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At least 991 records · Page 55Linked to original sources

PubMed1996

A comparison of the wear of cross-linked polyethylene against itself with the wear of ultra-high molecular weight polyethylene against itself.

Wear tests were carried out on reciprocating pin-on-plate machines which had pins loaded at 10 N and 40 N. The materials tested were irradiated cross-linked polyethylene sliding against itself, irradiated ultra-high molecular weight polyethylene sliding against itself and non-irradiated ultra-high molecular weight polyethylene sliding against itself. After 153.5 km of sliding, the non-irradiated ultra-high molecular weight polyethylene plates and pins showed mean wear factors under 10 N loads, or a nominal contact stress of 0.51 MPa, of 84.0 x 10(-6) mm3/N m for the plates and 81.3 x 10(-6) mm3/N m for the pins. Under 40 N loads, or a nominal contact stress of 2.04 MPa, the non-irradiated ultra-high molecular weight polyethylene pins sheared at 22.3 km. At the last measurement point prior to this failure, 19.1 km, wear factors of 158 x 10(-6) mm3/N m for the plates and 85.0 x 10(-6) mm3/N m for the pins had been measured. After 152.8 km. the irradiated ultra-high molecular weight polyethylene plates and pins showed mean wear factors under 10 N loads of 59.8 x 10(-6) mm3/N m for the plates and 31.1 x 10(-6) mm3/N m for the pins. In contrast, after 150.2 km, a mean wear factor of 0.72 x 10(-6) mm3/N m was found for the irradiated cross-linked polyethylene plates compared with 0.053 x 10(-6) mm3/N m for the irradiated cross-linked polyethylene pins.

Biocompatible Materials↗

PubMed2004

Compressive strength of glass ionomer cements with dental antibacterial agents.

Glass ionomer cements have been suggested for obturating carious teeth that have been prepared with dental hand instruments. In such cases, carious dentine may be inadvertently or deliberately left in situ. The residual bacteria may, over time, lead to secondary caries and restoration failure. Benefit may be gained from combining antibacterial agents with the glass ionomer cement to control residual bacteria. The aim of this study was to investigate the effects on the compressive strength of glass ionomer cement combined with oral antibacterial agents. Cationic antibacterial agents; chlorhexidine hydrochloride, cetylpyridinium chloride and cetrimide were added to the powder and benzalkonium chloride, a liquid, to the liquid of Fuji IX glass ionomer cement. These were prepared to concentrations of 1, 2 and 4 per cent by weight of the glass ionomer cement and compared to Fuji IX with no antibacterial agent. Test specimens were subjected to a compressive force to failure. Multiple analysis of variance showed highly significant reductions in compressive strength (p < 0.01) between the test materials and control group apart from one per cent benzalkonium chloride. Increasing concentration of the antibacterial agent had increasing adverse effects on the physical properties. The addition of the antibacterial agents tested to Fuji IX reduces the seven-day compressive strength which may affect the clinical performance of the material.

Analysis of Variance↗

PubMed1977

Sensitivity to isopropyl alcohol.

Positive patch test reactions to isopropyl alcohol in connection with proved allergy to ethyl alcohol have already been published. A case of allergy to isopropyl alcohol with positive reactions to isopropanol (unpurified test material) and negative reactions to ethanol and methanol has also been reported. We report a case of a occupationally acquired sensitivity to isopropyl alcohol in which, on testing with gas chromatographically purified material, positive patch test reactions were found to 1-propanol, 1-butanol, 2-propanol, 2-butanol and methanal (formaldehyde) but not to the primary alcohols methanol, ethanol and amyl alcohol; not to the aldehydes acetal (acetaldehyde) and butanal; nor to the ketones acetone, butanon and isobutyl ketone, nor to methanoic (formic)acid. A tentative explanation for this peculiar pattern of reactions is given.

