Orthodontic Open-Coil Spring Deactivation Forces Differ with Varying Activation Levels

Coil springs are used in orthodontics to deliver forces to move teeth. However, the optimal amount of activation to produce predictable, continuous deactivation forces, for the purpose of orthodontic tooth movement, is unclear. The purpose of this study was to evaluate the deactivation force characteristics of nickel-titanium open-coil springs after varying levels of activation. Methods: Four open-coil spring products were evaluated: Dentsply GAC 100 gram and 150 gram, Orthoclassic Orthodontics Medium 150 gram, and American Orthodontics nickel-titanium springs. Open-coil springs were compressed (activation) with a universal testing machine to 20, 40, 60, or 80% of original length (15 mm; n=15/product/activation level). Measurements were conducted at 37oC to simulate intraoral temperatures. Deactivation force values at 3 mm were compared among the four activation levels within each product using ANOVA/Tukey. Results: For all four open-coil spring products, deactivation force values at 3 mm significantly (p\u3c0.05) decreased with greater activation/compression level. When activated to 20% of original length, the force values at 3 mm compression upon deactivation were only 53-73% of the force level when activated to 80% of original length. When activated to 40% of original length, the force values at 3 mm compression upon deactivation were 65-91% of the force level when activated to 80% of original length. Conclusions: Deactivation forces of nickel-titanium open-coil springs at a given compression level are dependent upon the extent of prior compression. Orthodontists should be aware that force values in open-coil springs depend not only on material and structural factors, but amount of activation as well

An Update on Local Universality Limits for Correlation Functions Generated by Unitary Ensembles

We survey the current status of universality limits for $m$-point correlation functions in the bulk and at the edge for unitary ensembles, primarily when the limiting kernels are Airy, Bessel, or Sine kernels. In particular, we consider underlying measures on compact intervals, and fixed and varying exponential weights, as well as universality limits for a variety of orthogonal systems. The scope of the survey is quite narrow: we do not consider $\beta$ ensembles for $\beta \neq 2$, nor general Hermitian matrices with independent entries, let alone more general settings. We include some open problems

Smallest eigenvalues of Hankel matrices for exponential weights

AbstractWe obtain the rate of decay of the smallest eigenvalue of the Hankel matrices ∫Itj+kW2(t)dtj,k=0n for a general class of even exponential weights W2=exp(−2Q) on an interval I. More precise asymptotics for more special weights have been obtained by many authors

Coverage Issues in the Government Reimbursement of Drugs: Some Legal and Policy Issues

Although the 103rd Congress, despite much anticipation, did not enact any health care reform legislation, many of the problems which led to proposals and consideration of reform still remain. Health care costs are still increasing, though growth has slowed. Large portions of the United States population remain uninsured or underinsured. It would not be surprising if some form of health care reform reappeared on the scene some time in the near future