Teeth form embryologically from neuroectoderm that develops into the central and peripheral nervous systems. Tooth development begins in the fetus around 28 days, but mineralization does not occur until 14 weeks in uterus. Tooth eruption occurs when the formation and mineralization of the crown are almost complete, but before the roots are fully formed. Teeth have two distinct parts, the crown and the root, and are composed of four different tissues (Fig. 1).The crown, which is made of enamel, lies above the gum line and covers the sensitive root, which lies below the gum line. The root makes up two thirds of the tooth's total length, goes through the periodontal ligament, and attaches into a socket in the alveolar bone of the jaw.

The four tissues that make up a tooth are:

• Enamel: Outermost white covering of a tooth.
• Dentin: Soft bonelike material that supports the enamel and carries some nerve fibers.
• Pulp: The centre of the tooth that contains blood, lymph vessels, and nerves.
• Cementum: Covers the root of the tooth and the periodontal ligament connects the cementum and the jaw bone.