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Biomedical subjects

D C Watts

Publications and source records attributed to D C Watts.

At least 91 records · Page 5Linked to original sources
PubMed1990

Sensitivity to ambient light of visible light-cured composites.

Fourteen representative visible light-cured composite materials, including a total of 29 shades, have been examined for sensitivity to ambient light. The assessment was based upon a procedure recommended in an International Standard (ISO/DIS 4049). All but four of the 29 formulations exceeded the critical working time of 60 s when exposed to ambient illumination of 20 klx. These four composite resins exhibited working times greater than 60 s under 10 klx illumination, and the maximum working time observed at 10 klx was 227 s. These data confirm the finite working time of light-cured resins under clinical lighting conditions.

Composite Resins↗
PubMed1990

Finishing composite restorative materials.

A clinically realistic in vitro study was performed to determine the best method for smoothing trimmed surfaces of seven composite restorative materials. Soflex discs produced the smoothest surface, and little advantage appeared to be gained by prior smoothing of the surface with stones or points. A polishing paste, even when used with intermediate finishing agents, produced a rougher surface than that left by the discs.

Composite Resins↗
PubMed1990

Radiographic inhomogeneity of posterior composites.

A radiographic technique has been devised for determining the structural inhomogeneity between successive specimens fabricated from any given dental composite. This has been applied to nineteen composites currently recommended for the restoration of Class I and Class II cavities. The inhomogeneity data fell within clearly defined bands, with some light-cured posterior composites exhibiting an inhomogeneity parameter of zero. Other hands had average inhomogeneities of 1.5%, 2.5%, 3.8% and 6.8%. The level of inhomogeneity exhibited by a composite system may be an important factor in material selection and in long-term clinical performance.

Chemical Phenomena↗
PubMed1990

Variation in the thickness of the composite lute with an indirect composite inlay system.

The findings of an initial investigation of variations in the thickness of the composite lute around inlays of a fine particle hybrid, light- and secondary-cured indirect composite resin inlay system are reported. The lute thickness varied between 10 microns and 90 microns, and was found to be thinnest and most uniform in the region of occlusal cavosurface margins. Although the marginal adaptation of the inlays investigated was generally considered to be satisfactory, sections of the lute were found to exhibit porosity and to contain a number of voids. It is concluded that whilst the lute thickness and marginal adaptation of composite bonded inlays of the type investigated may be found to be acceptable, further work is desirable to investigate ways to limit porosity and voids in lutes and to form and finish the cavomarginal elements of tooth-coloured inlays in such a way that the limiting layer of luting material may be better protected from the rigors of function in the oral environment.

Composite Resins↗
PubMed1990

Cermet--an ideal core material for posterior teeth?

Both amalgam and composite have limitations as core materials. Cermet cements, with their ease of preparation and placement, cariostatic effect, and adhesion to tooth substance, have some advantages over both of these commonly used materials. This article reviews the suitability of glass-ionomer/cermets for use in building up cores on posterior teeth, and provides a guide to the clinical technique.

Composite Resins↗
PubMed1990

Effects of approximal finishing strips.

The effects of a representative sample of approximal finishing strips on the surfaces of restorations, the approximal margins of restorations and on the surfaces of enamel adjacent to restorations have been evaluated using scanning electron microscopy. The results indicate that the sample of finishing strips investigated tend to damage the surface of enamel and fail to leave restorations with either ideal surface finish or marginal adaptation. Guidelines are suggested for the choice of approximal finishing strips in selected clinical situations.

Dental Bonding↗
PubMed1989

Dynamic mechanical properties of an inlay composite.

A visible light-cured composite resin (Brilliant DI) has been studied over a wide range of temperature and frequency by a dynamic mechanical flexural method. The derived data of logarithmic modulus and loss tangent (tan delta) show considerable changes following a secondary-cure process applied to the material. This involved the application of heat and intense light with temperatures rising to 120 degrees C in 7 min. Following this oven-cure the resin phase exhibited enhanced stiffness with the activation-energy barrier for molecular motion at the glass-transition rising from 220 to 291 kJ/mol. This study clarifies the nature and extent of the internal molecular changes which may be produced in the fabrication of a composite inlay.

Chemical Phenomena↗
PubMed1989

Some physical factors influencing tactile perception with disposable non-sterile gloves.

Some of the physical factors considered to influence tactile perception with disposable, non-sterile gloves have been investigated. While it is apparent that tactile perception is influenced by a number of factors, the results of the present work indicate an inverse relationship between dentists' assessments of tactile awareness and stiffness measurements of the glove material.

