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Results for “Compressive Strength”

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At least 1,225 records · Page 68Linked to original sources

PubMed1999

Development and evaluation of radiopaque light cure composite.

After the development of a two-paste chemical cure composite, evaluation of its physicochemical properties, toxicological evaluation and in-vivo experiments in dogs teeth with histopathological study of dental tissues, a clinical trial was carried out and commercial production recommended. As the shelf life of the material was not enough, a light cure composite was developed, its material characteristics, toxiclological study, in-vivo experiments in dogs with histopathological evaluation and clinical trials carried out. However, the material was radiolucent, and could not be seen in an x-ray and differentiated from a cavity after filling was done. This led to the development of radiopaque light cure composite. Compressive strength, diametral strength, and microhardness were tested with 200-250 phr range of incorporated radiopaque glass particle filler of the size 0.7 to 1.0 micron this improved the properties when compared to conventional composites. The composite was non-toxic and suitable for animal studies. In vivo studies are underway in dogs with histopathological studied of the pulp and dentin. The material awaits clinical trials prior to commercial production.

Animals↗

PubMed2001

Chemical characteristics and leachability of organically contaminated heavy metal sludge solidified by silica fume and cement.

This paper discusses the development of mixtures with silica fume as a stabilization/solidification agent and binder for industrial wastewater residue containing organic and heavy metal contaminants. The UCS (Unconfined Compressive Strength) gradually increased to 66.7% as the silica fume content increased to 15%. The leaching of TOC and chromium decreased as more OPC was substituted with silica fume. When the mix had 5% silica fume, it retained about 85% TOC, and chromium leached out 0.76 mg-Cr/g-Cr in acidic solution. Also, microstructural studies on the solidified wastes through the scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction analysis showed that the silica fume caused an inhibition to the ettringite formation which did not contribute to setting, but coated the cement particles and retarded the setting reactions. The results indicated that the incorporation of silica fume into the cement matrix minimized the detrimental effects of organic materials on the cement hydration reaction and contaminant leachability.

Adsorption↗

PubMed2001

Stabilization of heavy metals on spent fluid catalytic cracking catalyst using marine clay.

Spent fluid catalytic cracking catalyst is a hazardous solid waste generated by petroleum refineries containing vanadium and nickel. The marine clay was used as a matrix to stabilize vanadium and nickel and produce bricks which were then fired at various temperatures. TCLP leaching tests indicated that stabilizing brick had low metal leaching, with a maximum of 6.4 mg/l for vanadium and 19.8 microg/l for nickel. Compressive strength of stabilizing brick was found to range between 20 N/mm2 and 47 N/mm2. It is believed that stabilization and encapsulation mechanisms are responsible for the stabilization of vanadium and nickel. Encapsulation is a process whereby the marine clay matrix forms a physical barrier around the heavy metals which are thus prevented from leaching out into the environment. Incorporation involves the formation of bonds between the marine clay matrix and the heavy metals which thus become incorporated in the clay microstructure.

Aluminum Silicates↗

PubMed1999

The theory and practice of internal 'tunnel' restorations: a review of the literature and observations on clinical performance over eight years in practice.

The tunnel or 'internal' restoration to restore an approximal caries lesion was first described in 1984. The technique allows the operator to conserve the important external anatomical features of the tooth, thereby saving considerable clinical time while leaving relatively little of the material externalized. The development of a new generation of glass-ionomer materials with higher flexural and compressive strengths appears to satisfy the main objective of carious dentine replacement facilitated by a 'keyhole' internal preparation. The long-term clinical evaluation of these materials is difficult since new formulations are being continually developed. The literature was reviewed. Clinical cases restoring approximal caries lesions in permanent molars and premolars were observed in a private practice. Over the course of eight years 60 tunnel restorations were placed in 48 regularly attending patients. The materials used in both total and partial tunnel restorations were Ketac Silver, Hi-Dense and Fuji IX. At eight years a failure rate of 15% was seen in the 50 restorations observed at last dental examination. The findings suggest that modern tunnel techniques may offer a restorative technique worthy of consideration in treating primary approximal caries lesions.

Adolescent↗

PubMed2002

Biomechanical properties of regenerated bone by mandibular distraction osteogenesis.

