Like ancient Hawaiians, many surfers wear shark tooth necklaces for superstitious reasons as well. Wearing a shark tooth is said to prevent sharks from attacking you and protect you while you're at sea. Sailors often wear them for good luck and protection from drowning.
Sharks razor sharp teeth can cut through almost anything like a knife. Their teeth are made of calcium phosphate, a very tough material. But a shark can actually shed their teeth thousands of times throughout their lifetime, growing new ones in their place.