Search PubMed⌕ Search

Biomedical subjects

F J Gil

Publications and source records attributed to F J Gil.

At least 37 records · Page 2Linked to original sources
PubMed2002

Surface hardening by anodizing and heat treatments of Ti6Al4V alloys for articular prostheses.

This paper presents a study of the surface hardening of Ti6Al4V alloy produced by electrochemical anodizing and by different heat treatments, in addition to studying the annealing of the martensitic structure. Results of the combination of both methods produce hardening over 1300 HV and an important improvement on the tribological behaviour. These values could improve wear resistance of this alloy in applications like articular prostheses.

Alloys↗
PubMed2001

Early introduction of cereals into children's diets as a risk-factor for grass pollen asthma.

BACKGROUND: The prevalence of asthma has increased from the 1950s to the 1990s. The relationship between diet and asthma is an area of controversy that has never been fully evaluated. Attempts at dietary prevention of asthma have produced conflicting results. We have recently identified allergens from cereals that show cross-reactivity with proteins in grass pollen. An early intake of cereals in the diet during early life might cause IgE sensitization to cereals. It is not known whether such sensitization predisposes the development of allergy to pollen. METHODS: To test this hypothesis, a cross-sectional study and an observational case-control analysis of reviewed data were carried out on 16381 patients who had been admitted to our Allergy Unit between 1989 and 1999. All the patients underwent allergy tests to identify asthma risk-factors. All information in our data base was analysed using the SPSS computer system. RESULTS: There has been an increase of 7.8% in incidences of allergic asthma and a 7.3% increase in asthma due to grass pollen in the last decade. Grass-pollen asthma was associated with sensitization to cereals. The early introduction of cereals in the diet of children was found to be a risk factor for grass-pollen asthma (OR = 5.95; 95% CI 3.89-9.10). CONCLUSIONS: These findings document the progression of allergic asthma during a decade in a large sample of people who were influenced by similar environmental conditions and studied with the same diagnostic methods. This study represents the largest database of patients in which a common food is shown to be a risk factor for asthma.

Adult↗
PubMed2000

Galvanic corrosion behavior of titanium implants coupled to dental alloys.

The corrosion of five materials for implant suprastructures (cast-titanium, machined-titanium, gold alloy, silver-palladium alloy and chromium-nickel alloy), was investigated in vitro, the materials being galvanically coupled to a titanium implant. Various electrochemical parameters E(CORR), i(CORR) Evans diagrams, polarization resistance and Tafel slopes) were analyzed. The microstructure of the different dental materials was observed before and after corrosion processes by optical and electron microscopy. Besides, the metallic ions released in the saliva environment were quantified during the corrosion process by means of inductively coupled plasma-mass spectrometry technique (ICP-MS). The cast and machined titanium had the most passive current density at a given potential and chromium-nickel alloy had the most active critical current density values. The high gold content alloys have excellent resistance corrosion, although this decreases when the gold content is lower in the alloy. The palladium alloy had a low critical current density due to the presence of gallium in this composition but a selective dissolution of copper-rich phases was observed through energy dispersive X-ray analysis.

Journal Article↗
PubMed1999

Effect of porosity and environment on the mechanical behavior of acrylic bone cement modified with acrylonitrile-butadiene-styrene particles: I. Fracture toughness.

The elastomeric copolymer acrylonitrile-butadiene-styrene (ABS) was added to a conventional acrylic bone cement matrix. The results obtained show that although strength and stiffness decreased with an increasing second phase volume fraction, ductility and toughness both increased. The crack propagation became stable for specimens containing over a 5% volume fraction of the second phase. The fracture toughness increased up to 60% when the amount of ABS reached 20% (v/v). For larger amounts linear elastic fracture mechanics techniques could not be used properly. The effects of porosity and environmental conditions on the mechanical behavior were also studied. The mechanisms that control the fracture process were investigated by means of scanning electron microscopy.

