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Biomedical subjects

A G Andreopoulos

Publications and source records attributed to A G Andreopoulos.

33 records · Page 2Linked to original sources
PubMed1994

Repair of denture base resins using visible light-cured materials.

Specimens of denture base resins were repaired with autopolymerizing and visible light-cured (VLC) repair materials. Flexural properties were measured and revealed that the highest strength and toughness of joint are obtained by the autopolymerizing repair material and are independent on the base resin. The VLC materials exhibited a lower repair strength (22% to 58%) and toughness (9% to 33%) than those of the autopolymerizing resin. No interaction between base and repair material was detected, which was attributed to poor adhesive bonding created at the interface.

Acrylic Resins↗
PubMed1994

Plasticization of biodegradable polymers for use in controlled release.

The design of a plasticized, biodegradable polymeric material, suitable for application as a controlled-release system, was attempted. A poly(DL-lactic acid) oligomer was plasticized with 1,2-propylene glycol and glycerol. The latter plasticizer showed poor compatibility whereas 1,2-propylene glycol was compatible with the polymer up to high concentrations. The mixtures prepared displayed considerable depression of processing temperature and enhanced delivery of salicylic acid, in the early stages of release. It seemed, therefore, feasible to produce systems which allow easy and safe processing and can be injected into a body cavity, without the need for surgical retrieval after completion of the release. Furthermore, the differential rate of drug delivery might be of profound interest for cases where elevated drug doses are necessary in the beginning of treatment.

Biodegradation, Environmental↗
PubMed1994

Evaluation of various reinforcements for maxillofacial silicone elastomers.

Various reinforcements have been evaluated according to their effect on the mechanical properties of a silicone elastomer used for the preparation of maxillofacial prosthetic compositions. Emphasis was given to silica reinforcing fillers since fibrillar reinforcements [e.g., short aramid, glass or high modulus polyethylene (UHMPE)] seemed not to improve mechanical properties. An optimal behaviour at filler concentration 35% was determined. As a measure of the crosslinking density, the swelling of specimens immersed in various solvents, at 25 degrees C, was also investigated.

Chemical Phenomena↗
PubMed1993

Some physical properties of an improved facial elastomer: a comparative study.

An attempt was made to evaluate some properties of clinical importance of a new facial elastomer, Cosmesil HC2. A comparative study versus Silskin II and Cosmesil SM4 was also carried out and took into account the effect of weathering after exposure to ultraviolet radiation. The results showed that Cosmesil HC2 is a resilient material and yet displays good tensile characteristics. The results also showed that weathering does not significantly affect Cosmesil HC2 elastomer's tear strength. The overall effect of irradiation was moderate in all materials tested.

Chemical Phenomena↗
PubMed1993

Design and properties of maxillofacial prosthetic materials.

Maxillofacial reconstruction by prosthetic means is a valuable contribution that medicine offers to the public. Materials design and properties are the main problems faced by scientists in this field. Materials used for intraoral prostheses are not ideal, but they have been perfected to the point of practical use. Denture resins, gold, chromium-cobalt alloys, and porcelain are widely used and produce acceptable results in the oral cavity. In this review, the properties and performance of some polymeric materials used in maxillofacial prosthetics are discussed, and new trends in research and development are also reported.

Humans↗
PubMed1991

Surface treated polyethylene fibres as reinforcement for acrylic resins.

The use of poly(methyl methacrylate) as a bone and dental cement material over several decades has provided us with experience related to processing and performance. A recognized disadvantage of such cements is their mechanical behaviour, expressed by low crack propagation resistance, impact strength, fatigue resistance and reduced fracture toughness. Many attempts have been made to resolve these problems either by modifying the poly(methyl methacrylate) chemical structure via copolymerization or incorporating reinforcing additives. The latter is of great importance, because it can lead to the preparation of composite materials with considerably improved performance. Besides reinforcement, the incorporation of additives, such as fibres, results in better processing characteristics, e.g. lowers polymerization exotherm. In this work, poly(methyl methacrylate) reinforced with Tekmilon ultra high modulus polyethylene fibres was studied, focussing on the interfacial bonding between matrix and reinforcement. Some finishing agents were used to treat the fibres and their efficiency was mainly evaluated through the effect on the mechanical properties of the composite material prepared.

Acrylic Resins↗
PubMed1991

Repairs with visible light-curing denture base materials.

Visible light-curing interpenetrating networks are newly developed materials suitable for several dental applications. These materials have several advantages, including versatility and good physicomechanical properties, but also present some weaknesses, such as increased water sorption and poor adhesion to plastic teeth. The suitability of a visible light-curing resin as a repair material, ie, its bending strength, was examined. Results were compared to those obtained with a self-curing acrylic resin. The visible light-curing resin led to repairs with lower strength.

Acrylic Resins↗
PubMed1989

Gel content determination in cross-linked polyethylene.

Gel content is the dominating parameter which affects properties and prescribes the behaviour of a given type of cross-linked polyethylene. Researchers have determined the gel content by several methods based on solvent extraction, a process which dissolves the linear thermoplastic polymer but swells only the cross-linked fraction. In this work, a comparative evaluation was made using model samples to select the most effective solvents and the suitable extraction conditions leading to increased reliability.

Gels↗
PubMed1989

Properties of poly(2-hydroxyethyl acrylate) networks.

Hydrogels, based on poly(2-hydroxyethyl acrylate) cross-linked with 1,4 butanediol dimethacrylate, were studied in respect to their swelling and mechanical behaviour. The determination of Young's modulus at r.t. permitted the calculation of average molecular weight between cross-links. This value could, in turn, be correlated with water-swelling data to give indicative values of the interaction parameter for the system poly(2-hydroxyethyl acrylate)-water.

Absorption↗
PubMed1987

Diffusion characteristics of alginate membranes.

The diffusive properties of alginate membranes prepared by the interfacial reaction of sodium alginate solution with gypsum substrates were studied. The penetrants of primary importance for the above study were methyl methacrylate (MMA) and water, since alginate membranes are used as mould release agents, during the casting of poly(methyl methacrylate) (PMMA) in gypsum moulds in a water bath. Vapour sorption measurements were carried out at various temperatures. The effect of temperature and the combined action of water and MMA on the swelling behaviour of the membrane was also investigated. The results indicate that the water sorption of alginate membranes is non-Fickian, in spite of the linearity of the curves obtained by plotting Mt/M infinity versus t 1/2, at least for a short time period. The membrane treatment with methyl methacrylate, leads to considerably lower equilibrium sorption, possibly because of the formation of a thin film of poly(methyl methacrylate) on the membrane surface.

Alginates↗
PubMed1985

Stability of some soluble alginate solutions.

The stability of some water alginates against bacterial degradation was studied. The study was based on viscosity and pH measurements of some typical alginate solutions, containing suitable additives during an extended time period (222 days).

Alginates↗
PubMed1985

Sodium alginate as a mould release agent.

The use of sodium alginate as a mould release agent during the casting of epoxy or polyester resins in plaster moulds is discussed. The optimal concentration of a retarder is determined, taking into consideration the setting behaviour and the adhesive bond strength. The above characteristics are critical for the application and efficiency of the coating.

Alginates↗
PubMedDate not supplied

The effect of bonding agents on the bond strengths of facial silicone elastomers to a visible light-activated resin.

Three bonding agents were evaluated to determine their effect on the strength of the bond when Silskin II and Cosmesil SM4 silicone facial elastomers were polymerized to a light-activated denture resin. A silane bonding agent proved to be superior, whereas a light-activated bonding agent had inferior bonding characteristics. Intensive heat aging had no significant effect on bond strength.

Acrylic Resins↗