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Biomedical subjects

F J Gil

Publications and source records attributed to F J Gil.

50 records · Page 3Linked to original sources
PubMed1999

In vitro corrosion behaviour and metallic ion release of different prosthodontic alloys.

The corrosion resistance for six metallic alloys often used in clinical dentistry, was evaluated by measuring their polarisation resistance in an artificial saliva environment. The critical current density (icr), the passive current density (ip), the corrosion potential (Ecorr) and the critical pitting potential (Ecp), were studied. Metallic ion release from the different alloys was analysed in a saliva environment at 37 degrees C. The nickel-chromium alloy exhibited important corrosion and a high quantity of ions was released. The titanium presented a low value of ion release and a good corrosion resistance due to the passive film on the metal surface. The high gold content alloy provided the best corrosion resistance.

Chromium Alloys↗
PubMed1998

The cement setting reaction in the CaHPO4-alpha-Ca3(PO4)2 system: an X-ray diffraction study.

The setting reactions of calcium phosphate cements in the CaHPO4-alpha-Ca3(PO4)2 (DCP-alpha-TCP) system have been investigated. X-ray diffraction (XRD) analyses were performed on DCP-alpha-TCP cement samples of varying calcium to phosphorus (Ca/P) ratios after setting for 24 h in Ringer's solution at 37 degrees C. XRD measurements showed that the intensity of the DCP peaks decreased linearly as the Ca/P ratio of the mixture increased. However, the intensity of the peaks of a new calcium-deficient hydroxyapatite [CDHA; Ca9(HPO4)(PO4)5OH] precipitating phase increased linearly as the Ca/P ratio increased. Alpha-TCP was not detected after 24 h of setting in any sample. A two-phase mixture XRD model was applied to explain the results, and suitable fits were obtained between observed and expected values of the relevant peak heights. The method used for this study also can be applied to studies of the kinetic behavior of other cement systems.

Bone Cements↗
PubMed1998

Improvement of the mechanical properties of new calcium phosphate bone cements in the CaHPO4-alpha-Ca3(PO4)2 system: compressive strength and microstructural development.

The hardening properties of calcium phosphate cements in the CaHPO4-alpha-Ca3(PO4)2 (DCP-alpha-TCP) system have been investigated with interest focused on the compressive strength and microstructure development. Previous studies have shown that the addition of CaCO3(CC) leads to a modification of the calcium-deficient apatite structure of the reaction product, which results in a material more similar to the apatite in bone mineral. The addition of 10% w/w of CC to the initial DCP-alpha-TCP powder mixture resulted, with time, in a retardation of the development of compressive strength. However, the optimum compressive strength reached values up to 40% higher than CC-free samples. This retarding effect also has been monitored as a function of the calcium to phosphorus (Ca/P) ratio of the DCP and alpha-TCP mixture, showing the importance of the final cement properties of the relative quantities of the reactants in the mixture.

Bone Cements↗
PubMed1998

Occupational asthma by Anisakis simplex.

BACKGROUND: No cases of occupational asthma caused by the inhalation of antigens from Anisakis simplex have been published. OBJECTIVE: The purpose of this study was to evaluate the possibility that A simplex can play a role in the asthma experienced by 2 workers when handling fish and fish flour. METHODS: Skin prick and bronchial challenge tests with A simplex were performed. We also carried out measurements of specific IgE to A simplex and immunoblotting. RESULTS: Both patients had strong positive skin test responses, challenge test responses, and specific IgE to A simplex. Immunoblotting showed that both patients also had IgE against several bands in the fish flour extract, suggesting contamination by Anisakis allergens. CONCLUSION: These 2 patients provide evidence for occupational asthma caused by A simplex, based on in vivo and in vitro tests for Anisakis-specific IgE.

Allergens↗
PubMed1998

In vitro thermomechanical ageing of Ni-Ti alloys.

NiTi alloy is used as a biomaterial due to its pseudoelastic behaviour. It exhibits a great potential in dental and orthopedic applications where constant correcting loads are required. In order to use such materials, it is necessary to investigate the effect of the cyclic straining upon the transformation stresses and temperatures of the material, the effect of thermal cycling and the ageing at different temperatures and times of heat treatment. The aim of this work is to study the load and thermal cycling and the ageing with the temperature of a superelastic NiTi shape memory alloy.

Biocompatible Materials↗
PubMed1998

Shape memory alloys for medical applications.

