Molecular hydrodynamics: Vortex formation and sound wave propagation.

In the present study, quantitative feasibility tests of the hydrodynamic description of a two-dimensional fluid at the molecular level are performed, both with respect to length and time scales. Using high-resolution fluid velocity data obtained from extensive molecular dynamics simulations, we computed the transverse and longitudinal components of the velocity field by the Helmholtz decomposition and compared them with those obtained from the linearized Navier-Stokes (LNS) equations with time-dependent transport coefficients. By investigating the vortex dynamics and the sound wave propagation in terms of these field components, we confirm the validity of the LNS description for times comparable to or larger than several mean collision times. The LNS description still reproduces the transverse velocity field accurately at smaller times, but it fails to predict characteristic patterns of molecular origin visible in the longitudinal velocity field. Based on these observations, we validate the main assumptions of the mode-coupling approach. The assumption that the velocity autocorrelation function can be expressed in terms of the fluid velocity field and the tagged particle distribution is found to be remarkably accurate even for times comparable to or smaller than the mean collision time. This suggests that the hydrodynamic-mode description remains valid down to the molecular scale.

Effects of desensitizing agents for cervical dentin hypersensitivity: A randomized clinical trial.

PURPOSE: To evaluate the clinical efficacy of five commercially available desensitizing agents with different mechanisms applied to hypersensitive teeth. METHODS: A randomized clinical trial was conducted on subjects suffering dentin hypersensitivity in Korea University Guro Hospital from October 2013 to April 2015. A total of 64 subjects met the selection criteria and were randomly assigned to five commercially available desensitizing agents, and applied according to the manufacturers' instructions. Before and after application of desensitizing agents, subjects were evaluated with the Visual Analogue Scale (VAS) at baseline, 1 week, 1 month and 3 months. The difference between the degree of reduction of hypersensitivity in relation to time were evaluated with the repeated-measures ANOVA (P<0.05). RESULTS: Practitioner and subject-measured VAS values at 1 week, 1 month and 3 months showed a significant difference in all products compared with the first visit. On the other hand, no statistically significant differences between the products was shown. Desensitizing agents used in this clinical trial relieved dentin hypersensitivity up to 3 months. CLINICAL SIGNIFICANCE: The five tested desensitizing agents with different mechanisms were clinically effective in relieving dentin hypersensitivity up to 3 months and showed statistically significant pain reduction when compared to baseline scores.

Implant- and Tooth-Supported Fixed Prostheses Using a High-Performance Polymer (Pekkton) Framework.

The type of prosthetic restoration used in implant rehabilitation greatly contributes to the recovery of masticatory function as well as quality of life in patients. Frameworks for implant-supported prostheses are typically made by casting metal or milling either titanium or zirconia. Recently, nonmetal, polymer-type materials were suggested as framework materials. Polyetherketoneketone (PEKK), a high-performance polymer, was recently introduced in the dental field with potentially wide-ranging applications. This case history report describes implant- and tooth-supported fixed prostheses created using a new high performance polymer (Pekkton, Cendres+Metaux) framework for a fully edentulous maxilla and partially edentulous mandible.

Thermodynamics of d-dimensional hard sphere fluids confined to micropores.

We derive an analytical expression of the second virial coefficient of d-dimensional hard sphere fluids confined to slit pores by applying Speedy and Reiss' interpretation of cavity space. We confirm that this coefficient is identical to the one obtained from the Mayer cluster expansion up to second order with respect to fugacity. The key step of both approaches is to evaluate either the surface area or the volume of the d-dimensional exclusion sphere confined to a slit pore. We, further, present an analytical form of thermodynamic functions such as entropy and pressure tensor as a function of the size of the slit pore. Molecular dynamics simulations are performed for d = 2 and d = 3, and the results are compared with analytically obtained equations of state. They agree satisfactorily in the low density regime, and, for given density, the agreement of the results becomes excellent as the width of the slit pore gets smaller, because the higher order virial coefficients become unimportant.