Biology of the teeth

[Marquetta]

A tooth is divided into the crown, which is the part above the gum line, and the root, which is the part below the gum line.
The crown is covered with white enamel, which protects the tooth. Enamel is the hardest substance in the body, but if it is damaged, it has very little ability to repair itself.
Under the enamel is dentin, which is similar to bone but is harder. Dentin surrounds the central (pulp) chamber, which contains blood vessels, nerves, and connective tissue. Dentin is sensitive to touch and to temperature changes.
The blood vessels and nerves enter the pulp chamber through the root canals, which are also surrounded by dentin. In the root, dentin is covered by cementum, a thin bonelike substance. Cementum is surrounded by a membrane (periodontal ligament) that cushions the tooth and attaches the cementum layer, and thereby the whole tooth, firmly to the jaw bone.
People have two sets of natural teeth:

Primary (baby) teeth: The first teeth to appear, later replaced by permanent teeth
Permanent (adult) teeth: The teeth that replace primary teeth

There are 20 primary teeth: one pair each of upper and lower central (front) incisors, lateral incisors, canines (cuspids), first molars, and second molars.
There are 32 permanent teeth: one pair each of upper and lower central incisors, lateral incisors, canines, first bicuspids, second bicuspids, first molars, second molars, and third molars (wisdom teeth). Wisdom teeth, however, vary—not everyone gets all four wisdom teeth, and some people do not get any wisdom teeth.