There is only one fixed line, which is wrong.

Shark's teeth are not permanent, only a fixed row, but there are four or five rows behind a row. The outermost teeth are upright, and the back rows of teeth are spare, and one row covers the other.

Of course, sharks will also wear their teeth during their growth, which also requires timely replacement of their back teeth. Therefore, sharks change their teeth very frequently in their lives.

Characteristics of shark teeth:

Once the external teeth of sharks are worn, the internal teeth will be supplemented to keep their hunting tools up to date.

Sharks often keep a row of new teeth larger than the old ones. The reason for this is that in order to cooperate with the growth of sharks, sharks' teeth are serrated, so that sharks can not only bite their prey tightly, but also effectively tear it apart when facing large prey.