Answer:

New teeth grow continuously inside shark’s mouth discarding the old ones and renewing them immediately.

Therefore, sharks do not have a particular reason to grow new teeth, but they do it all their life going through thousands of teeth during their lifetime.

Some guess that sharks produce up to 30,000 teeth during their entire life.

Usually, their mouth has several rows of teeth, therefore when they lose one because of struggling with prey or just because they are renewing it, the correspondent tooth from the row behind it goes forward to fill the space in the jaw.

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