Abstract: A chlorohexidine adduct comprising one molecule of chlorohexidine with six molecules of hydrogen fluoride and a process for its preparation are described, said adduct displaying a high anti-bacterial effectiveness vis-a-vis Streptococcus mutans even in very small concentrations and being valuable as anti-plaque agent and for caries prevention.

Abstract: In a method for the optical distinction of a dental material applied to a substrate from natural teeth, false teeth or parts thereof 0.00001 to 1% by wt. of a fluorescent substance having an absorption maximum in the wave length range of 360 to 480 nm and a fluorescence maximum in the wave length range of 480 to 600 nm is incorporated in the dental material, the dental material is applied to the substrate and irradiated with a light source emitting light of a wave length in the region of 360 to 480 nm and is then viewed through a light filter filtering out at least partially the light of a wave length in the region of 360 to 480 nm.

Abstract: The irradiation apparatus for the photopolymerization of plastic embedding masses for histological preparations has a preparation support located in a housing and a plurality of irradiation lamps, with one lamp above and one lamp below the preparation support forming one lamp pair. In order to cure photopolymerizable embedding masses in a manner that does not harm the embedded preparations or specimens, and in particular to avoid an abrupt rise in the reaction heat, and so that a small number of irradiation lamps is sufficient, the preparation support is a rotary support plate having a plurality of light pervious preparation holding means located about its outer circumference, and the lamps are positioned such that in operation, the holding means sequentially pass in between the lamps of each lamp pair, and the centers of the holding means are located on a circle that is concentric with the axis of rotation of the support plate.

Abstract: Optically active carboxylic acids ##STR1## where R.sup.1 is an organic radical which is linked to the asymmetric C' atom via a carbon atom and R.sup.2 is one of the radicals R.sup.1 (but not the same radical), halogen or an organic radical which is bonded to the asymmetric C' atom via an oxygen atom, are prepared by reacting a ketene II ##STR2## with an alcohol in a homogeneous liquid phase in the presence of a tertiary amine III and then converting the resulting ester into the acid, using an optically active alcohol IV.