Because shark's teeth fall off very easily, sharks usually have 5-6 rows of teeth at the same time. Except for the outermost row of teeth, the other rows are "supine", just like tiles on the roof. Once the outermost tooth falls off, the inner row of teeth will move forward immediately to make up for the vacant position to replace the fallen tooth. Most species replace one tooth at a time, and only the Brazilian Dharma shark can replace an entire row of teeth at a time.
Shark's teeth will be constantly updated and replaced throughout his life. The replacement teeth first grow in the grooves of the upper and lower jaws, and then move forward slowly like a conveyor belt. The frequency of replacement may range from about 10 days to several months. At the same time, the larger teeth of sharks will constantly replace the smaller teeth during their growth. So sharks often have to change tens of thousands of teeth in their lifetime. According to statistics, a shark needs to replace more than 20,000 teeth in 10 years.
Under normal circumstances, sharks change their teeth for two reasons. First, their teeth are damaged and fall off during predation; The other is that they reach a certain age. Under normal circumstances, every new tooth replaced by a shark will be bigger and more durable than the old one.