Plaques are the primary cause for caries and parodontal diseases. Plaques are soft, whitish yellow bacterial dental stains. They consist of a matrix (basic substance) and of bacteria to more than 50 %. 1 mg plaque, i.e. one one-thousandth gram, contains approx. 700 million microorganisms. Plaque bacteria use saccharides from human nutrition for their further energy supply. Sugar such as glucose, saccharose (white sugar) or fructose can quickly enter into and be processed in the plaque. These sugar types are therefore highly cariogenic. The penetrated sugar is degraded by the bacteria, which results in the formation of acids such as lactic acid. These acids activate caries. The plaque becomes thicker, it "grows".

The plaque's pH value is reduced. Once the pH reaches 5.5 or lower, the volume of acid is so large that it can no longer be balanced (neutralised) by the saliva's buffering effect. The result is increased demineralisation of the enamel and subsequently possible caries.