Teeth are hard calcified structures firmly anchored in the sockets of soft fleshy gum tissue called gingiva that covers the ridge of bone in the jaw.
Within a few hours of brushing a soft film of plaque begins to coat the surface of teeth. At first the plaque is easily removed and you can scrape it off without much effort using a toothbrush. Within a day however, plaque begins to absorb hardening minerals from saliva. And in a couple of weeks, it turns into cement-like calcified tartar that can only be removed with a dental tool. It collects on and between teeth and in the gum pockets.
The mouth is also home to bacteria, even a healthy mouth. There's just no way around it. And bacteria love plaque because it is a particularly cozy environment in which to grow. As soon as plaque begins to build, bacteria colonize like mad. They feast on and ferment sugars and starches from food, which then produces tooth-damaging acid that can cause enamel erosion, decay and cavities.