OBJECTIVE: To study the biomechanical properties of the new bone generated by mandibular distraction osteogenesis (DO). METHODS: A total of 11 healthy adult goats were randomly divided into 2 groups, the experimental group (n=9) and the control group (n=2). For the goats in the experimental group, the bilateral mandibles were gradually lengthened for 10 mm with distraction appliances. Three goats were sacrificed respectively at 2, 4 and 8 weeks after completion of distraction. Compressive, three-point bending and shearing tests were conducted on the standard regenerated bone samples and the whole unilateral mandibular specimens. For the goats in the cont rol group, no operation was made and the whole unilateral mandible was taken as the test specimen. RESULTS: The compressive strength and bending stiffness of the new bone reached the normal level at 4 and 8 weeks after completion of distraction, respectively. But the shearing strength remained significantly weaker than that of the controls at 8 weeks after distraction. CONCLUSIONS: The distraction appliance can be removed and the lengthened mandible should be exposed to adaptive functional exercise at 8 weeks after completion of distraction.

Animals↗

PubMed2002

[Use of bioactive glass ceramics in the treatment of tibial plateau fractures].

PURPOSE OF THE STUDY: The surgical treatment of proximal tibia fractures requires a reduction and fixation of the split condyle, elevation of the depressed interfragment of articular surface. The golden standard is the application of autogenous bone grafts for filling in the defect in the cancellous bone of the tibial condyle. Bioactive glass-ceramics material may be successfully used for the filling. Gass-ceramics BAS-O is biocompatible and bioactive and has also suitable mechanical properties and therefore it was used in combination with autogenous bone marrow in order to speed up osteogenesis. MATERIAL: The study covered 12 patients, 4 men and 8 women, with a fracture of the proximal tibia classified according to AO as type B3.1, B3.2 and C3.2. The average follow-up period was 5.5 years (range, 2 to 8 years). METHOD: After the assessment of the type of fracture and revision of soft tissues the depressed interfragment of articular surface was elevated and the defect was completely filled with BAS-O granules in combination with 10 ml of autogenous bone marrow. The broken condyle was fixed by screws or buttress plate. During the first year the process of healing was checked by radiographs at 3-month intervals. All 12 patients were invited for a follow-up examination where the radiograph of the proximal tibia was assessed in two projections and the clinical condition was evaluated using Rasmussen criteria. RESULTS: According to the Rasmussen criteria 12 patients achieved the value of 21-29 points with the average of 26.4 of 30 possible points. The volume of the BAS-O filling was 7.1-44.3 ccm and did not change throughout the whole period of the follow-up. The depression of an interfragment of articular surface prior to operation was 3-17 mm, average 6.3 mm. The residual depression after the operation was 0-4 mm, average 1.7 mm. No symptoms of loosening, extrusion or surrounding of the BAS-O material by fibrous tissue was found. The integration with the surrounding bone occurred during the first 3 months. DISCUSSION: The bioactive coral hydroxyapatite has been successfully used to fill similar defects by a number of authors. Among the benefits of BAS-O granular system is an easy handling and a fast integration with the bone tissue of the recipient due to the development of a hydroxyapatite layer on its surface after the contact with tissue fluid. Autologous bone marrow was added to the system in order to initiate osteogenesis and a faster healing of the defect. The mentioned material is suitable also from the mechanical viewpoint as neither deformation nor resorption was found in the followed-up patients. We reduced the surgery duration and morbidity and improved the patients comfort. CONCLUSIONS: Part of the surgical management of the fracture of the tibial plateau with a depressed segment of subchondral bone is its elevation. For filling in of the traumatic defect in the cancellous bone of the proximal tibia the bioactive, glass-ceramics, granular material BAS-O may be successfully used. Mechanical and chemical properties (compression strength, non-resorption) ensure its stable position in the filling as well as a constant volume. Osteointegration was accelerated by adding 10 ml of autologous bone marrow. The use of the glass-ceramics material reduces the surgery duration, improves the patient's comfort and decreases the probability of incidence of complications.

Adult↗

PubMed2002

Composite resorbable polymer/hydroxylapatite composite screws for fixation of osteochondral osteotomies.

