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J Q Whitley

Publications and source records attributed to J Q Whitley.

11 recordsLinked to original sources
PubMed1992

Frictional coefficients of ion-implanted alumina against ion-implanted beta-titanium in the low load, low velocity, single pass regime.

The frictional coefficients were measured for four wire alloys against the flats of polycrystalline alumina cylinders using a low load, low velocity, single pass device. Ion-implantations of titanium into polycrystalline alumina flats and nitrogen into beta-titanium wires reduced the static and kinetic coefficients from 0.50 and 0.44 before implantation to 0.20 and 0.25 after implantation, respectively. These results are similar in magnitude to frictional coefficients for unimplanted, control couples of stainless steel, cobalt-chromium, and nickel titanium wires against polycrystalline alumina flats. For orthodontic applications, we conclude that more efficient and reproducible appliances can be engineered for tooth movement if ion-implantation is used to reduce the abrasion of beta-titanium by polycrystalline alumina.

Aluminum Oxide↗
PubMed1991

Comparison of the frictional coefficients for selected archwire-bracket slot combinations in the dry and wet states.

Coefficients of friction were evaluated in the dry and wet (saliva) states for stainless steel, cobalt-chromium, nickel titanium, and beta-titanium wires against either stainless steel or polycrystalline alumina brackets. For both operators' experiments, an 0.010" stainless steel ligature wire pressed each archwire into the 0.018" or 0.022" bracket slot at 34 degrees C. In the dry state and regardless of slot size, the mean kinetic coefficients of friction were smallest for the all-stainless steel combinations (0.14) and largest for the beta-titanium wire combinations (0.46). The coefficients of the polycrystalline alumina combinations were generally greater than the corresponding combinations that included stainless steel brackets. In the wet state, the kinetic coefficients of the all-stainless steel combinations increased up to 0.05 over the dry state. In contrast, all beta-titanium wire combinations in the wet state decreased to 50% of the values in the dry state. The mixed reports that saliva may promote adhesive and lubricious behaviors may have some substance.

Aluminum Oxide↗
PubMed1990

Effects of surface roughness on the coefficients of friction in model orthodontic systems.

Orthodontists, like others (Engel, P.A. (1976) Impact Wear of Materials. Elsevier Scientific, New York.), often equate the smoothness of surfaces with the absence of friction. To investigate whether the surface roughness of opposing materials influence the coefficients of friction and ultimately the movement of teeth, arch wires were slid between contact flats to simulate orthodontic arch wire-bracket appliances. From laser specular reflectance measurements, the RMS surface roughness of these arch wires varied from 0.04 microns for stainless steel to 0.23 microns for nickel titanium. Using the same technique, the roughnesses of the contact flats varied from 0.03 microns for the 1 micron lapped stainless steel, to 0.26 microns for the as-received alumina. After each of the arch wire-contact flat couples was placed in a friction tester, fifteen normal forces were systemically applied at 34 degrees C. From plots of the static and kinetic frictional forces vs the normal forces, dry coefficients of friction was obtained that were greater than those reported in the dental literature. The all-stainless steel couples had lower kinetic coefficients (0.120-0.148) than the stainless steel-polycrystalline alumina couple (0.187). When pressed against the various flats, the beta-titanium arch wire (RMS = 0.14 microns) had the highest coefficients of friction (0.445-0.658), although the nickel titanium arch wire was the roughest (RMS = 0.23 microns). Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) verified that mass transfer of the beta-titanium arch wire occurred by adhesion onto the stainless steel flats or by abrasion from the sharply faceted polycrystalline alumina flats.

Aluminum Oxide↗
PubMed1990

Coefficients of friction for arch wires in stainless steel and polycrystalline alumina bracket slots. I. The dry state.

The surface roughness and the coefficients of friction were measured for sixteen arch wire-bracket combinations. The sample included one rectangular arch wire product from each of the four principal alloy groups and one bracket product from among the stainless steel and polycrystalline alumina inventory. Although subsamples representing both the 0.018-inch and the 0.022-inch slot sizes were evaluated, no differences were observed in their rankings. When tested over a series of eight incident angles, the optical surface roughness of representative stainless steel and alumina brackets averaged 0.148 and 0.193 microns, respectively. After testing at a single angle (82 degree) and referencing a nomogram, the roughness of the stainless steel, cobalt-chromium, beta-titanium, and nickel-titanium arch wire surfaces averaged 0.053, 0.129, 0.137, and 0.247 microns, respectively. When the various arch wire-bracket couples were pressed against an 0.010-inch stainless steel ligature wire at 34 degrees C and otherwise prevailing atmospheric conditions, the coefficients of friction ranged from stainless steel (lowest) to cobalt-chromium, nickel-titanium, and beta-titanium (highest)--regardless of bracket product or slot size. These results corroborated earlier observations in which the same arch wire products were drawn between stainless steel or alumina contact flats. In the current research, the average coefficient of kinetic friction for the stainless steel couple (0.139) was less than that for the stainless steel arch wire against a polycrystalline alumina bracket (0.174).

Aluminum Oxide↗
PubMed1989

Effects of sliding velocity on the coefficients of friction in a model orthodontic system.

Four arch wire alloy products were evaluated against 400- or 600-grit finished stainless steel contact flats at 34 degrees C under prevailing atmospheric conditions. Six relative velocities (10, 1.0, 0.1, 5 x 10(-2), 5 x 10(-3), and 5 x 10(-4) mm/min) were evaluated as many as three times each in order to simulate a range of sliding motion which approaches the mean rate of tooth motion--that of 2.3 x 10(-5) mm/min. Measurements of the static and kinetic coefficients of friction were rather invariant for the stainless steel and nickel titanium arch wire products. In contrast, a slight increase and a definite decrease of both coefficients occurred for the cobalt-chromium and the beta-titanium arch wire products, respectively. On the presumption that tooth motion routinely occurs over a wide range of sliding rates, the stainless steel couple produced the lowest and the most consistent coefficients of friction, whereas the beta-titanium wire on stainless steel flats produced the highest and the most erratic coefficients of friction. These observations should prevail whenever the film layer of saliva breaks down at, for example, the contact points of arch wire and bracket wings.

Chromium Alloys↗
PubMed1988

Creep rupture of polypropylene sutures as a function of diameter, radiation dose and temperature.

The failure of polypropylene (PP) sutures was studied via creep rupture tests. Linear relationships were generated from plots of log time to break (tB) versus stress (sigma). At a constant sigma the results showed that tB was inversely proportional to the suture diameter (7-0, 6-0, 5-0 and 4-0) and to the radiation dose (0, 15, 20, 25 and 50 Mrad). Moreover, for the 6-0 suture size at a 15 Mrad dose, tB decreased with increasing temperature (26, 37, 44, 50 and 60 degrees C). For this creep rupture process the activation energy equalled 91.2 kJ/mol (21.8 kcal/mol). A mechanism for failure was presented which assumes that these sutures are bundles of oriented, semicrystalline microfibrils.

Dose-Response Relationship, Radiation↗
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↗
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↗