1-Propanol↗

PubMed1980

Alcohol dehydrogenase in cultured human skin fibroblasts. Human fibroblast alcohol dehydrogenase.

Studies of ethanol oxidation and other metabolic pathways in humans are often limited by the availability of a reproducible test material. Because of this we have tested human fibroblasts for ethanol metabolism and alcohol dehydrogenase content. Seven different cell lines have been studied and found to contain an enzymatic activity identified as alcohol dehydrogenase by the following criteria: it is NAD+-dependent, the Km for ethanol is like human liver, it is completely inhibited by 25 microM 4-pentylpyrazole. The fibroblast activity was analyzed by isoelectric focusing and found to contain several isozymes also present in the human liver sample. In addition, fibroblasts contain 2 major isozymes which migrate anodally to any isozymes previously reported in human liver. Thus, fibroblasts appear to be useful material for comparing enzymatic aspects of ethanol metabolism in alcoholics and nonalcoholics.

Acetaldehyde↗

PubMed1993

Biocompatibility and biodegradation of different hyaluronan derivatives (Hyaff) implanted in rats.

Hyaluronan (HL), a naturally occurring glycosaminoglycan, has been chemically modified through the esterification of its carboxylic groups with different types of alcohol. The physico-chemical properties of these new biopolymers allow the preparation of many biomaterials which may be used in several medical applications. In the present study both the biocompatibility and biodegradation of some water-insoluble HL esters have been evaluated, either as raw material or as manufactured devices after subcutaneous and intraperitoneal implantation in male rats. The inflammatory response and the degree of resorption for each tested material are reported. The relationships between the degree of esterification and the type of alcohol used with the above parameters are also investigated.

Animals↗

PubMed1995

Wettability of denture soft-lining materials.

Data on the wettability of long-term resilient denture base lining materials have previously been obtained by static methods. This study determined the dynamic contact angle of a range of long-term resilient lining materials and the surface free energy properties of these materials. This method was a rapid and convenient method for determining wettability parameters. The equilibrium contact angle revealed the Flexor and Novus materials to be the least wetted with the Molloplast-B material, and CoeSuper-Soft material was wetted similarly to Trevalon material. The contact angle hysteresis indicated that all the soft-lining materials tested would improve denture stability under dislodgment forces. The surface-free energies appeared to be similar for all the soft-lining materials but were significantly lower than that of Trevalon.

Acrylic Resins↗

PubMed2002

Effect of ethylene vinyl acetate (EVA) closed cell foam on transmitted forces in mouthguard material.

OBJECTIVES: To compare transmitted forces through ethylene vinyl acetate (EVA) mouthguard material and the same EVA material with gas inclusions in the form of a closed cell foam. METHOD: EVA mouthguard materials with and without foam gas inclusions and 4 mm thick were impacted with a constant force from an impact pendulum. Various porosity levels in the foam materials were produced by 1%, 5%, and 10% by weight foaming agent. The forces transmitted through the EVA after energy absorption by the test materials were measured with a force sensor and compared. RESULTS: Only minor non-significant differences in transmitted forces through the EVA with and without foam were shown. CONCLUSIONS: The inclusion of gas in the form of a closed cell foam in 4 mm thick EVA mouthguard materials did not improve the impact performance of the EVA mouthguard material.

Dental Stress Analysis↗

PubMed2001

Black copper phosphate cement: does it have a future?

The aim of this study was to compare the in vitro compressive strength and solubility of a black copper cement with one established restorative material (a conventional glass ionomer cement) and two temporary restorative materials (a zinc phosphate and a zinc polycarboxylate cement). The mean compressive strength of black copper cement varied with the powder: liquid ratio, with an intermediate ratio having a comparable strength to that of the zinc polycarboxylate cement (the best material in this respect). The solubility of the black copper cement at all mixing ratios was significantly greater than that of all other test materials.

Algorithms↗

PubMed2004

Surface hardness properties of resin-modified glass ionomer cements and polyacid-modified composite resins.

