William A. Brantley

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.

Comparison of bending and tension tests for orthodontic wires

Stainless steel, cobalt-chromium-nickel (Elgiloy), nitinol, and beta titanium wires with diameters from 0.010 to 0.040 inch and in rectangular sizes from 0.017 X 0.025 to 0.019 X 0.025 inch were evaluated with the American Dental Association specification no. 32 bending test and the conventional tension test. The modulus of elasticity (E) and yield strength (YS) obtained with the two mechanical testing procedures are reported for as-received wires and after heat treatment at 900 degrees F for the stainless steel and selected Elgiloy wires. Measured values of E and YS in bending were almost invariably higher than the corresponding values obtained in tension. The only general agreement between the modulus of elasticity in bending and tension was for the 0.040-inch diameter stainless steel wires. Anomalously high values of E in bending were also found for most of the heat-treated stainless steel and Elgiloy groups. Difficulties with the bending test are attributed to loading effects at both ends of the test span and deviation of the bent specimen from a circular arc. Improved procedures are described for performing the tension test on the relatively small cross-section orthodontic wires.

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.

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.

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 Youngs 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 Youngs modulus and flexural yield strength is discussed.

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.

Comments on Stiffness Measurements for Orthodontic Wires

The mechanical behavior of orthodontic wires is typically investigated under bending conditions, which are representative of clinical use (THUROW, Edgewise Orthodontics, 1966). The stiffness in bending, which indicates the amount of force or bending moment required to produce elastic deflection, represents the same basic mechanical response as the stiffness for uniaxial loading (Youngs modulus). The dominant deformation for both loading modes involves normal strains and stresses parallel to the specimen axis. However, bending deflection is dependent on details of the loading system and the speci-

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 Youngs modulus and flexural yield strength, in a manner similar to that previously found for larger-diameter wires.

Effects of appliace size, arch wire diameter, and alloy composition on the in vitro delivery of the quad-helix appliace

Abstract The quad-helix appliace is a fixed lingual arch wire appliace that produces slow maxillary expansion for the treatment of maxillary constriction or crossbite in the primary and mixed dentitions. Despite considerable success in the clinical treatment of patients, there is little quantitative information about the force delivery of this appliace. The purpose of this investigation was to characterize the in vitro force delivery of the quad-helix appliance. Appliances of four sizes were fabricated from Elgiloy blue and stainless steel wires with diameters of 0.032, 0.036, and 0.038 inch. The force delivery in grams for 8-mm activation was determined from the force-extension characteristics using an Instron mechanical testing machine. The results show that the force delivery on the quad-helix appliace is affected significantly by changes in the appliance size and arch wire diameter, but is independent of alloy type (stainless steel of Elgiloy blue). The quantitative results from this investigation should provide worthwhile information for clinical appliance selection and treatment of patients with varying arch dimensions.

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.