A method of obtaining a preparation of biological origin for oral hygiene toprevent the onset of tooth decay, comprises steps of fermentation of bacteriain a culture medium, separation of the same and purification of the culturemedium in which the bacteria have been cultivated, the step of fermentation ofbacteria including a combined addition of starch and cellulose to the culturemedium to the final concentration in the culture medium between 0.2 g/l and 2g/l, and preferably of 0.5 g/l each.