2. The number of teeth varies from small to large.
3. The number of teeth changes from multiple dentition to double dentition.
4. The distribution of teeth is from extensive to gradually concentrated in the upper and lower jaws.
5. The root of the tooth is from scratch, and the attachment mode between the tooth and the jaw is from the end tooth to the lateral tooth, and finally to the alveolar tooth.
1. Attachment mode of teeth and jaws: (1) deciduous teeth: These teeth have no roots, and only attach to the edge of jaws through fibrous membranes, which are easy to fall off. Most teleost fish have terminal teeth.
(2) Lateral teeth: In addition to the tooth root connected to the jaw, one side of the tooth is attached to the inner edge of the jaw. Although these teeth do not have perfect roots, they are stronger than the end teeth, such as the teeth of reptiles.
(3) Molar teeth: These teeth have perfect roots located in the alveolar fossa, and blood vessels and nerve endings enter the pulp cavity from the apical foramen. The teeth of mammals including humans are alveolar teeth.