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Biomedical subjects

W A Brantley

Publications and source records attributed to W A Brantley.

At least 73 records · Page 4Linked to original sources
PubMed1985

Comparison of accuracy of multiunit one-piece castings.

An investigation was conducted to evaluate the accuracy of one-piece castings of FPDs consisting of three, four, and five units with a ceramometal alloy cast in a large circular ring. A three-piece aluminum mold with stainless steel dies simulating the various lengths of the FPDs was used. A total of 18 castings, six castings for each FPD, were fabricated. Marginal discrepancies of the castings on the dies and the length of the castings were compared before and after sectioning the castings at the connectors. The following conclusions were drawn from the study. Seating of the castings improved approximately 50% after sectioning, which indicates that the castings were distorted. The distortion was a three-dimensional phenomenon, with the greatest discrepancy on the mesiogingival surface of the anterior retainer and on the distolingual surface of the posterior retainer. The distortion was least for the three-unit FPDs and greatest for the five-unit FPDs. The lingual-facial diameter of the castings at the gingival axial line angle was significantly larger than the dies in most cases. The mesiodistal diameter of the castings at the gingival axial line angle was smaller than that of the dies but was only significant with the three-unit FPDs. Although the castings were slightly oversized or undersized, the primary reason the castings did not seat was warpage.

Dental Alloys↗
PubMed1984

Weldability of beta titanium arch wires.

Beta titanium arch wire segments were joined in a variety of configurations by means of four different commercial welders available to the orthodontist. Test specimens were prepared using the point-to-point and flat-to-flat electrode configurations and a range of settings on each welding apparatus. Tension-shear and tension-twist tests were conducted to determine force values to rupture the welded joints; 90 degrees cold-bend tests provided a measure of relative ductility near the joints compared to the as-received wires. Results indicated that the flat-to-flat electrode configuration is preferred for obtaining strong welded joints with low levels of distortion. Optimum settings have been determined for each of the four welders. Microstructural observations of the beta titanium and joint structure are presented; these are correlated with the energy level settings for the welding process.

Dental Alloys↗
PubMed1984

Variability of effective root torque as a function of edge bevel on orthodontic arch wires.

The effective torque delivered by a variety of arch wire-bracket combinations has been measured experimentally in terms of the deviation angle, by means of a torque-meter apparatus, and compared to theoretical values calculated from both nominal and measured bracket slot and wire dimensions. Edgewise brackets with both 0.018 and 0.022 inch slot widths from two manufacturers were used, with three different arch wire sizes for each slot size. Stainless steel, nickel-cobalt, and beta titanium wires from a total of three manufacturers were employed. The present effective torque values were less than the theoretical values previously reported by Dellinger and Creekmore, who had separately focused on manufacturer tolerances associated with the wire cross sections and slot widths, respectively. Differences between the experimental and theoretical values of deviation angle were in agreement with measurements of the wire-bracket tolerances and with microscopic observations of differences in the edge bevel at the corners of the arch wires. The average edge bevel contribution to the measured deviation angle varied from 0.2 degrees to 12.9 degrees for the various wire-bracket groups, and the average percentage contribution from 3 to 63%. The edge bevel contribution to the deviation angle was higher for stainless steel wires than for nickel-cobalt wires marketed as square-cornered. The highest deviation angles and edge bevel contributions were found for the beta titanium wires.

Equipment Design↗
PubMed1982

Changes in bracket slot tolerance following recycling of direct-bond metallic orthodontic appliances.

Stainless steel direct-bond orthodontic brackets manufactured by three different companies were evaluated for changes in ability to be torqued by a rectangular arch wire after being recycled by three commercially available methods. Through two successive recycles, no clinically significant changes in the fit of the arch wire to engage the bracket were found for any of the three different methods. Greater experimental values of bracket tolerance or fit in degrees for wire twist, compared to theoretical calculations by previous investigators, were attributed to beveled edges found on the rectangular arch wires.

Chemical Phenomena↗
PubMed1979

Measurement of bending deformation for small diameter orthodontic wires.

The stiffness tester and torque meter were found to yield nearly the same measurements of bending deformation for orthodontic wires as small as .007 inch diameter, provided the different bending apparatus are calibrated to each other. Although frictional losses in the test apparatus did not appear to be significant, the test span length does significantly affect measured values of Young's modulus and flexural yield strength, in a manner similar to that previously found for larger-diameter wires.

Chromium Alloys↗
PubMed1978

A comparison of properties for zinc phosphate cements mixed on room temperature and frozen slabs.

The following conclusions may be drawn from this study: 1. More powder may be incorporated into the cement liquid when the cement is mixed on a frozen slab rather than a room temperature slab. 2. A dramatic increase in the working time and decrease in setting time occur with frozen-slab mixes. 3. No statistically significant difference in compressive strength was found for the room temperature and frozen-slab mixes. 4. Solubility and disintegration values for room temperature and frozen-slab mixes of the three cements not containing fluoride were below the maximum limit of ADA Specification No. 8.

Chemical Phenomena↗
PubMed1978

Bending deformation studies of orthodontic wires.

