that: a) the interaction of factors, Alloy x Thickness, Alloy x Casting Technique and Thickness x Casting Technique did not change the order of effects that the factors showed separately but gave rise to effects of different magnitude for any observed sense; b) the simultaneous interaction of the factors Alloy x Thickness x Casting Technique confirmed the superiority of the L3 alloy, the thickness E3 and the F2 casting technique.
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PMID:[Fatigue of retentive clasps of removable partial dentures. Effect of alloys, thickness and casting techniques. 2]. 209 55

This study was designed to determine whether the mechanical cyclic stressing that occurs during normal mastication contributes to margin breakdown of dental amalgam restorations. The method used appears to duplicate the mechanical stresses developed in vivo during mastication, as the result of tooth flexing. We evaluated one low-copper alloy--NTD--and three high-copper alloys--Dispersalloy, Phasealloy, and Tytin. We prepared simple amalgam restorations in a cavity centrally located in an aluminum beam. Each specimen received five periods of three-point cyclical loading (1.7 hertz, 4200 cycles at 37 degrees C). The margin area was subjected to SEM examination prior to and at the completion of each period of cycling. At the beginning of each period of cycling, beam deflection was set to establish a maximum theoretical stress of 1, 2, 4, 6, or 8 MPa. For all brands, cycling resulted in margin gap formation and surface wrinkling. Wrinkling in Dispersalloy occurred as a wide band of shallow wrinkles, whereas that in NTD occurred as a narrow band of deep wrinkles. At 21,000 cycles, very little void formation and fracturing had occurred in the Dispersalloy or NTD restorations. In contrast, the Phasealloy and Tytin restorations developed extensive fracturing even after 4200 cycles. Fracture surface analyses of Phasealloy and Tytin indicated that creep fatigue rupture was the fracture mechanism responsible for margin breakdown in these amalgam restorations, when subjected to cyclic compressive loading similar to that experienced during mastication.
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PMID:Amalgam margin breakdown caused by creep fatigue rupture. 263 4

The fatigue behaviour of acrylic sheet specimens containing reinforcers were investigated. Three different kinds of reinforcers namely, stainless steel, aluminum reinforcer and three flex wire were used as strengtheners in acrylic resin sheets. The tests were carried out on alternating bending fatigue testing machine specially designed to test sheet specimens. By applying static and dynamic bending moments of any desired magnitude within the permissible capacity likits of the machine the fatigue lives of the specimens were determined. Experimental results showed that stainless steel strengtheners had a significant positive effect on the fatigue behaviour of acrylic resin.
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PMID:[Effects of various prosthodontic strengtheners on fatigue behaviour of acrylic resins]. 263 35

Deferoxamine (DFO) has been widely used in the treatment of aluminum toxicity in patients on chronic dialysis. Mucormycosis is an opportunistic infection caused by fungi of the Mucorales order and some reports suggested a role for DFO in the precipitation of this infection. A 50-year-old man had been on hemodialysis for 16 years. 6 weeks before admission, he was begun on DFO because of aluminum toxicity. 2 weeks before admission, general fatigue and fever developed and followed by headache and loss of vision. He was admitted to this hospital with disturbed consciousness. His clinical course and a CT scan of the head suggested cerebral infarction. Within 24 hours he required ventilatory support and died 5 days after the admission. On autopsy, rhino-cerebral mucormycosis was demonstrated with a mycotic thrombus involving the left middle cerebral artery. Dialysis-related mucormycosis has recently appeared in the literature. We feel that hemodialysis patients on DFO may be at risk for potentially fatal mucormycosis infections. With a possible relationship between DFO treatment and this fatal opportunistic infection, caution should be given before using this drug and the indications should be definitive.
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PMID:[A case report of rhinocerebral mucormycosis in hemodialysis patient receiving deferoxamine]. 274 4

One hundred forty-five male welders from a West Coast shipyard were studied cross-sectionally and across a Monday work shift by pulmonary function tests and a questionnaire. Ten years of welding was associated with chronic bronchitis in 23.3% of nonsmokers compared to 3.3% in male controls, shortness of breath in 31.5% of nonsmokers compared to 1.5% in controls, and chest pain or heaviness in 38.4% compared to 4.4% in controls. Men who welded aluminum but had never smoked had more frequent wheezing, chest tightness, phlegm, feverishness and fatigue than those welding mild (black) or stainless steel. There were no significant cross-shift effects from welding exposure on measurements of pulmonary function. Although baseline expiratory flows were reduced slightly when compared to Caucasian-predicted values, ethnic specific comparisons for the largest subgroup showed only that FEF25-75 was reduced to 92.9 percentage of predicted values. Diffusing capacities for carbon monoxide were significantly reduced as compared to referents. The pulmonary function values of 25 current smokers were indistinguishable from the 41 who had never smoked, which probably reflects their low consumption of cigarettes.
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PMID:Respiratory symptoms and functional impairment from acute (cross-shift) exposure to welding gases and fumes. 281 87