Dentists↗
PubMed1989

Effects of a solution of a succinic aldehyde on elastomeric impressions.

This study investigates the effect of a 10 per cent solution of a succinic aldehyde on impressions of three representative elastomeric materials. For each material ten specimens were required for each of six immersion periods ranging from 10 min to 72 h at 23 degrees C and including immediate and delayed immersions. Control groups, each of five specimens, were investigated in air and water. The specimens were formed against a standard ruled block (ADA No. 18). Before and after immersion/storage the impression surface of each specimen was assessed, scored and measured to determine dimensional stability and any attenuation and loss of detail. The results indicate that following all immersion/storage periods there was no loss of detail. Whereas dimensional changes of c. -0.5 per cent and +1.0 per cent were observed for the addition and condensation cured silicones, respectively, after 72 h immersion in the solution, zero dimensional changes were observed following the recommended immersion period for sterilization (4 h). However, with the polyether impressions, a 4 per cent expansion occurred after 4 h in the test solution and 9 h in the aqueous control. No significant differences were found between data relating to immediate and delayed immersions. It is concluded that the immersions in the test solution had no effect on surface detail; only the silicone impressions exhibited acceptable dimensional stability during prolonged immersions (4-72 h) in the test solutions and aqueous control, and that the polyether specimens withstood immersion in the test solution for the 10-min period recommended for disinfection.

Aldehydes↗
PubMed1989

The use of a cone and plate viscometer for determination of flow properties of unfilled resins and etching gels.

A cone-plate viscometer was employed for studying the rheological characteristics of certain unfilled resins and etching gels. Of these, BIS-GMA monomer and its diluted mixtures exhibited Newtonian, dilatant and thixotropic behaviour depending on the shear rate. Other unfilled resins also exhibited various types of behaviour. At high shear rates reproducible hysteresis loops were obtained for etching gels which may be useful in characterization.

Acid Etching, Dental↗
PubMed1988

Residual debris and bond strength--is there a relationship?

A study was undertaken to test the theory that there is a relationship between bond strength at the separate interfaces of the direct bonding system and the amount of residual debris remaining on the enamel surface following removal of a bonded appliance. In separate experiments, shear loads were applied at the complete direct bonding system and at the separate interfaces--namely, those at the adhesive/enamel and the adhesive/bracket base--using a chemically cured and a visible light-cured materials in combination with two designs of bracket bases. An assessment of residual debris following bond failure was made. For the complete direct bonding system, analysis showed that a foil mesh/chemically cured adhesive combination produces significantly more residual debris on the enamel than any other combination (P less than 0.05). No significant differences (P greater than 0.05) in shear bond strengths were detected for any bracket base/adhesive/enamel combination. Furthermore, no significant differences (P greater than 0.05) were detected between the shear bond strengths at the adhesive/enamel and adhesive/bracket base interfaces. These results suggest that the amount of residual debris following removal of the bonded bracket is not related to the shear bond strength at the separate interfaces but is governed by factors caused by bracket base design and properties of the adhesive used.

Adhesiveness↗
PubMed1988

Mechanical properties of elastomeric impression materials.

Dental elastomeric impression materials of different consistencies, representing addition and condensation silicones, polysulphides and a polyether, were studied to determine their mechanical properties in terms of tearing energy, tensile properties and modulus determined at high strain rates. Whilst the polysulphides had the greatest resistance to tearing, they were more extensible, had lower moduli of elasticity and lower tensile strengths than the silicones. The polyether resembled the silicones in many respects.

Chemical Phenomena↗
PubMed1987

Development of carboxypeptidase K (creatine kinase conversion factor) in man.

The developmental appearance of carboxypeptidase K in human plasma was determined by quantifying the creatine kinase (CK) isoforms present and by measuring the conversion of tetrathionate-blocked CK in vitro. Analysis of plasmas from second and third trimester fetuses, newborns and adults showed that isoforms were absent from second trimester fetuses, were present in similar amounts in third trimester fetuses and newborns, and had increased to about twice this amount in adults. Carboxypeptidase K activity was correspondingly absent from second trimester fetuses but present in the other three groups in statistically indistinguishable amounts. Carboxypeptidase N was present in all groups although activity was low in second trimester fetuses. Addition of cobalt ions activated both carboxypeptidases K and N in all samples and unmasked carboxypeptidase K in second trimester samples.

Adult↗