Shark is a kind of fish with high frequency of tooth replacement, which changes teeth every 7-15 days on average, and can change 20,000-30,000 teeth in a lifetime. They change their teeth to keep their teeth sharp. Sharks often prey on other fish, and they will lose their teeth in the process of biting their prey. In order to avoid the inconvenience caused by aging and damage of teeth, they need to change their teeth frequently. The replacement teeth grow in the groove between the upper and lower jaws in their mouth. When the upper teeth age, new teeth will grow and replace the original teeth.