In vivo Effects of a SnF2 Gel on Acid-softened Enamel

The purpose of this investigation was to study the intra-oral rehardening of acid-softened enamel and fluoride uptake from SnF2 gel. Bovine enamel slabs were softened with 0.1 mol/L lactate buffer at pH 4.0 for 14 hrs and then mounted in a mandibular removable Hawley appliance. Control slabs were worn for 96 hrs by seven adult males whose teeth were brushed daily with a fluoride-free dentifrice. Test slabs were exposed once/day to 0.4% SnF2 gel. The gel was swabbed onto the slabs for one minute before being replaced in the mouth unrinsed. The natural dentition was brushed 4x/day with a fluoride-free dentifrice. Microhardness testing was performed after a intra-oral exposure (IOE) and after acid-resistance-testing (ART) following immersion in 0.01 mol/L lactate buffer for 24 hrs at pH of 4.0. Fluoride uptake was measured on separate controls, test slabs, and test slabs after ART, with 0.5 mol/L HClO4 etches of from 15 to 60 sec. The F content was measured with a F-ion-specific electrode and the phosphate content by spectrophotometry. Following IOE, microhardness recovery was 35.6% for control and 37.9% for test slabs, and control slabs retained 1.4% resistance to acid, as compared with 18.6% for the test slabs. The F content of control slabs was significantly less than that of SnF2-treated slabs from 5 to 60 μm in depth, and the F content of SnF2-treated slabs after ART was significantly less at depths of from 5 to 35 μm than that of SnF2-treated slabs not exposed to ART. Both control and SnF 2 enamel slabs demonstrated rehardening after IOE, but only SnF 2-treated enamel retained a significant fraction of that rehardening after ART.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67414/2/10.1177_00220345860650051401.pd

The Concordiasi Project in Antarctica

International audienceThe Concordiasi project is making innovative observations of the atmosphere above Antarctica. The most important goals of the Concordiasi are as follows: 1. To enhance the accuracy of weather prediction and climate records in Antarctica through the assimilation of in situ and satellite data, with an emphasis on data provided by hyperspectral infrared sounders. The focus is on clouds, precipitation, and the mass budget of the ice sheets. The improvements in dynamical model analyses and forecasts will be used in chemical-transport models that describe the links between the polar vortex dynamics and ozone depletion, and to advance the understanding of the Earth system by examining the interactions between Antarctica and lower latitudes. 2. To improve our understanding of microphysical and dynamical processes controlling the polar ozone, by providing the first quasi-Lagrangian observations of stratospheric ozone and particles, in addition to an improved characterization of the 3D polar vortex dynamics. Techniques for assimilating these Lagrangian observations are being developed. A major Concordiasi component is a field experiment during the austral springs of 2008-10. The field activities in 2010 are based on a constellation of up to 18 long-duration stratospheric super-pressure balloons (SPBs) deployed from the McMurdo station. Six of these balloons will carry GPS receivers and in situ instruments measuring temperature, pressure, ozone, and particles. Twelve of the balloons will release drop-sondes on demand for measuring atmospheric parameters. Lastly, radiosounding measurements are collected at various sites, including the Concordia station