Biomedical subjects

M Braden

Publications and source records attributed to M Braden.

At least 19 recordsLinked to original sources

PubMed1992

Refractive index and molar refraction of methacrylate monomers and polymers.

The refractive indices of a number of methacrylate monomers have been measured and corresponding molar refraction data calculated. Similar determinations were made on a number of methacrylate polymers. The molar refraction values determined were in excellent agreement with the values calculated from the published molar refraction values of the chemical groups involved. There was little difference between the molar refraction values of monomers and that of the repeat unit in the corresponding polymers, in marked contrast to the molar volumes. The ratio of refractive index to molar volume was reasonably consistent for all methacrylates studied (0.25-0.30 approximately).

Chemical Phenomena↗

PubMed1992

Dimensional stability of condensation silicone rubbers.

The linear shrinkage during 24 h after setting of a number of proprietary condensation silicone dental impression materials was studied. Weight loss and change in volume were measured over the same time period by weighing similar specimens in air and water. The weight-loss data conformed to a linear t1/2 plot, indicating that the loss of volatile material was diffusion controlled. From the diffusion coefficient so determined, linear shrinkage values predicted from the weight loss data were compared with the experimental results. For all except the highly-filled putty materials, the correspondence between theoretical and experimental data was reasonable; in the case of the putty materials, the shrinkage was very much greater than that predicted theoretically. This is possibly due to elastic memory effects consequent on moulding the putty materials.

Biocompatible Materials↗

PubMed1992

Modified Arrhenius equation for the frequency dependence of the transition temperature of polymers--a note on some further observations.

Activation energies obtained from differential mechanical thermal analysis work on polymers have been observed to relate to similar behaviour of diffusion coefficients of gases in polymers. Comparison of the two techniques showed the additional energy terms to be virtually identical and the pre-exponential factors to relate to segmental motion of a five-unit carbon atom.

Biocompatible Materials↗

PubMed1992

Reinforcement of polymers of 2,2 bis-4(2-hydroxy-3-methacryloyloxy propoxy) phenyl propane by ultra-high modulus polyethylene fibres.

A study has been made of the reinforcement of 2,2 bis-4(2 hydroxy-3-methacryloyloxy propoxy) phenyl propane/tetra-hydrofurfuryl methacrylate copolymers with ultra-high modulus polyethylene fibres. The fibres were orientated longitudinally, in loadings up to 50% w/w, and both untreated and surface treated fibres were studied. Modulii up to approximately 35 GPa were achieved in the axial direction, and the specimens could not be broken in the simple flexure test employed. Electron microscopy of fractured specimens showed extremely good contact between resin and fibre. No deterioration in properties was observed over 6 months in water.

Biocompatible Materials↗

PubMed1992

Novel acrylic resins for dental applications.

A heat-cured resin based on a copolymer of bis-phenol-A glycidyl methacrylate (bis-GMA) and tetrahydrofurfuryl methacrylate (THFM) was investigated. Workable pastes were made by adding 90/10 w/w bis-GMA/THFM copolymer powder to a 70/30 w/w monomer of the same composition. The organic filler content was 60-64% w/w. Young's modulus, flexural strength, impact strength, hardness, water absorption and desorption, linear thermal expansion, polymerization shrinkage and glass transition temperature were determined. The materials studied showed high elastic modulus, hardness and glass transition temperature. A relatively low linear thermal expansion was obtained but poor impact strength and low flexural strength, indicating brittleness. Acceptable values were obtained for water absorption.

Acrylic Resins↗

PubMed1992

Further observations on high impact strength denture-base materials.

Previous studies have shown that high impact strength can be conferred on denture-base poly(methyl methacrylate) polymers by modification with acrylic-terminated butadiene-styrene block copolymers, and that the acrylic end-group was necessary for effective reinforcement. It is now shown that, by solvent extraction studies, grafting of the copolymer occurs both with acrylic-terminated and non-terminated block copolymers. It is therefore concluded that the mode of grafting is different, and some possible mechanisms are discussed.

Acetone↗

PubMed1992

Thermal expansion of glassy polymers.

