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Biomedical subjects

H J Wilson

Publications and source records attributed to H J Wilson.

At least 19 recordsLinked to original sources
PubMed1992

The fit of all-ceramic crowns cemented with different luting agents.

In this article the fit of all-ceramic crowns, cemented with different luting agents (zinc phosphate and resin cements), was investigated using a scanning electron microscope. The marginal opening of all-ceramic crowns cemented with zinc phosphate cement was 111.9 +/- 40.6 microns which was significantly greater than the 46.7 +/- 12.9 microns marginal opening of Cerestore crowns cemented with resin cement. Total film thicknesses of the cements were not uniform and there were certain discrepancies from margins to walls and to tip due to the die spacer.

Aluminum Oxide↗
PubMed1990

An investigation of test-house variability in the mechanical testing of dental materials and the statistical treatment of results.

The suitability of a test for standard specification testing depends inter alia on the ability to repeat the tests in a reproducible manner at a number of test centres. This work involved the investigation of three tests currently proposed as standard specification tests for dental materials. It was found that one test (compressive strength of cements) is inappropriate for inclusion in standards due to an unacceptable variation in test results between test centres. The treatment of results suggested in standards should place less emphasis on the mean value of a relatively small number of test specimens and the use of a simple form of probability theory in which, say, 80 per cent of specimens are required to achieve a certain pass level. In some standards there may be a need to increase the numbers of test specimens significantly in order to achieve a more meaningful and reliable result. The use of Weibull statistics can be adopted as a means of identifying tests which are suitable for inclusion in standard specifications, although it is doubtful that a test at this level of sophistication is required or desirable for inclusion in the standards themselves.

Composite Resins↗
PubMed1990

Clasp retention and composites: an abrasion study.

An in vitro test for screening the abrasion resistance and abrasivity of composite resins when used to provide tooth undercuts for removable partial denture clasps is described. In the present study nine composite resins were tested against wrought stainless steel round clasps. The results indicated that the abrasion of any of the composites tested was unlikely to cause a noticeable loss of retention in the clinical situation. However, there was marked abrasion of the clasps by two of the composites which would be likely to be clinically relevant.

Analysis of Variance↗
PubMed1989

Home births.

Explore the source record for details and available documents.

Delivery, Obstetric↗
PubMed1989

The determination of elastic recovery of impression materials at the setting time.

One of the prime requisites of an elastomeric impression material is that it should possess adequate elastic recovery on removal from undercut areas. Most standard methods of measuring elastic recovery rely on the preparation of specimens in moulds. The specimens are subsequently removed and subjected to compressive or tensile stresses several minutes after the setting time. The equipment described in this paper has been developed to enable elastic recovery values to be determined at times in the vicinity of the setting time. A shear strain is induced in the material for a short time and the resulting recovery recorded graphically. Results indicate that there is a significant improvement in elastic recovery from just prior to until just after the setting time.

Chemical Phenomena↗
PubMed1989

Rigidity of elastomeric impression materials.

The rigidity of an impression material should be less than a certain value in order that excessive forces are not required when taking impressions of undercut areas. Conversely, the impression should be sufficiently rigid to withstand the weight of stone whilst pouring the cast without distortion. This paper describes a method of determining elastic modulus values at times as early as the setting time of the material. Results indicate that the elastic modulus values increase from the setting time to 30 min after the start of mix. Values are presented for a representative range of elastomeric impression materials.

Chemical Phenomena↗
PubMed1989

Consistency, working time and setting time of elastomeric impression materials.

This paper describes the development of an instrument for determining consistency, working time and setting time of elastomeric impression materials. The operating principle involves the application of a fixed compressive strain and the resulting stress is measured. This instrument has been called a Comprheometer. Temperature control is achieved by water circulation so that simulated room or open-mouth temperatures can be used. Values of consistency and working time are presented for a range of elastomeric materials at room temperature. Also, setting times determined under oral conditions are recorded.

Chemical Phenomena↗
PubMed1989

An investigation of the polymerization of orthodontic adhesives by the transillumination of tooth tissue.

Prepared samples of light-activated composite were cured by transillumination of tooth tissue in healthy volunteers. Positioning of the samples and the direction of illumination was designed to simulate curing during direct bonding. The effectiveness of curing was investigated by determination of surface microhardness. The degree of polymerization of the specimens cured by transillumination was found to be reduced compared to the control samples cured by direct exposure to the light source.

Adult↗
PubMed1989

The effect of bracket type and ligation method upon forces exerted by orthodontic archwires.

The effects of bracket type and ligation method upon the forces exerted at 1.5-mm deflection by three archwire materials were measured in a simulated clinical situation. Significant force differences were found when archwires were used in standard edgewise or straightwire brackets, respectively, and also when Alastik modules were used for ligation instead of steel ligatures.

Alloys↗
PubMed1988

Forces exerted by orthodontic aligning archwires.

The forces produced by 10 orthodontic archwires were measured in a simulated clinical situation and also with the wires in simple three point loading. All tests were made to a maximum deflection of 3 mm. At 1.5 mm deflection the forces exerted when each wire formed part of a fixed appliance ranged from 1.5 to 8.3 N. When the same wires were used as simple beams the forces exerted ranged from 0.3 to 3.0 N. The findings indicate that the forces generated by orthodontic mechanisms cannot be calculated from straightforward physical principles.

Alloys↗