The aim of this study was to evaluate biomechanically the healing of an osteochondral fragment created in the distal sheep femur in response to fixation with a resorbable composite screw made of polylactide and hydroxylapatite. Pure poly(L-lactide) screws were used for comparison. At follow-up times of 4 or 8 weeks, specimens were examined with standard radiography, biomechanics, and histology. The intact contralateral femur served as a control. Only minimal signs of polymer degradation were seen in the histologic specimens. At 8 weeks, most osteotomies had healed completely and there was no difference in compressive strength and elastic modulus of cylindrical cores between the two types of biodegradable implants used. The width of the repair tissue at the tissue-implant interface was 250+/-50 micro m representing a clear transition zone of newly formed trabecular bone separating the implant from the surrounding plexiform bone. We conclude that relatively large polylactide implants, blended with hydroxyapatite, are capable of fixing an osteochondral fragment in an animal model. Biomechanical data assessing the quality of the bone formed at the osteotomy sites were found to be equivalent when compared to the control poly(L-lactide) implants of similar design and size. In addition, hydroxylapatite composite implants showed benign tissue responses and good implant osteointegration. Results suggest that hydroxylapatite composite screw implants can be used for similar indications as pure poly(L-lactide) implants in current clinical use.

Absorbable Implants↗

PubMed2003

[BMP-2 gene modified tissue-engineered bone repairing segmental tibial bone defects in goats].

OBJECTIVE: To evaluate the effectiveness of the tissue-engineered bone substitute loaded with adenovirus mediated human bone morphogenetic protein-2 gene (Adv-hBMP-2) transfected bone marrow derived mesenchymal stem cells (BMSC) in the repair of diaphyseal segmental bone defect of large animal. METHODS: The right tibial bone defects (2.6 cm) model of 26 goats were established and divided into 5 groups: I. Adv-hBMP-2 transfected BMSC/calcined bone (CB) group (n = 9); II. adenovirus-beta-galactosidase (Adv-betagal) gene transfected BMSC/CB group (n = 6); III. untransfected BMSC/CB group (n = 6); IV. single CB group (n = 3); VI. untreated group (n = 2). The above tissue-engineered bone substitutes were implanted in the bone defects respectively except group VI. Roentgenography, histomorphometrical analysis and biomechanical measurement were studied at various times. RESULTS: X-ray: at 4 - 8th weeks after implantation, more bony callus was found in the bone defects of group I. The complete healing rates of group I, II, III, IV, and V were 5/8, 1/5, 0/5, 0/2, 0/1 respectively at 26th week after implantation. Histomorphometrical analysis showed much more new bony callus including cortical bone formed in group I than those of other groups. The compression strength of the implanted bone substitute of group I is significantly higher than those of group II and III. CONCLUSION: The tissue-engineered bone substitute loaded with human BMP-2 gene transfected BMSC can repair diaphyseal segmental bone defect of large animal (goat).

Animals↗

PubMedDate not supplied

Occupational biomechanics and low-back pain.

The basic principles of biomechanics are introduced and explained as they relate to the field of ergonomics, especially regarding the lumbar spine. The discussion is organized into the following sections: biomechanics--an overview, spinal structures and loading, biomechanical basis for low-back pain, compressive strength of the lumbar spinal column, biomechanical models, intra-abdominal pressure, lifting technique, and practical applications. The conclusion lists nine guidelines for understanding the internal stresses placed on the lower back by lifting and thereby for avoiding low-back injuries in the workplace.

Biomechanical Phenomena↗

PubMed2003

Influence of porosity and composition of porous carriers on the uptake of nutrients.

The current paper assesses the potential of industrial solid wastes utilization such as blast furnace slag (BFS) and zeolite synthesized from fly ash (ZFA), which are effective as well as economically attractive for the uptake of phosphate and ammonium from polluted seawater. The solidification of BFS and ZFA has been developed in different proportions of BFS/ZFA (30/70, 50/50 and 70/30 (w/w)) with different porosities (25%, 40% and 52%, respectively) to cylindrical porous carriers using a Hydrothermal Hot-Pressing (HHP) method. The concentrations of heavy metals in ZFA and BFS were too low to affect the aquatic environment. The main finding is that the high rate of BFS (70%) in porous carriers enhanced phosphate uptake explained by the higher percentage of calcium (35.7%) in porous carriers and high pH conditions. The efficient ammonium uptake was observed with high rate of ZFA (70%) in porous carriers. Results found through this experimental work imply that porous carriers with BFS/ZFA proportion of 70/30 are suitable for potential practical application in the aquatic environment due to their efficient uptake of phosphate and ammonium. The choice was made upon their porosity (40%) and their compressive strength (56 kgf/cm2) which are relatively higher than those with BFS/ZFA proportion of 30/70 and 50/50.