The shape memory alloys exhibit a number of remarkable properties, which open new possibilities in engineering and more specifically in biomedical engineering. The most important alloy used in biomedical applications is NiTi. This alloy combines the characteristics of the shape memory effect and superelasticity with excellent corrosion resistance, wear characteristics, mechanical properties and a good biocompatibility. These properties make it an ideal biological engineering material, especially in orthopaedic surgery and orthodontics. In this work the basis of the memory effect lies in the fact that the materials exhibiting such a property undergo a thermoelastic martensitic transformation. In order to understand even the most elementary engineering aspects of the shape memory effect it is necessary to review some basic principles of the formation and the characteristics of the martensitic phase. The different properties of shape memory, superelasticity, two-way shape memory, rubber-like behaviour and a high damping capacity are reviewed. Some applications proposed in recent years are described and classified according to different medical fields.

Alloys↗
PubMed1998

Improvement of the friction behaviour of NiTi orthodontic archwires by nitrogen diffusion.

The lack of low friction coefficient for the NiTi superelastic archwires makes difficult the optimal use of these materials in orthodontic applications. In this study, the decrease of this friction coefficient has been achieved by means of nitrogen diffusion heat treatments. The titanium nitride coating has been characterised by means of optical and scanning electron microscopy. Transformation temperatures, critical stresses, hardness and friction coefficient have been determined. Besides, the metallic ion release studies showed that the titanium nitride coating prevents biodegradation.

Biocompatible Materials↗
PubMed1997

Metallic ion release in artificial saliva of titanium oral implants coupled with different metal superstructures.

In this work the metallic ion release in oral implants with superstructures of different metals and alloys used in clinical dentistry has been determined. This study has been realized in a saliva environment at 37 degrees C. The measurements of the ion release were carried out by means of the Inductively Coupled Plasma Mass Spectrometry technique. The titanium oral implant coupled with a chromium-nickel alloy releases a high quantity of ions and the implant coupled with the titanium superstructure presents a low value of ion release.

Chromium Alloys↗
PubMed1996

New aspects of the effect of size and size distribution on the setting parameters and mechanical properties of acrylic bone cements.

The effect of the size and the size distribution of poly(methyl methacrylate) (PMMA) beads on the classical kinetic parameters, peak temperature and setting time, for acrylic bone cement formulations prepared with PMMA particles in the range 10-60 microns of average diameter and a relatively wide size distribution is analysed. In addition, the combined effects of the concentration of the free radical initiator benzoyl peroxide and the activator N, N-dimethyl-4-toluidine for the different particle sizes are studied and compared with those commercially available formulations like CMW or Rostal. The results obtained indicated that the use of PMMA particles with average diameter of 50-60 microns, and a relatively wide size distribution (10-140 microns diameter), significantly changes the curing parameters (peak temperature and setting time) of the cement formulations in comparison with the classical behaviour of the commercial systems of CMW and Rostal, without any noticeable loss in the mechanical properties, such as tensile strength, elastic moduli, and compressive strength and plastic strain.

Benzoyl Peroxide↗
PubMed1996

A study of load cycling in a NiTi shape memory alloy with pseudoelastic behaviour used in dental prosthetic fixators.

NiTi alloy used in dental prosthetic fixators shows pseudoelastic behaviour and exhibits a great potential in dental and orthopaedic applications where constant correcting loads are required. In order to use such materials in dental prosthetic fixators, where the device is cyclically deformed, it is necessary to investigate the effect of the cyclic straining upon the transformation stresses and temperatures of the material. The aim of this work is to study the load cycling of a pseudoelastic NiTi shape memory alloy to be applied in the making of dental prosthetic fixators.

Biocompatible Materials↗
PubMed1995

A study of the abrasive resistance of metal alloys with applications in dental prosthetic fixators.

Wear is one of the main surface failure mechanisms in materials and it will play a leading role in substitutive dental biomaterials. The aim of the present study is to compare the abrasive wear of different metallic materials used in dental applications. The results show that the abrasive wear of alloys based on precious metals such as Pt, Pd, Au and Ag is higher than for Ti and Ti based alloys. The alloy with the highest wear resistance is the Co-Cr which exhibits as well the highest hardness and Young's modulus. Since the method corresponds to a well-established abrasive wear standard, the behaviour of the different materials can be easily compared.

Alloys↗
PubMedDate not supplied

Low cycle fatigue behavior of Ti6Al4V thermochemically nitrided for its use in hip prostheses.

Titanium and its alloys have many attractive properties including high specific strength, low density, and excellent corrosion resistance. Besides, titanium and the Ti6Al4V alloy have long been recognized as materials with high biocompatibility. These properties have led to the use of these materials in biomedical applications. Despite these advantages, the lack of good wear resistance makes difficult the use of titanium and Ti6Al4V in some biomedical applications, like articulating components of prostheses. Some surface treatments are available in order to correct these problems, like thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Low cycle fatigue behavior in air of Ti6Al4V alloy has been studied. Results show a reduction of low cycle fatigue life up to 10% compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.

Journal Article↗