Your teeth are covered with a civilization of bacteria.
We all know that dental plaque exists but we don’t know what it actually is. These are bacteria (they look like bubble gum in the picture) that produce a pink substance which is an acid. In the first few hours it’s neutralized with saliva, then the plaque becomes thicker, our saliva can’t get inside, and the acid starts dissolving our tooth enamel. And this is what leads to dental cavities.