Dental caries, also known as tooth decay or a cavity, is a disease where bacterial processes change carbohydrate like sugar in food left on teeth to acid that demineralises hard tooth structure (enamel, dentin, and cementum).
If demineralisation exceeds saliva and other remineralisation like from
calcium, these tissues progressively break down, producing dental
caries (cavities, holes in the teeth). Two groups of bacteria are
responsible for initiating caries: Streptococcus mutans and Lactobacillus. If left untreated, the disease can lead to pain, tooth loss and infection. Today, caries remains one of the most common diseases throughout the world. Cariology is the study of dental caries.


source: Wikippedia