Enamel: The most outer layer. Hardest substance of the body.

Dentin: The layer under the enamel. Because dentin is softer than enamel, cavities enlarge faster.

Pulp: The nerve of a tooth.

Gum: Surface tissue that covers alveolar bone.

Cementum: The outer layer of the root of the tooth.

Periodontal ligament: Tissue that joins the alveolar bone and cementum.

Alveolar bone: Bone under the gums that anchors the roots of tooth.

Blood vessel and nerve: Nerve tissue that connected to the pulp.