1, the tooth of toothed shark has a special structure, which consists of multiple layers, including a layer of material called "bioceramics". When the teeth of toothed sharks wear or fall off, new teeth will grow in the alveolar space in the middle and back of the mandible to replace the old teeth.

2. Ivory fish's teeth can wear and repair by themselves.

3. The teeth of bull sharks have similar characteristics, which can keep growing and changing.

4. Crocodile's teeth have similar characteristics, and they can keep growing and changing.