Ammonia↗

PubMed2004

Hydroxyapatite/PMMA composites as bone cements.

Currently PMMA is the polymer most commonly used as a bone cement for the fixation of total hip prostheses. Ideally, a bone cement material should be easy to handle, biologically compatible, nonsupporting of oral microbial growth, available in the particulate and molded forms, easy to obtain, nonallergenic, adaptable to a broad range of dental and medical applications, in possession of high compressive strength, and effective in guided tissue regenerative procedures. One of the problems associated with the conventional types of bone cement used is their unsatisfactory mechanical and exothermic reaction properties. The purpose of this in vitro study was to investigate and compare the mechanical properties (three-point bending strength, energy-to-break, and modulus of elasticity) and physical properties (setting time, water sorption, and exothermic heat) of HA/PMMA (HA group) and bovine-bone originated HA/PMMA (BB group) composites. Composites samples were fabricated by admixing method. It was found that the addition of HA and BB particles increased the water sorption. Generally 10 v/o 20 v/o HA and 0 v/o to 10 v/o BB ratio combinations had significant beneficial effects on the mechanical properties. The heat generated during polymerization was influenced by the different admixtures. More than 40 v/o HA and 40 v/o BB should be mixed into PMMA to reduce the peak temperature. Overall evaluation indicated that the BB group had better properties than the HA group.

Bone Cements↗

PubMed2004

Ultrasonic testing of reactive powder concrete.

Concrete is a critical material for the construction of infrastructure facilities throughout the world. Traditional concretes consist of cement paste and aggregates ranging in size from 6 to 25 mm that form a heterogeneous material with substantial compressive strength and a very low tensile strength. Steel reinforcement is used to provide tensile strength for reinforced concrete structures and as a composite the material is useful for structural applications. A new material known as reactive powder concrete (RPC) is becoming available. It differs significantly from traditional concrete; RPC has no large aggregates, and contains small steel fibers that provide additional strength and, in some cases, can replace traditional steel reinforcement. Due to its high density and lack of aggregates, ultrasonic inspections at frequencies 10 to 20 times that of traditional concrete inspections are possible. This paper reports on the initial findings of research conducted to determine the applicability of ultrasonic testing techniques for the condition assessment of RPC. Pulse velocities for shear and longitudinal waves and ultrasonic measurement of the modulus of elasticity for RPC are reported. Ultrasonic crack detection for RPC also is investigated.

Journal Article↗

PubMed2004

[Preparation and degradation of poly(DL-lactide)/calcium phosphates porous scaffolds].

The porous foams were prepared by the solvent-casting and particulate-leaching technique using poly(DL-lactide) (PDLLA), poly(DL-lactide)/hydroxyapatite (PDLLA/20wt%HA), and poly(DL-lactide)/beta-tricalcium phosphate(PDLLA/20wt% beta-TCP) respectively. Observations by scanning electron microscopy indicated that the HA and beta-TCP were homogeneously dispersed in the polymer matrix, and the pores of the foams are interconnected, resulting in continuous pore structures. The porosity of PDLLA/HA and PDLLA/beta-TCP foams was lower than that of the pure PDLLA foams, but the compression strength was higher than that of the pure PDLLA foams. The results of the degradation in vitro showed that both HA and beta-TCP had significant inhibitory effects on the degradation of PDLLA, especially the HA. It is expected that the composite foams are of use as scaffolds for bone tissue engineering.

Biocompatible Materials↗

PubMed2003

[Application of calcium phosphate bone paste to fracture treatment].

Calcium phosphate bone paste (Biopex) is a viscous and injectable bioactive ceramic. The final maximum compressive strength is 80-90 Mpa, which is much higher than that of cancellous bone and slightly lower than that of cortical bone. Filling cancellous bone defects with this material could stabilize metaphyseal fractures in patients with osteoporosis and prevent subsequent reduction loss. Applications of this material to various fracture treatments have been reported and it was demonstrated that this material is useful if some complications are carefully avoided. Further studies are needed to determine the most suitable method for individual fractures to maximize the benefit and minimize the adverse effects.

English Abstract↗

PubMed2006

Preliminary evaluation of a load-bearing BMP-2 carrier for segmental defect regeneration.

