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Biomedical subjects

R G Craig

Publications and source records attributed to R G Craig.

At least 91 records · Page 5Linked to original sources
PubMed1983

Stress analysis of a tooth restored with a post and core.

An idealized axisymmetric finite element model of a second premolar restored with a post and core was used to study the distribution and magnitude of stresses as a function of the following parameters: the diameter of the post, the length and the shape of the post, and finally the interface characteristics between post and cement. Emphasis was directed toward the cement layer interposed between the post and the tooth. Bonding between the post and the cement appeared to be the most important parameter to achieve optimal mechanical behavior of the tooth-prosthesis combination.

Crowns↗
PubMed1983

Cigarette staining and cleaning of a maxillofacial silicone.

In this study, a maxillofacial silicone elastomer was stained with cigarette smoke. The stain was then removed by solvent extraction using 1,1,1-trichloroethane. The cigarette smoke produced large color changes in the elastomer as measured from spectrophotometric reflectance curves. The solvent was totally effective in removing the cigarette stain without changing the color of the silicone base.

Color↗
PubMed1982

Stain removal from a pigmented silicone maxillofacial elastomer.

The removal of environmental stains from a pigmented maxillofacial elastomer was carried out by solvent extraction under network swelling. Silastic 44210 was pigmented with 11 maxillofacial pigments prior to staining. Samples were stained with lipstick, methylene blue, and disclosing solution. These stains were then removed by solvent extraction with 1,1,1-trichloroethane. Color parameter measurements both before and after staining and after solvent extraction demonstrated the effectiveness of removing these stains by solvent extraction while causing little or no change in the color of the pigmented samples.

Color↗
PubMed1981

Cytotoxic effects of dental cements on two cell culture systems.

Four dental cements and one bis-GMA composite were tested in cultures of human periodontal ligament fibroblasts and mouse 3T3 fibroblasts. It was found that these cell types reacted to the cements with different intensities, and that there were differences in evaluation by phase contrast microscopy and succinic dehydrogenase histochemistry.

Animals↗
PubMed1981

Stain removal from a silicone maxillofacial elastomer.

In this study, environmental stains were removed from maxillofacial elastomers by solvent extraction. Silastic 44210, an RTV silicone with proven color and physical property stability, was stained with lipstick, disclosing solution, and methylene blue. These stains were then removed by solvent extraction with each of four chemically dissimilar solvents, namely: toluene, benzene, 1,1,1-trichloroethane, and n-hexane. An additional series of samples was prepared with 11 maxillofacial pigments, not for staining, but for evaluation of pigment stability. Results obtained from spectrophotometric measurements before and after solvent extraction demonstrated the effectiveness of solvent extraction in removing stains, while there was little or no change in the color of the pigments or the base elastomer.

Chemical Phenomena↗
PubMed1980

Formulation and evaluation of a hydrophobic composite plastic.

A hydrophobic co-polymer, heptafluorobutylmethacrylate co-para vinyl phenol, was compounded with ethylene glycol dimethacrylate and silanated quartz to produce a hydrophobic composite. The experimental composite had satisfactory working properties and had mechanical properties comparable to commercial composite but a higher modulus of resilience. The wear resistance was equal to or greater than the commercial composite depending on whether a two-body abrasion test or a track width versus normal load test was used for the evaluation. The thermal coefficient of expansion and water sorption values were somewhat higher than those of commercial composites.

Chemical Phenomena↗
PubMed1980

Tear energy of elastomers for maxillofacial applications.

The energy necessary to generate a unit area of torn surfaces was measured for six elastomers with low moduli of elasticity. Four polyurethane materials and two commercial maxillofacial materials were included. The latter had tear energy values between 0.63 and 6.56 erg/cm2, while the polyurethanes ranged from 8.49 to 50.0 erg/cm2. Three of the materials demonstrated non-Hookian behaviour during testing, violating an assumption of the tear energy analysis. A method of compensating for this discrepancy is described.

Chemical Phenomena↗
PubMed1980

Physical properties of maxillofacial elastomers under conditions of accelerated aging.

The stability of the physical properties of various commercially available maxillofacial prosthetic materials was evaluated with the use of an accelerated aging chamber. The tensile strength, maximum percent elongation, shear strength, tear energy, and Shore A hardness were determined before and after accelerated aging. Results indicate that silicone 44210, a RTV rubber, is a promising elastomer for maxillofacial application.

Chemical Phenomena↗
PubMed1980

Physical properties of a pigmented silicone maxillofacial material as a function of accelerated aging.

The effects of accelerated aging on a pigmented elastomer were evaluated by using a weathering chamber. Silastic 44210, a maxillofacial material with proven color and physical property stability, was chosen for pigmentation with 11 maxillofacial pigments. The values of ultimate tensile strength, maximum percent elongation, shear strength, Shore A hardness, and permanent deformation were determined for the pigmented elastomer before and after accelerated aging for 900 h. Results obtained indicate that the incorporation of 0.2% by weight of pigments can alter the physical and mechanical properties of the base elastomer. Accelerated aging had no effect on the physical properties of the pigment/elastomer combinations.

Chemical Phenomena↗
PubMed1980

Neutron activation analysis of microleakage around a hydrophobic composite restorative.

Neutron activation analysis with dysprosium as a tracer was employed to determine quantitatively the microleakage around the restorations of an experimental hydrophobic composite, as well as a commercial composite. Only a negligible uptake of tracer was obtained for the experimental composite, whereas a five-fold uptake was recorded for the commercial composite. Capillary penetration of fluid around a restoration could be greatly reduced by using a hydrophobic composite.

Absorption↗
PubMed1979

Comparison of the accuracy of denture bases by a non-parametric method.

A comparison of the accuracy of denture bases made from a conventional acrylic and four modified acrylic resins was made with the use of a non-parametric method. Twenty-five identical maxillary stone casts were made and five dentures for each resin were processed by conventional compression moulding techniques. The fit of each denture at the molar-to-molar region on its cast was evaluated by five evaluators who independently ranked the twenty-five dentures from best to worst fit after processing, after polishing, and after storage in water at 37 degrees C for 42 days. The ranking data were analysed by Kendall's coefficient of concordance, the Kruskal-Wallis statistic, and the Mann-Whitney test. Excellent agreement among observers was obtained. After storage in water, two modified acrylic resins, Hydrocryl and Vitalon II, had a better fit on their casts than the conventional acrylic, Lucitone Hypro. Luciton 199 had the same and Hircoe had a poorer fit than Lucitone Hypro.

Acrylic Resins↗