Bonding of brackets using a caries-protective adhesive patch

OBJECTIVES: The purpose of this study was to assess the shear bond strength (SBS) of metal brackets when placed with a caries protective adhesive patch. METHODS: Forty stainless steel brackets (Ormco) were bonded to 40 bovine enamel samples according to the following conditioning/bonding procedures using a resin-based orthodontic luting material (Heliosit Orthodontic, N=10 per group): (A) 35% phosphoric acid (30s), rinse and dry; (B) as in A but additional placement of a prototype adhesive patch (Ivoclar Vivadent) using a bonding agent (Heliobond); (C) application of a two-step self-etch adhesive (AdheSE); (D) as in C but additional patch placement. Samples were stored at 37 degrees C for 24h. SBS was measured with a universal testing machine with a crosshead speed of 0.5mm/min and the adhesive remnant index (ARI) was determined under a stereomicroscope (16x). RESULTS: Mean SBS (standard deviation) values were as follows: (A) 16.6 (6.4)MPa; (B) 12.2 (5.8); (C) 12.9 (5.0); and (D) 10.5 (4.7). Analysis of variance followed by Bonferroni correction revealed no statistically significant differences. In 2 (B) and 4 (D) specimens, complete retention of the adhesive patch was observed. CONCLUSIONS: All treatment groups showed adequate bond strength values. The adhesive patch could therefore be applied in combination with orthodontic brackets and seal the enamel adjacent to the bracket

Isotropic-Nematic Transition in Liquid-Crystalline Elastomers

In liquid-crystalline elastomers, the nematic order parameter and the induced strain vary smoothly across the isotropic-nematic transition, without the expected first-order discontinuity. To investigate this smooth variation, we measure the strain as a function of temperature over a range of applied stress, for elastomers crosslinked in the nematic and isotropic phases, and analyze the results using a variation on Landau theory. This analysis shows that the smooth variation arises from quenched disorder in the elastomer, combined with the effects of applied stress and internal stress.Comment: 4 pages, including 4 postscript figures, uses REVTeX

In vitro tooth cleaning efficacy of electric toothbrushes around brackets

This in vitro study assessed the cleaning efficacy of different electric toothbrushes around upper incisor brackets. Standard and Mini Diamond™ brackets were fixed on black-stained teeth. The teeth were coated with white titanium oxide and brushed in a machine twice for 1 minute each. Twelve different brush heads with either a wiping or an oscillating-rotating action were tested. After brushing, the teeth were scanned, the black surfaces were assessed planimetrically and a modified plaque index for orthodontic patients (PIOP) was introduced. Tooth areas, which were black again after brushing indicated tooth surface contact of the filaments and were expressed as a percentage of total area. The remaining white areas around the brackets indicated 'plaque-retentive' niches. Analysis of variance was used for individual comparison of the brush types. Bonferroni/Dunn adjustment was applied for multiple testing. The Sonicare® toothbrush handle with the brush head 'Compact ProResults' (81.7 per cent) and the brush head 'Standard ProResults' (80.8 per cent), as well as the sonic Waterpik® toothbrush SR 800E with the standard brush head (78.2 per cent), showed statistically significantly better cleaning efficacy than all others. The poorest cleaning efficacy was observed for the oscillating-rotating Braun Oral-B Professional Care with the brush head 'Ortho' (less than 50 per cent). The planimetric findings were in correspondence with the results of the PIOP assessment. Cleaning efficacy of electric toothbrushes around brackets on upper incisors was different between the tested brushes. The PIOP was practicable, effective, and easy to use, although it has to be verified in a clinical stud

Magnetic moment of welded HTS samples: dependence on the current flowing through the welds

We present a method to calculate the magnetic moments of the high-temperature superconducting (HTS) samples which consist of a few welded HTS parts. The approach is generalized for the samples of various geometrical shapes and an arbitrary number of welds. The obtained relations between the sample moment and the density of critical current, which flows through the welds, allow to use the magnetization loops for a quantitative characterization of the weld quality in a wide range of temperatures and/or magnetic fields.Comment: RevTeX4, 4 pages, 2 figures. Submitted to Supercond. Sci. Techno

Imaging local diffusion in microstructures using NV-based pulsed field gradient NMR

Understanding diffusion in microstructures plays a crucial role in many scientific fields, including neuroscience, cancer or energy research. While magnetic resonance (MR) methods are the gold standard for diffusion measurements, spatial encoding in MR imaging has limitations. Here, we introduce nitrogen-vacancy (NV) center based nuclear magnetic resonance (NMR) spectroscopy as a powerful tool to probe diffusion with an optical readouts. We have developed an experimental scheme combining pulsed gradient spin echo (PGSE) with optically detected NV-NMR spectroscopy, which allows for the local quantification of molecular diffusion and flow within microscopic sample volumes. We demonstrate correlated optical imaging with spatially resolved PGSE NV-NMR experiments probing anisotropic water diffusion within a model microstructure. Our optically detected PGSE NV-NMR technique opens up prospects for extending the current capabilities of investigating diffusion processes with the future potential of probing single cells, tissue microstructures, or ion mobility in thin film materials for battery applications.Comment: 37 pages, 5 figures, 2 table

Soft and non-soft structural transitions in disordered nematic networks

Properties of disordered nematic elastomers and gels are theoretically investigated with emphasis on the roles of non-local elastic interactions and crosslinking conditions. Networks originally crosslinked in the isotropic phase lose their long-range orientational order by the action of quenched random stresses, which we incorporate into the affine-deformation model of nematic rubber elasticity. We present a detailed picture of mechanical quasi-Goldstone modes, which accounts for an almost completely soft polydomain-monodomain (P-M) transition under strain as well as a ``four-leaf clover'' pattern in depolarized light scattering intensity. Dynamical relaxation of the domain structure is studied using a simple model. The peak wavenumber of the structure factor obeys a power-law-type slow kinetics and goes to zero in true mechanical equilibrium. The effect of quenched disorder on director fluctuation in the monodomain state is analyzed. The random frozen contribution to the fluctuation amplitude dominates the thermal one, at long wavelengths and near the P-M transition threshold. We also study networks obtained by crosslinking polydomain nematic polymer melts. The memory of initial director configuration acts as correlated and strong quenched disorder, which renders the P-M transition non-soft. The spatial distribution of the elastic free energy is strongly dehomogenized by external strain, in contrast to the case of isotropically crosslinked networks.Comment: 19 pages, 15 EPS figure