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Biomedical subjects

D T Turner

Publications and source records attributed to D T Turner.

35 records · Page 2Linked to original sources
PubMed1977

Temperature control of a bone cement by addition of a crystalline monomer.

The peak temperature reached during the polymerization of a bone cement was reduced by addition of solid N-vinylcarboazole to the powder component. It was also necessary to saturate the liquid component with N-vinylcarbazole to prevent dissolution from the modified powder component on mixing. It is believed that this technique is generally applicable and opens up the possibility of achieving temperature control of bone cements with choice from a range of crystalline monomers.

Bone Cements↗
PubMed1976

Influence of application technique on microstructure and strength of acrylic restorations.

An investigation was made of the influence of application techniques on the microstructure and properties of an acrylic tooth restorative. Mixtures of acrylic powder and monomer ("Sevriton Simplified") were applied by the brush technique of Nealon (J. Prosth. Dent., 2, 513, 1952) and by two bulk flow techniques. While similar porosities (about 4%) were observed, the brush technique resulted in a greater quantity of grains from the acrylic powder. Despite this, there was little difference in values of compression modulus, compressive yield stress, and diametral compressive strength. The mechanical strength of the materials studied was less than one-half that of high molecular weight poly(methyl methacrylate) (PMMA). Crack propagation studies established that the interface between the grains and matrix was not a source of weakness. However, as the matrix was crosslinked this could not be checked by solution methods of polymer characterization.

Acrylic Resins↗
PubMed1975

Fractography of poly(methyl methacrylates).

For convenience in clinical manipulation, it is the practice to fabricate PMMA protheses from mixtures of powder and monomer. When the monomer is subsequently polymerized an unusual 2-phase polymeric material results in which grains of PMMA are dispersed in a matrix of the same polymer. The mechanical properties of the 2-phase materials are inferior in certain respects relative to 1-phase polymers. The purpose of the present work is to evaluate the failure of 2-phase materials by microscopical examination of their fracture surfaces. A granular microstructure was clearly distinguishable and a distinction made between materials which fail exclusively by transgranular fracture and others which additionally exhibit intergranular fracture. In order to interpret markings observed on the fracture surfaces of the complex 2-phase systems a study was made of the influence of molecular weight on the fractography of 1-phase PMMA. Molecular weight was reduced by degradation of samples by exposure to gamma-rays. The spacing of periodic rib markings on fracture surfaces was found to decrease with molecular weight and this relationship used to provide an estimate of the molecular weight of polymer in the matrix of 2-phase materials.

Dental Stress Analysis↗
PubMedDate not supplied

Improved photochemical bonding of composites to dentin using 4-methacryloxyethyl trimellitate anhydride.

The main objective was to evaluate the use of 4-methacryloxyethyl trimellitate anhydride (4-META) to improve bonding of composite materials to dentin. Bowen's resin, containing camphoroquinone, was polymerized by exposure to visible light. In composites, made with a silanated silicate, inclusion of 4-META (3%) had little effect in increasing mechanical strength or adhesion to bovine teeth. However, direct application of 4-META via acetone solution was found to be an effective way of increasing tensile adhesive strength; by 240% to dentin (to 7.2 MPa) and by 160% to enamel (to 10.8 MPa). Applying the experience mentioned above, 4-META was used to bond a proprietary photocuring microfilled composite material to Class V cavities in freshly extracted human teeth. After thermal cycling between water baths held at 5 degrees C and 60 degrees C, all dentin restorations without 4-META failed, as judged by marginal leakage of a dyestuff. In contrast, using 4-META there was no leakage in 9 out of 10 cases. In restorations involving enamel, 4-META failed to prevent marginal leakage at the enamel margins but did prevent penetration along the dentin/composite interface. It is concluded that 4-META shows great promise for preventing marginal leakage at dentin/composite interfaces.

Acrylic Resins↗
PubMedDate not supplied

Influence of 4-methacryloxyethyl trimellitic anhydride on composites subjected to hygrothermal cycling.

Pastes were made by spatulating a hydroxyapatite powder into triethylene glycol dimethacrylate (TEGDMA) that contained benzoyl peroxide. For comparison, similar pastes included 5 wt-% 4-methacryloxyethyl trimellitic anhydride (4-META) in the TEGDMA. Composites were made by heating at 120 degrees C under pressure. Inclusion of 4-META reduced the rate of diffusion of water by about one-third, at 27 degrees C. Also after thermal cycling in water, inclusion of 4-META decreased the fractional drop in compressive strength by about one-half. Examination of fracture surfaces indicated that inclusion of 4-META improved the wetting of filler particles and gave more coherent composites. All these findings are consistent with the view that 4-META acts as a coupling agent.

Acrylates↗
PubMedDate not supplied

Characterization of cross-linked two-phase acrylic polymers.

A cross-linked network was formed in the particulate disperse phase carried over from the soluble pearls only in one material tested (L). The preparation of this material involved a slow rate of polymerization that allowed sufficient time for imbibition of the cross-linking monomer by the particles. In two of the materials (CR and S), the particulate phase was extractable and the remaining cross-linked matrix could be characterized for equilibrium swelling by volumetric measurements. Equilibrium swelling values were used to estimate densities of elastically effective chains in the network.

Acrylic Resins↗