Cavity, or tooth decay, can happen anywhere on a tooth. This means that no area of the tooth is ever safe from the decay attack. Cavities can enter the top, sides, or even its root (if exposed) Smooth surface caries occurs where there is no pit, groove, or other fault on a tooth. It occurs in areas where bacterial plaque collects, such as between teeth, along the gumline, and in difficult-to-clean areas.