Healthy tooth (lower premolar). A tooth is made up externally of two parts: the crown, visible in the oral cavity and protected by enamel (in white), and the roots, implanted in the gum, a root for the lower premolars, in some cases, two roots . The tooth includes an internal cavity, the pulp chamber, filled with dental pulp (in brown), a connective tissue rich in blood and lymphatic vessels and nerve fibers. The pulp chamber continues at the root level through the root canal, through which the vessels and nerves enter. Dentin (pinkish beige) constitutes the major part of the tooth, and gives it its shape and rigidity, it is striated by numerous small channels, the dentinal tubules, which contain the ends of the nerves. The root is implanted in the maxilla, surrounded by the gum that covers the bone. Between the root and the bone, the root is surrounded by the cementum (in yellow) and the alveolar-dental ligament (in white).