Oral hygiene often stops during meth use, resulting in a buildup of gooey plaque on the teeth. This plaque is a sticky mass of bacteria and food residue that builds up quickly. Undisturbed by brushing and flossing, the bacteria form mature colonies that are very good at metabolizing carbohydrates. The bacterial waste product is acid that dissolves tooth structure, in turn creating a safe harbor for accumulation of bacteria in a cavity.

Enamel is a crystalline structure that is relatively acid resistant, but is only a thin layer on the surface of a tooth. Once the cavity works through the enamel layer, it enters the dentin, which makes up the majority of the tooth structure.

Dentin is not very acid resistant, and is actually comprised of a network of fine tubes called tubules. There is a hollow space in the crown of the tooth that contains a mass of soft tissue known as the pulp, which contains nerves, blood vessels and a variety of cells to help nourish the tooth. The dentinal tubules are filled with cellular fluids, and they radiate from the walls of the pulp chamber to the enamel layer.

When decay penetrates through the enamel to the dentin, the bacteria are treated to an environment that invites rapid growth of decay. Decay can easily progress to the point where the pulp is inflamed, and when decay enters the pulp this soft tissue can become necrotic. Further complications include abscesses or cysts in the bone at the end of the root, and loss of enough tooth structure that the tooth is no longer restorable.