In this study the top and bottom surface hardness of two polyacid-modified composite resins (PMCRs), one resin-modified glass ionomer cement (RMGIC), and one composite resin were evaluated. The affect of water storage on their hardness was also investigated. The study was conducted using four different groups, each having five specimens obtained from fiberglass die molds with a diameter of 5 mm and a height of 2 mm. Measurements were made on the top and bottom surface of each specimen and recorded after 24 hours and again at 60 days. All tested materials showed different hardness values, and the values of top surfaces of the specimens were found to be higher than the bottom surface in all test groups. There was no statistical difference in the Vickers hardness (HV) values when the test specimens were kept in water storage. In conclusion Hytac displayed microhardness values higher than Vitremer and Dyract. We found the order of HV values to be Surfil > Hytac > Dyract > Vitremer, respectively. Vitremer presented the lowest microhardness level and Surfil the highest.

Analysis of Variance↗

PubMed1999

Structural properties of sutures used in anchoring multistranded hamstrings in anterior cruciate ligament reconstruction: a biomechanical study.

Sutures are frequently used in anchoring hamstring or quadriceps tendon grafts in cruciate ligament reconstruction. Trumpet like widening of the femoral bone canal was found in patients having had anterior cruciate ligament reconstruction with hamstring autograft. We investigated 5-mm Polylene tape (Genzyme, Boston, MA) and Mersilene tape (Ethicon, Somerville, NJ) as well as No. 6 Ethibond sutures (Ethicon) for ultimate load, stiffness, and elongation under tension of 50 N, 150 N, 250 N, and ultimate load. The Mersilene and Polylene tapes were tested in single loops and Ethibond in double loops having a length of 30 mm. The length is similar to that used intraoperatively for the graft fixation. The suture materials were loaded using a material testing machine at a strain rate of 60 mm/min. The ultimate loads of the loops with knots were 474 N +/-24.7 N for Polylene, 437 N +/-38.2 N for Mersilene, and 338 N +/-16.8 N for Ethibond, and was statistically significant (analysis of variance [ANOVA], P<.05). The elongation under a tension load of 50 N was similar for Ethibond (1.2+/-0.216 mm) and Polylene (1.3+/-0.32 mm). Mersilene (1.7+/-0.34 mm) showed an increased elongation (ANOVA, P=.03). The stiffness for Ethibond was 37.1+/-2.7 N/mm, for Mersilene 38.4+/-3.8 N/mm, and for Polylene was 47+/-3.1 N/mm. The Polylene tape appears to be the most suitable material in terms of strength and stiffness. Nevertheless, the stiffness of all the tested materials is greatly inferior to the stiffness of the commonly used grafts. We believe that a stiffer graft construct might reduce motion during the early period of ingrowing.

Anterior Cruciate Ligament↗

PubMed1992

Validation of the 3-oz water swallow test for aspiration following stroke.

A 3-oz water swallow test identified 80% (16/20) of patients aspirating during a subsequent videofluoroscopic modified barium swallow examination (sensitivity, 76%; specificity, 59%). It also identified patients with more severe dysphagia aspirating larger amounts (sensitivity, 94%; specificity, 26%) or thicker consistencies (sensitivity, 94%; specificity, 30%) of test material. The 3-oz water swallow test is a sensitive screening tool for identifying patients at risk for clinically significant aspiration who need referral for more definitive modified barium swallow evaluation.

Aged↗

PubMed1982

Electron-optical microscopic study of incipient dental microdamage from experimental seed and bone crushing.

