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Biomedical subjects

J F McCabe

Publications and source records attributed to J F McCabe.

At least 127 records · Page 7Linked to original sources
PubMed1990

The effect of storage media upon the surface microhardness and abrasion resistance of three composites.

The effects of various storage media [distilled water, lactate (pH 4.0), and citrate (pH 6.0) buffers] upon the hardness and wear factor values of three composites [Occlusin (O), P-30 (P), and Fulfil (F)] were studied. Over the one-year storage period, the hardness of all three materials stored in citrate buffer was unchanged. In the case of P in water and all materials stored in lactate buffer, a reduction was observed. There was no significant difference (P greater than 0.05) between the wear factors of specimens after one year or one week of water storage. Specimens of F stored in citrate buffer had a wear factor (P less than 0.01) higher than that of those stored in water. The other materials were not affected by storage in the lactate or citrate buffers. A reduction in surface hardness for some materials did not result in an increase in wear rate. This indicates that the softening effect was limited to a thin surface layer. Although not significant in vitro, this effect would probably increase the rate of in vivo wear, since the softened material would be lost, exposing a fresh surface to further attack. This would adversely prejudice the material's long-term clinical durability by impairing its resistance to abrasion.

Buffers↗
PubMed1990

Onset of elasticity in setting elastomers.

A controlled stress-rheometer used in creep/recovery mode was used for detection of the onset of elasticity in setting elastomers. The time for the materials to develop 5-20% elastic recovery corresponded with the time to reach a phase angle of 60 degrees in an oscillatory test.

Dental Impression Materials↗
PubMed1989

The influence of using vacuum-dried poly(alkenoic) acids upon the physical properties of a glass polyalkenoate (ionomer) cement.

Some of the physical characteristics of two glass polyalkenoate cements have been measured. The two cements differ in terms of the presentation of the poly(alkenoic) acid used to form the cement and in the method of mixing of the materials. The 'conventional' cement uses an aqueous solution of poly(acid) and is an encapsulated mechanically mixed material. The alternative material contains a vacuum-dried poly(acid) powder with the ion-leachable glass, and is mixed by hand with a 15 per cent aqueous solution of tartaric acid. There were some minor differences between the two products, including a delay in the onset of the setting reaction for the material containing the vacuum-dried poly(acid) powder. These differences would probably have little significant effect upon the clinical performance of the materials.

Carboxylic Acids↗
PubMed1989

The effect of placement technique upon the compressive strength and porosity of a composite resin.

This paper examines the effect of two placement techniques upon the compressive strength and level of porosity of specimens of a composite resin. Those specimens prepared by a condensation technique had a significantly lower mean compressive strength (P less than 0.05) and value of Weibull modulus (P less than 0.05) than specimens prepared using a smearing technique. No significant differences in the overall mean percentage area occupied by porosity and mean number of pores were demonstrated (P greater than 0.05) between the two placement techniques. Specimens prepared using the smearing technique, however, had significantly smaller mean maximum pore diameters (P less than 0.05) than those prepared using the condensation technique. It is therefore desirable when placing composite resins to reduce to a minimum handling procedures that are likely to influence the levels of porosity within the material.

Composite Resins↗
PubMed1989

Rheological properties of elastomers during setting.

A controlled stress rheometer has been used to monitor the changes in rheological properties occurring in five elastomeric impression materials during setting. The rheometer differs from conventional rotary viscometers in that the torque is the controlled variable, and the resulting deformation is measured. The use of such an instrument in oscillatory mode enables a range of rheological parameters--including viscosity, rigidity, and elasticity--to be monitored during setting. The polyvinylsiloxane impression materials develop elasticity at a rate that would not be apparent from measurements of viscosity or rigidity alone. This highlights the potential danger of basing the evaluation of clinically important properties, such as working time, on simple measurements of viscosity or rigidity.

Dental Impression Materials↗
PubMed1989

Output from visible-light activation units and depth of cure of light-activated composites.

A simple and reproducible method for monitoring the intensity of radiation from composite light-activation units has been developed. The method depends upon the use of a cadmium sulfide photo-conductive cell, the electrical resistance of which varies with the amount of light falling upon its surface. Filters were used for selection of the wavelength of light that is thought to be most effective in activating polymerization. The use of broad-band wavelength filters failed to give results for light intensity that correlated with depth of cure. Narrow-band interference filters, having a band width of only 10 nm and being selective within the wavelength range of from 460 to 480 nm, produced results for light intensity that correlated with depth of cure. The depths of cure for various types of composite material were measured with use of a penetrometer that enabled the thickness of unpolymerized material at the base of the test mould to be determined. The depth of cure was inversely proportional to the attenuation of light caused by the composite resin at 470 nm. The relationship between depth of cure and light intensity at 470 nm was not a simple linear one over all intensity values. Above a certain critical value of intensity (about 550 lux for a 3.5-mm aperture in these experiments), the depth of cure appeared to be almost independent of intensity. Below this critical value, depth of cure fell markedly with decreasing intensity.

Composite Resins↗
PubMed1988

Composite laminate veneers: a clinical study.

A 2-year clinical trial of a composite laminate veneer system for masking discoloration or hypoplasia on the anterior teeth of patients has been undertaken. Three hundred and twenty restorations were placed in seventy-nine patients, of these 273 restorations in sixty-eight patients have been followed over a 2-year period. The technique produced an acceptable improvement in the aesthetics of the patients in the trial. However, the veneers were susceptible to chipping (52% of lateral incisor veneers and 79% of central incisor and canine veneers showed some evidence of material loss after 2 years) and marginal staining (75% of veneers showed some evidence of marginal staining after 2 years) during function. The veneer restorations had a deleterious affect upon the gingival health of the teeth on which they were placed.

Adolescent↗