Most adult humans naturally have 32 develop teeth. A tooth is a multilayer structure
divided into two basic sections: the crown (the top of the tooth above the natural gum) and the
root (the part of the tooth below the natural gum line). The place where the crown and the root
meet is called the neck. The surface of the crown is made of enamel. Enamel is a hard calcified
tissue that is primarily composed of calcium crystals. Beneath the enamel of a tooth is a second
layer of hard tissue called dentin. The hollow interior of a tooth is called the pulp, which is
surrounded by dentin.
Tooth pulp contains blood vessels, lymph vessels, and nerves. The root of a tooth is
covered with cementum. The outer portion of the root is comprised of a hard outer layer which
covers an inner layer of dentin. The teeth are held by the periodontal ligament, and each tooth is
held in an alveolus (socket). There is an opening at the bottom tip of each root through which the
blood vessels, lymph vessels, and nerves pass into the socket and jawbone.