The thermal expansion of a number of glassy polymers of interest in dentistry has been studied using a quartz dilatometer. In some cases, the expansion was linear and therefore the coefficient of thermal expansion readily determined. Other polymers exhibited non-linear behaviour and values appropriate to different temperature ranges are quoted. The linear coefficient of thermal expansion was, to a first approximation, a function of both the molar volume and van der Waal's volume of the repeating unit.

Biocompatible Materials↗

PubMed1991

Study of polymeric systems based on 2,2 bis-4(2-hydroxy-3-methacryloyl-oxypropoxy) phenyl propane.

2,2 bis-4(2-hydroxy-3-methacryloyloxypropoxy) phenyl propane is the basic monomer for a large number of proprietary dental composite filling materials. In this paper, studies have been made of its copolymers with various comonomers. 2,2 bis-4(2-hydroxy-3-methacryloyloxypropoxy) phenyl propane--tetrahydrofurfuryl methacrylate copolymers, at about the 95/5% v/v level, showed an enhanced modulus over that of the test material itself, to give a Young's modulus of -4.8 GPa. This reflected an enhanced activation energy of the glass transition temperature, indicating a very specific free volume effect of the diluent monomer. Further studies 2,2 bis-4(2-hydroxy-3-methacryloyloxypropoxy) phenyl propane-tetrahydrofurfuryl methacrylate room temperature polymerized copolymers showed that enhanced modulus could be achieved by including in the system small amounts of inhibitor; 0.3% v/v 2,6 di-tertiary butyl phenol elevated the Young's modulus of a benzoyl peroxide--NN-dihydroxy ethyl p-toluidine cured system from 3.1 to 3.6 GPa. Such resins may be useful in improved dental fissure sealants and composite filling materials.

Benzoyl Peroxide↗

PubMed1991

Residual monomer in acrylic polymers.

Three proprietary dental resins were found to include acrylates (as distinct from methacrylates). As acrylates are well known to have adverse skin reactions, the nature and content of the acrylates were obtained. One resin contained methyl acrylate, and the other two ethyl acrylate. Also, the extractable free monomer from one proprietary and one experimental bone cement was determined as a function of time. This was carried out: (a) on unpolymerized material as soon as it formed a coherent dough; and (b) on already polymerized material. The extraction of n-butyl methacrylate from the experimental bone cement was very much less than that of methyl methacrylate from the proprietary bone cement. In both cases, whilst the kinetics of loss for short times appeared to conform to diffusion theory, subsequent loss did not; this was attributable to both continued polymerization of the monomer and to the concentration dependence of the diffusion coefficient.

Acrylates↗

PubMed1991

Heterocyclic methacrylates for clinical applications. I. Mechanical properties.

The mechanical properties of a number of heterocyclic and one cyclic methacrylate have been studied for their potential in low polymerization shrinkage systems. This study included both homopolymers and room temperature polymerizing systems using poly(ethyl methacrylate) powder with a heterocyclic methacrylate monomer. The one cyclic methacrylate studied, isobornyl methacrylate, gave an extremely brittle polymer; furthermore, it would not form a dough with poly(ethyl methacrylate). The homopolymers gave Young's moduli in the range 1.38-2.19 GN/m2, i.e. lower than poly(methyl methacrylate). The moduli of poly(ethyl methacrylate)/monomer systems are theoretically predictable from the moduli of the homopolymers involved. The above materials were generally ductile and the mechanical properties indicated a useful class of materials for clinical use.

Biocompatible Materials↗

PubMed1991

Heterocyclic methacrylates for clinical applications. II. Room temperature polymerizing systems for potential clinical use.

A number of useful room temperature polymerizing resins were formulated, based on poly(ethyl methacrylate) powder and a range of low shrinkage heterocyclic methacrylate monomers. N,N-dimethyl-p-toluidine or p-tolyl diethanolamine were used as activating amines, but the latter material is less active and some care is necessary with respect to the source of the monomer. Isobornyl methacrylate is a useful diluent monomer to reduce the exotherm.

Biocompatible Materials↗

PubMed1991

Heterocyclic methacrylates for clinical applications. III. Water absorption characteristics.

