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Biomedical subjects

J K Harcourt

Publications and source records attributed to J K Harcourt.

At least 37 records · Page 2Linked to original sources
PubMed1993

The effect of post adaptation in the root canal on retention of posts cemented with various cements.

This laboratory study compared the retention of prefabricated posts in well-fitting and loose-fitting post canals using different cement materials. Eighty-three human teeth were prepared for post placement. One of zinc phosphate cement, polycarboxylate cement, glass ionomer cement or resin cement was used to cement each post in place. A tensile force was applied to remove each post and the separation force was recorded. Posts cemented with the resin cement were the most difficult to dislodge. Posts cemented into loose-fitting canals exhibited greater resistance to dislodgment than posts cemented into well-fitting canals irrespective of the type of cements used.

Dental Cements↗
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↗
PubMed1989

The bond strengths of various adhesives used for Maryland Bridges.

The tensile bond strengths of three groups of adhesives to two electrolytically etched alloys were studied. It was found that the bis-GMA composite resins gave statistically similar bond strengths. The newer Japanese acrylics tested gave statistically higher results than the bis-GMA resins. The clinical significance of these results is discussed.

Acid Etching, Dental↗