This article deals with the use of carbon-fiber-reinforced-carbon materials for the manufacture of hip prosthesis stems. It considers the manufacturing process of carbon-carbon (C-C) composites made of carbon fibers infiltrated either with dense pyrolytic carbon or silicon carbide (SiC) through chemical vapor infiltration. The chemicophysical properties of these composites are examined according to their structures. The long-term response (2 years) of cortical bone to various types of carbon-carbon was evaluated mainly for bone contact and ingrowth. Carbon-carbon coated with calcium phosphate was found to speed up the bone formation as compared to pyrolytic carbon or SiC coatings. The low modulus of elasticity of the C-C materials could be responsible for quicker bone contact as compared to a much stiffer material like sintered aluminum oxide. The biomechanical performance of C-C hip stems was assessed through (a) implantations into cadaver femurs, (b) fatigue testing, and (c) finite element analysis. These tests showed: (a) a better stress transfer as compared to a metal prosthesis having the same design, (b) no fatigue damage, (c) a computerized stem stress distribution in accordance with the fractures obtained during static mechanical testing.
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PMID:Development of a carbon-carbon hip prosthesis. 362 86

The tensile median fatigue limits and fracture mode of 4-META cement were evaluated after bonding Ni-Cr, Ni-Cr-Be, and Co-Cr alloys to enamel. Alloy surfaces, 6 mm in diameter, were grit blasted with 50 microns Al2O3 and cemented to etched bovine enamel under a 2 kg load. Samples were cycled in tension to failure or 10(6) cycles at 5 Hz in Ringer's solution at 37 degrees C. Two-point strategy was used to determine median fatigue limits (S50). Fracture modes were evaluated by SEM on samples failing before 10(6) cycles. Results indicated differences between all sample groups where S50 (Ni-Cr-Be) > S50 (Co-Cr) > S50 (Ni-Cr). Failure analysis revealed mixed cohesive fractures near both interfaces with small areas of delamination within the cement. Comparison to reported median fatigue limits of two commercially available cements were discussed.
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PMID:Tensile fatigue of 4-META cement bonding three base metal alloys to enamel and comparison to other resin cements. 778 18

Massive cortical autografts and allografts have been found to incorporate into host bone very slowly and thus are subject to complications such as fatigue fracture and infection. In order to understand and improve the process of osteogenesis in these types of bone grafts, a new experimental model was developed using bone discs from rat calvaria prepared by demineralization and drilling of 0.5 mm diameter holes with a pulsed, 2.94 microns wavelength Erbium:Yttrium-Aluminum-Garnet laser. Four types of bone discs were analyzed: untreated (Type I), demineralized (Type II), laser-ablated (Type III), and laser-ablated then demineralized (Type IV). The discs were transplanted into a subcutaneous site in adult Sprague-Dawley rats and followed for as long as 6 weeks. Histologic analysis of the discs at weekly intervals with use of hematoxylin and eosin staining confirmed the presence of new bone growth in Type-II and Type-IV discs. The amount of new bone growth in each disc was estimated by determining the mineral x-ray attenuation coefficient, which is proportional to mineral density, from digitized radiographs of the discs. The results showed that the processes of demineralization (P < 0.001) and laser ablation with demineralization (p < 0.05) were both significant in enhancing new bone growth in this model. This study demonstrated that osteoinduction can be fostered in cortical bone through the processes of demineralization and laser ablation. To the extent that laser ablation may allow maintenance of structural integrity while altering the surface geometry in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts might be improved.
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PMID:Effect of Er:YAG laser holes on osteoinduction in demineralized rat calvarial allografts. 861 52

Massive cortical bone allografts have been found to incorporate slowly into host bone and thus are subject to complications such as nonunion, fatigue fracture, and infection. To better understand and improve the process of osteoinduction in these types of bone grafts, a new experimental model was developed with use of diaphyseal cortical bone grafts from rat tibiae that were prepared by partial demineralization and drilling of 0.33 mm diameter holes with a pulsed, 2.94 microns wavelength, erbium:yttrium-aluminum-garnet laser. Six types of grafts were analyzed: untreated (Type I), demineralized 25 microns deep (Type II), demineralized 150 microns deep (Type III), laser perforated (Type V), laser perforated and then demineralized 25 microns deep (Type V), and laser perforated and then demineralized 150 microns deep (Type VI). The graft was orthotopically transplanted in the tibia of an adult Sprague-Dawley rat and followed for as long as 4 months. Histologic evaluation at 1 and 4 months postoperatively with use of hematoxylin and eosin staining confirmed that there was new bone growth in Types II, III, V, and VI grafts. The amount of growth was estimated by comparing bone mineral density before implantation with values obtained after retrieval of the graft. These measurements were correlated to histomorphometric analysis of graft incorporation. The results show that the processes of partial demineralization (p < 0.000001) and laser perforation with partial demineralization (p < 0.000001) were both significant in enhancing bone growth in this model. New bone growth was significantly increased when the grafts were prepared with extensive demineralization (p < 0.015). This study demonstrates that osteogenesis in cortical bone grafts can be fostered through the process of partial demineralization and laser perforation. To the extent that minimal partial demineralization and laser perforation allow maintenance of structural integrity while altering the osteoinductive properties in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts may be improved.
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PMID:Improved osteoinduction of cortical bone allografts: a study of the effects of laser perforation and partial demineralization. 942 Jun 6


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