The water absorption and desorption behaviour of poly(isobornyl methacrylate) and poly(tetrahydropyran-2-ylmethyl methacrylate) obeyed diffusion laws on repeated absorption/desorption cycles. However, the polymers of 2,3-epoxypropyl, tetrahydrofurfuryl and tetrahydropyranyl methacrylates did not obey diffusion laws, did not equilibrate after 2 yr immersion in water and exhibited very high uptake values (30-90%). For 2,3-epoxypropyl methacrylate, the sample disintegrated. A clearly detailed structure of the heterocyclic ring is critical. The use of these monomers in room temperature polymerizing poly(ethyl methacrylate)/monomer systems generally reflected the behaviour of the related homopolymers.

Absorption↗

PubMed1991

Shear properties of some dental and other polymers.

The shear modulus and elastic limit in shear were determined for a number of polymers of clinical interest, using a static torsion method. In particular, ultra-high modulus polyethylene was studied as a function of draw ratio, and compared with corresponding Young's modulus data. Materials of high shear moduli of potential clinical value are described.

Biocompatible Materials↗

PubMed1990

Soft prosthesis materials based on powdered elastomers.

A new class of soft prosthesis material has been developed, based on the combination of a powdered elastomer and a methacrylate monomer that polymerizes to an elastomer. Such systems are processable by conventional dental technology. This principle avoids the use of plasticizers. Natural rubber, butadiene styrene and butadiene acrylonitrile elastomers have been used, together with a number of higher alkyl methacrylates (C8-C13) and 2-ethoxyethyl methacrylate. Such systems have been evaluated with respect to mechanical properties, including tear strength, adhesion to denture base poly(methyl methacrylate), water sorption and visco-elastic properties. A number of potentially viable systems have emerged, which may be useful in external prostheses. Many have high long-term water absorption, which makes questionable their long-term usefulness interorally. Nevertheless, there is still considerable scope for development in this area.

Absorption↗

PubMed1990

Formulation of tissue conditioners.

Dental tissue conditioners are compliant gels, formed in situ under a denture from a polymer powder and a plasticizer system. Hitherto, the powder has been poly(ethyl methacrylate) and the liquid a phthalate/ethanol mixture. These materials are temporary, because they harden from plasticizer leaching. The current work has been aimed at producing material with extended oral lifetimes. A range of n-butyl/ethyl methacrylate copolymers have been studied, together with various ester-ethanol liquid systems, with respect to gelation behaviour with various alcohols and esters, viscoelastic behaviour of the set gels, and water extraction. Materials based on poly(ethyl methacrylate) show that gelation speed depends upon particle size, and the degree of ball milling of the powder, and the molar volume of the plasticizer. Systems based on n-butyl/ethyl methacrylate copolymers need less or no ethanol in the liquid system, although gelation speed is very temperature dependent. The gels from these last materials are more compliant, and retain their compliance longer in aqueous media than those based on poly(ethyl methacrylate).

Biocompatible Materials↗

PubMed1990

Load deformation behaviour during a diametral test.

The deformation of a cylinder in the diametral mode proved to be a linear function of the applied load for silicate cements, glass ionomer cements and glass. Two theoretical analyses were investigated, namely, Hertzian indenter theory and integration of the Hondros diametral theory. Whilst both theories predicted the experimentally observed linear behaviour, neither were quantitatively correct. Furthermore, the Hondros theory contained an experimentally inaccessible parameter, the angle subtended by the contact width at the centre.

Dental Cements↗

PubMed1989

Water absorption of methacrylate soft lining materials.

The water absorption of soft methacrylate prosthetic materials is very high compared with rigid methacrylates and is not at an equilibrium value even after 6 yr. This very high and prolonged uptake can be explained qualitatively in terms of the presence of water soluble impurities which form sites for the formation of water droplets. These droplets grow until the osmotic and elastic forces balance; this mechanism can be accompanied by creep or even rupture under the osmotic pressure. Desorption on the other hand, is rapid and obeys diffusion laws, giving diffusion coefficients of 5-7 X 10(-8) cm2 s-1.

Absorption↗

PubMed1989

Modified Arrhenius equation for the frequency dependence of the transition temperatures of polymers.

A linear relationship was established for several polymers between the pre-exponential factor and the activation energy of a modified form of the standard Arrhenius equation. In addition, the energy term itself was modified such that the alpha and beta absorptions were related to the number of carbon atoms available for segmental motion. At large activation energies the modified Arrhenius relationship suggested upper limits of 495.5K and 321K for the alpha and beta transition temperatures, respectively.

Biocompatible Materials↗