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Biomedical subjects

H Oysaed

Publications and source records attributed to H Oysaed.

11 recordsLinked to original sources
PubMed1990

Dynamic mechanical properties of multiphase acrylic systems.

The influence of type and quantity of five different dimethacrylate crosslinking agents on the dynamic mechanical properties of multiphase acrylic systems has been studied. These materials, commonly used in bioengineering, were processed by polymerization of a mixture of liquid methacrylate monomers, and poly(methyl methacrylate) powder. The specimens were made with various ratios of methyl methacrylate and dimethacrylate crosslinking agents in the monomer liquid. Two different processing conditions were used, heat-polymerization at 100 degrees C and autopolymerization at 45 degrees C. By using a forced torsional vibration apparatus the storage modulus (G'), loss modulus (G"), and dissipation factor (tan delta) were determined over the temperature range -60 degrees C to 140 degrees C at frequencies of 0.1, 1.0, 10, and 100 rad/s. In the autopolymerized materials, the glass transition temperature (Tg), as determined via tan delta data, increased with increasing quantities of crosslinking agents. The storage modulus likewise increased. In the heat-polymerized materials only minor variations in modulus and tan delta with type and quantity of crosslinking agents were observed. Tg values of the heat-polymerized materials were, in all cases, greater than those of the autopolymerized materials.

Biocompatible Materials↗
PubMed1989

Creep studies of multiphase acrylic systems.

The influence of type and quantity of five different crosslinking agents on tensile creep properties of multiphase acrylic systems has been studied. The polymeric materials, commonly applied in bioengineering, were processed by polymerization of a mixture of liquid methacrylate monomers and poly(methyl methacrylate) powder. The specimens were made with various ratios of methyl methacrylate and crosslinking agents in the monomer liquid. Two different processing conditions were used, i.e., heat-polymerization at 100 degrees C and autopolymerization at 45 degrees C. Creep behavior was determined at 37 +/- 0.2 degrees C and 50 +/- 0.5 degrees C. The investigation showed higher creep values for autopolymerized than for heat-polymerized materials. In heat-polymerized materials the creep curves showed little variation with type and quantity of crosslinking agents at low stress levels. However, at high stress levels the creep values decreased with increasing quantity of crosslinking agents. The autopolymerized materials showed a more inhomogeneous structure, and great variation in creep. Both among the heat-polymerized and autopolymerized materials, the systems with diethyleneglycol dimethacrylate clearly deviated from the others by showing higher creep values.

Biopolymers↗
PubMed1988

Release of formaldehyde from dental composites.

Polymeric composite materials may contain releasable degradation products or unreacted constituents. Release of formaldehyde from nine different composites was investigated by means of HCHO-hydrazone derivative analyzed with high-performance liquid chromatography. Formation of formaldehyde was found in all the investigated materials. The highest concentrations were observed in specimens polymerized in contact with air. A correlation coefficient, r = 0.83, was found between released formaldehyde and the thickness of the unpolymerized surface inhibition layer. The formaldehyde concentrations were reduced when the inhibition layer was removed prior to testing. A continuous release of formaldehyde was evident during the first ten days. The release decreased with time, but was still detectable after 115 days.

Chromatography, High Pressure Liquid↗
PubMed1987

Composites for use in posterior teeth: composition and conversion.

The purpose of this investigation was to determine the composition, as well as the conversion after polymerization, of some dental composite materials. Eight posterior composites and two anterior composites were investigated. The weight and volume fractions of inorganic fillers were determined by combustion and pycnometric analyses. The monomers were analyzed qualitatively and quantitatively by high performance liquid chromatography, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. Infrared multiple internal reflection spectroscopy was applied for determination of conversion of the methacrylate groups. The conversion in light activated materials was examined at shallow depths, that is, the level of optimal conversion. This investigation demonstrated that the conversion can be correlated with the composition of monomers and oligomers used in the materials.

Acrylic Resins↗
PubMed1986

Composites for use in posterior teeth: mechanical properties tested under dry and wet conditions.

The purpose of this investigation was to determine some mechanical properties of eight different posterior composites, and how they are affected by water sorption. Creep characteristics in compression were expressed as compliance/log time functions. Stress-strain relationship at a constant loading rate was determined both in compression and flexure, and presented as elastic modulus, ultimate strength, and ultimate strain. Water sorption increased creep values for all materials. Generally, the materials with the highest water sorption had the highest increase in creep. Water sorption decreased the elastic modulus and ultimate strength values. The creep values decreased and the elastic modulus increased with increasing quantity of inorganic fillers.

Absorption↗
PubMed1986

Water sorption and filler characteristics of composites for use in posterior teeth.

The purpose of this investigation was to determine the water sorption and solubility, as well as the filler composition and extent of chemical degradation in water, of eight different posterior composites. With one exception, the materials with the largest quantity of fillers had the least water sorption and solubility after three months in water at 37 degrees C. The emission spectroscopy results showed that silicon was the major element in all the fillers except one, which had both silicon and strontium as major elements. Other components registered in quantities of 5-10 wt-% were barium, aluminum, zinc, and zirconium. The leaching of inorganic ions into water from the fillers varied depending on filler composition and filler treatment.

Absorption↗
PubMed1982

Conversion in denture base polymers.

The purpose of this investigation was to determine residual monomers, the insoluble gel fraction, and singly reacted dimethacrylate monomers in heat-polymerized, auto-polymerized conventional and pour-type denture base materials. Residual monomers were determined by HPLC analysis of tetrahydrofuran extracts of denture base polymers. The gel fraction was determined by gravimetric analysis of the nonextractable portion. The pendant methacrylate groups in the gel fraction were determined by quantitative IR (infrared) spectrometry. It was demonstrated that the heat-polymerized materials had the lowest content of residual monomers. Generally, the content of pendant methacrylate groups in the gel was dependent on the initial quantity of crosslinking agent in the monomer liquids. The gel fractions of the heat-polymerized materials were larger than the quantity of reacted monomers and were also dependent on the quantity of crosslinking agent. These findings showed that some of the linear prepolymer, poly(methyl methacrylate) (PMMA), had been incorporated into the crosslinked polymer system. The gel fraction of the auto-polymerized pour-type materials corresponded to the quantity of reacted monomers, whereas the conventional auto-polymerized materials took an intermediate position between pour type materials and heat-polymerized materials in this respect.

Acrylates↗
PubMed1982

Compressive creep of light cured resin based restorative materials.

Creep characteristics of four light activated composite of different composition were determined at 37 and 50 degrees C. The creep properties were compared with the composition of the materials. The microfill material had higher creep values than those with conventional inorganic particles; possibly due to the inhomogenous distribution of the agglomerated inorganic microfill particles. Furthermore, the fraction of inorganic particles was less than in the conventional composite materials. One conventional composite, however, had nearly the same creep values as the microfill material. The content of a large monomer molecule and poor conversion in this conventional composite material may have contributed to a plasticizing effect. The composite material with the lowest creep values had an oligomer/monomer system leading to short branches with pendant methacrylate groups after polymerization and relatively good conversion.

Chemical Phenomena↗