Acrylic Resins↗
PubMed1999

Effect of porosity and environment on the mechanical behavior of acrylic bone cement modified with acrylonitrile-butadiene-styrene particles: part II. Fatigue crack propagation.

The aim of this study was to investigate the effect of adding an elastomeric second phase, acrylonitrile-butadiene-styrene, on the fatigue crack propagation behavior of poly(methyl methacrylate) bone cement. Moreover, the influence of porosity and environmental conditions was studied. When comparing the plain cement to the modified cement, a decrease in the crack propagation rate was observed at between 1 and 2 orders of magnitude. The storage in a physiological environment (saline solution at 37 degrees C) also caused a decrease in the crack propagation rate of about 2 orders of magnitude for the plain and modified cement prepared in air or under a vacuum. Porosity did not have any noticeable effect on the fatigue crack propagation behavior of the cement.

Acrylic Resins↗
PubMed1999

Effect of copper addition on the superelastic behavior of Ni-Ti shape memory alloys for orthodontic applications.

Transformation temperatures and mechanical properties such as transformation stresses at different temperatures, superelasticity characteristics, and load cycling behavior have been investigated in NiTiCu orthodontic archwires with various copper concentrations. The results have been compared with the conventional NiTi orthodontic archwires. The addition of copper was effective in narrowing the stress hysteresis and in stabilizing the superelasticity characteristics against cyclic deformation, with the result that the slope of the load-deflection unloading curve of the alloy is lower than NiTi. Moreover, it produced greater stability of both the transformation temperature and the force applied to the teeth for a determined design and wire cross-section. On the other hand, the presence of copper in NiTi orthodontic archwires reduced the ageing effect. Studies of ion release in artificial saliva showed only small quantities after long periods of immersion.

Copper↗
PubMed1999

Modified acrylic bone cement with high amounts of ethoxytriethyleneglycol methacrylate.

One cause of arthroplasty failure is the brittle mechanical behavior of bone cements. However, the improvement of cement formulations must also be accompanied by the maintenance of a wide variety of characteristics. New bone cements were obtained by the substitution of high percentages, up to 60% (v/v), of methyl methacrylate (MMA) by a higher molecular weight and more hydrophilic monomer, ethoxytriethyleneglycol methacrylate (TEG). The essential advantages of these materials were the decrease of maximum temperature together with a decrease in the residual monomer content with respect to conventional cement formulations. The water absorption process obeyed diffusion laws and the equilibrium water content increased by the introduction of higher percentages of the hydrophilic component. This characteristic had an appreciable effect on the viscoelastic behavior analyzed by DMTA. These modified bone cements had reduced polymerization shrinkage and similar levels of porosity. Tensile test revealed that the introduction of TEGMA gave rise to an important modification of the mechanical behavior, with a noticeable increase in the fracture strain. This fact was also confirmed by means of the analysis of the fracture surfaces by SEM.

Absorption↗
PubMed1999

Influence of the modification of P/L ratio on a new formulation of acrylic bone cement.

The use of smaller powder/liquid (P/L) ratio favours the handling and wetting of poly(methyl methacrylate) (PMMA) beads in bone cement formulations. In this paper a P/L ratio of 1.86 is tested to overcome adhesion problems found in hydroxypropyl methacrylate (HPMA) modified bone cements and the influence on bone cement characteristics was analysed. The reduction of the P/L ratio leads to higher temperature peaks and shorter setting times, whereas the residual monomer content increases slightly. Water uptake obeys the diffusion laws, and the introduction of a more hydrophilic monomer gives rise to an increase of this parameter, which does not present significant changes with modification of the P/L ratio. Polymerization shrinkage is slightly greater because of the introduction of higher proportions of monomer in the formulation. Mechanical properties are similar to those obtained with conventional P/L ratios. The analysis of scanning electron microscopy (SEM) reveals an improvement of the adhesion between phases with respect to P/L = 2 formulations.

Acrylic Resins↗
PubMed1999

Radiopaque acrylic cements prepared with a new acrylic derivative of iodo-quinoline.