No living analogue exists for the hypothetical early hominid hard/tough-seed, coarse-root-eating, and bone-crushing masticatory adaptation. To investigate possible microdamage/microwear to dental enamel caused by such usage, puncture-crushing experiments were carried out on single human teeth, using an Instron compression apparatus on the following six test materials: Makapansgat Limeworks chert (e.g., taphonomy), fresh steer longbone, mongongo nuts, Grewia berries, Carob beans, and wild-onion bulbs. Pairs of extracted unworn third molars were utilized, with one tooth acting as the control. The teeth were mounted, ultrasonically cleaned, and two-stage replicas made with a vinyl polysiloxane elastomer and araldite epoxy resin. After Instron loading and materials failure (1.2-395.0 kg) the test items and the crowns were prepared for comparison with scanning electron microscopy and dispersive x-ray elemental analysis and mapping. The results revealed that although grit adhering to food item surfaces caused microscratches (0.1-1.0 micron wide) similar in appearance to those caused by opal phytoliths in grasses, the dicotyledonous seed coats per se were unable to score enamel. This suggests microscratch morphology alone may not provide a reliable indication of food type. In some cases puncture-crushing of bone and hard legumes produced a localized microfracture pattern (crazing with cracks less than or equal to 0.1-1.0 micron wide) that was readily distinguishable from the simulated taphonomic damage caused by chert fragments, suggesting only analysis of enamel mistaphonomic damage caused by chart fragments, suggesting analysis of enamel microfracture patterns may provide clues as to early hominid dietary adaptations.

Bone and Bones↗

PubMed2002

Biocompatibility studies on biodegradable polyester-based composites of human osteoblasts: a preliminary screening.

A series of biodegradable composites with natural hydroxyapatite, designed for possible use in orthopedics applications, were preliminarily screened for biocompatibility by employing primary cultures of human osteoblasts in a direct contact method. The cells were seeded at low density onto the materials under investigation and allowed to grow for 2 weeks. They then were analyzed for morphology, proliferation, viability, alkaline phosphatase activity (AP), osteocalcin (OC) production, and extracellular matrix mineralization. The results showed that all materials have good biocompatibility. Cell viability tests demonstrated that in all cases the values were comparable to the control, and the addition of hydroxyapatite always resulted in an enhancement of performance with respect to the plain polymer. AP and OC analysis confirmed that all composites allowed the expression of phenotypic markers. Scanning electron microscopy provided direct evidence of intense cell adhesion and proliferation on the tested materials.

Biocompatible Materials↗

PubMedDate not supplied

Assessment of tissue reactions to biomaterials: a model system using the foreign body response in the mouse lung to intravenously injected divinyl copolymer beads.

We have developed a reproducible model of granuloma formation in the mouse lung using a narrow size range (45-53 micron) of divinyl benzene copolymer beads as a standard test material. Approximately 10,000 beads are given by intravenous injection into the tail veins of mice whence they embolize to the lung and incite granuloma formation. This delivery system eliminates the superimposed inflammatory reaction due to trauma that occurs when materials are directly implanted at the test site by surgical incision. Granuloma size was quantitated at intervals from 3 h to 6 weeks by tracing mid-bead granuloma areas on the ground glass screen of a light microscope at a known magnification and measuring the areas with a digitizer interfaced with a microcomputer programmed to prepare histograms and to merge data from replicate experiments. At 3 h only a few polymorphonuclear leukocytes could be observed adhering to the beads. At 48 h, the time of maximum granuloma size (mean area = 7501 micron2), the granulomas consisted of both polymorphonuclear and mononuclear leukocytes. After 6 weeks, the granulomas were smaller, composed predominantly of mononuclear leukocytes and had a mean area of 2893 micron2. This model system allows the analysis of a large number of measurements, is reproducible, and provides a useful method for comparing the hosts' inflammatory response to a variety of potential biomaterials, as well as for determining the effectiveness of antiinflammatory drugs.

Animals↗

PubMed2007

In vitro pyrogen test--A new test method for solid medical devices.

