Every tooth consists of a crown and a root. The part exposed to the mouth is called the crown; Root embedded in alveolar bone; The joint between the crown and the root is called the neck.

The tissue on the crown is the hardest tissue in the human body, called enamel. Enamel covers the crown, making the crown white or light yellow. This is because enamel is a translucent calcified tissue, which can reveal the yellow color of dentin. Enamel is resistant to chewing and abrasion. The tooth enamel is thickest at the cusp and thinner at the neck.

The crown of a tooth generally has several faces: the front teeth are composed of four faces and the front teeth, and the rear teeth are composed of five faces. Details are as follows:

1. Lip surface and buccal surface: the side of the anterior teeth close to the lips is called the lip surface, and the side of the posterior teeth close to the buccal mucosa is called the buccal surface.

Second, the lingual surface and palatal surface: the side of the teeth close to the tongue is called the lingual surface, and the lingual surface of the maxillary teeth is close to the palate, also known as the palatal surface.

Third, the mesial surface and the distal surface: the tooth surface near the midline of the face is called the mesial surface. The tooth surface far away from the center line of the plane is called the distal plane.

Occlusal surface: the upper and lower teeth of the posterior teeth are opposite, and the surface where food is chewed is called occlusal surface. The upper and lower teeth of the front teeth are opposite, and they can bite the cutting end of something, just like the blade part of a kitchen knife, called the blade.

The surface of teeth is not as smooth as a mirror, but uneven, with many uneven areas. Protruded areas, such as crest, lingual protrusion and cusp; Ditches, nests, crevices and other sunken areas.

The outer layer of the root is covered with enamel, and its hardness is equivalent to that of ordinary bones. Cementum is yellow in color, thicker at the apical part of teeth and the root bifurcation part of molars, and thinner at the neck of teeth. Sensitive symptoms are easy to appear when the cementum in the neck of teeth is damaged by trauma.