Robert P. Kusy

A review of contemporary archwires: Their properties and characteristics

The materials used by orthodontists have changed rapidly in recent years and will continue to do so in the future. As esthetic composite archwires are introduced, metallic archwires will likely be replaced for most orthodontic applications in the same way that metals have been replaced by composites in the aerospace industry. Archwires are reviewed in the order of their development, with emphasis on specific properties and characteristics, such as strength, stiffness, range, formability, and weldability. Because an ideal material has not yet been found, archwires should be selected within the context of their intended use during treatment.

Friction between different wire-bracketconfigurations 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.

Flexible (Kapton-based) microsensor arrays of high stability for cardiovascular applications

The design, fabrication and performance characteristics of Kapton-based planar mini and semimicro potentiometric sensors with an Ag/AgCl or a quinhydrone-based redox internal reference electrode are described. The ion-selective membranes cast from conventional and various modified PVC matrices and containing different pH-sensitive ionophores are ranked on the basis of their performances in hostile environments. The adhesive bonding strength of the different PVC membranes to the polyimide-coated Kapton substrate was quantitatively evaluated as a function of fabrication procedure and sample solution contact. The long-term stability of the electrodes was characterized by the alterations of the analytical parameters of the sensors over a period of time, as well as by determining the resistance changes of their sensing membranes.

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.

Evaluation of the frictional resistance of conventional and self-ligating bracket designs using standardized archwires and dental typodonts.

The frictional behavior of four conventional and four self-ligating brackets were simulated using a mechanical testing machine. Analyses of the two-bracket types were completed by drawing samples of three standardized archwires through quadrants of typodont models in the dry/wet states. Pretreatment typodonts of an oral cavity featured progressively malocclused quadrants. As nominal dimensions of the archwires were increased, the drawing forces of all brackets increased at different rates. When coupled with a small wire, the self-ligating brackets performed better than the conventional brackets. For the 0.014-inch wires in the upper right quadrant, the maximum drawing forces averaged 125 and 810 cN for self-ligating and conventional brackets, respectively. When coupled with larger wires, various designs interchangeably displayed superior performance. For the 0.019- x 0.025-inch wires in the upper left quadrant, the maximum drawing forces averaged 1635 and 2080 cN for self-ligating and conventional brackets, respectively. As the malocclusion increased, the drawing forces increased. For example, in the least malocclused quadrant and with the smallest wire, maximum drawing forces for self-ligating and conventional brackets averaged 80 and 810 cN, respectively, whereas in the most malocclused quadrant tested with the same wire size, maximum drawing forces for self-ligating and conventional brackets averaged 870 and 1345 cN, respectively. For maximum values between the dry and wet states, significant differences between ambient states existed only for the In-Ovation brackets in the lower left quadrant. These test outcomes illustrated how bracket design, wire size, malocclusion, and ambient state influenced drawing forces.

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.

Influence of angulation on the resistance to sliding in fixed appliances

The resistances to sliding were studied as a function of five angulations (0 degrees, 3 degrees, 7 degrees, 11 degrees, and 13 degrees) using nine different couples made of stainless steel, single crystal sapphire, or polycrystalline alumina brackets against stainless steel, nickel titanium, or beta-titanium arch wires. After 22 mil brackets were mounted to fixtures and 21 x 25 mil arch wires were ligated with 10 mil stainless steel ligatures, the arch wires were slid through the brackets at 1 cm/minute in the dry state at 34 degrees C. The resistance to sliding was measured by one computer while five normal forces (nominally 0.2, 0.4, 0.6, 0.8, and 1.0 kg) were serially maintained by another computer. A second couple was prepared for each material combination with five normal forces that were each 0.1 kg less. Statistical fits of linear regressions were such that p <.001 for most tests. When couples were in the passive configuration at low angulations, all stainless steel wire-bracket couples once again had the least resistance to sliding. When the angulation exceeded about 3 degrees, however, the active configuration emerged and binding quickly dominated as the resistance to sliding increased over 100-fold. Under these conditions, the relative rankings among the materials transposed; couples of stainless steel had the most resistance to sliding, whereas, couples of the more compliant alloys, such as nickel titanium wire, had the least. Results suggested that the active configuration and subsequent binding emerged when no bracket clearance remained. This binding component increased in importance with angulation and was additive to the frictional component, that is, they followed the principle of superposition.

Orthodontic biomaterials: from the past to the present.

‘‘Men will never barter their souls or spill blood for it; yet this time-tested stainless steel, with the single exception of intrinsic value, offers more desirable characteristics to the fine-metal worker than do the precious metals themselves. The craftsman asks only that his material be chemically inert, naturally beautiful, strong yet amenable to his artistry; it is the buyer who measures precious metals by price.’’ (Commercial advertisement touting stainless steel [ca 1935]1)

Influence of the molecular weight of poly(methyl methacrylate) on fracture morphology in notched tension

Abstract Specimens of poly(methyl methacrylate) (PMMA) were prepared by radiolysis of a polymer from an initial viscosity-average molecular weight ( M v ) of 1.2 × 10 6 down to 2.6 × 10 3 . At a molecular weight of 1 × 10 5 , abrupt changes in fracture morphology were observed correlating with a similarly abrupt decrease in fracture surface energy (γ). As the molecular weight was decreased further, the fracture morphology resembled more that of very brittle materials such as silicate glasses. Evidence was obtained that Wallner lines can influence the disposition of ribs but not their spacing. An empirical relationship was established between functions of rib spacing ( r ) and fracture surface energy.

Responses of H(+) selective solvent polymeric membrane electrodes fabricated from modified PVC membranes.

Potentiometric responses of a novel class of pH sensitive ionophores, namely several phenoxazine derivatives, were tested in different modified PVC matrices. The ionophores were compounded into liquid membranes as usual or were covalently coupled to the polymeric matrix. The general analytical performance of the membranes and other membrane characteristics (i.e., resistance and response time, as measures of membrane decomposition or structural changes) were followed in time. The transient responses of membranes with mobile ionophores in high molecular weight (HMW) and carboxylated PVC (PVC-COOH) were compared to those with immobilized ionophores. The response time of membranes with immobilized ionophores was found to be between those with mobile ionophores in HMW (fast response) and PVC-COOH (sluggish response). Accordingly, the rate of response was correlated primarily to the -COOH content of the membranes.