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Biomedical subjects

J Q Whitley

Publications and source records attributed to J Q Whitley.

At least 19 recordsLinked to original sources
PubMed1999

Assessment of second-order clearances between orthodontic archwires and bracket slots via the critical contact angle for binding.

Twenty-six archwires and 24 brackets were selected from among the hundreds of products available that nominally have from 18 to 22 mil bracket slots and 14, 16, 17, 18, 19, and/or 21 mil archwire sizes. After the archwires and brackets were dimensioned, a minimization-maximization algorithm was applied to the measurements in order to establish the likely boundaries of the critical contact angle for binding (thetac) as defined by the presence and absence of second-order clearance. From among the myriad archwire-bracket permutations possible, 64 combinations were identified--20 using the bracket slot as the controlling dimension and 44 using the bracket width. Using a previously derived mathematical expression that relates the dimensions of each archwire-bracket couple to its calculated thetac, the corresponding sets of indices were plotted. The results show that the maximum value of the calculated thetac can never exceed about 5 degrees , or else sliding mechanics will always be hampered. Other outcomes were validated experimentally using 5 of the 64 archwire-bracket couples by measuring the resistance to sliding (RS) at 15 different contact angles (theta) ranging from theta=0 degrees to theta=12 degrees and by subsequently determining a measured thetac. These values agreed with the calculated thetac values. When the practitioner knows the thetac, treatment time might be reduced because the teeth do not need to be over-aligned prior to employing sliding mechanics (i.e., by not making theta< thetac) These results underscore the importance of exact wire and bracket dimensions on packaging; otherwise, sliding mechanics can be compromised by miscalculating thetac.

Algorithms↗
PubMed1998

Evaluation of titanium brackets for orthodontic treatment: part I. The passive configuration.

The static and kinetic frictional coefficients of commercially pure titanium brackets were evaluated in the passive configuration in the dry and wet states against stainless steel, nickel-titanium, and beta-titanium arch wires. For comparison, stainless steel brackets were evaluated under identical conditions. Titanium brackets were grayer in color and rougher in texture than the stainless steel brackets. Bracket slots were up to 0.002 inch greater than the nominally stated values. Remarkably, the static and kinetic frictional coefficients of the couples formed by titanium and stainless steel brackets were comparable. When evaluated against stainless steel and nickel-titanium arch wires in the dry state at 34 degrees C, the static coefficient averaged.12 and.20, respectively, independent of bracket alloy. When evaluated against stainless steel and nickel-titanium wires in the wet state at 34 degrees C using human saliva, the static coefficient averaged.15 and.20, respectively, independent of bracket alloy. Only the beta-titanium arch wires increased by about 15%, when tested in either the dry or the wet state against titanium versus stainless steel brackets. Noteworthy, too, was the decrease of both coefficients in the beta-titanium wire couples from their previously reported values. Analyses of electron spectroscopy for chemical analysis spectra and depth profiles show that these new brackets are titanium only in the bulk. Indeed the immediate surfaces are composed of, at least, 80 atomic percent (at.%) carbon and oxygen; whereas, the titanium that is present (>11 at.%) is mostly in the form of titanium dioxide. The presence of this quite thin passivating layer, which resides on top of an oxygen-hardened titanium substrate, reduces the galling and fretting that would normally be expected in such materials. Pending the outcome of future angulation tests, these frictional measurements show that titanium brackets are not only comparable to stainless steel brackets but also are more biocompatible with nickel having been eliminated from their constitution.

Dental Alloys↗
PubMed1997

Friction between different wire-bracket configurations and materials.

Friction opposes tooth motion whenever sliding mechanics is employed. Understanding what friction is and how to manage it is of paramount importance to the successful practitioner. In this article, the coefficients of friction are summarized between different arch wire-bracket couples as a function of material, geometric, and external parameters. From this vantage point, friction can then be evaluated within the context of other factors that affect sliding-binding and notching.

Dental Alloys↗
PubMed1994

Zirconia brackets: an evaluation of morphology and coefficients of friction.

The frictional characteristics of two types of zirconia (Harmony, Hudson Ltd., Sheffield, U.K., and Toray, Yamaura Corp., Tokyo, Japan) brackets were compared with those of polycrystalline alumina (Transcend 2000, Unitek Corp., Monrovia, Calif.) brackets in both dry and wet states. To compare the couples, four arch wire alloys were studied: stainless steel, cobalt-chromium, nickel titanium, and beta-titanium. Under dry conditions, the highest frictional coefficients were seen with the Harmony/beta-titanium couple (uk = 0.64); the lowest values were seen with both Transcend 2000/stainless steel (uk = 0.13) and Toray/cobalt-chromium couples (uk = 0.13). Beta-titanium arch wires produced the highest coefficients of friction against each type of ceramic bracket, except against Toray arch wires in the wet state. The presence of human saliva produced only slight changes in the frictional behavior of zirconia brackets. We conclude that currently available zirconia brackets offer no significant improvement over alumina brackets with regard to their frictional characteristics.

Aluminum Oxide↗
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

Relationship of the diameter and tensile strength of nylon sutures to the USP specification and the effect of preconditioning.

Nylon monofilament sutures were tested in a straight pull as well as a conventional knot pull tensile test. In each test, sutures were evaluated following storage under prevailing atmospheric conditions or saturation in whole human blood. Blood saturation decreased the ultimate tensile strength by as much as 20%. The present investigation of sutures that were stored under prevailing atmospheric conditions substantiated the proposal previously made for polypropylene monofilaments--that 60% of the ultimate tensile strength could be established as a fundamental USP criterion for Class I monofilament sutures.

Humans↗
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↗
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↗