Large segmental defects in bones can result from tumor removal, massive trauma, congenital malformation, or non-union fractures. Such defects often are difficult to manage and require multiple-phase surgery to achieve adequate union and function. In this study, we propose a novel design of bone morphogenetic protein 2 (BMP-2) carrier for tissue engineering of segmental defect regeneration. The tube-shaped BMP-2 carrier was fabrication from a poly(propylene fumarate)/tricalcium phosphate (PPF/TCP) composite via casting technique developed in our laboratory. An in vitro evaluation showed that the compressive strength of the carrier decreased about 48% in 12 weeks while maintained a pH in the 6.8-7.4 range. In vivo study was conducted by implanting carriers loaded with 10 microg of BMP-2 in 5 mm rat femur gap model for 15 weeks. X-ray evidence of bridging was first found in the BMP group at 3 weeks. Bridging in all animals (N = 4) in the BMP group was found at 9 weeks. No x-ray evidence of bridging was found in the No BMP group (N = 3). pQCT analysis indicated that the bone mineral density of the callus in the BMP group has reached the level of native femur at 15 weeks after implantation, while the callus in the No BMP group has a bone mineral density at a lower level of 84% to the native femur. Histology analysis shows that a normal fatty bone marrow was restored and mineralized callus formed and bridged the segmental defect.

Animals↗

PubMed1991

[Study of pressure resistance of galvano-crowns].

Ceramic veneered galvano crowns demonstrated an axial loading limit of 220 N on incisors and of 297 N on canines. Compressive strength values are only slightly lower at 45 degrees loading. These use of a bonding agent did not significantly affect strength.

Chromium Alloys↗

PubMed1990

Constant-volume polymerization of composites by addition of ammonia-modified montmorillonite.

Polymerization shrinkage is a major limitation of dental composites. It generates internal stresses within bonded restorations and leads to marginal leakage, sensitivity and recurrent decay in the absence of adequate bonding. A method is presented for formulating composites that cure at constant volume by adding to the resin system small amounts of the hydrated mineral montmorillonite (MMT), which has been modified by replacing part of its hydration water with ammonia (NH3). The polymerization exotherm of composites containing ammonia-modified montmorillonite (NH3/MMT), cured at ambient temperatures, raises their temperature to between 60 and 80 degrees C, which causes the NH3/MMT particles to swell and counteract polymerization shrinkage. The polymerization shrinkage was measured for the BIS-GMA resin system, without filler, to which had been added NH3/MMT. The addition of 4 to 5 weight percent NH3/MMT resulted in zero polymerization shrinkage. An experimental composite was formulated using the BIS-GMA resin system, hydroxyapatite filler and 4 weight percent NH3/MMT. Cured samples developed compressive strength and hardness comparable to reported values for dental composite resins. Porosity was not detected by scanning electron microscopy. The use of NH3/MMT for formulating polymeric systems that cure at constant volume should be explored for application in direct dental composites.

Bentonite↗

PubMed1990

Establishment of an implant selection protocol for predetermined success.

Previously, implant selection was confined to radiographs and to plastic implant templates for evaluation of existing bone. The aim of this study was to determine implant support areas in a compressive mode and to establish a standard via an implant selection protocol. Successful implant selection, regardless of the device design, is relevant to a patient's muscular efficiency and implant support values based on bone quality and size of prescribed bridge. The compressive areas of support, in mm2, of 15 implant designs were computer-analyzed and graph-evaluated. Major/minor diameters and the lengths of screws and cylindrical types of devices were calculated. In addition, the length, width, vents, and any lateral support areas of blade types were recorded. Average muscular force data, provided by clinical transducer studies, and literature reports of the mechanical properties of trabecular bone were correlated with computer bone analyses. These studies determined the quality of maxillary and mandibular bone to be 10 MPa and 15 MPa, respectively. Results indicated that four-unit bridges, at 50 lbs of applied force, require an area 31.14 mm2 of implant support in a compressive mode in the maxilla, and a support area of 20.76 mm2 in the mandible. Five-unit bridges require 40.84 mm2 in the maxilla and 27.23 mm2 for the mandible, because of the moment force, or torque, on the implant. Findings indicated that by determining: (1) the patient's muscular efficiency at implant sites (quantifying dynamic values of the forces and moments on implants supporting functioning bridges); (2) implant support values based on the compressive strength of the cancellous bone at implant sites; and (3) the size of the prescribed bridge, it is possible for the success (or failure) of a selected implant to be predetermined.

Alveolar Process↗