Medical devices manufactured for implantation into humans must be free of any contamination with viable bacteria. However, remnants of dead bacteria and bacterial components alone may induce an inflammatory immune response. Pyrogen tests for such inflammatory contaminations are generally performed either by determining the content of lipopolysaccharide in rinsing solutions of batch samples by limulus amoebocyte lysate assay, by injecting the rinsing solutions into rabbits or by implanting batch samples into rabbits and measuring change of body temperature. In this study, we show that the in vitro pyrogen test (IPT), which measures the release of the inflammatory cytokine IL-1beta in fresh or cryopreserved human whole blood, can be used to assess the pyrogenic contamination of implantable medical devices. This test was used to check neurosurgical implants, namely aneurysm clips, as a proof of principle. Owing to the direct contact of the test material with the blood cells, this test does not require rinsing procedures, which have variable efficacy. The use of human blood ensures the detection of all substances that are pyrogenic for humans and reflects their relative potency. The safety of the products as delivered could be confirmed. The effects of sterilization and depyrogenization procedures on intentional pyrogenic contaminations of samples could be followed. This new application of the already internationally validated method promises to replace further rabbit pyrogen tests. It generates extremely sensitive results with an extended range of detectable pyrogenic contaminants.

Equipment and Supplies↗

PubMed1976

Contact angles and wetting of pharmaceutical powders.

Contact angles of pharmaceutical powders were determined by the h-epsilon method, which consists essentially of measuring the maximum height of a drop of liquid fomed on a presaturated compact of the material. Determinations with aspirin as the test material indicate that the measured value is independent of the particle size of the powder and the porosity of the cake. The method was extended to include determinations on mixed powder systems. The results show that the hydrophobic material dominates with large particle-size powders; with small particle sizes, a linear relationship between the cosine of the contact angle of the mixed system and the proportion of the components is obtained. Results are presented for a wide variety of materials of pharmaceutical interest.

Aspirin↗

PubMed1989

Strength of microvascular anastomoses: comparison between the unilink anastomotic system and sutures.

The Unilink system, a mechanical anastomotic device, was compared with standard suture techniques in terms of anastomotic strength under conditions of uniaxial loading. Twenty-five rabbits underwent Unilink and suture anastomosis of both carotid arteries and facial veins. Animals were sacrificed at 1 hour (five animals), 2 weeks (10 animals), and 16 weeks (10 animals), and all vessels were tested by constant loading in a material testing machine. The maximum load required to disrupt the anastomosis as well as the site of vessel failure were recorded. All 100 anastomoses were fully patent as evaluated by clinical testing. At 1 hour and 2 weeks, the Unilink arterial anastomoses were consistently and significantly stronger than the sutured anastomoses. At 16 weeks the sutured arterial anastomoses were significantly stronger than Unilink. The Unilink anastomoses, however, remained approximately 50% stronger than unoperated normal vessels. No statistical differences were observed in the strength of venous anastomoses at any of the intervals tested. There were no statistical differences in the sites of failure of the vessels under loading (i.e., at the anastomosis or proximal or distal to it) between the two techniques.

Anastomosis, Surgical↗

PubMed1979

Assessment of tissue conditioning materials for functional impressions.

The validity of two types of tissue conditioning materials was studied and compared with that of two commonly used impression materials. The effect of three important factors on the accuracy of the impressions was observed. These factors were thickness of the impression material, time of compression of the impression, and the time interval before pouring the impression. A chrome-cobalt master cast was specially designed and 500 impressions were made and poured, resulting in 900 casts. Conclusions reached from this investigation were that: 1. Visco-Gel and Coe-Comfort tissue conditioning materials can be used as impression materials. 2. The dimensional accuracy of Visco-Gel is better than that of the Coe-Comfort impressions. 3. There is no significant difference between using a tray with a space of 1.5 mm or 3.0 mm for the impression material. 4. The less bulky the impression, the less time is required for compression with fewer inaccuracies. 5. It is preferable to pour the cast in the impression immediately or within 2 hours. 6. Both kinds of materials tested can be used as duplicating materials under certain conditions.

Dental Impression Materials↗