Sharks don't just have one layer of teeth, they have about five layers of teeth.  whenever a shark loses a tooth a new one moves to take it's place.  shark teet are very sharp.  Mako sharks teeth are curved back so if the thing it's attacking tries to pull out of the sharks mouth it's teeth will just stab deeper in the fish.  The now extict Megelodon shark had a jaw that could fit a full grown man!  Whale sharks have thousands of teeth, but all thoughs teeth are dull.  Tiger sharks have sarated teeth.