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Biomedical subjects

J Q Whitley

Publications and source records attributed to J Q Whitley.

25 records · Page 2Linked to original sources
PubMed1988

Surface roughness of orthodontic archwires via laser spectroscopy.

Using specular reflectance, the surface roughness of six representative orthodontic archwire products was determined. Among the four alloy groups which are commonly used in orthodontics, stainless steel appears the smoothest, followed by cobalt-chrome, beta titanium, and nickel-titanium. A clearer understanding of the parameters which contribute to sliding mechanics will be possible when these results are combined with future experiments on the coefficient of friction.

Chemical Phenomena↗
PubMed1985

In situ replication techniques: II. Quantitative methodologies for replicate materials.

Because replicate materials have requirements different from those of recording or impression materials, quantitative methodologies were sought using commercial impression materials. Two satisfactory objective techniques resulted, a laser-scattering and a capillary flow test. Using high-resolution gratings to stimulate tooth detail (less than 1 micron), the reproduction quality of 36 two-stage replicas was determined in diffraction, reflection, and in an unblazed state. Using precision bore glass tubes (0.25, 0.5, 1, and 2 mm diameters) to simulate the high-energy surface of enamel, the flow characteristics of nine elastomers (the first stage replicates) and four epoxies (the second stage replicates) were determined at isobaric conditions. Because the laser spot size was relatively large (0.6 mm) and the pressure differential was small (25 mm Hg), both the global resolution and the low shear rate characteristics could be measured. Of the commercial materials tested, Reprosil Light had the best combination of fluidity and resolution, regardless of which positive material was used. Although Permagum Low, Silene Wash, and Xantopren Blue scored high in one of the two tests, none of these materials could compare to Reprosil Light within the context described herein.

Capillary Action↗
PubMed1984

Influence of the suture diameter on the tensile strength of polypropylene monofilaments and its relationship to the USP specification.

Ethylene gas sterilized polypropylene monofilaments were tested in a straight pull as well as in a conventional knot pull tensile test. In either case an analysis of the results indicates that the occurrence of "surface steps" may explain the relationship between strength and suture diameter. The present investigation not only shows that the polypropylene specification could be established on a more fundamental basis (using 60% of the ultimate tensile strength as the generalized criterion) but also suggests that other sutures should be evaluated similarly.

Pharmacopoeias as Topic↗
PubMed1983

Creep rupture behavior of polypropylene suture material and its applications as a time-release mechanism.

The controlled failure of polypropylene (PP) sutures is studied via creep rupture tests. From plots of log time (tB) vs. stress (sigma), linear relationships are generated over the failure times of 1-1000 h. Results show that as a function of stress, the time dependence varies with irradiation dose (15, 20, 25, and 50 Mrad), irradiation atmosphere (air and vacuum), suture diameter (7-0, 6-0, 5-0, and 4-0), and test temperature (26 and 37 degrees C). For a given stress, the time to failure is least for the greatest dose in the presence of air and at the highest temperature. When suture loops are wrapped around a small wire sheave, however, failure occurs in the largest suture as much as two decades sooner than the smallest suture studied. Within the limitations stated herein, they are independent of test method, loop diameter, aging, and humidity. Consequently, after irradiation in vacuum and postirradiation heat treatment, the processed material may be stored at room temperature for at least 1 month. Such materials are advocated when the time release of a dental or medical device is required, for example, in the self-activating cleft palate appliance.

Biomechanical Phenomena↗
PubMedDate not supplied

Molecular weight distribution of a bulk ultra-high molecular weight polyethylene product--impax 5M + UHMW-NAT.

A bulk ultra-high molecular weight polyethylene product, IMPAX 5M + UHMW-NAT, was fractionated using an increasing-temperature sequential-extraction technique. In the presence of an inert atmosphere and an antioxidant, 5 g of material were methodically dissolved in decahydronaphthalene over the temperature range, 80-191 degrees C. Initially, intrinsic viscosities were measured in decalin at 135 degrees C by single point capillary viscometry. From this data the viscosity average molecular weights were estimated using a logarithmic expression. Results showed that the intrinsic viscosities (molecular weights) increased linearly with extraction temperature over a range from 10 to 40 dL/g (1 to 8 X 10(6)) and that the molecular weight distribution was log normal. Mass balances both before and after extraction indicated that less than 0.3% of the material had a molecular weight less than 10(6) and that less than 0.1% of the material was gel. Zero shear viscometry of bulk fractionated polymer and powdered whole polymers confirmed that capillary viscometry increasingly underestimates the true intrinsic viscosities as the polymer chain lengths (molecular shear forces) increase. Indeed, the actual molecular weights ranged from about 2-14 X 10(6). Knowledge of the molecular weight distribution of bulk products and the presence of either volatiles or crosslinked networks is critical for the continued design and development of superior wearing and fatigue-resistant implants.

Humans↗
PubMedDate not supplied

Finishing of MGC Dicor material.

The occlusal surfaces of inlays and onlays milled by the CEREC system are essentially flat, and surface morphology must be produced with rotary instruments. Six methods of finishing a machinable glass-ceramic material (Dicor MGC) were investigated using laser specular reflectance to assess the relative surface smoothness. The results indicated that all the methods produced a similarly smooth surface.

Analysis of Variance↗