Impression materials: effect of hydrophilicity and viscosity on ability to displace water from dentin surfaces.
The water-displacing ability of hydrophilic and hydrophobic impression materials was determined and related to the hydrophilicity and viscosity of the materials. The water-displacing ability of the materials was determined on a network of grooves in a dentin surface covered by a drop of water. After setting of the material, the number of crossings reproduced in the impression was calculated in percent of the total number of crossings. The hydrophilicity was assessed by measuring the contact angle between water and impression material. To determine viscosity, a rotoviscosimeter was used. Impression materials with contact angles less than 70 degrees showed a significant negative correlation between water-displacing ability and contact angle, i.e. the reproducing ability decreased with decreasing hydrophilicity of the materials. Impression materials with contact angles above 70 degrees showed a significant positive correlation between water-displacing ability and viscosity, i.e. the water-displacing ability improved with increasing viscosity.
Penetration of restorative resins into acid etched enamel. I. Viscosity, surface tension and contact angle of restorative resin monomers.
It has been a controversial question whether an intermediate layer of low-viscous, non-composite resin between composite restorative and etched enamel is beneficial. It was the purpose of the present work to investigate some of the factors that govern the penetration of resins into the capillary pores of etched enamel surfaces. Viscosity, surface tension and contact angle on human enamel were measured using monomer mixtures similar to those found in commercial restorative resins. Employing a cylindrical model of relevant dimensions of the capillary pores, and on the basis of Poiseuille's equation the time of penetration was calculated for a relatively high-viscous and a relatively low-viscous monomer mixture. It was concluded that viscosity as such is not a limiting factor for the penetration of restorative resin monomers into the pores of etched enamel surfaces.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.