Shark teeth are in parallel rows. In the front row are the teeth they use to catch and eat their prey. Several rows of replacement teeth keep growing behind the teeth they are using. As their teeth fall out, the new teeth come forward. Sharks keep growing new teeth as long as they live. Studies by scientists at Mote Marine Labs have shown that, on average, a Nurse Shark will replace each front row tooth every ten days to two weeks during the summer, when actively feeding, and every one to two months during the winter, when they are less active.
Different sharks have different shaped teeth according to what they like to eat the most. The Mako Shark has thin, pointed teeth for grabbing and holding prey. The Great White Shark has serrated, wedge-shaped teeth for cutting. Small conical teeth, like the Nurse Shark's are for crushing shells of crabs and mollusks found on the bottom of the ocean.
A rough formula for calculating the size of a shark, using its teeth, is to measure the length of one side of the tooth in inches, then multiply by ten to calculate the total length of the shark in feet. This estimate only applies to large triangular-shaped teeth, but if you ever find one you will be able to imagine just how big the shark was that it came from. Shark Anatomy