A novel iodine-containing methacrylate, 2,5-diiodo-8-quinolyl methacrylate, has been synthesized and used in the preparation of acrylic radiopaque cements. The effect of incorporation of this monomer to the self-curing resins, on the curing parameters, swelling behaviour and mechanical properties was studied. The incorporation of the radiopaque compound 2,5-diiodo-8-hydroxyquinoline to the solid phase was also carried out for comparative experiments. A decrease in the peak temperature and an increase in the setting time was observed with the addition of the radiopaque monomer, however, the curing parameters did not appreciably change with the addition of the radiopaque compound to the solid phase. Swelling of the modified cements was in the same range as that of the radiolucent cement; however, the diffusion coefficients calculated according to the Fick's law were higher for the iodine-containing materials. The addition of 5 wt% of the iodine-containing methacrylate provided a significant increase in the tensile properties with respect to either control radiolucent formulations or BaSO4-containing formulations. Biocompatibility of the modified cements was studied by implantation of rods of the cements into rats and histological analysis of the surrounding tissue.

Animals↗
PubMed1999

Titanium levels in rats implanted with Ti6Al4V treated samples in the absence of wear.

The effect of implantation time and implant nitriding on titanium ion concentration in several tissues of rats carrying Ti6Al4V implants was studied by means of inductively coupled plasma-mass spectroscopy (ICP-MS). Histological studies were also performed in order to check for tissue degeneration due to the Ti6Al4V implantation. The animals were divided into four groups: one received Ti6Al4V implants, the second received nitrided Ti6Al4V implants, the third group received nitrided and descaled Ti6Al4V implants and the last one was the control group. Half the animals of the implanted groups received the Ti6Al4V implant for 30 days, while the other half received the implant for 120 days. Spleen, muscle, kidney, lung, brain and bone samples were retrieved from these rats as well as the control group. Ion concentration measures did not show significant differences between control and implanted rats for the studied period of time, although histological studies showed minor differences, especially on liver tissue samples.

Journal Article↗
PubMed1999

Evaluation by Vickers indentation of fracture toughness of a phosphate biodegradable glass.

Indentation tests are commonly used for the evaluation of fracture toughness of brittle materials, particularly glasses and ceramics, because this technique requires only a small polished area on the specimen surface from which a large number of data points can be generated rapidly. However, a wide variety of equations for the calculation of fracture toughness of ceramic materials by means of Vickers indentation are available. Such equations are obtained phenomenologically and their parameters adjusted in such a way that the KIC values obtained are in good agreement with those obtained by conventional methods. This is the reason why it is necessary to check which type of equation reproduces more accurately the results obtained by means of conventional methods for the material which is going to be investigated. In the present work seven different fracture toughness equations widely used in glass and ceramic studies are considered and the results are compared with those obtained by conventional methods, such as single-edge notch beam (SENB) specimens tested in three-point bending. The role played by the applied indentation load is considered.

Journal Article↗
PubMed1999

Calcium phosphate bone cements for clinical applications. Part I: solution chemistry.

Calcium phosphate cements have been the subject of many studies in the last decade because of their biocompatibility, their capacity to fill bone cavities and their hardening properties; properties which are desirable in a broad range of surgical applications. The setting and hardening of these materials are controlled by dissolution-precipitation chemical reactions at room or body temperature and involve crystalline phase transformations.

Journal Article↗
PubMed1999

Incorporation of a controlled-release glass into a calcium phosphate cement.

