The teeth are the hardest substances in the human body. Besides being
essential for chewing, the teeth play an important role in speech. Parts of the
• Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of
calcium phosphate, a rock-hard mineral.
• Dentin: A layer underlying the enamel. Dentin is made of living cells, which
secrete a hard mineral substance.
• Pulp: The softer, living inner structure of teeth. Blood vessels and nerves
run through the pulp of the teeth.
• Cementum: A layer of connective tissue that binds the roots of the teeth
firmly to the gums and jawbone.
• Periodontal ligament: Tissue that helps hold the teeth tightly against the
A normal adult mouth has 32 teeth, which (except for wisdom teeth) have
erupted by about age 13:
• Incisors (8 total): The middlemost four teeth on the upper and lower
• Canines (4 total): The pointed teeth just outside the incisors.
• Premolars (8 total): Teeth between the canines and molars.
• Molars (8 total): Flat teeth in the rear of the mouth, best at grinding
• Wisdom teeth or third molars (4 total): These teeth erupt at around age 18,
but are often surgically removed to prevent displacement of other teeth.
The crown of each tooth projects into the mouth. The root of each tooth
descends below the gum line, into the jaw.