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Biomedical subjects

J K Harcourt

Publications and source records attributed to J K Harcourt.

15 recordsLinked to original sources
PubMed1992

An investigation of the composite resin/porcelain interface.

Failures at composite resin/porcelain interfaces under shear-like loading were examined. Porcelain surfaces were treated with hydrofluoric acid and/or one of two silane coupling agents, using two different composite resin cements. The results showed that after seven days storage, bond strengths of specimens which had undergone porcelain surface treatment were greater than the cohesive strength of the porcelain itself, resulting in brittle fracture of the porcelain. The diluted restorative composite resin performed as well as the commercial composite resin cement. Silane pretreatment of porcelain was important as the bond strength of etched/silane primed specimens was significantly higher than the etched only specimens. However, one primer appeared to be more efficient than the other in bond promotion. Some explanations for the differences in bond strengths are offered.

Acid Etching, Dental↗
PubMed1990

The effects of disinfectants on the dimensional stability of alginate impression materials.

Glutaraldehyde and hypochlorite solutions have been shown to be effective disinfectants for use in the dental surgery. However, their use in the disinfecting of alginate hydrocolloid impression materials must be open to question since these materials are dimensionally unstable when immersed in aqueous solutions for any length of time. This project investigated the dimensional changes noted in casts poured into alginate impressions which had been stored for up to 60 minutes in either hypochlorite or glutaraldehyde solutions. All changes measured were considered to be within clinical tolerance.

Alginates↗
PubMed1990

Determination of adhesive bond strength to dentine. A new method.

Specimens for the determination of adhesive bond strength to dentine were prepared using suitable surfaces of freshly extracted teeth from 15 patients who were having immediate dentures fitted. As soon as possible after extraction, shallow cavities were cut into the dentine to a depth of 1 mm using a high-speed round bur (diameter 4.2 mm) under water coolant. The cavities were restored using dentine bonding agents and single increments of light activated composite resin. The restored teeth were cut down to approximately 5 mm in diameter and 3 mm thick and were either placed in previously prepared sites in the buccal or occlusal surfaces of their respective dentures or in containers of tap water. Patients were instructed to remove their dentures only for cleaning with a soft nylon brush and toilet soap, while the laboratory specimens were stored at ambient temperature. After one week, the tensile force needed to dislodge each restoration from its cavity was determined using a universal testing machine. Previously reported laboratory methods for bond strength determination have usually employed a flat dentine surface. However, this study more closely resembled the clinical situation in that the smear layer was produced by a rotary cutting instrument, and the effects of polymerization shrinkage when curing the composite resin were simulated. Furthermore, it was easier to confine the bonding agent to the desired dentine surface.

Adhesives↗
PubMed1979

The ultrastructural localization of the corrosion products of dental amalgam.

The ultrastructural localization of corrosion products released from dental amalgam implants in rat subcutaneous tissue was studied by means of a sulphide-silver technique. Implants stimulated a prolonged inflammatory response with delayed granulation tissue formation and slow and faulty collagen formation. The metallic corrosion products were found both in cells and in association with matrix components. Intracellular metal deposits were predominantly in the cytoplasmic matrix and in vacuoles in the early (19 day) lesions, but at 60 days there was metal in many nuclei, both viable and dead. Collagen fibrils had metal on the surface and vascular basement membranes had granules of bound metals.

Animals↗
PubMed1978

Toxic effects of dental amalgam implants. Optical histological and histochemical observations.

Dental amalgam and porcelain control discs were implanted in the subcutaneous tissue of rats. Amalgam implants exerted a toxic effect caused by release of metal ions which was characterized by prolonged inflammation, delayed granulation and disordered collagen formation. Dental porcelain was found to be a suitable biocompatible control which provided a bulk similar to that of dental amalgam but induced only an uncomplicated granulation response.

Animals↗
PubMed1978

A review of modern impression materials.

A number of new elastic impression materials have been developed over the past few years. The working time, setting time, elasticity at set, permanent deformation, dimensional change on setting and long-term stability were determined for several of these impression materials. The new addition type silicone impression materials proved superior to the other materials tested, but all materials were capable of giving good clinical results.

Dental Impression Materials↗
PubMed1975

Silane coupling agents in stainless steel and polymethyl methacrylate systems.

Smooth stainless steel rods coated with silanes were embedded in acrylic resin dough. The strength of the bond between treated rods and polymerized resin was improved compared with that found in the untreated rods under all conditions of the tests. The strength increased with age when specimens were left in air; immersion in water lessened the increase in strength.

Acrylic Resins↗