Bending deformation has been measured for orthodontic wires ranging in diameter from .010 to .051 inch. Results establish a revised expression for Young's modulus and show that either the stiffness tester or the torque meter will yield essentially the same measured values of bending properties. The dependence of test span length in determining Young's modulus and flexural yield strength is discussed.

Chemical Phenomena↗
PubMedDate not supplied

Fundamental studies of maxillofacial materials: Part 1. Differential scanning calorimetric analyses of a heat-polymerized silicone.

Differential scanning calorimetry was used to evaluate the effects of polymerizing conditions and the addition of pigments for a heat-activated maxillofacial silicone (MDX 4-4515). Unpigmented specimens were examined in the starting condition and after polymerizing at 100 degrees C for 1 hour, 4 hours, and 20 hours, and specimens of four different pigmented silicones processed 1 hour at 100 degrees C were also included. The DSC scanning was performed from -150 degrees C to 200 degrees C at 10 degrees C per minute, and a strong melting-recrystallization peak at approximately -40 degrees C was found for all eight specimen groups (N = 5). Modulated differential scanning calorimetry resolved this peak into separate melting and recrystallization peaks, and confirmed the existence of a very weak glass transition peak in this silicone at approximately -125 degrees C. The mechanical properties of the MDX 4-4515 silicone appear to be dominated by melting and recrystallization, rather than the glass transition, and differences may exist in the viscoelastic and creep behavior for the unpigmented and pigmented materials.

Analysis of Variance↗
PubMedDate not supplied

Crystallographic characteristics of plasma-sprayed calcium phosphate coatings on Ti-6Al-4V.

The purpose of this study was to investigate the crystallographic characteristics of 3 sets of plasma-sprayed hydroxyapatite (HA) coatings prepared with different degrees of crystallinity on Ti-6Al-4V substrates. X-ray diffraction analyses were performed on the coatings to determine mean percent crystallinity, calcium phosphate phases present, average crystallite size, and residual strain. The mean percent crystallinity for the 3 sets of coatings ranged from 49 to 60%. The coatings that achieved the highest crystallinity consisted almost entirely of HA. As the coating crystallinity decreased, increasing amounts of alpha- and beta-tricalcium phosphate and tetracalcium phosphate were detected. The mean HA crystallite size for the 3 sets of coatings ranged from 0.02 to 0.05 micron. Differences in mean interplanar spacing for selected crystallographic planes of HA, compared with the pure ICDD (International Center for Diffraction Data) powder standards, implied that the coatings were in an uneven state of tensile strain.

Alloys↗
PubMedDate not supplied

New high-palladium casting alloys: 1. Overview and initial studies.

High-palladium alloys for metal ceramic restorations, based on the Pd-Cu-Ga and Pd-Ga systems, were introduced to the dental profession during the past decade. These alloys have become increasingly popular because they are much less expensive than the gold-based alloys, and recently marketed high-palladium alloy compositions have excellent mechanical properties. A summary of the important melting and casting considerations for these somewhat technique-sensitive alloys is presented together with an overview of important dental materials science aspects and the results of a dental laboratory survey. A maxillary central incisor coping was chosen as the clinically appropriate specimen shape, and the gas-oxygen torch melting technique was found to produce castings with clinically acceptable levels of marginal sharpness and little evidence of microporosity. The etched as-cast high-palladium alloys exhibited fine-scale multiphase microstructures, and a noteworthy finding was that relative proportions of the microstructural constituents frequently varied for thin versus thick sections of the cast specimens.

Crowns↗
PubMedDate not supplied

Mechanical property and microstructural variations for recast low-gold alloy.

Using polystyrene plastic patterns meeting the dimensional requirements of ANSI/ADA specification no. 5, tension test specimens were recast multiple times from a popular Type III gold (46%) alloy. The alloy was melted by electrical heating in a graphite crucible and four conditions were compared: new alloy and alloy cast two, three, and four times (n = 4). After casting, age-hardened specimens were loaded at an elongation rate of 0.5 mm/min until failure, and the stress-strain plots were recorded. Values of yield strength, tensile strength, and percentage elongation for the specimen groups were analyzed by one-way analysis of variance, followed by the Student-Newman-Keuls multiple range test. Significant decreases (P < .01) in yield strength and percentage elongation occurred with recasting, although there were no significant differences (P > .05) in tensile strength. Scanning electron microscope examination revealed that the number of casting defects increased with remelting, and that their presence dominates the tensile fracture process. The variation in mechanical properties of the alloy with remelting was attributed to these casting defects.

Analysis of Variance↗
PubMedDate not supplied

Fracture toughness of high alumina core dental ceramics: the effect of water and artificial saliva.

The fracture toughnesses of two high alumina core ceramics were determined by using the single edge notched specimen method. Measurements were made in air, water, and artificial saliva. Fracture toughnesses of 1.89 and 1.75 MPa.m1/2 were obtained for Cerestore and Vitadur N samples, respectively, tested in air. Values obtained from Vitadur N samples that were tested in deionized water were significantly lower than those that were measured in air. Values for samples of both ceramics that were tested in artificial saliva were not significantly different from those that were tested in air. The fracture mode was a combination of intergranular and transgranular for Cerestore and predominantly transgranular for Vitadur N.

Air↗