A so-called controlled-release glass was synthesized occurring in the system CaO-Na2O-P2O5. A certain sieve fraction of this glass was incorporated in a calcium phosphate cement, of which the powder contained alpha-tricalcium phosphate (alpha-TCP), dicalcium phosphate (DCP) and precipitated hydroxyapatite (HA). The glass appeared to retard the cement setting slightly and it reduced considerably the compressive strength after aging in aqueous solutions which were continuously refreshed. Scanning electron microscope (SEM) pictures and X-ray diffraction (XRD) patterns of the samples after 5 weeks of aging showed that the glass was not dissolved but that large brushite crystals were formed. Thereby, aging in CaCl2 solutions resulted in more brushite formation than aging in NaCl solutions. The brushite crystals did not reinforce the cement. Neither was the aged glass-containing cement weaker than it was before the brushite formation right after complete setting. In conclusion, the incorporation of controlled-release glasses into a calcium phosphate cement and subsequent aging in aqueous solutions did not result in the formation of macropores in the cement structure, but that of brushite crystals. This incorporation reduced the compressive strength of the cement considerably.

Journal Article↗
PubMed1999

Production and characterization of new calcium phosphate bone cements in the CaHPO4-alpha-Ca3(PO4)2 system: pH, workability and setting times.

The initial setting properties of calcium phosphate cements in the CaHPO4-alpha-Ca3(PO4)2 (DCP-alpha-TCP) system have been investigated. Interest was focused on the pH, workability, cohesion time and initial and final setting times. The addition of CaCO3 modified the structure of the cement reaction product such that it became more similar to the apatite phase in bone mineral. The addition of 10% w/w of CaCO3 reduced the viscosity of the cement pastes resulting in an increase in initial and final setting times and improved injectability.

Journal Article↗
PubMed1999

Improvement of the mechanical properties of acrylic bone cements by substitution of the radio-opaque agent.

Acrylic bone cements become radio-opaque by the addition of an inorganic compound, commonly BaSO4 or ZrO2. However, the use of these additives has some negative effects such as loss of mechanical properties, risk of release and bone resorption. The use of the monomer 2,5-diiodo-8-quinolyl methacrylate (IHQM), which shows adequate polymerization and radio-opacity properties, is proposed as a new X-ray opaque, methacrylate iodine-containing agent. The aim of this study is to determine the effect of this new radio-opaque agent on the mechanical properties of acrylic bone cements. The addition of the iodine-containing methacrylate provides a statistically significant increase in the tensile strength, fracture toughness and ductility, with respect to the barium sulphate-containing cement. This effect can be attributed to the fact that the use of a radio-opaque monomer eliminates the porosity associated with the barium sulfate particles, which show no adhesion to the matrix. However, some reinforcing effect must also be attributed to the iodine-containing monomer, since the tensile and fracture toughness values reached are even higher than those shown by the radiolucent cement.

Journal Article↗
PubMed1999

Calcium phosphate bone cements for clinical applications. Part II: precipitate formation during setting reactions.

Calcium phosphate bone cements (CPBC) have been of great interest in medicine and dentistry due to their excellent biocompatibility and bone-repair properties. In this article, a review is presented of the scientific literature concerning precipitate formation during setting reactions of CPBCs. Firstly, the available information has been classified according to the intended final product or calcium phosphate formed during setting reactions. Taking the final product into account, a second classification has been made according to the calcium phosphates present in the original powder mixture. This is the most natural classification procedure because it is based on thermodynamic reasons supported by solubility diagrams for the calcium phosphate salts. By understanding the thermodynamics of calcium phosphate salts in an aqueous solution at room or body temperature it is possible to optimize the manufacturing technology involved in the production of CPBCs. Knowledge of the limitations of this thermodynamic approach opens up new possibilities in the search for CPBCs with better in vitro and in vivo properties for clinical applications.

Journal Article↗
PubMed1999

Comparison of the abrasive wear resistance between amalgams, hybrid composite material and different dental cements.

This paper reports on the abrasion wear of various restorative dental materials (three amalgams and two dental cements and a hybrid composite material) commonly used in dentistry. The mechanical properties, surface roughness and the volume loss by abrasion were determined for the different materials studied. The results showed a better profile for the amalgams versus the composite materials due to the failure of the polymeric matrix of the latter materials. However, the amalgams exhibited corrosion observed by means of Scanning Electron Microscopy.

Composite Resins↗