1. A dentifrice containing chitosan or a pharmaceutically acceptable acid addition salt thereof, fluoride ions and abrasive material for use against erosive demineralization of the teeth, the dentifrice is a toothpaste containing a liquid phase and containing tin, dissolved in the liquid phase. 2. The dentifrice according to claim 1, the use of which is the prevention of erosive demineralization of teeth or the treatment of teeth susceptible to erosive demineralization of teeth. The dentifrice according to claim 1, wherein the chitosan or a pharmaceutically acceptable acid addition salt thereof and fluoride ions are dissolved in the liquid phase. The dentifrice according to claim 1, 2 or 3, wherein the chitosan is unmodified chitosan. The dentifrice according to claim 4, the use of which is the treatment of teeth subject to erosive demineralization of the teeth, or the prevention of erosive demineralization of the teeth, and the toothpaste contains one or more abrasive materials in such a total amount that gives the toothpaste a value for removing plaque (PCR) of at least 50.6. The dentifrice according to claim 1, wherein said dentifrice contains from 200 to 2000 ppm, preferably from 1000 to 1800 ppm of fluoride ions, from 0.05 to 1% chitosan or a pharmaceutically acceptable addition salt thereof acids, from 3,000 to 4,000 ppm of tin dissolved in the liquid phase, from 17 to 27% glycerol, from 17 to 27% sorbitol and from 0.3 to 1% gluconate, with all percentages being relative to toothp1. Средство для чистки зубов, содержащее хитозан или его фармацевтически приемлемую соль присоединения кислоты, фторид-ионы и абразивный материал, для применения против эрозионной деминерализации зубов, причем данное средство для чистки зубов представляет собой зубную пасту, содержащую жидкую фазу и содержащую олово, растворенное в жидкой фазе.2. Средство для чистки зубов по п.1, применение которого представляет собой предупреждение эрозионной деминерализации зубов или лечение зубов,
